Influence of Processing State on Recovery Stress in NiTiNb Shape Memory Alloy

Abstract

Self-made tension machine was used to measure the evolution of recovery stress under different processing state for NiTiNb alloy. Then, SEM was used to investigate the microstructure evolution. The results show that the range of the highest recovery stress for forged NiTiNb alloy is between 210-215MPa. Otherwise, the recovery stress level of the samples enduring cold drawing and hot rolling is basically same, which all belong to the rage of 210-220MPa. After forging, the firstly precipitated TiNi phase particles become fine, only 5-8μm. The Nb tablets in eutectic microstructure, which originally contributed between TiNi phase particles, appear spheroidization.

Feasibility of self-pre-stressing concrete members using shape memory alloys

“…The as-cast microstructure is representative of the microstructure prior to thermo-mechanical processing. The SEM image in Figure 3(b) shows the typical eutectic micro-constituent, which is made up of β-Nb-rich particles and α-NiTiNb matrix (Siegert et al, 2002; Wang et al, 2014; Zhao, 2000). Deformation processing breaks up the net-like structure (Siegert et al, 2002; Wang et al, 2014; Yan et al, 2012).…”

“…It is well known that the unique stabilization of martensite, which is the cornerstone of NiTiNb shape memory behavior, is attributed to the micro-constituent morphologies (Cai et al, 1994; Kusagawa et al, 2001; Melton et al, 1988; Siegert et al, 2002; Wang et al, 2014; Yan et al, 2012; Zhao, 2000). The microstructure images in Figure 3(c) and (d) underscore differential micro-constituent morphologies resulting from different thermo-mechanical processing done by the different companies, which show the sheet and rod materials, respectively.…”

“…First, the process of self-post-tensioning with SMA tendons and the required conditions on the transformation temperatures of the SMAs are discussed. The alloys are typically cast and further cold- or hot-worked into rods, sheets, tubes, wires, and so on for practical application (Siegert et al, 2002; Wang et al, 2014; Yan et al, 2012). Thus, in this work, commercially available rod and sheet NiTiNb materials are contrast with respect to a cast NiTiNb alloy in order to benchmark the influence of differential deformation processes.…”

Shape Memory Effect in Cast Versus Deformation-Processed NiTiNb Alloys

“…The influence of Nb addition to NiTi with respect to plastic deformation giving rise to the wide hysteresis has been expounded upon by Zhang et al [3,4], Zhao et al [5][6][7][8][9][10], and Piao et al [11][12][13]. More recently, the NiTiNb classes of SMAs have garnered interests due to the wide hysteresis levels matching operating temperatures for civil engineering applications requiring pre-stressing or constraint stressing [14][15][16][17][18][19]. Furthermore, the materials are expected to exhibit damping potential [20,21] as well as good oxidation resistance [22].…”

“…Several investigations characterize the impact of deformation processing conditions on the microstructure [19,25,[31][32][33][34][35]. Ultimately, the findings show that the deformationprocessed microstructure is made up of oriented b-Nb-rich microconstituents that are dispersed throughout the matrix similar to aligned discontinuous fiber (or nanowire)-reinforced composites [36][37][38].…”