Effect of quenching rate on the average grain size and martensitic transformation temperature in rapidly solidified polycrystalline Ni₅₀Mn₃₇Sn₁₃ alloy ribbons

Abstract

The present investigation was undertaken to investigate the effect of quenching rate on the microstructure of Ni 50 Mn 50 À x Sn x ribbon alloys and its influence on the martensitic starting phase-transition temperature M S . The study was performed on melt-spun ribbons of a ferromagnetic shape memory alloy (FSMA) of composition Ni 50 Mn 37 Sn 13 produced by varying the speed of the rotating copper wheel between 15 and 50 m s À1 . The resulting samples have a chemical composition close to the nominal one and at room temperature crystallize in a cubic single-phase austenite with the highly ordered L2 1 -type crystal structure without a significant variation in the cell parameter. The average grain size varies between 1.4 and 7.3 mm, while M S increased from 212 to 258 K. Our results suggest that in these materials the average grain size of the parent austenite phase limits the size of the martensite variants, giving rise to its stabilization, while a multivariant transformation mode is maintained.

Thermal and Structural Analysis of Mn49.3Ni43.7Sn7.0 Heusler Alloy Ribbons

“…Nevertheless, a thermodynamic approach is not enough to explain the sample behavior. From the microstructural point of view, the main conclusion is that small grains have a stabilizing effect in the austenitic phase increasing thermal hysteresis, probably because they limit the volume of the individual martensite variants [15,24]. Consequently, in our work it was found that thermal hysteresis is lower/higher in samples with higher/lower grain size and thickness (R3 and R4 / R1 and R2).…”

“…For practical purposes, a good estimation of both terms can be made in accordance with reference [24]: and:…”

“…Nevertheless, recent works take into account that heat exchange, Q, during the transformation process is not exactly equal to the change in enthalpy, ΔH, of the transformation [24]. The difference between Q and ΔH is determined by the contribution of: (a) the elastic energy Eel and (b) the irreversibly dissipated energy Wd:…”

Wheel speed-dependent martensitic transformation and magnetocaloric effect in Ni–Co–Mn–Sn ferromagnetic shape memory alloy ribbons

“…Aside from the bulk, the ribbon samples of these NiMn-based FSMAs have also attracted increasing attention because rapid quenching by melt spinning is an effective method to synthesize highly textured polycrystalline samples, which can reduce or even avoid the prolonged annealing process [23][24][25][26][27][28][29][30][31][32][33][34]. Ribbons are appropriate MCE materials in practical applications because they can improve the technical characteristics of a refrigeration unit by optimizing the heat transfer between the working body and heat exchange [31].…”

On the correct estimation of the magnetic entropy change across the magneto-structural transition from the Maxwell relation: Study of MnCoGeBx alloy ribbons

“…Among them, Gd 5 (Si x Ge 1-x ) 4 [1,16], La(Si,Fe,X) 13 (X= Co, Mn) [17,18], MnFe(P,X) with X = As, Ge, Si [6,19], non-stoichiometric NiMn-X-based Heusler-type (X= Ga, Sn, In, Sb) [20][21][22][23][24][25][26] or Mn(Co,Ni)Ge-based alloys [27][28][29][30][31][32][33][34][35][36][37]. It is worth noting that MnCoGe-based alloys have one of the largest contributions of S st to S T , giving rise to one of the highest reported GMCE in terms of the maximum value of S T [14].…”