russell kirkman mate 198b final design report

RUSSELL KIRKMAN Mate 198B Final Design Report

Mate 198B Final Design Report

Improving Processing Parameters for the Manufacture of Reactive Foil

For Dr. Richard Chung, Mate 198B Spring 2015,

Dr. Michael Oye, NASA Ames ASL, &

Jacques Matteau, Indium Corporation

Project locations:

San Jose State University, San Jose, CA

Engineering Building 105

NASA AMES Research Park, Mountain View, CA

Building N239 ASL (Advanced Studies Labs) MACS Facility

By Russell Kirkman

May 15, 2015


TABLE OF CONTENTS

1. INTRODUCTION………………………………………………………..……………...1

1.1 Reactive Multilayer Films (RMF's)

1.2 Commercial Interest and Manufacture

1.3 Design Project Motivation and Goals

1.4 Functional Requirements, Performance Specifications, & Success Criteria.........4

1.5 Constraints and Limitations

2. TECHNICAL BACKGROUND............……………….…………………...

2.1 Technical Aspects of Reactive Multilayer Films

2.2 Cold-Rolling Parameters and Technique

3. EXPERIMENTAL METHODS AND RESULTS...….………………………..

3.1 Experimental Plan and Required Resources

3.2 Results and Analysis

4. SUMMARY AND CONCLUSIONS...........................……………………………..

5. REFERENCES…………………............................…………………………………..........

6. BRAODER CONSIDERATIONS.....................…………………………………….…

6.1 Environmental, Health, and Safety

6.2 Ethics and Social Responsibility

7. ACKNOWLEDGEMENTS...................................................................................................

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1. Introduction

1.1 Reactive Multilayer Films (RMF's)

Welding, brazing, and soldering are methods of joining materials that have been refined

since the first arc welding systems were developed at the beginning of the 20th century. These

processes have been used reliably for many years in applications for industries including

aerospace, automotive, and electronics. The common aspect of these methods for joining

materials is the application of high temperature to induce controlled melting and re-solidification

of the materials joining them together. Some of the drawbacks to these common methods of

bonding are the capacity to damage the materials being joined from the rapid application of high

temperatures, the addition of lower melting point and softer intermediate materials reducing the

mechanical properties of the bond, and the inability to form a complete surface bond across the

interface. Due to these issues, alternative ways of bonding have been explored that reduce or

eliminate the problems associated with traditional methods. One of the ways that has been

developed in recent years is bonding utilizing a class of materials called Reactive Multilayer

Films (RMF). These materials consist of nanometer scale layers of two or more alternating

species that form a composite laminate as shown in Figure 1.

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Figure 1. Reactive Multilayer Films (a) SEM of cross section (b) Reactive Film ignition [1].

1.2 Commercial Interest and Manufacture

Similar in some respects to materials such as Thermite mixtures, intermetallic reactants,

and metal fuels, RMF's exhibit a rapid exothermic reaction when a point source of thermal,

mechanical, or electrical energy is applied to the material. The release of energy can then be used

as a heat source for metal and ceramic bonding applications. One of the ways the bond is

superior to those made with traditional methods in that the crystal structure of the material is not

as damaged much past the surface interface which aids in maintaining bond strength and rigidity.

Additionally, the entire surface is mated rather than around the edge of the joint, and there is a

chemical bond that is formed between the surfaces. Currently, commercial production of an

Aluminum and Nickel composite is done through sputtering techniques (see Figure 2).

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Figure 2. Diagram of sputtering chamber showing method of depositing film layers [2].

Sputtering, although effective for layering thin films, requires complicated equipment including

vacuum chambers, ion beam sources, and gas controls. It is also a batch style process where a

single film is grown onto one substrate at a time limiting the production throughput of the

material. In addition to the high energy costs to run and maintain the equipment, expensive

technicians with sufficient training are required to operate the equipment safely and properly.

1.3 Design Project Motivation and Goals

The high costs associated with the process limits the commercial viability of RMF's for

many industrial applications where the technology would improve the quality and speed of

production for joining materials. The capital requirements needed to manufacture RMF's using

sputtering methods yields a material that is more expensive for end users when compared to

other techniques currently used for bonding and joining. The higher cost to the end user is one of

the main reasons that RMF's have not yet been adopted in industry as a new de facto standard for

bonding even though the quality of the bond can be improved over traditional methods. This

project seeks to design an alternative process of manufacture using cold-rolling techniques (See

Figure 3) for RMF's that will reduce the cost of production so that it becomes more viable in the

market as a replacement for traditional methods such as brazing, welding, and soldering.

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Figure 3. (a) Cold rolling mill at San Jose State (b) Representation of mating layersA secondary goal of the project is to explore the feasibility of a zirconium and aluminum RMF

system as an alternative to the nickel and aluminum laminate currently manufactured by Indium

Corporation located in Clinton, NY USA. Through support of this project, both Indium

Corporation and NASA Ames ASL (seeks to aid in the development of a lower cost process for

the manufacture of a RMF system with alternative materials thereby expanding the range of

commercially viable bonding applications.

1.4 Functional Requirements, Performance Specifications, & Success Criteria

In addition to lowering the manufacturing cost for RMF's, the new process design should

also be scalable to handle larger volume production and higher throughput. The process must be

capable of mating a number of layers of two materials into a laminate. The process must also be

carried out at temperatures far below the magnitude required to ignite the material to prevent

premature reaction and diffusion between layers during manufacture. It should consume less

energy and require less complex equipment than that needed to run a sputtering process. In

addition to energy efficiency, the design should minimize the amount of wasted material. With

sputtering processes, much of the material is left inside the chamber which further adds to the

costs associated with this method of manufacture. The new process design should be repeatable

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and yield predictable results which can be controlled through refinement of relevant parameters

using statistical analysis. It should be flexible in the respect that other RMF materials may be

similarly processed in addition to the zirconium and aluminum system chosen as the constituents

for this design project. Success of the process design for the manufacture of RMF''s includes

meeting the above functional requirements and performance specifications in addition to yielding

a laminate material consisting of alternating layers of reactive materials, such as zirconium and

aluminum chosen for this design project. The process should minimize wasted raw materials and

be capable of producing well mated layers of sub-micron scale thicknesses while minimizing

diffusion between species. The measurable properties used to judge the performance success for

the process design include layer thickness and separation of elements verified using scanning

electron microscopy (SEM) equipped with energy dispersive x-ray analysis (EDX or EDAX).

Another measureable property using SEM/EDX is the amount of oxygen present in the material

in the form of natural oxides of the layered elements. The presence of oxide layers is thought to

be a barrier to the functionality of the material that results from the process design by separating

the reactive layers from each other in addition to absorbing energy needed to sustain a reaction

between them.

1.5 Constraints and Limitations

Prior to the inception of the process design, access to the required facilities, materials,

and technical support was evaluated as to the viability for supporting development. The major

constraints that were found included limited access to equipment, the quality of the equipment

available, and reserving the time on the tools being shared with multiple users. Access to

equipment at NASA Ames requires regular safety and other training updates to remain certified

for lab access. Access to tools is also shared, so there may be instances when there is limited

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time to access the machines. Security systems in the buildings both at NASA Ames and San Jose

State that house the equipment have a small chance of malfunctioning and locking the

instruments out of use. Restrictions to access to the NASA Ames campus was cleared through

the completion of required safety and security evaluations. In addition to access constraints, end

material thicknesses are limited due to the cost of raw materials. Ion beam sputtering was

initially thought to be the most viable candidate for the process; however, due to long processing

times, this method was abandoned). The expense of subsidizing the costs of machine time and

technicians for assistance in running the process plus making sure the tooling is functioning

properly limits the number of prototypes that can be generated. This also limits the number of

parameters that can be varied between process revisions and as a result, may be insufficient in

number to satisfy statistical significance. Other constraints related to equipment quality

encompass the flatness of the roller wheels and the alignment. Roller deformation is not

controllable during processing and thus becomes an issue when evaluating the repeatability and

accuracy of the layer thickness and geometry of the resulting material. Because the project is

supported by commercial manufacturer Indium Corporation, it is important that the process

development cycle meet the cost and time constraints as planned. See Figure 4 for an outline of

the major milestones planned for the senior design project.

Major Milestones for Process Design Plan:

Background/Research Research Properties for both Zr, Al and alloy ZrAl Train on Rolling Mill Project Proposal

Feasibility Study Specific Material, Equipment, & Support Specifications Source Raw Material, Availability and Cost Reserve Equipment and other Resources

Process Specifications

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Test Methods of Material Preparation Determine optimal settings for equipment Model System to fine tune settings prior to Manufacture

Manufacture Vary single independent parameter and correlate results to material properties Reiterate until desired properties are achieved

Test Design and Build Testing fixture Gather Ignition Data and relate to Process Specifications and Varied Parameters

Report Make Conclusions to relate background research to observed improvements Document Optimum Process Parameters for desired Materials Properties

Figure 4. Major milestones list showing general plan of action for completion of design project.2. Technical Background

2.1 Technical Aspects of Reactive Multilayer Films

There two most critical aspects of RMF's that make them a candidate as heat sources for

bonding applications consist of the high temperature that is reached during the reaction between

layers and the rapid rate at which the reaction propagates. By applying a point source of thermal

or electrical energy, atomic diffusion occurs perpendicular to the plane of layers allowing the

two constituents to form a bond causing a release of energy in the form of heat (see Figure 5).

Once the reaction begins, it propagates through the material parallel to the plane of the layers and

continues until the entire foil forms an intermetallic alloy.

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Figure 5. Reactive Multilayer Foil propagation and diffusion diagram [1].

The rate that the reaction propagates is determined by the Arrhenius relationship which is

comprised of two main components. The first part of the relationship is the frequency of

collisions between species and the second portion is the probability that a collision has enough

energy to establish a bond between the two particles (the exponential term) . Equation 1 shows

the relationship of the collision frequency and the probability of a successful bond.

k=A e−E A

RT Equation 1

The exponential term consists of the activation energy needed to establish a bond

between particles (EA measured in J), divided by the gas constant (R in J/mol K) and the

temperature (T measured in K). If the activation energy of the reaction is nearly zero or the

temperature is significantly high, the exponential term approaches unity and the rate becomes

nearly equal to the collision frequency (A in sec-1). The collision frequency is a function of both

the geometry of the reactant molecules and the probability that the geometry of the collision will

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create a bond. Equation 1 defines the relationship of the activation energy and temperature to the

rate of reaction. The relationship that governs the exothermic release of energy from the reaction

comes from the Arrhenius law which relates the activation energy to the enthalpy (heat flow) of

the reaction. Figure 6 shows the activation energy and reaction enthalpy (ΔHRX).

.

Figure 6. Gibbs Free Energy as a function of Reaction propagation showing the relationship between activation energy and enthalpy.

In the case of Reactive Multilayer Foils, the change in enthalpy (ΔHRX) is negative

representing an exothermic reaction. Once the activation energy is breached by inputting heat or

electricity into the material, the reaction has sufficient momentum to reach the product side of

the reaction. As the reaction coordinate moves from left to right bonding occurs forming a

ceramic or an intermetallic phase which has a lower energy than the original reactants. The

lowering of the energy from bonding of atoms results in the exothermic heat released from the

material. Gibbs Free Energy of the reactants and the products is governed by a series of

equations (see Equations 2 through 18 in Table 1) that represent the relationships between each

elements' pure solid and liquid phases as they interact with one another.

Table 1. Equations 2 through 18, the relationships of Gibbs Free Energy as a function of temperature and the specific heat capacity of each phase [3].

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As related to functionality of Reactive Multilayer Foils, the most important measure of

energy is the heat output from the reaction. To initiate the reaction, there needs to be a point

source of energy applied to the material that breaches the activation energy and allows the

diffusion of the layers and the bonding between reactants forming the intermetallic or ceramic

that becomes part of the mating between surfaces. Equation 19 relates the various energies

present in the process of ignition [4].

CPdTdt

=Q S+QRX−QL Equation 19

The heat capacity (Cp) at constant pressure multiplied by the rate of change in local

temperature of the multilayer as a function of time (dT/dt) is equal to the sum of the supplied

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external power (QS) and the energy released internally due to mixing (QRX) minus the heat loss to

the surrounding material (QL). This equation illustrates that the total heat exchanged to the

surroundings during reaction is directly related to the heat capacity of the material and how

severe the temperature change is over time. A short time change or a large temperature change

both produce a large amount of heat flow. Since the supplied external power and the energy

absorbed by the material are very small in magnitude in comparison to the heat loss to the

surrounding material, the heat flow is primarily negative indicating that there is quite a bit of the

energy lost to the surroundings (exothermic reaction).

To initiate the reaction, the activation energy (EA) much be sufficient to breach the

amount of energy per unit volume required to form the first alloy or ceramic bonds. This is, in

part, the reason that the ignition source needs to be a point source so that the volume the energy

source is interacting with is as minimal as possible to maximize the energy density and in turn

the opportunity for ignition. Once the initial volume begins to react, some of the energy is lost to

sustaining the reaction (QRX) from Equation 19.

Equation 20 [4] represents the temperature required to initiate reaction. It is a complex

relationship that involves a number of key variables, most important of note is the bi-layer

thickness (λ).

T ignition=

Ea

R

ln [2 gΔ HRX DO RT

λw ( fn (1−n ) )] Equation 20

The ignition temperature (Tignition) is in part a function of the activation energy (EA)

required to initiate the reaction between layers. If the activation energy is too high, then

regardless of the other variables, the ignition temperature required may too high for practical

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purposes. The denominator in the function is influenced by several factors. If there is a large heat

of reaction (Δ H RX) then the denominator is larger which translates into a lower ignition

temperature required. This makes sense since the energy required to initiate the reaction would

be smaller the more energy that is provided from the reaction of forming the alloy or ceramic

bonds. The mass diffusion pre-factor (D0) and the thermal resistance of the layers (RT) influence

the ignition temperature in the same way that the heat of reaction does. A larger value equates to

lower ignition temperature. The term containing the ratio of the fractional concentration of the

intermetallic phase being formed (f) to the atomic fraction of reactant (n) changes as the reaction

propagates. As the reactant is consumed, the intermetallic phase thickness increases (w) and

begins to overcome the fraction of the reactant remaining making the reaction propagate more

easily as it continues. It is this relationship that reveals the inverse relationship of the ignition

temperature to the reaction coordinate which equates to a highly exothermic reaction as

expected. Finally, the gas constant (R) and the geometric factor (g) play a small role in the

denominator, but coming back to the most important factor related to this design project, the bi-

layer thickness (λ) is the variable that has the most influence on the ignition temperature. If the

bi-layer thickness is large enough, it will easily dominate the term inside the natural log greatly

reducing the denominator which increases the ignition temperature. Equation 20 illustrates that

as the layer thickness increases, there is a sharp logarithmic increase in ignition temperature.

Using estimated values for the constants in Equation 20, Figure 7 shows a generalized model of

the ignition temperature (Tignition) as a function of the bi-layer thickness (λ).

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Figure 7. Ignition Temperature Tignition (ln (K)) vs. Bi-Layer Thickness λ (nm).

Notice the sharp increase near the smaller layer thicknesses as well as another sharp

increase as the thickness approaches the micron scale. Once the layer thickness gets larger than

the 200 to 300 nm range, the ignition temperature required begins to be more than reasonably

achievable. At very thin layers, the temperature required approaches room temperature as the

diffusion factor becomes dominant in the equation once the layer thickness is reduced

sufficiently. Utilizing titanium as a diffusion tracer, K¨oppers reported that the diffusion

coefficient is a proportional function of temperature as shown in Figure 8 [3]. As the temperature

increases to the left, the diffusion coefficient also increases confirming the proportionality.

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Figure 8. Calculated self-diffusion coefficients of Zr in hcp_Zr and impurity diffusion coefficients of Al in hcp_Zr, along with those of Ti in hcp_Ti and Al in hcp_Ti [3].

In conclusion to the first section of the technical background required to understand the

mechanisms at work regarding Reactive Multilayer Foils, oxidation was thought to be a factor in

the ignition temperature. Both zirconium and aluminum form natural oxide layers that can act as

diffusion barriers and thermal insulators preventing the ignition or propagation of the reaction.

As the materials are exposed to atmosphere, the oxygen in the air is energetically favorable for

bonding with the very top surface layers of the metals. To this end, it is important that oxide

layers be minimized so that the reaction is not inhibited.

2.2 Cold-Rolling Parameters and Technique (remember stress strain)

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The main focus of the process design centers around the cold-rolling technique used to

mate the different foil layers as well as reduce the thickness to a manageable scale where the

ignition temperature isn't too extreme. Cold-rolling presents a set of challenges when using it to

manufacture Reactive Multilayer Foils. Not only are there the concerns of roller geometry and

deformation, the rolling speed is also an important factor in the ability to roll together foils of

different metals. Figure 9 shows an example of the cold rolling procedure referencing nickel and

aluminum as the reactants.

Figure 9. Schematic of a typical cold rolling process [5].

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One of the most difficult aspects of cold rolling to control is the movement of the layered

foils during rolling. This sliding of layers prevents the retention of the layer geometry and results

in an undesired cross section profile with fewer, thicker layers rather than the desired multiple

thin layers. Another aspect of cold rolling that is important to the manufacture of mated foils is

the energy that is produced during deformation of the material. If the deformation is significant

enough, it is possible for the reactants to bond during rolling which renders the foil non-

functional. One of the benefits to the cold rolling process is the increase of defects and grain

boundaries that occurs during deformation from the movement of grains. These increase the

stored energy in the material and when the reaction propagates to these zones in the material, it

encounters a high energy density which further aids in propagation. The energy imparted to a

material during rolling is a function of the relationship between stress applied by the roller (σ)

and the modulus of the material (E) and the resulting strain (ε) (measured as volume change in

this case). See Equation 21.

σ=E ε Equation 21

3. Experimental Method and Results

The experimental procedure that was performed to evaluate the success of the process

design begins with the selection of materials. Several suppliers were researched and the most

viable suppliers were chosen based on the best price and delivery available. Because the

intermetallic phase that is formed during bonding of the two reactants is determined by the molar

ratio of reactants, the molar ratio was translated to a thickness ratio. Thicknesses that equate to

the atomic ratios are calculated by taking the molar ratio of the target intermetallic (2:1) and

multiplying each by their molar masses (g/mol) to yield a mass ratio (g). Each mass is then

17


divided by the respective solid density (g/cm3) for each pure element which equals the volume

(cm3). The volume is then translated to a thickness by dividing by the common cross sectional

area of the initial foils. The thickness ratio can then be multiplied by a common factor to match

the material availability. For this design project, the aluminum and zirconium intermetallic that is

targeted is Al2Zr. Once the layer ratio was calculated, foils of minimum 99.4% purity were

ordered with thicknesses of 0.060 mm for the aluminum foil and 0.080 mm for the zirconium

foil. (The ideal thickness ratio to achieve the desired intermetallic species for the zirconium foil

is calculated to be 0.070 mm, but due to availability issues, a thickness of 0.080 mm was

obtained as the closest alternative. Excess zirconium was assumed to remain after reaction.)

Figure 10 shows the area of the phase diagram that applies to the target intermetallic. By

selecting the thicknesses of the separate pure layers prior to processing, the ratio of aluminum to

zirconium of 2:1 can be achieved.

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Figure 10. Al and Zr phase diagram with target intermetallic ratio and congruent melt point [6].

Once the starting thicknesses were calculated and the foils obtained, they were cut into 4

equal pairs consisting of 100 mm by 200 mm sections. The Aluminum layer was placed on top of

the zirconium layer and cleaned with acetone immediately prior to placing in a 460 °C oven for

10, 30, 50 & 70 minutes (Samples 1-4). Because native oxide layers were thought to be a

possible barrier to ignition and propagation of the reaction, pre-heating of the foils was

performed to intentionally form the most aggressive oxide layer possible as to assess the

magnitude that an oxide layer presence affects the reaction and/or mating of the foils. As noted

later in the reporting of results, even though the temperature of the foils were raised to a

significant portion of the melting temperature, the presence of an oxide layer post rolling process

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Congruent Melt

Intermetallic Phase


was minimal if at all. The amount of time allowed for oxidation in the oven didn't affect the

levels of oxidation layers post processing. To reach the desired layer thicknesses, the gap setting

of the roller was initially measured to be .635 mm using a reference thickness gauge. The roller

gap setting was reduced in between each pass through the roller so that after 8-10 passes, the gap

setting ended at 0.051 mm for samples 1 and 3 as well as 0.102 mm for samples 2 and 4. It was

determined that these end thicknesses would result in individual layer thicknesses on the sub-

micron scale as to optimize the potential for ignition and heat production.

The results of the thickness measurements post cold rolling process are summarized in

Figures 11 and 12. Figure 11 shows the layer thicknesses for the individual layers that resulted

from the reduction in roller gap setting. Figure 12 shows the overall sample thickness as a

function of the roller gap setting. Both materials' thickness measurements were obtained using

Scanning Electron Microscopy (SEM). The most important factor in these figures is the

discrepancy between expected thickness and actual thicknesses measured. If the roller gap was

set to 0.051 mm (51 microns) then the overall layer thickness should be equal to the gap setting.

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0 1 2 30.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

Material Type: 1 = Zirconium, 2=Aluminum

Thicknessμm

Figure 11. Individual layer thicknesses for zirconium and aluminum reactants post rolling.

0 50 100 150 200 250 300 3500.0

50.0

100.0

150.0

200.0

250.0

300.0f(x) = 1.38823529411765 x + 84.2R² = 1

Roller Setting Thickness (μm)

Total Sample Thick-

ness (μm)

Figure 12. Total sample thickness as a function of roller gap setting. Note that there is a linear relationship between the setting and the resulting thickness that is offset by 84.2 microns.

21


Measurements of layer thicknesses were obtained using SEM imaging. In Figure 13, the

red lines indicate the thickness measurements for the aluminum layers and the blue lines indicate

the thickness measurement locations for the zirconium layers.

Figure 13. SEM image f cross section of sample 3 showing measurement locations of layer thicknesses for aluminum (blue) and zirconium (red).

It is critical to note that the layer thicknesses are well above the desired level for

reasonable ignition (see previous section explaining ignition mechanics). This was thought to be

the most influential factor in the failure of the material to ignite from the application of a point

source. In order for the material to successfully ignite and produce an exothermic chain reaction,

the layers must be well below the micron scale, and as shown in Figure 11, the thickness of the

individual layers was much more than the sub-micron scale needed to achieve ignition of the foil.

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Figure 14 shows the overall layer thickness of sample 1 which was approximately 100 microns

thicker than the roller gap setting.

Figure 14. (a) SEM image of cross section of sample 1 showing offset between roller gap setting and resulting layer thickness.

After the results of the thicknesses were obtained by embedding a portion of sample 3 in

an epoxy resin and polishing it to enhance the imaging of the layer thicknesses, the sample was

then scanned using EDX (Energy Dispersive X-Ray detection) to map the presence of elements.

Because there was significant self-heating of the samples during rolling process, there was

suspicion that the foil had reacted during processing that was initiated from the heat produced

from deformation. Figure 15 shows the elemental maps for reactants and oxide presence.

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Figure 15. SEM/EDX element maps of cross section from sample 3 showing aluminum K α1, zirconium L α1, and oxygen presence via K α1 spectrum.

As shown by the previous figures, the minimal presence of oxygen indicates that after

processing via rolling procedure, there is little oxidation that is present and it is dispersed

throughout the material rather than concentrated in specific areas. This shows that the oxidation

that was intentionally induced from the pre-heating step does not remain after rolling or isn't

significant enough to register in EDX scans. In addition to the low presence of oxygen, Figure 15

shows that the aluminum and zirconium layers remained well separated even though they are not

thin enough for ignition. By evaluating using spectra analysis of point measurements made near

the interfaces, it was determined that there was little to no diffusion between layers from heating

24


during the rolling process. Figures 16 and 17 show the dominance of pure elements near

interfaces.

Figure 16. EDX Spectra of point measurements of the aluminum rich zone near layer interface..

Figure 17. EDX Spectra of point measurements of the zirconium rich zone near layer interface..

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4. Summary and Conclusions

The project goals consisted of designing a process for the manufacture of Reactive

Multilayer Foils and assessing the zirconium and aluminum system as a viable candidate for

RMF's. Results of the designed process were expected to show 16 layers; however, due to

slipping of the layers and the deformation of the foil geometry during rolling allowed the 16

layers to reduce to 4 layers as shown in the figures in the previous sections. During processing

some heating occurred which is thought to be due to the volume strain deformation of the

material and its bulk modulus as it relates to the stress applied by the roller. Diffusion between

layers was minimal as evidenced in the SEM images and EDX spectra. The overall thickness of

the foils was offset by a factor of about 85 micron resulting in layer geometries too thick to allow

for ignition at reasonable and achievable temperatures. Layer thickness was also not as expected

due to the sliding of the layers while rolling and the redistribution of grains as the material is

deformed. Post processing, the roller flatness was examined and found that the roller wheels had

become concaved due to heavy use. The force that was applied to the roller pair was also thought

to be insufficient to deform the individual layers to the desired sub-micron scale.

Lessons learned center around the aspects of the roller. It is now known that roller

geometry and flatness plays a crucial role in the outcome of the foil geometry which directly

affects the functionality as a reactive material. It has also been found that a roller set up with a

significantly larger force between rollers is required to deform the materials to the desired

geometry. One of the aspects of the process that can be fine tuned in future experimentation is

the rate of reduction in roller gap setting as a function of the thickness of the specimen. If the rate

of thinning is reduced to a much lower rate, the heating from deformation can be minimized

during rolling and therefore also minimize slipping and reorientation of layers and grains.

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Separation of elements was achieved as expected; however, the number of layers was expected

to remain the original 16 from folding the initial pair of foils three times (24 = 16). Pre-heating to

induce oxidation didn't affect the sample very much according to elemental analysis. The oxide

present is either diffuse enough as to not prevent ignition or the oxygen is out-gassed during

rolling. The ultimate knowledge gained through the design project is that cold-rolling methods

are sufficient to manufacture RMF's with good mating and minimal diffusion between layers.

The deciding factor in whether or not ignition of the foil takes place upon contact with a point

energy source is decided by the layer thickness. If the layers are larger than a micron in size, the

ignition temperature cannot be reached because the energy required to breach the bi-layer

thickness variable is too large to reasonably achieve.

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5. References

[1] [Image]. (2014) Retrieved on 11/6/2014. Retrieved From: www.Indium.com.

[2] [Image]. (2014) Retrieved on 11/6/2014. Retrieved From: http://www.crct.polymtl.ca/fact/documentation/TDNucl/TDnucl_Figs.htm.

[3] Bo, H., Liu, D. D., Liu, L. B., Zhang, L. J., Du, Y., Xiong, X., & Jin, Z. P. (2013). Computational study of atomic mobilities in Al–Zr solid solutions and the growth of ZrAl3 intermetallic phase. Calphad, 40(0), 34-40. doi:http :// dx.doi.org.libaccess.sjlibrary.org /10.1016/j.calphad.2012.11.003

[4] Adams, D. P. Reactive multilayers fabricated by vapor deposition: A critical review. Thin Solid Films, (0) doi:http :// dx.doi.org.libaccess.sjlibrary.org /10.1016/j.tsf.2014.09.042

[5] Qiu, X. (2007). Reactive multilayer foils and their applications in joining(Doctoral dissertation, Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Master of Science in Mechanical Engineering in The Department of Mechanical Engineering By Xiaotun Qiu BS, Tsinghua University, Beijing, China, 2004).

[6] [Image.]. (2015) Retrived on 5/1/2015. Retrived from: http://www.crct.polymtl.ca/fact/documentation/TDNucl/TDnucl_Figs.htm

[7] Barbee, T. W., Weihs, T. (1996). US5538795. Washington, DC: U.S. Patent and Trademark Office.

[8] Weihs, T. P., ReiSS, M., Knio, O., Swiston, Jr, A. J., Heerden, D. V. Hufnagel, T. (2006). US6991856. Washington, DC: U.S. Patent and Trademark Office.

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http://dx.doi.org.libaccess.sjlibrary.org/10.1016/j.tsf.2014.09.042




http://dx.doi.org.libaccess.sjlibrary.org/10.1016/j.calphad.2012.11.003




http://www.crct.polymtl.ca/fact/documentation/TDNucl/TDnucl_Figs.htm

http://www.indium.com/


6. Broader Considerations and Ethics

In contemplation of the effects on the environment and the implications of the ethics in

relation to the design project, the focus of the analysis will be centered around raw materials at

each end of the product life cycle. Because both Aluminum and Zirconium are mined from raw

ores, there was initially a concern regarding the effects on the environment over the handling of

the materials both pre and post use. For an environmentally and ethically responsible design, as

well as successful long term viability, it is necessary that the sources of the raw materials are

sustainable, meaning continuous supply without adversely impacting local environments or

cultures. After researching the possible impacts on the local people and their environment, it was

found that even though some ores are gathered in more developed parts of the world, the bulk of

Aluminum and Zirconium ore is strip mined near the equator leaving behind toxic gases and

residues in addition to requiring large amounts of energy to refine.

In an effort to prevent further environmental impact from strip mining, an alternative

source for raw materials is desired. Aluminum is highly recyclable and would be a viable source

for the amounts of the material that are needed for typical reactive foil applications. Relative to

the levels consumed by others such as aerospace and machinery industries, the amounts needed

for reactive foil production wouldn't be any more of a drain on supply than current consumption.

The materials that reactive foils would replace are primarily solders which already require mined

metals. If the raw materials of the reactive foils replaced the mined ones, it would reduce the

demand for more mining. Rather than mining raw ore and damaging tropical environments,

recycled sources would be desired.

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" With a share of 8 %, aluminium is the third most abundant element in the earth’s crust.

[...] The common raw material for aluminium production, bauxite is composed primarily of one

or more aluminium hydroxide compounds, plus silica, iron and titanium oxides as the main

impurities. [...] On a world-wide average 4 to 5 tons of bauxite are needed to produce two tons of

alumina, from which one ton of aluminium can be produced. In Europe, usually the average

bauxite consumption is 4.2 tons per tonne of aluminium. More than 160 million tonnes of

bauxite are mined each year. The major locations of deposits are found in tropic and sub-tropic

areas. Bauxite is currently being extracted in Australia, Central and South America (Jamaica,

Brazil, Surinam, Venezuela, Guyana), Africa (Guinea), Asia (India, China), Russia (and

Kazakhstan) and Europe (Greece)" [1].

"Zirconium is found in two minerals, zircon (zirconium silicate, ZrSiO4) and baddeleyite

(zirconium oxide, ZrO2). The most important of these ores, zircon, occurs as grains concentrated

in sand deposits in the southeastern United States, and in Australia and Brazil. Russia and Brazil

also have large deposits of baddeleyite. World resources are estimated to be more than 60 million

tons worldwide. Fourteen million tons of zirconium are in heavy-mineral sand deposits in the

United States. [...] Several American metal companies in Oregon and Utah recover zirconium

metal when recycling scrap metals created during metal production " [2].

Rather than continuing to strip mine habitats of populations near the equator, it would be

more sustainable to source local recycled raw materials where possible. The issue with recycling

the Aluminum post use is that after the reactive foil is that once reacted, it is now in a much more

thermodynamically and kinetically stable alloy configuration where one each Al atom and Zr

atom are the basis of the lattice. Such a strong bond between the two is difficult to be broken in

order to separate the Zr from the Al, so recycling of the Aluminum at the end of the product life

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cycle would require very high temperatures to reach the fully liquid state and even then, the solid

solution will be a mixture to some extent. Even though it takes more organization and

forethought to manufacture from recycled resources, it does have both a cost benefit and the

effect of reducing the strain on natural resources in underdeveloped nations near the equator [3].

Because of the impacts of strip mining and refining raw ores in regions near the equator,

it is advantageous to want to recapture as much material as possible. Recapture of the pure

elements for later use would be difficult however, due to the form the product is in at the end of

the life cycle. It is typical that the reactive foil ends in various intermetallic ZrnAlm phases after

reaction and is bonded quite strongly to the two materials being joined which complicates the

separation. This is especially complex in applications where dissimilar materials are being

joined.

The risk of climate change or contamination of the environment from use and

manufacture is low. Although there will be some wetting material needed to facilitate mass

production of the reactive foils, the overwhelmingly large amount of the used foil will remain as

ZrAl. By sourcing recycled raw materials and recapturing used material, the burden on the

environment is reduced. A second option to separating the alloyed material after use is breaking

it down to a powder and re-sourced for a different purpose. In this manner, although the product

life cycle is not a full complete circle, the exit is to another application so the overall impact on

the environment from the supply of the raw materials is minimized.

Carbon output and wastewater is significant in processing raw ores into metals. Strip

mining can cause erosion and ecosystem damage. Health issues related to this design project are

identified mainly as a chance for burning from unexpected ignition, electric shock during

application of an electrical energy source. Since foils are used as starting raw materials, there is

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little risk of carcinogens. There is also little to no danger with material allergy after manufacture.

Radio nuclides as well as air-born dust and metals can contaminate ground water, so debris and

unused portions of the material should be gathered and disposed of in an appropriate container

for nanomaterials. There is some danger handling final product but obtaining materials has

known health risks such as respiratory malfunction, vision and hearing degradation, and skin

rashes. It is important to be careful during manufacture and transport of these materials with high

reactivity. There is a high risk from misuse due to the large amount of energy that is released per

mass unit. There is a high hazard due to burning which leads to a known Danger. Fail-safe

design may not be possible due to functionality of the product and its intended use. It is critical

to be careful during manufacture/transport for materials with high reactivity. Instructions and

warnings must be sufficient to prevent burning of users during application. Liability can be

limited with implementing good labels/manual. Also, it should be stipulated and reminded

multiple times that the material should only be handled by trained persons.

Ethics concerned with the production of a reactive foil are minimal. There is a risk of

upsetting current economies by displacing some soldering and welding applications. For this

reason, it is imperative to oversee development of manufacturing tooling and ensure operators

are adequately trained as well as properly informed about risks and hazards. It is also a must to

educate customers on safe and appropriate use to prevent end user injury. Awareness of the

evolution of the process, the equipment operation, and raw materials is needed to ensure that

there is not a significant deviation from process parameters that greatly affect the outcome and/or

safety of operators. To accomplish this, the question “Is this safe and healthy” is always kept in

mind. It is also important to pay attention to hazards with inappropriate use of the material and to

take steps to prevent misuse. Limited access to materials is also used as method to maintain

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control of access. Accountability to the general public for a safe and healthy manufacturing and

application environments is of utmost importance. In order to accomplish control of the material

and prevent ethical or moral transgressions, continual vision past the obvious should be

maintained to be able to predict future concerns. To maintain credibility during the development

and execution of the design project, it is not sensible to act as expert in applications before

knowledge is gained from research and experimentation. Steps should also be taken so as not to

allow untrained users to access material due to danger. It would be a violation of the fundamental

principles of the engineering community to ignore the dangers of end use. Conflict between

society and employer isn’t seen as a major concern as the project is intended to improve a

processing technique and manufacture a substance with some known properties. Cheaper and

faster raw materials gathering techniques may damage environment and cause native

displacement. The conflict between balancing lower cost vs. safety should always fall on the side

of safety, health, and sustainability. Professionalism dictates not to make claims the material has

certain properties unless confirmed through experimentation. The product should not be

suggested for uses that are known to be unsuccessful. This violates the trust of the general public

and could work to erode the public’s outlook of materials and engineering. It has been

considered to make authorities aware if unsafe practices are not being halted.

References for Broader Considerations and Ethics Section:

[1] None, (2015). Aluminium Production Process. European Aluminium Association. Retrieved from: http://www.alueurope.eu/about-aluminium/production-process/

[2] None, (2015). Zirconium. Minerals Education Coalition. Retrieved from: https://www.mineralseducationcoalition.org/minerals/zirconium

[3] Kirkman, R. K. (2015). Reflection Paper 1. Mate 198B Senior Design Project Assignments. Unpublished manuscript, San Jose State University.

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7. Acknowledgements

Special Thanks goes to the following people for their assistance and/or guidance in supporting

my senior design project: Jacques Matteau, Dr. Michael Oye, and Dr. Richard Chung, Robert

Cormia, Dr. Craig England, Christina Peters, Dan Chafey, Brandon Pham, Dr. Wenonah

Vercoutere, Joseph Varelas, Dr. Edward Lam, and Vic Hageman.

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russell kirkman mate 198b final design report

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