Cyclic degradation in bamboo-like Fe–Mn–Al–Ni shape memory alloys — The role of grain orientation

Electron beam welding of Fe–Mn–Al–Ni shape memory alloy: Microstructure evolution and shape memory response

“…The quenching sensitivity in Fe-Mn-Al-Ni SMAs is extremely pronounced. 15,22 Thus, significant amounts of the secondary γ-phase evolve in the welding zone in the current work ( Fig. 1(b)).…”

“…[4][5][6][10][11][12][13][14][15] However, most Fe-based SMAs suffer rapid cyclic functional degradation, currently hindering industrial utilization. 10,15 In single crystalline material, the microstructural mechanisms for cyclic degradation are often related to dislocation formation and concomitant pinning of phase boundaries. In polycrystalline material, grain constraints and related load concentrations often deteriorate functional properties, pronouncedly with increasing material anisotropy.…”

“…Even grain boundary fracture can occur. 10,15,16 Recent studies showed that by adjusting the morphology and orientation of grains and grain boundaries with respect to the loading direction functional properties can be significantly improved in SMA systems. [16][17][18][19][20] In these studies, it was shown that an optimal ratio between grain size and sample size leads to significantly increased shape recovery following pseudoelastic deformation.…”

“…4,20,21 These bamboo-like microstructures exhibit distinctly improved functional properties. 15,17 Concerning an intended industrial application of Fe-MnAl-Ni SMAs as damping devices embedded in conventional constructions designed from structural materials, in-depth knowledge of the weldability of these alloys is important to effectively implement welding and post-welding treatments, i.e. cyclic heat treatment procedures, into robust industrial manufacturing routes.…”

“…1,2,16,23 Therefore, many studies have been conducted in order to understand the role of microstructures on functional properties of SMAs. 1,2,[15][16][17][18][19][20][21][22][23][24] In this regard, weakly textured SMAs often show rapid functional and structural degradation due to pronounced grain constraints between favored and non-favored grains in terms of transformability. 8,16,25,26 In particular, due to highly anisotropic material properties, most SMAs suffer from incomplete shape recovery as a result of defect generation at grain boundaries imposed by the grain constraints as well as defect generation at austenite-martensite phase boundaries and at martensite variant boundaries.…”