Wear-resistant CoCrNi multi-principal element alloy at cryogenic temperature

Traditional high strength engineering alloys suffer from serious surface brittleness and inferior wear performance when servicing under sliding contact at cryogenic temperature.Here,we report that the recently emerging CoCrNi multi-principal element alloy defies this trend and presents dramatically enhanced wear resistance when temperature decreases from 273 to 153 K,surpassing those of cryogenic austenitic steels.The temperature-dependent structure characteristics and deformation mechanisms influencing the cryogenic wear resistance of CoCrNi are clarified through microscopic observation and atomistic simulation.It is found that sliding-induced subsurface structures show distinct scenarios at different deformation temperatures.At cryogenic condition,significant grain refinement and a deep plastic zone give rise to an extended microstructural gradient below the surface,which can accommodate massive sliding deformation,in direct contrast to the strain localization and delamination at 273 K.Meanwhile,the temperature-dependent cryogenic deformation mechanisms(stacking fault networks and phase transformation)also provide additional strengthening and toughening of the subsurface material.These features make the CoCrNi alloy particularly wear resistant at cryogenic conditions and an excellent candidate for safety–critical applications.

Cryogenic wear behaviors of a metastable Ti-based bulk metallic glass composite

Bulk metallic glass composites(BMGCs)are proven to be excellent candidates for cryogenic engineering applications due to their remarkable combination of strength,ductility and toughness.However,few efforts have been done to estimate their wear behaviors that are closely correlated to their practical service.Here,we report an improvement of∼48%in wear resistance for a Ti-based BMGC at the cryogenic temperature of 113 K as compared to the case at 233 K.A pronounced martensitic transformation(β-Ti→α''-Ti)was found to coordinate deformation underneath the worn surface at 233 K but was significantly suppressed at 113 K.This temperature-dependent structural evolution is clarified by artificially inducing a pre-notch by FIB cutting on aβ-Ti crystal,demonstrating a strain-dominated martensitic transformation in the BMGC.The improved wear resistance and suppressed martensitic transformation in BMGC at 113 K is associated with the increased strength and strong confinement of metallic glass on metastable crystalline phase at the cryogenic temperature.The current work clarifies the superior cryogenic wear resistance of metastable BMGCs,making them excellent candidates for safety-critical wear applications at cryogenic temperatures.