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Nickel-titanium (NiTi) shape memory alloys (SMAs) undergo phase transformation between austenitic and martensitic phases in response to applied thermal or mechanical stress, resulting in unique properties and applications. However, machinability often becomes challenging due to property and temperature sensitivity attributes. The use of chilled air to influence machinability in macro-milling was investigated in this study. Other than that, differential scanning calorimetry (DSC) was used to determine the temperature of phase transformation. The results showed that milling with chilled air and minimal lubrication significantly improved machining performance by reducing tool wear and burr formation. Moreover, surface quality has also improved significantly. A notable discovery is that the machining process can change the critical conditions for phase transition, enabling new performance capability of tuning material hysteresis. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the high-speed machinability and phase transformation behavior of nickel-titanium shape memory alloys considering the process and post-process perspective. The tool wear results showed that PCD tool has great potential over carbide considering the limitation of quick tool wear in the high cutting speed range. Maximum tool life was achieved at the cutting speed of 130 m/min. The results obtained from differential scanning calorimetry indicated that the latent heats and transformation temperatures of nickel-titanium shape memory alloy are highly cutting speed dependent. Decrease of the cutting speed resulted in increased impair on these properties. It was found that the decrease of the cutting speed causes a decrease in the transformation enthalpy. The results revealed that increased transformation hysteresis is highly cutting speed related. Two hundred fifty m/min and 70 m/min cutting speed values resulted in 31.5 and 37.8 °C post-machining transformation hysteresis respectively. Compared to the unmachined sample, a minimal change in functional properties was achieved at the cutting speed of 250 m/min. Likewise, the lowest cutting speed (70 m/min) led to maximum subsurface hardening and deeper machining-induced layer according to metallurgical investigations. Residual austenite formation was evident on the subsurface of the machined specimens. [ABSTRACT FROM AUTHOR]

Shape memory alloys (SMAs) provide an attractive solid-state actuation alternative to engineers in various fields due to their ability to exhibit recoverable deformations while under substantial loads. This feature is of particular importance when utilising the smart composite materials reinforced by SMA. Many constitutive models describing this repeatable phenomenon have been proposed, where some models also capture the effects of rate-independent irrecoverable deformations in SMAs. This paper presents experimental investigations and numerical simulations on shape memory alloys. First, by consisting in determining the transformations of equiatomic Ti-Ni shape memory alloys by differential scanning calorimeter. Then, in order to validate a 3D numerical model of the pseudoelastic behaviour of SMA allowing a finite strain analysis, a set of experimental tests at various initial temperatures is proposed. Finally, the numerical simulations of uniaxial tests performed on shape memory alloys are presented and compared with experimental data, permitting the validation of the proposed modelling. Reasonably good correlation is obtained between the experimental and model predictions. [ABSTRACT FROM AUTHOR]