Abstract
This work investigated the isothermal holding time dependence of the densification, microstructure, weight loss, and tensile properties of Fe-Mn-Si powder compacts. Elemental Fe, Mn, and Si powder mixtures with a nominal composition of Fe-28Mn-3Si (in weight percent) were ball milled for 5 h and subsequently pressed under a uniaxial pressure of 400 MPa. The compacted Fe-Mn-Si powder mixtures were sintered at 1200 °C for 0, 1, 2, and 3 h, respectively. In general, the density, weight loss, and tensile properties increased with the increase of the isothermal holding time. A significant increase in density, weight loss, and tensile properties occurred in the compacts being isothermally held for 1 h, as compared to those with no isothermal holding. However, further extension of the isothermal holding time (2 and 3 h) only played a limited role in promoting the sintered density and tensile properties. The weight loss of the sintered compacts was mainly caused by the sublimation of Mn in the Mn depletion region on the surface layer of the sintered Fe-Mn-Si compacts. The length of the Mn depletion region increased with the isothermal holding time. A single α-Fe phase was detected on the surface of all of the sintered compacts, and the locations beyond the Mn depletion region were comprised of a dual dominant γ-austenite and minor ε-martensite.
Highlights
Fe-Mn-Si alloys have been intensively investigated due to the so-called shape memory effect (SME) caused by the reversible phase transformation between face-cantered cubic γ-austenite and hexagonal close-packed ε-martensite [1,2,3]
When the isothermal holding time increases to 1 h, the weight loss increases significantly to ~7.5 wt. %, which is a ~4-fold increase compared to its counterpart with no isothermal holding
The weight loss rate of the alloys sintered for 2 h and 3 h increases by only ~2 wt. % and 3 wt. %, as compared with that sintered for 1 h
Summary
Fe-Mn-Si alloys have been intensively investigated due to the so-called shape memory effect (SME) caused by the reversible phase transformation between face-cantered cubic (fcc) γ-austenite and hexagonal close-packed (hcp) ε-martensite [1,2,3]. In the family of metallic shape memory alloys (SMAs), Fe-Mn-Si SMAs exhibit relatively low costs of both raw materials and processing in comparison with their Ni-Ti alloys and Cu-based counterparts [4,5]. This makes Fe-Mn-Si shape memory alloys promising candidates for various civil engineering applications such as pipe joints and rail couplings [6,7,8,9,10]. Powder metallurgy (PM) is a cost-effective metal forming technology that provides various benefits for industrial production in comparison to melting and casting. The products manufactured by PM techniques exhibit a near net shape that requires few or no further machining steps [16,17,18,19]
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