The paper reports solution treatment (ST) and mechanical alloying (MA) effects on the structure and static/dynamic mechanical behaviour of PM-MA'ed FeMnSiCrNi shape memory alloys associated with the formation of thermally and stress-induced martensite. The specimens were subjected to tensile pre-straining, in order to stress induce martensite and their gauges were cut and prepared for X-ray diffraction (XRD) as well as for optical and scanning electron microscopy (SEM). XRD patterns allowed determining the presence of large amounts of α ′ -body centred cubic (bcc) besides ε-hexagonal close packed (hcp) martensite and γ-face centred cubic (fcc) austenite. The decrease in the amount of α ′ -bcc at specimens ST'ed at 1273 and 1373 K, with increasing pre-straining degree, was confirmed by XRD patterns and SEM micrographs. Dynamic mechanical analysis (DMA) was performed by strain sweeps (SS). The SS-DMA graphs displayed storage modulus plateaux which were associated with the formation of ε-hcp martensite.

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Abstract. By ingot metallurgy (IM, melting, alloying and casting), powder metallurgy (PM, using as-blended elemental powders) and mechanical alloying (MA of 50 % of particle volume), three types of FeMnSiCrNi shape memory alloy (SMA) specimens were fabricated, respectively. After specimen thickness reduction by hot rolling, solution treatments were applied, at 973 and 1273 K, to thermally induce martensite. The resulting specimens were analysed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), in order to reveal the presence of ε (hexagonal close-packed, hcp) and α' (body centred cubic, bcc) thermally induced martensites. The reversion of thermally induced martensites, to γ (face centred cubic, fcc) austenite, during heating, was confirmed by dynamic mechanical analysis (DMA), which emphasized marked increases of storage modulus and obvious internal friction maxima on DMA thermograms. The results proved that the increase of porosity degree, after PM processing, increased internal friction, while MA enhanced crystallinity degree.

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