Integrated Computational Materials Engineering •Advances in Spinodal Alloys •

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High-Tech Materials & Processes

AN ASM INTERNATIONAL PUBLICATION

SEPTEMBER 2013 • VOL 171, NO 9

www.asminternational.org

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Scientists have known about spinodalmaterials for some time, but it was notuntil J. Willard Gibbs first identified the

thermodynamic stability associated with spin-odal decomposition that ceramic scientistsbegan to explore their possibilities in the firsthalf of the 1900s. Researchers continued to ex-plore metallic systems in the latter part of the20th century, but it was not until the 1960s thatdetailed alloy imaging was realized using trans-mission electron microscopy.

Bell Laboratories exploited Cu-Ni-Sn alloysin the late 1960s, developing innovations andpatents in the 1970s. However, commercializa-tion of wrought Cu-15Ni-8Sn alloy was limitedand eventually abandoned due to hot crackingduring traditional hot rolling or forging. Al-though powder metallurgy made the system vi-able in the 1980s for low cross-section products

such as strip and wire, it was not until the early1990s that casting technology evolved to solvethe hot working problem associated with largersection product forms. See Table 1.

Materion Brush Inc. achieved a break-through in the 1990s after constructing a plantdedicated to a new casting process to producethe EquaCast microstructure, followed by ex-tensive development of hot working technol-ogy. The company now casts and hot workssections as large as 24-in. in diameter to pro-duce significant sizes of bar, tube, plate, andstrip, and development of cold worked tempersof all product forms is emerging.

Materion developed and commercializedCu-Ni-Sn alloys using lean sigma methodol-ogy and tools. End-user needs were brokendown into project packages and a series ofprojects helped to expand the alloy family by

Performance Advances in Copper-Nickel-Tin Spinodal Alloys

W. Raymond Cribb, FASM*

Michael J. Gedeon*Fritz C. GrensingMaterion Brush Inc.Mayfield Heights, Ohio

The uniquemetallurgy andmicrostructureof Cu-Ni-Sn alloys offer abeneficialcombination of strength, tribology, corrosion resistance,toughness, and reliabilityfor diverse applications inthe oil and gas,aerospace, mechanicalsystems, andelectronics industries.

*Member of ASM International

This article updates the current state of the art regarding Cu-15Ni-8Sn alloy manufactured under the tradenameToughMet 3, which uses vertical continuous casting and molten metal stirring to produce the so-called EquaCastmicrostructure. This casting technology enables hot working processes, extending the property combination optionsthat meet demanding application needs in aerospace bearings, oil and gas exploration components, tribologic partsfor mechanical systems and machinery, and electronic connectors. An article in the June 2006 edition of Advanced Materials & Processes provides more detail about the metallurgy and utility of ToughMet 3. Selected referencesfurther detail the alloy system.

TABLE 1 — EVOLUTION OF COPPER NICKEL TIN SPINODAL ALLOYS

Cast/wrought alloy inventions

(Bell Laboratories)

Powder metallurgy – small section(strip, wire)(Pfizer)

Casting scale-up(rod, tube)

(Materion Brush Inc.)

Cast shapes

Near-net-shapecastings

CX tempers

Large wrought productsinnovations

Cold worked products(rod, tube)

Cold worked products(strip, wire)

Expanded size ranges,expanded property

combinations

TS tempers

Hot worked products(rod, tube, forgings, plate)

Expanded size ranges

AT tempers

1970s

1980s

Early 1990s

Late 1990s

Early 2000s

Late 2000s

2010s

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Alloy Description

UNS C96970

ToughMet 2 CX Cast and spinodally

UNS C96900 hardened

ToughMet 3 CX

UNS C72900 Wrought andspinodally

ToughMet 3 AT hardened

UNS 72900

ToughMet 3 TS Wrought, cold worked,

UNS C72900 andspinodally

BrushForm 158 hardened

UNS C72700

BrushForm 96

Specifications and MMPDS handbook

appearances

—

ASTM B505

AMS 4595 (plate), AMS 4596 (rod and bar), AMS 4598 (tube),

ASTM B929, MMPDS-07 (rod, bar, and tube)

AMS 4597 (rod and bar),MMPDS-07 (rod and bar)

ASTM B740

ASTM B740

further developing and verifying process re-liability. Using production material, engi-neers were able to verify property sets.Production lots were separated by both timeand dimension to measure within and be-tween variation in the system. These resultswere valuable for developing manufacturingcontrol plans as alloy tempers were commer-cialized. In addition, this approach helpedsignificantly when introducing the alloy intothe materials community.

Spinodal alloy metallurgyMost copper-base alloys derive strength

from solid solution hardening, cold working,precipitation hardening, or a combination ofthese. In the ternary copper-nickel-tin alloysthat include Cu-9Ni-6Sn (ToughMet 2) andCu-15Ni-8Sn (ToughMet 3), the high mechan-ical strength options shown in Table 2 are pro-duced by controlled thermal treatment thatcauses spinodal decomposition.

Classic spinodal decomposition takes placespontaneously and does not require an incuba-tion period. Instead of the typical nucleation-and-growth process, spinodal decomposition is

a continuous diffusion process in which the orig-inal alloy decomposes into two chemically dif-ferent phases with identical crystal structures.Each phase in the spinodally hardened alloy ison the nanoscale and is continuous throughoutthe grains up to the grain boundaries.

Spinodal decomposition in copper-nickel-tin alloys triples the yield strength of the basemetal and results from the coherency strainsproduced by the uniform and high-number-density dispersion of tin-rich perturbations inthe copper matrix. Cold working prior to thespinodal hardening treatment adds additionalstrength and ductility.

Spinodal decomposition hardening onlyhappens under certain conditions—the solid-state phase diagram of a spinodal system mustcontain a miscibility gap, a region in which thesingle phase alloy separates into nanophases.The alloying elements must also have sufficientmobility in the parent matrix at the miscibilitygap to allow interdiffusion.

Spinodal heat treatmentHeat treatment steps for spinodal decom-

position include:

0.2% Offset yield

strength

90-100 ksi620-690

MPa

95-105 ksi655-725

MPa

90-110 ksi620-760

MPa

95-150 ksi655-1035

MPa

75-200 ksi515-1380

MPa

55-140 ksi380-965

MPa

Tensile strength

105-110 ksi725-760

MPa

100-110 ksi690-760

MPa

110-135 ksi760-930

MPa

106-165 ksi730-1140

MPa

95-205 ksi655-1415

MPa

90-160 ksi620-1105

MPa

rod, tube,customshape

rod, tube,plate

rod, tube,wire

strip

strip

10-5%

6-4%

15-4%

18-3%

22-1%

16-1%

HRC 27-29

HRC 27-30

HRC 26-32

HRB 97-HRC 36

HRB 89-HRC 38

HRB 91-HRC 45

—

—

9-4 ft lb12-5 J

30-4 ft lb40-5 J

—

—

—

—

45-30 ksi√in49-33

MPa√m70-40ksi√in77-44

MPa√m

–

—

TABLE 2 — PROPERTIES OF COPPER NICKEL TIN SPINODAL ALLOY PRODUCTS

Tensile

elongation

Hardness

CVN

impact

strength

K1cfracture

toughness

Product

form

s

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• Homogenization at a temperature above the miscibility gap to develop a uniform solid solution of a single phase

• Rapid quenching to room temperature toretain the solid solution state

• Reheating to a temperature within the spinodal region to initiate the reaction, and holding for sufficient time to complete the spinodal decomposition

Materion’s copper-nickel-tin alloys arespinodally hardened at the mill, eliminating theneed for heat treatment by users. In this pre-hardened condition, alloys are fully machinableand offer unique combinations of high strength,corrosion resistance, and low friction and wear.

Spinodal microstructureAlloys strengthened by spinodal decompo-

sition develop a characteristic modulated mi-crostructure. Resolution of this fine scalestructure is beyond the range of optical mi-croscopy and is only resolvable by skillful trans-mission electron microscopy. Alternatively,satellite reflections around the fundamentalBragg reflections in x-ray diffraction patternscan confirm spinodal decomposition in copper-nickel-tin and other alloy systems.

Tin-rich zones formed by spinodal decom-position during early heat treatment stages de-

velop an ordered structure in the peak-agedcondition, further enhancing strength. Overag-ing produces a discontinuous grain boundaryreaction consisting of a pearlitic a + g phasemixture that consumes spinodally hardenedgrains, leaving behind a soft microstructurewith reduced ductility.

Product evolutionAs shown in Table 1, product forms have

become more diverse, and in general, largerduring the 2000s. This stems from growingmarket awareness of the property combinationsthat can meet field service demands. Morespecifically, four major market segments—oiland gas, aerospace, mechanical systems, andelectronics—have spurred new product devel-opment. See Table 3.

Oil and gas—Demands in the explorationsegment of the oil and gas industry tradition-ally require inherent magnetic transparency,high strength, resistance to stress corrosioncracking (SCC), and antifriction characteris-tics of the system. Further needs for robust-ness during handling, make up, and in-servicedynamic loading require increased impacttoughness, notch strength, and fracturetoughness. These requirements are being metby two new tempers with significantly higher

Influencing material properties

K1C, CVN impact strength, notch strength ratioFatigue strength, fatigue crack propagation

Elastic modulus

Fatigue strength, wear resistance, corrosion resistance, stress relaxation resistance, statistical analysis of these properties

Hardness, elastic modulusWork hardening rateCoefficient of frictionYield strength, ultimate strengthThermal conductivity, electrical conductivity

Galvanic potential

Elevated temperature strength, stress relaxation resistanceFatigue strengthStress relaxation resistanceSpecific yield strengthStress relaxation resistance, yield strength

Market segment

Oil & gas

Oil & gas, aerospace

Electronic connectors

Oil & gas, aerospace, mechanical systems, electronic connectors

Oil & gasMechanical systems, aerospaceMechanical systems, aerospaceMechanical systems, aerospace, oil & gasMechanical systems, aerospace, electronic connectors

Oil & gas

Oil & gas, electronic connectors

Aerospace, mechanical systems, oil & gas

Mechanical systems, aerospaceAerospaceElectronic strip

Desired attribute

Resistance to fracture

Fatigue resistance

Vibration damping (stiffness)

Long life/reliability

Galling resistanceWear resistanceHeat generation, power lossAbrasion resistanceLow operating temperature

Compatibility with other alloys

Temperature resistance

Cracking/spalling resistanceInterference fit stabilityWeight/volume controlResistance to permanent deformation

TABLE 3 — DESIRED MATERIAL ATTRIBUTES

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strength, which provide engineered yield strengths of 95and 110 ksi and CVNs of 30-60 and 12-20 ft-lb. Alongwith significant improvements (20-40%) in notchstrength ratio (NSR) compared to standard hot worked(110 ksi yield strength) product at a stress intensity fac-tor of about 3.9 and in fracture toughness, these newtempers fulfill the need for field robustness over tradi-tional hot worked material.

Aerospace—Similarly in aerospace, traditional hotworked metal with 110 ksi yield strength meets perform-ance needs in landing gear where high compressionstrength and resistance to galling and seizing is important.Back extrusion and other hot working methods are meet-ing demands for larger diameters of tubular shapes and willsatisfy the need for larger, long-range jet aircraft and in-termediate-range commercial aircraft for longer service ofnose and main landing gear.

This effort is also creating growth in components re-quiring the tribological characteristics of ToughMet. Inaddition, the FAA-sponsored Metallic Materials Proper-ties Development and Standardization (MMPDS)process and Aerospace Materials Specification (AMS)have established property design minimums for rod, bar,tube, and plate for the AT and TS product tempers. Ex-tensive production and testing of these 110 and 150 ksiyield strength configurations are establishing use ofToughMet 3 in jet aircraft landing gear systems. Second-ary property testing is a part of the MMPDS system, in-cluding basic tensile properties, pin bearing,compression, shear, and selected physical properties, allhaving a statistical basis recognized by the FAA.

Spherical bearings for aerospace use require signifi-cantly higher strength than those used in other applica-tions due load concentration. To meet this need, a newtemper with 150 ksi yield strength and increased size ca-pability was developed to enable use in landing gear, par-ticularly when operating with gall-sensitive titanium andPH stainless steels.

Mechanical systems—Ground engaging machinery,mining equipment, and internal combustion enginesare finding success in adapting cast and wrought ver-sions of ToughMet 3 for bushing and bearing applica-tions. As such, these applications are steadily growing.The need to manage mechanical distortion during fab-rication is being met by FEA methods and develop-ment of precision machining methods using designedexperiments, tooling engineering, and measurementtechnology.

Plate and sheet forms are offered to service slidingcomponentry or roll formed bushings and bearings,along with rod, bar, and tube configurations in bothwrought and cast forms.

Electronics—Copper beryllium strip has long been thematerial of choice for high reliability signal and power con-nectors and springs due to its unique combination ofstrength, formability, and conductivity. Although copperberyllium can be used safely, alternative materials that donot contain beryllium are desired.

A natural extension of the ToughMet 3 plate prod-uct rolled into strip form satisfies this need. Brush-Form 158 is named after its nominal 15% nickel, 8%tin composition. It has strength, resilience, and forma-bility similar to copper beryllium and can be used in spring applications where conductivity is not as important, such as in electromagnetic shielding gaskets. BrushForm 96 (based on ToughMet 2 compo-sition) may be used for springs requiring additionalconductivity.

ToughMet 3 is available in small-diameter rod andwire for machined electronic connectors, such as coax-ial connectors used in telecommunications base sta-tions and down-hole drilling equipment, as well ascircular connectors used in trucks or military avionics.Its high strength, inherent resistance to both corrosionand atmospheric tarnishing, and stress relaxation re-sistance ensures reliable passage of critical electricalsignals, similar to the performance of traditional cop-per beryllium alloys.

Current trendsDemand for more mechanically robust products con-

tinues in oil and gas exploration markets and the TS tem-pers are beginning to satisfy this demand.

Environmental pressure is driving producers of per-formance components away from alloys containing beryl-lium, in spite of their superior attributes. In response, theCu-15Ni-8Sn alloy and associated tempers are gainingwider use.

Strip product forms are building the basis for passivemicro-mechanical products in the electronics industry.

Future prospectsMachining of finished parts in oil and gas, aerospace,

and mechanical systems necessitates a premium for thecomponents. Additional product forms will be available toimprove yields and minimize costs associated with ma-chining, material handling, and related infrastructure.

Bearings manufactured from strip, rolled into shape,and potentially welded will reduce the cost of machiningthin-walled bearings out of tube. Alternative additivemanufacturing or net shape processes might be able toreduce cost and enhance overall competitiveness withoutsacrificing performance. New property combinations—generally higher strength with higher ductility—are achallenge that will resolve by further development, re-sulting in new tempers and even new alloys.

Reproducibility during the production process is a keyfactor in maximizing yield, throughput, and overall prod-uct consistency. Continuous improvement using leansigma principles will increase consistency to levels in ex-cess of Cpk = 1.

Cu-Ni-Sn spinodal alloys are poised to meet currentand future demands for superior combinations of strength,tribology, corrosion resistance, toughness, formability/fab-ricability, optimized size and shape range, and improvedreliability.

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For more information:W. Raymond Cribb is director oftechnology of Materion Brush Inc., 6070 Parkland Blvd.,Mayfield Heights, OH 44124, 216/486-4200, raymond.cribb@materion.com, www.materion.com.

BibliographyW.L. Bell and G. Thomas, Applications and Recent De-

velopments in Transmission Electron Microscopy, Elec-tron Microscopy and Structure of Materials, Vol 1971, p23-59, University of California Press, 1972.W.R. Cribb, Copper Spinodal Alloys for Aerospace, Ad-

vanced Materials & Processes, ASM International, June2006.W.R. Cribb, Anti-Friction Behavior of Selected Cop-

per-Based Bearing Alloys, Brush Wellman, Cleveland,AT0023/0502.W.R. Cribb and F.C. Grensing, Mechanical Design

Limits for a Wrought Cu-15Ni-8Sn Spinodal Alloy, SAEAeroTech Congress, Paper 2009-01-3255, Seattle, No-vember 2009.W.A. Glaeser, Wear Properties of Heavy Loaded Cop-

per-Base Bearing Alloys, JOM, Vol 35, No. 10, p 50-55.D. Krus and W.R. Cribb, ToughMet Alloy: Improving

Thrust Bearing Performance Through Enhanced Mate-rial Properties, SAE Commercial Vehicle EngineeringCongress and Exhibition, Paper 2004-01-2675, Chicago,October 2004.S. Para, Spinodal Transformation Structures, ASM

Handbook, Vol. 9, p 140-43, 2004.Metallic Materials Properties Database and Standard-

ization (MMPDS) Handbook, Chapter 7, MMPDS-07,Federal Aviation Administration, 2012.J.T. Plewes, Method for Treating Copper-Nickel-Tin

Alloy Compositions and Products Therefrom, U.S.Patent, No. 3,937,638, February 1976.J.-C. Zhao and M.R. Notis, Spinodal Decomposition

Ordering Transformation and Discontinuous Precipita-tion in a Cu-15Ni-8Sn Alloy, Acta Metall.,Vol 46, No. 12,p 4203-4218.

Reprinted from the September 2013 issue of Advanced Materials & Processes magazine.

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