Holding-temperature effects on thermally and stress induced martensitic transformations in an FeMnSiCr SMA

Abstract

Abstract Dynamic mechanical analysis (DMA) involves applying a mechanical deformation under dynamic regime, with controlled amplitude and frequency, either isothermally or during temperature variation. These experiments, performed with strain sweep or temperature scan enable to monitor internal friction variation or to identify the presence of martensitic transformation that governs the mechanism of shape memory alloys (SMAs), respectively. These features of DMA device can be successfully handled in order to apply isothermal mechanical treatments with various frequencies and amplitudes. In the present paper, the experimental alloy was a Fe-Mn-Si-Cr SMA, obtained by ingot metallurgy, which was hot rolled, and water quenched to retain martensitic phases. The samples were subjected to solution treatments at 1050°C for five different periods of time: 2, 4, 6, 8 and 10 hrs. Heat treatment effects were evaluated by differential scanning calorimetry (DSC) before being mechanically treated by DMA strain sweeps with three different frequencies; 1, 5 and 10 Hz. A precipitation phenomenon was identified by DSC after 8 hrs. solution treatment time, which can be responsible for the decrease of internal friction average values. Storage modulus increased, during DMA strain sweeps, due to work hardening, but experienced a saturation tendency at a strain amplitude of 0.022 % for which a maximum internal friction value of 0.045 has been associated. Microstructural changes were evaluated by scanning electron microscopy.