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 e (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.
Highlights
Fe-Mn-Si shape memory alloy (SMA) have been intensively studied ever since their discovery in 1982, by A
The resulting specimens were analysed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), in order to reveal the presence of ε and α’ thermally induced martensites
The inventory of previously reported drawbacks of ingot metallurgy (IM) processing of Fe-Mn-Si-Cr-Ni alloys [4,5,6,7,8] suggest that an alternative approach for producing these alloys could be powder metallurgy (PM) which has been successfully applied to other SMAs, such as Ti-Ni, or to Cu base alloys [9]
Summary
Fe-Mn-Si SMAs have been intensively studied ever since their discovery in 1982, by A. PM processing enables to obtain accurate composition and MA has the potential to increase the compactness and to better control grain size, avoiding most of IM drawbacks. In order to investigate the structural differences between thermally-induced martensites observed in SMAs subjected to different processing routes, IM, PM and MA will be associated with hot rolling and coupled with two different solution treatment temperatures. The thermomechanical processing effects will be investigated during the reversion of thermally induced ε-hcp and α’-bcc martensite to γ-fcc austenite, by means of dynamic mechanical analysis (DMA) which are aimed to emphasize the correlations between storage modulus and internal friction variations with temperature and the characteristics of solution treated structures
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