Christopher DellaCorte

Glenn Research Center, Cleveland, Ohio

Michael Jefferson

Kamatics Corporation, Bloomfi eld, Connecticut

60NiTi Intermetallic Material Evaluation for

Lightweight and Corrosion Resistant Spherical

Sliding Bearings for Aerospace Applications

Report on NASA-Kamatics SAA3–1288

NASA/TM—2015-218723

November 2015
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Christopher DellaCorte

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Michael Jefferson

Kamatics Corporation, Bloomfi eld, Connecticut

60NiTi Intermetallic Material Evaluation for

Lightweight and Corrosion Resistant Spherical

Sliding Bearings for Aerospace Applications

Report on NASA-Kamatics SAA3–1288

NASA/TM—2015-218723

November 2015

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

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NASA/TM—2015-218723 1 

60NiTi Intermetallic Material Evaluation for Lightweight and 

Corrosion Resistant Spherical Sliding Bearings for 

Aerospace Applications 

Report on NASA-Kamatics SAA3–1288 

Christopher DellaCorte 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Michael Jefferson 

Kamatics Corporation 

Bloomfield, Connecticut 06002 

Abstract 

Under NASA Space Act Agreement (SAA3–1288), NASA Glenn Research Center and the Kamatics 

subsidiary of the Kaman Corporation conducted the experimental evaluation of spherical sliding bearings 

made with 60NiTi inner races. The goal of the project was to assess the feasibility of manufacturing 

lightweight, corrosion resistant bearings utilizing 60NiTi for aerospace and industrial applications. NASA 

produced the bearings in collaboration with Abbott Ball Corporation and Kamatics fabricated bearing 

assemblies utilizing their standard reinforced polymer liner material. The assembled bearings were tested 

in oscillatory motion at a load of 4.54 kN (10,000 lb), according to the requirements of the plain bearing 

specification SAE AS81820. Several test bearings were exposed to hydraulic fluid or aircraft deicing fluid 

prior to and during testing. The results show that the 60NiTi bearings exhibit tribological performance 

comparable to conventional stainless steel (440C) bearings. Further, exposure of 60NiTi bearings to the 

contaminant fluids had no apparent performance effect. It is concluded that 60NiTi is a feasible bearing 

material for aerospace and industrial spherical bearing applications. 

Introduction 

Materials that are suitable for use in bearings are generally limited to four broad categories each of 

which have advantages and disadvantages. The four categories are: (1) hardening steels, (2) superalloys 

and austenitic stainless steels, (3) ceramics and lastly, (4) non-ferrous alloys which include copper, zinc, 

and plastics. The hardening steels, such as M50 tool steel and 440C are inexpensive and have high 

hardness but generally poor corrosion resistance. Superalloys like Inconel and Stellite and austenitic 

stainless steels like 304LC, exhibit excellent corrosion resistance but low hardness. Ceramics such as 

silicon nitride are hard and chemically inert but are brittle and difficult to incorporate into machine 

designs because of their extreme rigidity and low thermal expansion coefficients. Finally, the non-ferrous 

alloys are inexpensive to produce but are weak and lack high temperature capability (Refs. 1 to 3). In 

most instances, design accommodations can be made to account for a bearing material’s shortcomings. In 

some instances, however, benefits could be realized through the use of a material that simultaneously 

provides high hardness, corrosion resistance, ease of manufacture and design incorporation into 

mechanical systems. Since 2004, the potential to realize such benefits has motivated NASA to research 

and develop NiTi intermetallics for bearing applications (Refs. 2 to 8). The concept, however, began 

much earlier in another government laboratory. 

 
NASA/TM—2015-218723 2 

The consideration of NiTi alloys for bearings can be traced to the pioneering work of William J. 

Buehler and his colleagues at the Naval Ordnance Laboratory (NOL) during the late 1950s (Refs. 9 and 

10). The designation NITINOL often used for these alloys is an abbreviation for Nickel-Titanium Naval 

Ordnance Laboratory. At that time, research was underway to develop high temperature, non-magnetic 

alloys for missile cone applications. Buehler’s early efforts identified both the 55 and 60 Nitinol alloys, 

which contained 55 and 60-weight percent nickel, respectively. 55 Nitinol, referred to hereafter as 

55NiTi, is soft and exhibits remarkable shape memory effects while 60 Nitinol (60NiTi) is hard and is 

dimensionally stable. Both alloys have apparent moduli comparable to titanium. Buehler abandoned work 

on the hard 60 Nitinol because it was very difficult to process and machine and it had the tendency to 

spontaneously fracture upon cooling after casting. By applying advanced manufacturing methods, bearing 

quality balls and races have been routinely produced opening the potential for bearings that exhibit 

excellent corrosion resistance and tribological behavior (Ref. 11). 

The nominal material properties of 60NiTi are shown alongside traditional bearing materials in 

Table 1. All of these materials have high hardness, above 55HRC, which assures good wear resistance. 

They all have high strength and temperature capability. Compared to the two metals 440C and M-50 tool 

steel, 60NiTi is about 15 percent lighter, has comparable thermal expansion coefficient, similar fracture 

toughness and Poisson’s ratio. 60NiTi has much lower (half) elastic stiffness (Young’s) modulus than the 

steels and one-third that of the ceramic silicon nitride. Like the ceramic, 60NiTi is immune to atmospheric 

corrosion. This blend of properties is unique and leads to a number of performance benefits with regards 

to bearings that are not immediately apparent from a cursory review of the properties alone. 

For instance, when used in a highly stressed, concentrated contact like a ball bearing, 60NiTi can 

withstand higher loads without suffering from permanent damage (e.g., denting) as might a conventional 

all steel bearing. The basis for this behavior lies within the contact mechanics of the ball-race interface. 

60NiTi has a reduced modulus and yet is hard. These properties lead to a broadened contact area, reduced 

stresses and higher load capacity (Refs. 2 and 5). Figure 1 shows this effect. 

Thus from a design standpoint, the use of 60NiTi and other emerging hard superelastic, low modulus 

alloys for bearings is enabling. Higher loads, smaller sizes and intrinsic corrosion resistance are all 

positive side effects of replacing iron-based alloys (steels). Of course, for the purposes of the present 

investigation on conforming-contact sliding bearings, the contact mechanics of 60NiTi and its variants are 

not specifically relevant. For the current work, sliding friction and wear behavior is primary. Nonetheless, 

if it is shown that 60NiTi tribologically performs well in the spherical bearing application and in the 

presence of fluid contaminants (hydraulic and deicing fluids), it may be beneficial to consider other 

aircraft applications involving highly stressed contacts such as ball bearings and gears. 

TABLE 1.—NOMINAL PROPERTIES FOR 60NiTi AND Si3N4 TEST SPECIMENS AND 

CONVENTIONAL BEARING STEELS 

Property 60NiTi 440C Si3N4 M-50 

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

Hardness 56 to 62 HRC 58 to 62 HRC 1300 to 1500 HV 60 to 65 HRC 

Thermal conductivity 

W/m-°K 

9 to 14 42 22 ~26 

Thermal expansion 1110–6/°C 1110–6/°C 310–6/°C 1210–6/°C 

Magnetic Non Magnetic Non Magnetic 

Corrosion resistance Excellent 

(Aqueous and acidic) 

Marginal Excellent Poor 

Tensile/(Flexural 

strength) 

~1000(1500) MPa 1900 MPa (600 to 1200) MPa 2500 MPa 

Young’s Modulus ~95 GPa 200 GPa 310 GPa 210 GPa 

Poisson’s ratio ~0.34 0.3 0.27 0.30 

Fracture toughness ~20 MPa/√m 22 MPa/√m 5 to 7 MPa/√m 20 to 23 MPa/√m 

Maximum use temp ~400 °C ~400 °C ~1100 °C ~400 °C 

Electrical resistivity ~1.0410–6 Ωm ~0.6010–6 Ωm Insulator ~0.1810–6 Ωm 
NASA/TM—2015-218723 3 

 

In the current report, highly loaded spherical sliding bearings are fabricated incorporating 60NiTi 

inner races (drilled balls) into conventional commercial aerospace grade reinforced polymer lined outer 

races (shells) made of stainless steel. These types of self-aligning slider bearings are used throughout the 

aerospace industry for the transmission of forces and motions in mechanisms such as airframe control 

surface actuator links (Ref. 12). Such applications are depicted in Figure 2 and a photograph of a 60NiTi 

(inner race) bearing is shown in Figure 3. 

These bearings are subjected to oscillatory motion under radial load according to the endurance test 

described by Aerospace Standard SAE AS81820 (Ref. 13). Bearings were tested in three groups, dry, 

contaminated with hydraulic fluid and contaminated with deicing fluid. The friction (torque) and wear 

results were collected and compared to conventional bearings made with 440C stainless steel balls 

(inner races). 
NASA/TM—2015-218723 4 

Test Articles/Procedures 

A lot of 25 spherical bearing assemblies were fabricated by Kamatics incorporating 60NiTi inner race 

balls with a 0.78-in. nominal outer diameter and 0.5-in. through hole bore. The ball is held inside a 

17-4PH stainless steel sleeve in which reinforced PTFE liner is molded in place. Figure 4 shows the 

Kamatics drawing for the spherical bearing assembly. Further details about the design, testing and use of 

spherical bearings are contained in the Kamatics design guide (Ref. 12). 

The lot of bearings were dispensed in the following manner: two bearings were destructively 

disassembled (cut) to confirm the molded liner uniformity, 14 bearings were subjected to oscillating 

sliding tests and then further measured and analyzed, and the remaining 9 bearings were retained for 

additional testing and characterizations. 

Six of the 14 test bearings were tested dry, with no fluid contamination. These six were subjected to 

25,000 oscillation (25) cycles at a rate of 17 cycles per minute, in ambient air under a load of 10,400 lb. 

This load corresponds to an average contact stress of 34 ksi and represents a fairly high load level 

intended to accelerate the wear and rapidly evaluate the bearing capabilities. 

Eight bearings were tested under a reduced (75 percent) load of 7800 lb (26 ksi) following 

contamination with either Skydrol 500B hydraulic fluid or AS8243 Anti-icing fluid. The contamination 

procedure includes a 24-hr soak in the contamination fluid, removal of the bearing from the fluid and the 

initiation of testing within 30 min. Four bearings each were tested in each of the two fluids. The test 

duration and oscillating rate were the same as the dry case. Only the test load was reduced to compensate 

for the fluid contamination. In all tests, the rotational breakaway torque limit was 210 in.-lb. 
NASA/TM—2015-218723 5 

Test Results and Discussion 

The tribology test data, shown in Table 2, consists of the breakaway torque and the liner wear. The 

torque and wear data averages are based upon six repeat tests for the dry conditions and four repeat tests 

for the contaminated conditions. The error represents one standard deviation. Liner wear was measured 

during and after testing by measuring the radial movement between the ball and liner in accordance to 

SAE 808120 (Ref. 13). An examination of the data shows clear comparability of the 60NiTi bearings and 

the baseline 440C bearing. 

The performance of the 60NiTi bearings is well within the torque limit (210 in.-lb) for this bearing 

and also well within the liner wear limit (0.006 in.). The photos shown in Figures 5 and 6 clearly illustrate 

that the 60NiTi surface is well lubricated by the PTFE filled liner material. The ball wear surfaces are 

smooth and free from deep gouges and wear patches. The wear behavior can be described as mild 

polishing type wear. Interestingly, the stainless steel bearing housing (outer surface) shows gouge marks 

from being pressed into and out of the test rig fixture. These gouges are considered normal and do not 

affect the bearing. 

Several bearings were disassembled after testing to more closely examine the 60NiTi surface wear 

characteristics and metallurgy. Figures 7 and 8 show representative wear surfaces and features before and 

after sliding. In these figures one can readily see the grinding marks remaining from the ball 

manufacturing process. These marks (scratches and gouges) can be reduced through polishing. This is 

standard procedure for rolling element bearings. However, for the spherical sliding bearings tested in the 

present study, the unpolished, ground surface generally performs better in sliding against the polymer 

liner. This may be because the ball surface topography encourages the transfer of liner material and the 

formation of a solid lubricant film. 

Figures 9 and 10 show ball surfaces after the sliding tests. These surface images were made after the full 

25,000 sliding cycle test sequence was completed. Comparing Figures 9 and 10 to Figures 7 and 8, one can 

see that that a mild polishing-type wear process has occurred. No deep gouging or material pullout from the 

ball surface is observed. In the following figures, a backscattered electron image and subsequent elemental 

x-ray analyses is presented which shows that only the normal phases and constituents of the 60NiTi are 

present. This is consistent with a benign, polishing wear process. For comparative purposes, the spectra in 

Figure 11 coincides with spectra reported previously for fracture surfaces of 60NiTi (Ref. 7, Fig. 15) again 

indicating the present bearing testing does not alter the 60NiTi material. 

The surface analyses of specimens that were tested following exposure to deicing fluid or hydraulic 

fluid are essentially the same as for the uncontaminated samples. From these results, we can conclude that 

the 60NiTi performs well tribologically in this application. 

TABLE 2.—SPHERICAL BEARING DATA SUMMARY 

[Test conditions: 25° rotation, 17 cycles per minute, 0.3 in.2 bearing area.] 

Bearing Environment Load, 

ksi 

No. total 

cycles 

Average torque, 

in.-lb 

Liner wear, 

in. 

60NiTi Dry 34 25,000 19311 0.00190.0007 

60NiTi Hydraulic fluid 26 25,000 19214 0.00260.0010 

60NiTi De-icing fluid 26 25,000 17611 0.00190.0011 

440C Dry 34 25,000 18819 0.00210.0009 
NASA/TM—2015-218723 6 
NASA/TM—2015-218723 7 
NASA/TM—2015-218723 8 
NASA/TM—2015-218723 9 
NASA/TM—2015-218723 10 

Summary Remarks 

The results of this Space Act Agreement clearly demonstrate that 60NiTi can be utilized for spherical 

bearings. Drilled balls were successfully fabricated from the baseline composition 60NiTi and these fully 

met the dimensional requirements set forth by Kamatics and the SAE specification. From a tribological 

performance perspective, the 60NiTi bearings exhibit comparable behavior to the more conventional 

440C stainless steel bearings. 

The use of 60NiTi carries advantages and disadvantages that must be considered prior to entering any 

commercialization development. 60NiTi has no iron content and therefore is both non-magnetic and not 

susceptible to rusting. Therefore it is well suited for wet and exposed corrosive applications where the use 

of a protective anti-corrosion oil or grease is impractical. Bearings for external locations on aircraft, 

marine machinery, submerged locations and food processing equipment are potential applications. 60NiTi 

has 15 percent lower density than steel and this can be helpful for mass critical applications. 60NiTi and 

its alloys are superelastic and can withstand concentrated loads to a higher level than steels without 

denting. Thus there may be an advantage to using 60NiTi in conforming contacts like the spherical 

bearings tested in this project and for conventional, high load capacity ball and roller bearings which are 

more sensitive to Brinell damage. 

60NiTi has characteristics that should be viewed as disadvantages as well. 60NiTi is made from high 

cost constituents. The NiTi processing route is intrinsically high cost. Elemental powders must first be 

pre-fused and then consolidated. Even in high-volume mass production, the material cost for 60NiTi will 

far exceed that of high quality bearing steel, typically by an order of magnitude. Following the current 

production path, 60NiTi bearings cost approximately five times more than comparable high-grade steel 

bearings. In full production the price is expected to drop perhaps by a factor of two. Thus the applications 

for 60NiTi must be in systems in which conventional steels cannot be used effectively. Based upon these 

considerations, 60NiTi and its variants are promising materials for highly loaded, highly corrosive, 

weight sensitive applications. 

 
NASA/TM—2015-218723 11 

Appendix—Visual Facsimile of the Signed Space Act Agreement 

The following three pages are a visual facsimile of the signed space act agreement. 
NASA/TM—2015-218723 12 
NASA/TM—2015-218723 13 

 
NASA/TM—2015-218723 14 

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Rolling Element Bearings Made From Superelastic Ni-Ti Alloys for Aerospace Mechanism 

Applications. NASA/TM—2011-217105, September 2012. 

3. DellaCorte, C.; Pepper, S.V., Noebe, R.D.; Hull, D.R.; and Glennon, G.: Intermetallic NickelTitanium Alloys for Oil-Lubrication Bearing Applications. NASA/TM—2009-215646, March 2009. 

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Superelastic 60NiTi for Rolling Element Bearings. NASA/TM—2012-216016, May 2012. 

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NASA/TM—2012-216029, September 2012. 

8. Stanford, M.K.: Promoted Ignition Testing to Determine the Gaseous Oxygen Compatibility of the 

Intermetallic Compound 60-NITINOL. NASA/TM—2012-216028, August 2012. 

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

Mechanical Properties of Alloys Near Composition TiNi.” J. of Applied Physics, Volume 34, No. 5, 

pp. 1475‒1477, 1963. 

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

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by Hot Isostatic Pressing.” Materials Science and Engineering, A280 (2000), pages 334‒348. 

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