EFFECT OF THE MARTENSITIC PHASE-TRANSFORMATION ON THE LOW-CYCLE FATIGUE BEHAVIOR OF POLYCRYSTALLINE NI-TI AND CU-ZN-AL ALLOYS

An investigation has been made into the low cycle fatique behaviour of NiTi and CuZnAl alloys in which the effect of the martensite transformation was studied. Testing was done at room temperature in tension-compression and the transformation temperature Ms was varied by making slight compositional changes. All alloys obeyed the Coffin-Manson law, but alloys tested near Ms showed lower slopes of log (plastic strain) versus log (cycles to failure) than conventional materials and significantly larger plastic and total strains for failure at 103 cycles. CuZnAl showed lower strains to failure than NiTi for the same number of cycles, and this is rationalized in terms of greater stress concentration in regions adjacent to the grain boundaries as a result of larger grains and martensite plates. © 1979.