Rolling Contact Fatigue of Superelastic Intermetallic Materials (SIM) for Use as Resilient Corrosion Resistant Bearings

Abstract Superelastic intermetallic materials (SIM), such as 60NiTi, are emerging as candidates for corrosion and shock-resistant rolling element bearings. Compared with metals, the intermetallic materials are more brittle and may be prone to rolling contact fatigue degradation. In this paper, a series of three ball-on-rod rolling contact fatigue tests were conducted using polished steel balls and NiTi rods prepared by vacuum casting and powder metallurgy techniques. The test protocol matched that used in ASTM STP 771 except that the steel balls were not intentionally roughened. In general, the NiTi rods exhibit fatigue damage at much lower stress levels than commercial bearing steels. At the lowest stress level tested (1.7 GPa), 60NiTi rods that were largely free from processing defects gave acceptably long lives, and testing was terminated without failure after 800 h. At elevated stress (2.5 GPa), failure occurred for some specimens, while others reached the preset test length goal of 800 h. Improperly prepared 60NiTi rods that had unconsolidated particles or significant ceramic inclusions occasionally experienced surface fatigue prior to completion of the test period even at the lowest stress level. Alloyed NiTi rods containing small amounts of Hf as a microstructural processing aid generally endured higher stress levels than the baseline 60NiTi composition. Two predominant fatigue failure mechanisms were observed: intergranular (grain boundary) fracture and intragranular (through the grains) crack propagation. The results suggest that further fatigue capability improvements could be obtained through process improvements, microstructural refinements and alloying. SIM currently available are recommended for mechanically benign applications involving modest stress levels and rates of stress cycle accumulation. Applications that include high continuous loads (stress) and high speeds for long durations should be avoided.

[1]  C. Dellacorte,et al.  Intermetallic Nickel-Titanium Alloys for Oil-Lubricated Bearing Applications , 2009 .

[2]  C. Dellacorte Resilient and Corrosion-Proof Rolling Element Bearings Made from Superelastic Ni-Ti Alloys for Aerospace , 2012 .

[3]  D. Lagoudas,et al.  Processing of TiNi from elemental powders by hot isostatic pressing , 2000 .

[4]  J. V. Gilfrich,et al.  Effect of Low‐Temperature Phase Changes on the Mechanical Properties of Alloys near Composition TiNi , 1963 .

[5]  T. Mccue,et al.  Addressing Machining Issues for the Intermetallic Compound 60-NITINOL , 2012 .

[6]  Douglas Glover,et al.  A Ball-Rod Rolling Contact Fatigue Tester , 1982 .

[7]  D. W. Smith,et al.  Microstructure, fatigue life and load capacity of PM tool steel REX20 for bearing applications© , 1999 .

[8]  D. Dane Quinn,et al.  Characterization of Ni19.5Ti50.5Pd25Pt5 high-temperature shape memory alloy springs and their potential applications in aeronautics , 2008, SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring.

[9]  C. Dellacorte,et al.  The Effect of Pre-Stressing on the Static Indentation Load Capacity of the Superelastic 60niti , 2013 .

[10]  James H. Mabe,et al.  Boeing's Variable Geometry Chevron, Morphing Aerostructure for Jet Noise Reduction , 2006 .

[11]  A. Palmgren Ball and roller bearing engineering , 1945 .

[12]  T. Tadaki,et al.  Shape Memory Alloys , 2002 .

[13]  C. Dellacorte,et al.  Static Indentation Load Capacity of the Superelastic 60NiTi for Rolling Element Bearings , 2012 .

[14]  C. Dellacorte,et al.  Processing Issues for Preliminary Melts of the Intermetallic Compound 60-NITINOL , 2012 .

[15]  M. Stanford Charpy Impact Energy and Microindentation Hardness of 60-NITINOL , 2012 .

[16]  Frederick T. Calkins,et al.  Boeing's variable geometry chevron: morphing aerospace structures for jet noise reduction , 2006, SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring.

[17]  C. Dellacorte,et al.  NITINOL 60 AS A MATERIAL FOR SPACECRAFT TRIBOELEMENTS , 2009 .