Effects of training on the thermomechanical behavior of NiTiHf and NiTiZr high temperature shape memory alloys

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING

卷:794

Article

Karakoc, O.¹  Atli, K. C.¹  Evirgen, A.¹  Pons, J.²  Santamarta, R.²  Benafan, O.³  Noebe, R. D.³  Karaman, I¹ 

[1] Texas A&M Univ, Dept Mat Sci & Engn, College Stn, TX 77843 USA

[2] Univ Illes Balears, Dept Fis, E-07122 Palma De Mallorca, Spain

[3] NASA, Mat & Struct Div, Glenn Res Ctr, Cleveland, OH 44135 USA

关键词: High temperature shape memory alloys;    NiTiHf;    NiTiZr;    Thermomechanical training;    Martensitic transformation;   

DOI  :  10.1016/j.msea.2020.139857

来源: Elsevier

【 摘 要 】

The effects of constant load thermal cycles (training) on the thermomechanical behavior of nano-precipitation strengthened Ni50.3Ti29.7Hf20 (NiTiHf) and Ni50.3Ti29.7Zr20 (NiTiZr) high temperature shape memory alloys (HTSMAs) were compared. Thermomechanical properties were determined as a function of the number of training cycles, which consisted of up to 2000 isobaric thermal cycles at 300 MPa, between lower and upper cycle temperatures of 35 and 300 degrees C, respectively. In addition, the stability of the trained alloys was determined after exposure to thermal treatments at temperatures above the upper cycle training temperature. Training at 300 MPa significantly improved the actuation strain capability of the NiTiHf HTSMA at low stresses (i.e., 50 MPa) and resulted in a two-way shape memory strain (TWSMS) up to 1.9%, but essentially had no effect on the 300 MPa response. Training had less notable benefits in the case of the NiTiZr, producing negligible TWSMS, and resulting in a decrease in actuation strain capability at 300 MPa with repeated cycling. The benefits of training to the NiTiHf HTSMA were maintained after aging at 400 degrees C but were lost after exposure to 500 degrees C and above. Since training was not notably beneficial to the NiTiZr alloy and resulted in a loss in strain capability at 300 MPa, the high temperature annealing treatment actually recovered strain capability in the alloy under high stresses. The superior TWSM response of the NiTiHf HTSMA as compared to the NiTiZr, was attributed to the higher melting temperature, and thus the lower homologous operating temperature of the former, when both alloys were tested over the same temperature range.

【 授权许可】

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