Fatigue-resistant NiTi micropillars with small hysteresis fabricated by micro severe plastic deformation

Abstract

Through compressing polycrystalline NiTi micropillars down to a 40% height reduction by nanoindentation equipment and subsequently manufacturing them by focused ion beam, cuboidal NiTi micropillars with a nanocrystal/nanolaminate heterostructure were obtained. Mechanical behavior and fatigue tests show that the heterostructured NiTi micropillars processed by micro severe plastic deformation (MSPD) have a large recoverable strain (4.5%), small hysteresis (4.3 MPa), and ultrahigh fatigue resistance (> 106 cycles) under a maximum applied stress of 2.5 GPa. These properties were attributed to the extreme grain refinement and homogeneous phase transformation occurring in the nanocrystals. The findings suggest that the MSPD holds great potential for fabricating superior materials for applications in small-scale engineering devices.