Effects of ternary additions on the thermoelastic martensitic transformation of NiAl

Abstract

Nickel-rich b-NiAl alloys, which are potential materials for high-temperature shape-memory alloys, show a thermoelastic martensitic transformation, which produces their shape memory effect. However, the transformation to Ni 5 Al 3 phase during heating of NiAl martensite can interrupt the reversible martensitic transformation; consequently, the shape memory effect in NiAl martensite might not appear after heating. The phase transformation process in binary Ni-(34 to 37)Al martensite was investigated by differential thermal analysis (DTA) method, and we found that the condition of reversible martensitic transformation was not the b : Ni 5 Al 3 transformation, but rather the M : Ni 5 Al 3 transformation occurring at 250°C to 300°C. Therefore, the transformation temperature of M : Ni 5 Al 3 determined the highest operating temperature for the shape memory effect. For verifying the critical temperature, the phase transformation process was investigated for eight ternary Ni-33Al-X alloys (X ϭ Cu, Co, Fe, Mn, Cr, Ti, Si, and Nb). Only Ti, Si, and Nb additions were found to be effective in dropping the M s temperature, and they facilitated the shape memory effect in Ni-33Al-X alloys. In particular, the addition of Si and Nb raised the transformation temperature of M : Ni 5 Al 3 , a potentially beneficial effect for shape memory at higher temperatures.

Phase and Structural Transformations in the Alloys Based on Monoaluminide of Nickel

“…В частности, интересные результаты в этом направлении опубликованы японскими и украинскими уче-ными по легированию рением. Проблемой легирования широким спектром элементов наиболее интенсивно в последние 2-3 года за-нимаются южнокорейские исследователи [81]. К сожалению, по данным этих авторов, в большинстве случаев стабилизация обра-тимости МП за счет введения третьего элемента сопровождается резким снижением критических температур МП, что крайне не-желательно для функциональных сплавов с ВТЭПФ.…”

Phase transformation and microstructural features of NiAl/Ni3Al two-phase alloys containing ternary elements

“…First, they elements must cause a sharp drop in the A s temperature, because the M s temperature (≒A s temperature) of binary Ni-34Al alloy is as high as 460 o C [11]. The A s temperature can be measured only if it is below 2 5 0 o C, because austenitic transformation above 250 o C could not be observed through DTA due to the preceding transformation to Ni 5 Al 3 [13]. Second, the amount of ternary additions should not exceed the solubility of β-single phase at 1300 o C so that the only precipitation phases are β and γ'.…”

“…6 shows the DTA results obtained from the re-heating of [Type II] alloys, which have already first undergone heating up to 5 5 0 o C. The 1.6Nb and 2.8Ti alloys, which showed a large exothermic peak on the first heating, did not show any phase transformation, but the 2.0Si alloy, which showed a much smaller exothermic peak on the first heating, exhibited an endothermic peak. It is reported that the transformation to Ni 5 Al 3 phase is an irreversible process, and both martensitic and austenitic transformation are reversible processes [13,16]. Therefore, no phase transformation during the re-heating indicates that the alloy containing Ti or Nb was transformed to Ni 5 Al 3 phase completely during the first heating.…”

“…*Corresponding author: shuns@kaist.ac.kr (austenite start) temperature of β'-martensite. The purpose of this study is to verify the relationship between microstructural features of NiAl/Ni 3 Al two-phase alloys and phase transformations of β'-martensites containing Ti, Si, and Nb, all of which sharply drop the A s temperature (≒M s temperature [11]) of β'-martensite [12,13]. In addition, various important factors governing β+γ' microstructures are proposed in detail.…”

Martensitic transformation and shape memory effect in Ni-Al based alloys

“…A lot of doping elements (Co, Ni, Pd, Pt, Cu, Ag, Au [7][8][9][10]) promote rising start temperatures of martensitic transformation in Ni-Al alloys.…”