Study On The Martensitic Transformation And Mechanical Properties Of ZrCu-base Shape Memory Alloy

The microstructrue and interface structure inside Zr₅₀Cu₅₀, ZrCuAl, ZrCuAlCo thermalmartensite have been studied by means of metalloscope, XRD, TEM and HREM. The phasetransformation of ZrCu-base alloy has been studied by DSC. The mechanical properties ofZrCu-base alloy have been revealed by means of tensile test at room temperature.The experiment results show that during quenching or straining the ZrCu austenite phasewith a B2structure could transform into two martensite phases with monoclinic symmetry.One is the base structure （B19’） and the other is the super strcture of the fomer （B33）, the bothof them are in P space group. By the TEM, we found that the shape of ZrCu-base matensite isplate-like and spearhead. The relationship of these matensite plates are tiwns, The microtwinsare （001） compound twins while the macrotwins are （011） Type I twins. We clearly observedthat （001） compound twins and （001） stacking faults in the matensite plate of ZrCu-basedalloy.The results of DSC show that the Ms of Zr₅₀Cu₅₀is up to112.6℃, Ms has beenimproved with the addition of Al, while Co has the the opposite effect, the both of themimprove the phase transformation hysteresis of ZrCu-based alloy.By the HRTEM we found that the interface between （011） Type I twins in Zr₅₀Cu₅₀isstraight and well-defined and with some dislocations. Steps appear at the interface of （001）compound twins in Zr₅₀Cu₅₀and ZrCuAl alloy, but the interface of （001） compound twins isstraight and well-defined. The shape of （001） compound twins is spearhead, which couldbecome finer, which will disappear at the neighbour. There are some dislocations in the tip,and some fault is in the neighbour. We think that these faults are the nucleus of the twin.The experiment results show that with the addition of Al, the grain size will becomesmaller. With the addition of Co, the σs and ε become well. The best mechanical property isZr_46.5Cu_46.5Al₇, the σbis up to1533.22MPa and the strain is3.95%.and is also the ductilefracture.