Effect of Carbon Addition on Recovery Behavior of Trained FeMnSi Based Shape Memory Alloys

Abstract

We investigate microstructures and recovery behavior of trained Fe14Mn5Si8Cr4Ni and Fe14Mn5Si8Cr4Ni0.12C alloys under different deformation strains by color optical micrographs, XRD, and SQUID. The training results in the formation of α′ martensite in Fe14Mn5Si8Cr4Ni alloy, while introduces Cr23C6 particles besides the α′ martensite in Fe14Mn5Si8Cr4Ni0.12C alloy. The stress‐induced ε martensite bands are thinner in trained Fe14Mn5Si8Cr4Ni0.12C alloy than in trained Fe14Mn5Si8Cr4Ni alloy. When the deformation strain is below 8%, the recovery strain of trained Fe14Mn5Si8Cr4Ni0.12C alloy is slightly lower than that of trained Fe14Mn5Si8Cr4Ni alloy. This result is attributed to the fact that the Ms temperature of Fe14Mn5Si8Cr4Ni0.12C alloy is much below the deformation temperature than that of Fe14Mn5Si8Cr4Ni alloy. When the deformation strain is above 8%, the recovery strain of trained Fe14Mn5Si8Cr4Ni0.12C alloy is higher than that of trained Fe14Mn5Si8Cr4Ni alloy. The reason for this result is that in trained Fe14Mn5Si8Cr4Ni0.12C alloy, both α′ martensite and Cr23C6 particles prevent stress‐induced ε martensite bands from colliding each other at large deformation strain, and the width of stress‐induced ε martensite bands is smaller as compared with trained Fe14Mn5Si8Cr4Ni alloy. It is concluded that carbon addition can improve the recovery strain of trained FeMnSi based shape memory alloys at large deformation strain.

Key criterion for achieving giant recovery strains in polycrystalline Fe-Mn-Si based shape memory alloys

“…In addition to the addition of interstitial atoms, the precipitation of second-phase particles, such as NbC [25,31,60], VN [61][62], VC [63][64], TiC [65], and Cr 23 C 6 [22], can also effectively strengthen the austenite and markedly improve the SME in Fe-Mn-Si based SMAs. Furthermore, it was reported that the precipitation of second-phase particles during the training or the TMTs is beneficial for further improving the recovery strain [66][67]. Unfortunately, polycrystalline Fe-Mn-Si based SMAs treated as above still cannot achieve the stated aim of a recovery strain more than 6%.…”

Thermodynamic Explanation for the Large Difference in Improving Shape Memory Effect of Fe–Mn Alloys by Co and Si Addition

“…[2] In 1986, Murakami and coworkers developed polycrystalline Fe- (28)(29)(30)(31)(32)Mn-(4-6.5)Si alloys showing almost complete SME as well. [3] In 1991, Otsuka et al developed Fe- (14)(15)(16)(17)(18)(19)(20)(21)(22)Mn-(5-6)Si- (8)(9)(10)(11)(12)Cr-(5-7)Ni alloys exhibiting good SME along with good corrosion resistance through alloying with Ni and Cr. [4] Thereafter, much research has been carried out on these Fe-Mn-Si-based alloys to further improve their recovery strain, including training, [5][6][7][8] thermo-mechanical treatment, [9][10][11] ausforming, [12,13] and precipitation of second-phase particles.…”