Bikas C. Maji

The effect of microstructure on the shape recovery of a Fe–Mn–Si–Cr–Ni stainless steel shape memory alloy

Abstract In this work the effect of varying the microstructure on the shape memory properties of a Fe-15Mn-7Si-9Cr-5Ni (wt.%) stainless steel shape memory alloy was evaluated using a simple bend test. The best shape recovery was obtained for a single-phase austenite microstructure and for a two-phase microstructure composed of an austenite matrix and Fe 5 Ni 3 Si 2 type intermetallic grain boundary phase. The maximum shape recovery was achieved at the reversion temperature of 600 °C and when the pre-stain was less than 2%.

Is the observation of {112} pseudotwins in the B2 phase of Ni-Ti-Fe shape-memory alloys a case of misidentification?

We present transmission electron microscopy observations and a crystallographic analysis that show that the only significant report on the observation of {112} pseudotwins in B2 structures by Goo et al. (1985, Acta metall., 3, 1725) is a misidentification of the {114} true twins.

Calorimetric Studies of Dissolution Kinetics of Ni2(Cr,Mo) Phase in Ni-Cr-Mo Alloys Using Non-Isothermal Approach

The kinetics of dissolution of ordered phase with Pt2Mo structure has been studied in two nickel chromium alloys – one without molybdenum and another with molybdenum - using differential scanning calorimetry. The activation energy for dissolution, determined using three nonisothermal approaches was found to be ~ 418 kJ /mole for both the alloys. This value agreed very well with the activation energy for coarsening of g″ precipitates in Ni-Cr-Mo matrix and is close to activation energy for mobility of chromium and molybdenum in complex nickel alloy matrix.

Microstructural Irreversibilities under Thermal Cycling in Ni-Ti-Fe Shape Memory Alloys

The thermal cycling (quenching in liquid nitrogen and reverting back to room temperature: austenite martensite reversible transformation) response of Ni-Ti-Fe shape memory alloys has been investigated. It was clearly noted that residual deformation, estimated in terms of noticeable differences in austenite grain size, depend on the relative clustering of fine grains. During repeated thermal cycling, the residual deformation, in-grain misorientation developments and retained martensite content scaled together: bringing out a clear picture of microstructural irreversibility.

Evolution of Texture and Microstructure during Cold Rolling and Annealing of Fe-14Mn-6Si-9Cr-5Ni Shape Memory Alloy

Evolution Texture and microstructure has been investigated in a Fe-14Mn-6Si-9Cr-5Ni shape memory alloy during cold rolling and annealing. The starting solution-annealed material show a nearly random texture with microstructure composed of equi-axed austenite grains with some e martensite plates inside. Cold rolling induces a strong alloy type texture with Brass {011}<211> and Goss {011}<100> as major components. Annealing of the cold deformed material produces a nearly random texture. The microstructural investigation reveals that with increasing cold deformation the amount of stress induced e and a’ martensite volume fraction increases. The electron back scattered diffraction (EBSD) phase mapping shows that reversion of the e martensite starts only after commencement of recrystallization.

The Application of Ni – Ti Shape Memory Alloys as Fasteners

Abstract This article covers the various materials aspects of the shape memory alloys that go into the design of fastening devices. A brief overview of the shape memory phenomenon and the martensite transformation during free and constrained recovery has been given to clarify the role of the martensitic transformation in the success of this application. Finally, the design of an Ni-Ti-Fe fastening sleeve has been discussed.