Nickel-Titanium-Hafnium alloy design in tribological systems

High hardness, compressive elastic strength and corrosion resistance of Ni-rich Ni-Ti-Hf alloys make them optimum candidates for space-age bearing applications. Intermetallic materials are shown to provide comparable resistance to degradation and wear under rolling contact fatigue conditions. Under rapid quenching processes, binary Ni-Ti alloy can experience high residual stress, initiating cracking and machining distortion. Conversely, a lack in rapid quenching leads to a decline in hardness. Elucidating the effect of hafnium ternary alloying on Ni-rich compositions benefits bearing element performances. Hf-alloying allows for a reduction in residual stress while retaining high strength and hardness of quenched binary Ni-Ti alloy. This alloy optimization study blends rolling contact fatigue, hardness and uniaxial compression testing with microstructural characterization using transmission electron microscope, connecting nano-scale effects with mechanical behavior. Understanding rolling contact fatigue performances, failure mechanisms, performances (hardness, strength, life) versus residual stresses within an optimized alloy design space allows the implementation of NiTiHf systems for tribology applications.