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Abstract. Fe-14Mn-6Si-9Cr-5Ni (mass %) shape memory alloy (SMA) specimens were obtained by powder metallurgy in as-blended state (0_MA) and with particle volume fractions of 10 and 20 % MA'd powders, respectively. After hot rolling and solution treatment, between 973 and 1373 K, the specimens were pre-strained up to 4 %, on a tensile testing machine. The influences of: (i) MA'd fractions, (ii) solution treatment temperature and (iii) pre-straining degree were analysed by X-ray diffraction (XRD), optical (OM) and scanning electron (SEM) microscopy. In this purpose, the gauges of pre-strained specimens were cut and metallographically prepared. Dynamic mechanical analysis (DMA) was employed to emphasize the reverse transformation, during heating, of thermally induced martensite, obtained after solution treatment. The results proved that, as an effect of PM-MA processing, mechanical properties were improved, the amount of stress induced martensite increased and the reverse martensitic transformation was enhanced.

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The surface micro-reliefs of primary martensite plates, representative for two shape memory alloys (SMAs) with different crystalline structures were compared from qualitative and quantitative point of view by scanning electron microscopy and atomic force microscopy, respectively. Qualitative evaluations revealed larger widths and heights of the primary plates of e hexagonal close packed (hcp) martensite, in an Fe-Mn-Si-Cr-Ni SMA than those of b 2 9 orthorhombic (9R) martensite, in a Cu-Zn-Al SMA. Quantitative evaluations were based on systematic dimensional measurements of the width and height of primary plate profiles. The measurements were performed on one hundred and twenty five profiles, five on each martensite plate belonging to five typical groups of primary plates, with length above 50 micrometers, of both e hcp and b 2 9 9R martensites. In order to compare the topographies of the two types of plates a statistical evaluation of the dimensional intervals of width and height of measured plates was performed.Keywords: Martensite micro-profile / scanning electron microscopy / atomic force microscopy / dimensional measurements / Schlüsselwörter: Martensit Mikrogefüge / Rasterelektronenmikroskopie / Rasterkraftmikroskopie / dimensionale Messungen /

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By means of atomic force microscopy (AFM) measurements, the evolution of surface relief characteristics of stress induced martensite plates was investigated on the surface of polished Fe-14Mn-6Si-9Cr-5Ni and Fe–28Mn–6Si–5Cr (mass. %) shape memory alloys (SMAs), subjected to various pre-straining degrees. Pre-straining degree was chosen as an independent variable, considering its influence on the reverse transformation of martensite. The specimens were cast by means of a levitation induction furnace and hot rolled to 1 mm-thickness in order to better reveal the shape memory phenomena. The specimens, cut by spark erosion to “dog-bone” shapes, were pre-strained by means of a tensile testing machine at room temperature (RT). The gauges of elongated specimens were analyzed by AFM. Qualitative 2D analyses were performed on AFM micrographs. Quantitative evaluations were based on systematic dimensional measurements of martensite profiles, allowing the determination of the average values of plate widths and heights for four pre-straining degrees of the two SMA systems under study. The variation tendencies of average values of martensite plate widths and heights with increasing the pre-straining were examined under the form of increasing rates of the plate widths and heights. The results show that, for the two SMA systems studied, the average widths and heights of stress-induced martensite plates varied between 80 and 188 nm for Fe-14Mn-6Si-9Cr-5Ni and between 101 and 192 nm for Fe-28Mn-6Si-5Cr. These dimensions experienced an increasing tendency with pre-straining degree, with a rate of about 30 nm/ % pre-strain.