Open AccessShock-induced transformation behavior in NiTi shape memory alloy
Author(s) -
Hongtao Liu,
Sun Guang-Ai,
Yandong Wang,
Bo Chen,
Xiaolin Wang
Publication year - 2013
Publication title -
wuli xuebao
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.199
H-Index - 47
ISSN - 1000-3290
DOI - 10.7498/aps.62.018103
Subject(s) - materials science , shape memory alloy , martensite , exothermic reaction , nickel titanium , shock (circulatory) , endothermic process , diffusionless transformation , phase (matter) , titanium alloy , alloy , composite material , thermodynamics , microstructure , chemistry , physics , medicine , organic chemistry , adsorption
The high-strain dynamic behavior of NiTi shape memory alloy has significant applications in several fields such as military af- fairs, aerospace. In order to investigate the transformation behavior in NiTi alloy, induced by dynamic mechanics, the shock-loading experiments are performed using a single stage gas gun at different temperatures and different shock velocities. Differential scanning calorimeter (DSC) and comprehensive physical property measurement system are employed to analyze the phase transformation in- duced by residual effects of shock waves in NiTi alloy. Three endotherms are observed in the first heating cycle, showing the presence of three-step reverse phase transformation; whereas during the second heating only one endotherm is seen, because the other two en- dotherms attributed to stress-induced martensite have disappeared. The exothermic and endothermic peak, owing to the transformation of shock-treated specimens, become small and their transformation temperature regions are broadened. This tendency indicates that the internal defects in the specimens, introduced by shock-treated, increase the resistance of phase transformation. The exothermic peaks of specimens, shock-treated at low velocity and high velocity, all shift to the low-temperature-zone, because the dislocations increase the hindrance to martensitic transformation. However, the endothermic peaks of specimens with low velocity shock-treated shift to high-temperature-zone, illustrating that the reverse martensitic transformation is also opposed by dislocations; while the endothermic peaks shift to low-temperature-zone for high velocity shock-treated, due to the decrease of transformation energy, caused by the re-duction of recoverable martensite. A small shoulder is detected in exothermic peak, whose shape becomes sharper with shock rate increasing. This result reveals that the intermediate phase (R-phase) results in two-stage phase transformation. The electrical resistivity measurement result further confirms that the two types of phase transformations associated with austenite to rhombohedral (A→R) and rhombohedral to martensite (R→M) can occur at the same time in a certain temperature range.