The changes in transformation temperatures under stress of Cu–12.7Al–5Ni–2Mn alloy
Introduction
Among the wide variety of alloys that exhibit the shape memory effect (SME) the most developed, as a consequence of their practical applications, are the nickel–titanium alloys and copper-based alloys, such as Cu–Zn–Al and Cu–Al–Ni [1], [2]. The SME in several of these alloys was studied as a function temperature and pressure to learn about their martensitic transformation behavior. Till now, only a small number of papers have been published on the effect of hydrostatic pressure on the thermomechanical behavior of SMs [3], [4], [5], [6], [7], [8], [9]. High pressure work on shape memory alloys (SMAs) is very sparse. The role of high pressure in influencing phase transitions and in unraveling the transition mechanism is very well known [10], [11], [12], [13]. According to the Clausius–Clapeyron equation, the volume change associated with the transformation is responsible for the shift of equilibrium temperature T0. The most important problem is determination of T0, since there is no way for direct measurement of this quantity and opinions differ as to what is the best approximation for the estimation of T0 [9].
DSC is extensively used for the investigation of transition temperatures. This paper presents the effects of stress on shape memory properties of Cu–12.7Al–5Ni–2Mn shape memory alloy.
Section snippets
Experimental
The chemical composition of the alloy used in this work and electron/atom (e/a) ratio are Cu–12.7Al–5Ni–2Mn (in wt pct) and 1.57, respectively. The alloy was supplied Scientific and Technical Research Council of Turkey. Cu–12.7Al–5Ni–2Mn alloy has been solution treated β-phase condition at 900 °C for 30 min for homogenization and quenched in iced-brine to retain in the β phase. The disk-type specimens were cut from roller rod alloy. The different stresses were applied on specimens prepared with a
Results and discussion
DSC curves for forward and reverse transformation of deformed shape memory alloy are shown in Fig. 1. The transformation temperatures and enthalpy changes calculated from DSC curves are given in Table 1. The variation of the transformation temperature with pressure is shown in Fig. 2. The transformation temperature of this alloy increases with increasing pressure. The effect of the stress induced-deformation on shape memory behavior of the alloy can be determined by the following relation [14],
Conclusions
The changes in transformation temperatures under stress of Cu–12.7Al–5Ni–2Mn shape memory alloy have been investigated. The transformation temperatures increase with increasing stress. Both the relationship between the stress induced-deformation and transformation temperatures, and the relationship between T0, temperature at which Gibbs free energy of austenite equals to that of martensite, and plastic deformation is linear.
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