Thermomechanical processing effects on the structure and properties of Fe-based SMAs. I. Evolution of phase structure

The paper analyses the effects of heat treatment (HT) and mechanical alloying (MA) on the evolution of phase structure of an Fe-Mn-Si-Cr-Ni Shape Memory Alloy (SMA) obtained by powder metallurgy (PM). Using various amounts of mechanically alloyed (MA'ed) powders, namely 0 and 40 vol. %, two groups of specimens with chemical composition Fe-14Mn-6Si-9Cr-5Ni (mass.%) were produced by PM. After blending, pressing, sintering and hot-rolling, each set of samples was subjected to five different heat treatment temperatures 973, 1073, and 1373 K, respectively. Tensile pre-straining tests were performed on all samples, with increasing pre-straining degrees up to 4.5 %, in order to stress-induce ε (hcp) martensitic phase in the material. Structural analysis was implemented by means of X-ray diffraction and SEM observations. XRD and SEM investigations revealed the formation of thermally induced α'-bcc martensite, besides ε-hcp, as a particularity of this powder metallurgy, mechanically alloyed, shape memory alloy. (paper)