phd case study x-ray diffraction (xrd) characterisation residual stress calculation typical exam...

$: PhD Case Study X-ray diffraction (XRD) characterisation Residual stress calculation Typical exam question Laser surface modification$
Laser Surface Modification of Metalsand

XRD Characterisation

Presentation Outline

PhD Case Study

X-ray diffraction (XRD) characterisation

Residual stress calculation

Typical exam question

Laser surface modification

Material Processing Research Centre, Dublin city University

Laser Surface Modification


4

LASER - light amplification by stimulated emission of radiation: highly directional, coherent, and monochromatic beam of light

Laser in material processing can be used for many purposes i.e. cutting, surface modification

Several laser surface modification methods exist: Transformation hardening Laser alloying/cladding Glazing

Laser Surface Treatment


5

Effects of Laser on materials


6

Rofin DC-015, CO2 laser specifications: 10.6 µm wavelength Power capacity of 1500W Operates in both continuous and pulsed mode Pulse width ranges between 26µs to ~ 500ms

Laser System


7

Laser system processing parameters


Power (W) 100 - 1500

Beam geometry Circle

Focus Surface

Spot size (mm) 0.09 – 1

Traverse speed (mm/min) upto 5000

Overlap (%) 10 - 30%

Assist gas Argon

Laser Mode TEM00

Operation Mode Cont./ Pulsed

Case Study: PhD Research


9

One in four hundred people receive hip replacement surgeries in Ireland*

Up to 250,000 annual hip replacements surgeries in USA

Approximately 20% simply being replacements of failed implants

Success rate has significantly gone up but material life is low

Typical life of an artificial hip being 15 – 20 years

Patients undergo revision surgeries throughout their lifetime

One main challenge is developing a life long artificial hip replacement

Excessive wear debris and loosening of the implant are primary causes of failure

Improving tribological properties of the implant will greatly improve its lifetime

*http://www.wrongdiagnosis.com/h/hip_replacement/stats-country.htm#extrapwarning

Case Study: PhD Research


The aim of this study is to produce surface engineered implant alloy capable of having

improved tribological properties using high speed laser treatment

Using high speed laser treatment to achieve a rapid cooling rate

Rapid laser treatment can produce an amorphous structure

Aims of the Study


Advantages of laser surface engineering Superior bonding with the substrate

Simple oxidation elimination techniques

Improved depth control and reduced distortion

Little or no sample preparation required

Less time/ energy and material required compared

to convectional coating techniques

Typical Results

Increasing Energy

Topology and microstructure

LHS – Topology

RHS - cross-sectional

microstructure analysis

Effects of energy fluence

a) 524 J/cm2

b) 1048 J/cm2

c) 2096 J/cm2

Depth of processing

Overlapping

Homogeneity of treatment

Grain structure orientation

(a)

(b)

(c)

50 μm

50 μm

50 μm

100 μm

100 μm

100 μm

Microstructure Analysis

12Material Processing Research Centre, Dublin city University

SEM cross section micrographs of samples processed using the same energy fluence (1310 J/cm2): Titanium alloy Stainless steel

(a)

(a)

(b)

(b)

Meltpool and Roughness Analysis

MELTPOOL ANALYSIS ROUGHNESS ANALYSIS

13Material Processing Research Centre, Dublin city University

40 50 60 70 80 90 100 1100

10

20

30

40

50

60

70

80

90

100

7.9

12.6

15.7

20.4

23.6

Residence time (μs)

Mea

n de

pth

of p

roce

ssin

g (μ

m)

Irradiance (MW/cm2)

5.0E+06 1.0E+07 1.5E+07 2.0E+07 2.5E+070

2

4

6

8

10

12

14

50μs

67 μs

83 μs

100 μs

167 μs

Irradiance (W/cm2)

Rou

ghne

ss (

μm

)

Residence Time

Laser treatment of HVOF - WC-CoCr coatings

80 130 180 230 280 3301400

1500

1600

1700

1800

1900

2000

0.20.6

Peak Power (W)H

ardn

ess

(Hv)

Beam Spotsize (mm)

UNTREATED LASER TREATED

(a)

(b)

(c)

(a) & (b) Surface Topology

(c) Cross-sectional microstructure

X-ray Diffraction


X-rays are a form of electromagnetic radiation that have high energies and short

wavelengths (on the order of atomic spacings for solids)

X-ray diffraction occurs when waves encounter a series of regularly spaced

obstacle that:

(1) are capable of scattering the wave

(2) have spacings comparable in magnitude to the wavelength

X-rays diffraction can therefore be used for material characterisation of metal

Phase identification of metals

Determination of crystal structures

Residual stress measurements

X-ray Diffraction



Diffraction of x-rays by planes of atoms (A-A’) and (B-B’).

•Two parallel x-rays of wavelength λ impinging on a crystal surface at angle θ.

•Parallel to the surface is a row of crystal planes, separated by distance dhkl

• Assumptions: the same thing happen at the deeper planes reached by other penetrating X rays.

•From simple geometry, SQ=QT= dhkl sinθ which emerges as Bragg’s Law

•Interplanar spacing, dhkl


T= x-ray source, S = Specimen, C = detector, and O = axis.

X-ray diffractometer

Diffraction pattern


polycrystalline -iron

Stress Measurements


Stress MeasurementsX-ray diffraction can be used as a form of uniform stress measurement

When stress is applied lattice spacings change from stress free values

measuring the change in lattice position gives strain

Consider conventional stress measurement technique – electric resistance

Strain is measured by resistance caused by extension of the gauge

In x-ray method, the strain gauge is spacing of lattice planes

Applied stress is force per unit area – if the external force is removed the stress

disappears

Residual stress is the stress that persists in the absence of an external force

Residual stress causes fatigue crack resulting in failure of components


Stress MeasurementsX-ray stress measurement assumes uniaxial stress

Uniaxial stress considers stress in a single direction

Consider a rod of cross sectional area A stressed

elastically in tension by force F

Stress σ = F/A in y direction but none in x or z

direction

The stress σy produces a strain

If the bar is isotropic the strain is related by:


x-rays

XRD Stress MeasurementsBack reflection x-ray measurement is used to measure strain

using x-rays:

Residual stress measurements are given by:

Where,E – Young modulus

dn – spacing of planes parallel to the axis under stress

d0 - the spacing of same planes in absence of stress

ν – Poisson's ratio


Ti-6Al-4V XRD pattern


Questions


Q1. Figure 1 below shows the as-received XRD pattern for Ti-6Al-4V alloy:


Calculate the peak positions (2θ) for peak 1, 2, 3 and 4 given the following:• Cu Kα (λ = 1.5405 Å) radiation system used• Order of reflection, n = 1

Peak dhkl (Å)

1 2.555

2 2.341

3 2.243

4 1.7262

Q2. Subsequent to laser treatment, shift in peak positions were observed :


(b) Determine the dhkl (interplanar spacing) of the peaks given the following:

(c) Calculate the residual stress σy given that:• Young modulus of Ti-6Al-4V alloy, E = 113.8 GPa• Possion’s ratio, ν = 0.342

Peak 2θ

1 35.5

2 38

3 40

4 55

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Determination of Crystal Structures

W.D. Callister, Materials science and engineering an introduction, 5th Edition, Chp 3

Stress measurement using XRD

B.D. Cullity and S.R. Stock, Elements of X-ray Diffraction, 3rd Edition, Chapter 15

Case Study: PhD research

Online: Applied Physics A - Process mapping of laser surface modification of AISI

316L stainless steel for biomedical applications

Online: Int. Journal of Material Forming - Surface modification of HVOF thermal

sprayed WC-CoCr coatings by laser treatment

Additional Reading Material

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Applied Physics A: DOI 10.1007/s00339-010-5843-5 Process mapping of laser surface modification of AISI 316L stainless steel for biomedical

applications

Accepted 10 June 2010

Int. Journal of Material Forming: DOI 10.107/s12289-010-0891-0 Surface modification of HVOF thermal sprayed WC-CoCr coatings by laser treatment

Accepted 17 June 2010

Analysis of Microstructural changes during Pulsed CO2 Laser Surface Processing of AISI

316L Stainless Steel Accepted for publication – Advanced Materials Research (AMR)

Publications


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Question 1

Question 2

(b)

(c)

Formulas


31

Question 1

Solutions


Peak dhkl (Å) θ 2θ

1 2.555 17.54 35.092 2.341 19.21 38.423 2.243 20.09 40.174 1.726 26.5 53.00

Question 2

Peak 2θ dhkl σy (GPa)

1 35.5 2.527 3.642 38.74 2.322 2.703 40.72 2.214 4.304 53.68 1.706 3.86

phd case study x-ray diffraction (xrd) characterisation residual stress calculation typical exam...

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