Microstructure and surface oxidation behavior of an austenitic Fe-Mn-Si-Cr-Ni-Co shape memory stainless steel at 800 °C in air

Iron-Based Shape Memory Alloys in Construction: Research, Applications and Opportunities

“…Studies have found that Fe-SMA strips have a positive effect in countering the relaxation behavior of structures at elevated temperatures [ 142 ]. Furthermore, corrosion, creep, and relaxation behavior under extreme environments (e.g., high-temperature and chlorine environments) have been investigated which confirmed the suitability and reliability of Fe-SMA [ 120 , 143 , 144 , 145 , 146 , 147 , 148 , 149 , 150 ]. Another attractive advantage of Fe-SMA-based strengthening strategy is its re-prestressing property, i.e., HCF-induced relaxation in recovery stress can be restored through repeated rounds of thermal activation [ 18 , 134 , 151 ].…”

High temperature cyclic oxidation behavior of a low manganese Fe12Mn9Cr5Si4Ni-NbC shape memory stainless steels

“…However, in Figure 10, literature values of k p are put together for comparative purposes in an Arrhenius plot, where open symbols accounts for cyclic tests and filled symbols for isothermal ones. A hypothetical linear fitting is presented (R²=0.87), excluding the points regarding the alloy with Co [4] and the alloy oxidized after vacuum annealing [8], showing that for all the other alloys, independently of the Mn content there is a similar and high mass gain. Clearly, the only successful attempts for decreasing mass gain during oxidation in air at high temperature in these SMSS alloys were, therefore, through the Co addition or vacuum annealing.…”

“…The Fe-based shape memory alloys (SMA) Fe-Mn-Si-Cr-Ni were developed as a cheapest alternative option to traditional NiTi SMA [1,2]. Furthermore, studies demonstrated that this kind of alloy can be used to join tubes by the shape memory effect [3] and have suggested applying them at high temperature [4]. Despite the high percentage of Mn being a problem for metallic alloys employed at high temperatures, in the last decade, studies regarding high temperature oxidation of this austenitic alloys were developed.…”

“…They observed that during oxidation at high temperature the oxide layer presents Mn-rich oxides (Mn 2 O 3 and Mn 3 O 4 ) and Mn-Cr-spinel, causing depletion of Mn and generating a ferrite layer near the metal/oxide interface. After that, several studies were developed in order to try improving the oxidation resistance of these alloys, named as shape memory stainless steels (SMSS) [4,[6][7][8].…”

“…The explanation was that higher amounts of Si and Cr, both ferrite-stabilizers elements, facilitated ferrite stabilization at 800 °C during oxidation due to Mn depletion, making the Mn diffusion rate faster when compared with the austenitic structure [9]. Additions of Co [4] have been also…”