92 elastic modulus coupled with an ability to endure large strains elastically. The combination of excellent  corrosion resistance and high dent resistance (arising from the high hardness, low modulus and superelasticity) distinguish 60NiTi from the tool steels and cerami cs commonly used in bearings. Table I  compares bearing relevant properties of 60NiTi to conventional materials.      Table I .  Thermophysical and mechanical properties of  60NiTi and other bearing materials   Property  60NiTi  440C  Si3N4 M-50  Density  6.7 g/cc  7.7 g/cc  3.2 g/cc  8.0 g/cc   Hardness  56‒62 Rc  58‒62 Rc  1300‒1500 Hv*  60‒65Rc   Thermal Cond. W/m -°K ~9‒14  24 33 ~36  Thermal Expansion  ~11.2×10‒6/°C 10×10‒6/°C 2.6×10‒6 ~11×10‒6/°C  Magnetic  Non Magnetic  Non Magnetic   Corrosion Resistance  Acceptable  (in acids)  Marginal  Acceptable Poor   Tensile/Flexural  Strength  ~1000/1500 MPa 1900 MPa 600‒1200 MPa  (Bend Strength)  2500 MPa  Young’s Modulus  ~90‒115 GPa  200 GPa  310 GPa  210 GPa  Poisson’s Ratio  ~0.34  0.30 0.27 0.30  Fracture Toughness  ~20 MPa/√m  22 MPa/√m  5‒7 MPa/√m  20‒23 MPa/√m   Max. Use Temp  ~400  °C ~400  °C ~1100  °C ~400  °C  Elect. Resistivity  ~1.04×10‒6 Ω-m ~0.60×10‒6 Ω-m Insulator  ~0.18×10‒6 Ω-m  *Vicker’s hardness, Hv, is a scale used for ceramic materials with hardness values beyond HRC 75.    A NASA application requiring corrosion resistance and high load capacity is inside the International Space Station (ISS) Urine Processor Distillation Assembly [7] . The Urine Process or Distillation Assembly  (DA) is a key component of the wastewater treatment system on the ISS.  The DA functions as a rotating  still that processes waste fluids into steam (gaseous water) . Figure 1 shows a cross section of the Urine  Processor [8] . It consi sts of a rotating drum made from titanium alloy supported on a pair of 50- mm ball  bearings and is driven by a motor at a constant speed of 200 rpm. The wastewater is introduced into the  drum through a feed tube. Through centrifugal action, the rotating mot ion of the drum forces the  wastewater into contact with the drum walls . The drum walls are heated and this boils the wastewater,  forming steam that is drawn from the evaporator drum, condensed and then further treated downst ream  into clean water. The 50- mm bore ball bearings that support the rotating drum are directly exposed to the  acidic wastewater and the steam environment and have experienced corrosion problems when made from steel. The use of NiTi is intended to avoid the corrosion problems yet provide good load capacity  and wear life.    In a previous test and development program, 60NiTi ball bearings were designed and fabricated for use in the DA centrifuge [9].  Corrosion tests were performed to confirm the chemical compatibility with the  wastewater env ironment and static load experiments were done to show that the bearings would endure  anticipated launch loads. As a proof of concept, short -term (~20 hr) bearing tests were run in a simulator  test rig that duplicated the load, speed, temperature and moist ure conditions found inside the DA, albeit  without the l ow pH acidic fluid nature. These tes ts were successful and a flight bearing project was  initiated.    During the ground test phase of the project, a pair of 60NiTi centrifuge bearings were installed in a fully  operational DA and placed into a long- term test program intended to run for up to 2000 hr. After only  200 hr , nickel and titanium particles were observed in the process  fluid filtration system. After 235 hr  of  run time audible bearing noise was emanating from the centr ifuge and the test was halted. An inspection  revealed catastrophic failure of the hub- side (left side in Figure 1)  60NiTi centrifuge bearing. The second  bearing of the pair, which operated on the same shaft on the motor -side of the DA,  remained in good  condition and showed no signs of distress. In the following sections of this paper, the results of the hub-