Evolutions of superelasticity and elastocaloric effect of Ti50Ni48Fe2 and aged-hardened Ni-rich Ti49.2Ni49.3Fe1.5 shape memory alloys under cyclic compressive deformation

The transformation and superelasticity characteristics of solution-treated Ti50Ni48Fe2 and aged-hardened Ti49.2Ni49.3Fe1.5 shape memory alloys during cyclic compressive deformation were investigated. The Ti50Ni48Fe2 alloy could not be precipitation hardened, while the Ti49.2Ni49.3Fe1.5 alloy, aged at 400 degrees C, was hardened by Ti3Ni4 precipitates. During the cyclic deformation, the B2 reversible arrow R reversible arrow B19' transformation peaks broadened and spread to a large temperature span. At the same time, the superelasticity behavior became linear, and the associated elastocaloric cooling capacity decreased to a stable value. Among these samples, Ti49.2Ni49.3Fe1.5 alloy aged at 400 degrees C for 150 h exhibited the largest recoverable strain in superelasticity and retained the largest cooling effect after 1000 deformation cycles. Furthermore, it showed elastocaloric cooling of -4.1 degrees C to -7.0 degrees C at operating temperatures of -40-80 degrees C. Experimental results revealed that B19' transformation was suppressed significantly by cyclic deformation, and thus the transformation occurred in a wide temperature range of -160 to -50 degrees C. Additionally, the linear superelasticity exhibited a low slope of the Clausius-Clapeyron relation of about 0.5 MPa/degrees C. These features allow the alloys to exhibit super-elasticiy and the elastocaloric effect over a wider temperature range. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The investigation showed that Ti49.2Ni49.3Fe1.5 alloy aged at 400 degrees C for 150 h exhibited the largest recoverable strain in superelasticity and retained the largest cooling effect after 1000 deformation cycles. The linear superelasticity exhibited a low slope of the Clausius-Clapeyron relation of about 0.5 MPa/degrees C, allowing the alloys to exhibit super-elasticity and the elastocaloric effect over a wider temperature range.