Characteristics Of Wear Resistance And Strain Fatigue In Fe-Mn-Si Shape Memory Alloy

In this paper, the wear resistance and characteristics of strain fatigue in four kinds of Fe-Mn-Si shape memory alloys with different components are measured by sliding friction test and cyclic bending fatigue test. Then phase-transformation and their micromechanisms of these alloys during the processes of wear abrasion and strain fatigue are respectively studied by electron scanning microscope(SEM),X-ray diffraction (XRD) etc, on the basis of which the conception of stress self-accommodation in shape memory alloy is presented.It's found that the wear resistance of Fe-Mn-Si shape memory alloy in dry friction is bad, behaving the same friction-wear characteristics to common austenitic materials, with adhesive wear mechanism. In contrast, it takes on excellent friction wear resistance in oily friction with abrasive wear mechanism, and its mass loss doesn't increase with the load increased, but exists a certain load under which the mass loss of the alloy is littlest. It is known from XRD analysis and SEM observation, that stress induced γ→ε martensitic phase transformation and its phase transformation pseudoelasticity in Fe-Mn-Si shape memory alloy can improve its wear resistance in oily friction by reducing crack-tip stress, restraining plastic sliding deformation and delaying the formation and extension of microcracks.Fe-Mn-Si shape memory alloy shows good strain fatigue resistance with cyclic bending fatigue life of 1127 times under the strain of 3% much better than stainless steel with 71 times in the same test conditions. And its cyclic tension-compression fatigue life is 1300 times under the strain of 1.5%, also much better than heavy rail steel with 110 times and stainless steel with 150 times in the same test condition. The bending-fatigue fractured section of Fe-Mn-Si shape memory alloy specimen possesses nearly 100% s martensite with quasi-cleavage rupture type. Further studies show that repetitive stress induced y→ε martensitic transformation and its reverse transformation in the cyclic course can enhance the fatigue life of Fe-Mn-Si shape memory alloy by reducing crack-tip stress, restraining plastic sliding deformation and delaying the formation and extension of microcracks.The conception of stress self-accommodation characteristics of shape memory alloy is summarized and its phase-transformation process is modeled on previous studies of wear resistance and fatigue resistance in Fe-Mn-Si shape memory alloy. Furthermore the nature ofstress self-accommodation is clarified on the basis of which full-mechanical training and semi-mechanical training methods to improve shape memory effect are designed, and new application of Fe-Mn-Si shape memory alloy in self-accommodation seamless rail is prospected too.