Christopher DellaCorte

Glenn Research Center, Cleveland, Ohio

Nickel-Titanium Alloys: Corrosion “Proof” 

Alloys for Space Bearing, Components and 

Mechanism Applications

NASA/TM—2010-216334

June 2010
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Christopher DellaCorte

Glenn Research Center, Cleveland, Ohio

Nickel-Titanium Alloys: Corrosion “Proof” 

Alloys for Space Bearing, Components and 

Mechanism Applications

NASA/TM—2010-216334

June 2010

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

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Level of Review: This material has been technically reviewed by technical management. 
Nickel-Titanium Alloys: Corrosion “Proof” Alloys for Space 

Bearing, Components and Mechanism Applications 

Christopher DellaCorte 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Abstract 

An intermetallic nickel-titanium alloy, 60NiTi (60 wt% Ni, 40 wt% Ti), is shown to be a promising 

candidate tribological material for space mechanisms. 60NiTi offers a broad combination of physical 

properties that make it unique among bearing materials. 60NiTi is hard, electrically conductive, highly 

corrosion resistant, readily machined prior to final heat treatment, and is non-magnetic. Despite its high Ti 

content, 60NiTi is non-galling even under dry sliding. No other bearing alloy, metallic or ceramic, 

encompasses all of these attributes. Since 60NiTi contains such a high proportion of Ti and possesses 

many metallic properties, it was expected to exhibit poor tribological performance typical of Ti alloys, 

namely galling type behavior and rapid lubricant degradation. In this poster-paper, the oil-lubricated 

behavior of 60NiTi is presented. 

Introduction 

Binary nickel-titanium (Ni-Ti) alloys are in widespread use in the medical and dental industries in 

applications where their biocompatibility and unique superelastic or shape memory effect (SME) 

characteristics are readily exploited (Ref. 1). The Ni-Ti family of alloys traces their origins to pioneering 

work of William J. Buehler and his colleagues at the Naval Ordinance Laboratory during the late 1950s 

(Refs. 2 and 3). The designation NITINOL often used for these alloys is an abbreviation for NickelTitanium Naval Ordinance Laboratory. Buehler’s early efforts identified both the NITINOL 55 and 

NITINOL 60 alloys, which contained 55 and 60 wt% Ni, respectively. NITINOL 55 is soft and was found 

to be easier to mechanically work and form than NITINOL 60 that was prone to excessive work 

hardening. Several hand tools were fabricated from NITINOL 60 to take advantage of its high hardness, 

electrical conductivity, non-magnetic behavior and corrosion resistance (Ref. 4). 

Materials for high-performance bearings, gears and other mechanical components require a number of 

specific properties and characteristics. Among these key attributes are high strength and hardness, high 

thermal conductivity, and the ability to be manufactured to very high levels of precision with regards to 

final dimensions and surface finish. In addition, excellent corrosion resistance and good tribological 

properties are often of importance especially for applications in extreme environments. Spaceflight 

hardware destined to operate in the vacuum of space, beyond the realm of atmospheric corrosion, often 

must be stored for extended periods before launch, and are subject to bearing and gear corrosion 

problems. In select applications involving electric machines and sensitive instrumentation, good electrical 

conductivity and non-magnetic properties can also be highly desirable. Unfortunately, no currently 

deployed material possesses all of these properties. 

Traditional tool steel-based bearing materials, such as M50 and 52100 enjoy widespread application 

due to their high hardness, ease of manufacture and good tribological properties. However, these alloys 

suffer from corrosion attack if not protected and though electrically conductive they are also highly 

magnetic. In addition, when used as bearing rolling elements, their high density leads to high centrifugal 

forces and limited fatigue life. These considerations have driven the search and development of alternate 

bearing and mechanical component alloys, namely stainless steels and ceramics. 

Stainless steels such as 440C are widely used in the bearing and gear industry where corrosion 

resistance and high hardness are required. These martensitic stainless steels are reasonably low cost, easy 

NASA/TM—2010-216334 1 
to machine prior to heat treatment and are dimensionally stable. When prepared through vacuum melting 

processes, they achieve very uniform, fully dense microstructures which lead to fine surface finishes and 

good fatigue behavior. Despite being referred to as “stainless”, however, the 400 series martensitic steels 

are prone to corrosion and are more accurately referred to as “corrosion-resistant” alloys rather than 

stainless. They are also highly magnetic. 

Silicon nitride ceramics, on the other hand, are essentially corrosion proof. They can be polished to 

very fine surface roughness and are quite wear resistant. Silicon nitride’s low density compared to steels 

also makes it ideal for ultra high-speed applications because lower centrifugal stresses result. These 

attributes make silicon nitride the material of choice for high stiffness, high load, and high-speed bearings 

and for applications that include corrosive conditions and aggressive sliding environments. Such 

applications include bearings for gas turbine hot sections, cryogenic oxidizer turbopumps and components 

for diesel engine fuel injection systems. Though non-magnetic, silicon nitride is an electrical insulator. It 

is also more expensive to manufacture than steels owing to the complexity and cost of the hightemperature, high-pressure powder metallurgy processing required. Another shortcoming of silicon nitride 

is the difficulty of fabrication it into bearing raceways and other complex geometries. 

Historically, metallic alloys with high concentrations of Ti are poor tribological materials in that they 

do not respond well to lubrication by organic fluids (Ref. 5). For instance, alloys such as Ti-6Al-4V 

exhibit galling behavior in dynamic contacts even under conditions well lubricated by oils and greases. 

During contact, Ti readily transfers to the counter-face leading to rough surfaces, high friction and wear. 

In addition, Ti alloys are recognized as being chemically aggressive causing degradation of many 

lubricants (Ref. 6). When Ti alloys must be used due to other attributes like high specific strength or 

corrosion resistance, tribological contact is avoided through the use of thick barrier coatings and 

claddings. 

Based upon a wealth of negative experience with Ti alloys in tribological contacts, 60NiTi would 

appear an unlikely candidate as a bearing material. On the other hand, ceramic materials with high 

concentrations of Ti can exhibit desirable tribological properties. Titanium carbide (TiC) and titanium 

dioxide (TiO2) are good examples. TiC coatings are often used to improve the surface finish and 

performance of stainless steel rolling elements in bearings and TiO2, in the form of rutile, has been put 

forth as a potential solid lubricant under certain conditions (Refs. 6 and 7). These ceramic materials, 

however, are brittle and cannot be used as structural elements. In this work, we present evidence that 

hardened NiTi alloys can be produced that are devoid of shape memory or superelastic behavior and that 

such alloys display excellent tribological properties under oil-lubricated contact conditions. 

Materials and Procedures 

The 60NiTi balls evaluated here were manufactured via a proprietary high-temperature powder 

metallurgy process roughly similar to that described in the literature (Ref. 8). Pre-alloyed 60NiTi powder 

was hot isostatically pressed (HIPed) into rough, spherical ball blanks that were then ground, polished, 

and lapped to produce high quality (Grade 5) bearing balls 0.5 in. (12.7 mm) in diameter. 60NiTi plates 

were cut from cast and hot rolled plate stock. A multi-step thermal process (heat treatment) was used to 

enable rough machining of the plates and grinding of the bearing balls in a softened state followed by 

lapping to a very fine surface finish in the final hardened condition. The finished 60NiTi ball specimens, 

shown in the photograph in Figure 1, are bright and shiny in appearance and resemble conventional 

polished steel balls. 

The elemental composition of the bearing material, as measured by atomic emission spectroscopy and 

energy dispersive, semi-quantitative x-ray analysis, were consistent and showed the specimens are 

nominally 55 at % Ni with the balance Ti. This translates to 60 wt% Ni, 40 wt% Ti, hence the historical 

designation of NITINOL 60 or 60NiTi. Density was measured at 6.71 g/cc and is about 15 percent lower 

than 440C stainless steel. Table I displays known and estimated properties of 60NiTi. 

NASA/TM—2010-216334 2 
TABLE 1.—NOMINAL COMPARATIVE PROPERTIES FOR CONVENTIONAL BEARING 

ALLOYS AND NiTi55 AND 60NiTi NITINOL 60 GRADE 5 TEST BALLS 

[Representative thermophysical and mechanical properties of bearing materials.] 

Property NiTi-60 NiTi-55 440C Si3N4 M-50 

Density 6.7 g/cc 6.5 g/cc 7.7 g/cc 3.2 g/cc 8.0 g/cc 

Hardness 56 to 62 Rc 35 to 40 Rc 58 to 62 Rc 1300 to 1500 Hv 60 to 65Rc 

Thermal Conductivity 

W/m-°K 

18 9 24 33 ~36 

Thermal Expansion ~10×10-6/°C ~10×10-6/°C 10×10-6/°C 2.6×10-6 ~11×10-6/°C 

Magnetic Non Non Magnetic Non Magnetic 

Corrosion Resistance Excellent Excellent Marginal Excellent Poor 

Tensile/Flexural 

Strength 

~1000 MPa ~900 MPa 1900 MPa 600 to 1200 MPa 

(Bend Strength) 

2500 MPa 

Young’s Modulus ~114 GPa ~100 GPa 200 GPa 310 GPa 210 GPa 

Poisson’s Ratio TBD ~.3 .3 .29 .30 

Fracture Toughness TBD TBD 22 MPa/√m 5 to 7 MPa/√m 20 to 23 MPa/√m 

Maximum Use Temp ~400° C ~400° C ~400° C ~1100 °C ~400 °C 

Electrical Resistivity ~80×10-6 Ω-cm ~80×10-6 Ω-cm ~36×10-6 Ω-cm Insulator ~60×10-6 Ω-cm 

*TBD means “to be determined” 

Figure 2 shows the cross sectional microstructure of the 60NiTi ball specimens in the final hardened 

and polished condition. Microhardness measurements indicate values in the range of 56 to 62 on the 

Rockwell C scale in the hardened condition. As with most HIPed or sintered powder compacts, the prior 

particle boundaries are quite evident and are delineated by oxides and other tramp phases. Despite 

containing only Ni and Ti, Ni-rich NITINOL microstructures can be very complex due to a series of 

metastable intermetallic phases that can exist depending on thermal history (Ref. 9). Analysis of the 

60NiTi ball specimens reveals multiple discrete phases (NiTi,) with NiTi dominating at approximately a 

77 percent volume fraction. The balance is made up from Ni4Ti3 at 11 percent, Ni3Ti at 10 percent, and 

NiTi2 at 2 percent. 

NASA/TM—2010-216334 3 
Preliminary differential scanning calorimetry (DSC) results for the bearing blanks and finished 

bearings suggest that the 60NiTi bearing blanks may have a slight amount of martensite that could form if 

cooled below –15 °C but in the hardened condition are microstructurally stable down to at least –100 °C. 

This indication is corroborated by our physical measurements of the bearing balls and plates that have 

been dimensionally stable throughout the processing, handling and research activities undertaken. Buehler 

also reported excellent stability during the early alloy development (Ref. 3). 

To assess its tribological properties, spiral orbit tribometer (SOT) tests were conducted using a single 

60NiTi ball loaded between two rotating disks, lubricated with synthetic oil and tested in a vacuum. In 

this test, the 60NiTi ball is marginally lubricated with a small quantity (~25 μg) of oil and undergoes 

mostly rolling contact interrupted by a scrubbing/sliding event every disk rotation. The SOT is depicted in 

Figure 3 and described in detail in References 6 and 10. It is basically a thrust bearing with one ball and 

flat races (plates). One of the plates is stationary and the other rotates to drive the ball into an orbit that is 

an opening spiral. The ball contacts a “guide plate” at the end of each orbit, which forces the ball back 

into its initial orbital radius. A piezoelectric force transducer supporting the guide plate senses the 

frictional force developed on the ball as it slides on the rotating plate during the contact of the ball with 

the guide plate. During this contact, the coefficient of friction is obtained from this force and the load 

imposed on the system. The tribometer is housed in a stainless steel chamber that can be evacuated by a 

turbomolecular pump to ≤2×10–8 Torr. It can be operated either in vacuum environment or at atmospheric 

pressure. 

The plate specimens were 440C stainless steel or 60NiTi. They were lapped flat and their final polish 

resulted in an arithmetic mean surface roughness, Ra, <25 nm (1 μin) determined by optical 

interferometry. The 60NiTi balls were 12.7 mm (0.5 in.) diameter, Grade 5. The final surface cleaning 

procedure for all ball and plate specimens was by lightly rubbing with aqueous slurries of silicon carbide 

polishing powders, followed by sonication in deionized water. This preparation results in a surface on 

which water exhibits zero contact angle (spreads) and which exhibits an XPS spectrum devoid of 

impurities other than a small feature due to adventitious carbon. 

NASA/TM—2010-216334 4 
The plates were initially clean and only the ball was lubricated. For the tests in the boundary regime, 

the ball was first weighed and then lubricated by dripping a dilute solution of the lubricant, ~ 1 mg of 

lubricant per ml of hexane solvent, onto the ball rotating on a small bench lathe. The ball is reweighed 

after evaporation of the solvent and the lubricant charge is obtained from the weight difference. About 

20 mg (24 nl) of lubricant, a multiply alkylated cyclopentane (MAC) designated by the trade name 

Pennzane 2001A, were used on each ball. Tests were run here at a system load of 30 lb, which resulted in 

a track width of ~0.4 mm and corresponds to a Hertz pressure of 1.06 GPa. The test conditions result in 

operation in the boundary-lubrication regime. Considering the small quantity of lubricant present in the 

tribosystem, test lifetimes on the order of a few tens of thousands of revolutions are typical for good 

tribological materials like 440C and past experience with the SOT, indicates its relevance in mimicking 

the tribological conditions typical of a space ball bearing application (Ref. 6). 

Results and Discussion 

Under these conditions, considered representative of precision bearings, performance (life and 

friction) was comparable to that observed with 440C bearing balls. Figure 4 shows the friction results for 

tests of 60NiTi balls running against 440C plates (left graph) and NITINOL 60 plates (right graph) in the 

SOT. Typical lubricant lifetimes were approximately 30,000 to 60,000 revolutions indicating a slow 

lubricant consumption rate. In one test using both 60NiTi plates and ball, the rig was permitted to run 

well beyond the complete consumption of lubricant. The friction climbed to a coefficient of around 0.35 

but was stable and no galling tendencies were observed. 

In comparison, SOT tests of balls sputter coated with pure, thin Ti films degrade the lubricant, 

experience high friction and seizure within a few dozen revolutions. Unlike traditional Ti alloys, the 

60NiTi alloy performs well indicating it is a good candidate for bearings and mechanical components. 

Being impervious to the corrosion issues facing traditional bearing materials especially during storage 

before launching is a major asset. 

NASA/TM—2010-216334 5 
Summary 

This research effort has identified 60NiTi alloy as a promising candidate material for bearing and 

mechanical component applications. 60NiTi, when appropriately processed and fabricated, is 

dimensionally stable, hard, wear-resistant, non-galling, and tribochemically benign in the presence of 

liquid lubricants. Such behavior is in stark contrast to conventional alloys that contain large amounts of 

the metal Ti. It is believed that the good tribological performance under oil lubrication observed for 

60NiTi may extend to the entire NiTi family of alloys since they all share similar phase constituents and 

basic atomic level bonding. The tribochemistry of 60NiTi and its metallurgical relatives are under further 

study. 

The identification of a viable bearing material that is non-magnetic, electrically conductive, 

hardenable, displays favorable tribochemistry and is non-corrosive is a major research finding. No other 

bearing material yet discovered has such a broad combination of properties. While it is clear that near 

term niche applications such as aerospace bearings and gears exist, many non-obvious applications are 

also likely to present themselves. These include wear-resistant, corrosion-proof knives and cutters, 

electric machine structural and dynamic components, high-performance fasteners, valve components and 

many others. 

Clearly, much more research will be required to understand the 60NiTi material and its metallurgical 

relatives. The relationships between mechanical and physical properties, atomic structure, micro-scale 

ordering and surface chemical interactions remain to be investigated. Nonetheless, the NiTi metallurgical 

system clearly has engineering potential well beyond shape memory alloy applications. 

References 

1. S.A. Shabalovskaya: “Surface, Corrosion and Biocompatibility Aspects of Nitinol as an Implant 

Material,” Bio-Medical Materials and Engineering, Vol. 12, 2002, pp. 69–109. 

2. Buehler, W.J., J.V. Gilfrich, and R.C. Wiley: “Effect of Low-Temperature Phase Changes on the 

Mechanical Properties of Alloys near Composition TiNi,” J. of Applied Physics, Vol. 34, No. 5, May 

1963, pp. 1475–1477. 

3. Bueher, W.J.: ”Intermetallic Compound Based Materials for Structural Applications,” Proceedings of 

the 7th Navy Science Symposium: Solution to NAVY Problems Through Advanced Technology, 

May 14–16, 1963, U.S. Naval Aviation Medical Center, Ensacola, Florida, Vol. 1. Office of Naval 

Research, Arlington, VA, May 1963. 

NASA/TM—2010-216334 6 
NASA/TM—2010-216334 7 

4. W.J. Buehler: “NITINOL Re-Examination,” White Oak Laboratory Alumni Association Leaf, Winter 

2006, volume VIII, Issue I, www.wolaa.org. 

5. R.W. Roberts and R. S. Owens; Titanium Lubrication, Nature, Vol. 200, Oct. 26, 1963, pp. 357–358. 

6. Jones, W.R.Jr., Pepper, S.V., Wheeler, D.R., Jansen, M.J., Nguyen, Q.N., and Schroer, A., “The 

Effect of Stress and TiC Coated Balls on the Lifetime of a Perfluoropolyalklether Using a Vacuum 

Rolling Contact Tribometer,” Tribology Transactions, Vol. 43 (2000), 4, pp. 685–688. 

7. M.N. Gardos, H.H. Hong, and W.O. Winer: “The Effect of Anion Vacancies on the Tribological 

Properties of Rutile (TiO2-x), Part II: Experimental Evidence,” STLE Tribology Transactions, 

Vol. 33, No. 2, April 1990, pp. 209–220. 

8. M.D. McNeese, D.C. Lagoudas, and T.C. Pollock; “Processing of TiNi from Elemental Powders by 

Hot Isostatic Pressing,” Materials Science and Engineering A280 (2000), pp. 334–348. 

9. K. Otsuka and X. Ren: “Physical metallurgy of Ti-Ni-based shape memory alloys,” Prog. Mater. Sci., 

Vol. 50, pp. 511–678, 2005. 

10. W.R. Jones, Jr., S.V. Pepper, M.J. Jansen, Q.N.Nguyen, E.P. Kingsbury, S.H. Loewenthal, and R.E. 

Predmore: “A New Apparatus to Evaluate Lubricants for Space Applications-The Spiral Orbit 

Tribometer (SOT),” NASA/TM—2000-209935. 
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14. ABSTRACT

An intermetallic nickel-titanium alloy, 60NiTi (60 wt% Ni, 40 wt% Ti), is shown to be a promising candidate tribological material for space 

mechanisms. The 60NiTi offers a broad combination of physical properties that make it unique among bearing materials. The 60NiTi is 

hard, electrically conductive, highly corrosion resistant, readily machined prior to final heat treatment, and is non-magnetic. Despite its high 

Ti content, 60NiTi is non-galling even under dry sliding. No other bearing alloy, metallic or ceramic, encompasses all of these attributes. 

Since 60NiTi contains such a high proportion of Ti and possesses many metallic properties, it was expected to exhibit poor tribological 

performance typical of Ti alloys, namely galling type behavior and rapid lubricant degradation. In this poster-paper, the oil-lubricated 

behavior of 60NiTi is presented. 

15. SUBJECT TERMS

Intermetallic; Titanium alloys; Nickel alloys; Lubrication; Tribology; Spacecraft lubrication; Gears; Transmissions 

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