Study On Structure And Properties Of Cu-Al-Ni Based High Temperature Shape Memory Alloy

Cu-Al-Ni shape memory alloy has been widely studied as its low cost,wide phase transition temperature range,excellent superelasticity of single crystal and shape memory effect.However,the development and application of polycrystalline Cu-Al-Ni are severely restricted due to its large grain size,high anisotropy factor,high brittleness and poor thermal stability.In this paper,Cu-12Al-4Ni high-temperature shape memory alloy was used as the matrix.It was proposed to improve the thermal stability of the alloy by doping Mn element,and then Gd element was selected to improve its mechanical properties and shape memory effect.First,Cu-12Al-4Ni-x Mn alloys were prepared by alloying method.Metallographic microscope,X-ray diffraction(XRD)and scanning electron microscope(SEM),transmission electron microscope(TEM),differential thermal analyzer(DTA),electronic universal testing machine and electrochemical workstation were used to research microstructure martensite phase transformation,,thermal stability,mechanical properties,shape memory effect and the corrosion behaviour on Cu-12Al-4Ni high temperature shape memory alloys.The microstructure observation results showed that Mn element had little effect on the grain size of the alloys.The microstructure of Cu-12Al-4Ni-x Mn alloys was composed of 2H and 18R martensite at room temperature.After Gd element doping,the microstructure of the alloy changed into a single 18R martensite variant,and the second phase Al Cu₄Gd appears in the matrix.The Gd element significantly refined the grain size of Cu-12Al-4Ni-1.5Mn alloys,which decreased an order of magnitude from2 mm to 200?m.It was found that the phase transformation of Cu-12Al-4Ni-x Mn alloys were carried out in two steps,which was supported by the existence of 2H and 18R martensite in the matrix.In addition,the thermal stability of Cu-12Al-4Ni-x Mn alloys were significantly improved at x?1.5.After the addition of Gd element,the phase transition of Cu-12Al-4Ni-1.5Mn-y Gd alloys changed to one-step phase transition,and the thermal stability is not affected.Mn element had the effect of solution strengthening.With the increase of Mn content,the compressive fracture strength of Cu-12Al-4Ni-x Mn alloys increased gradually and reached the maximum value of 587 MPa at x=2.The compressive fracture strain increased firstly and then decreased,reaching the maximum value of 12.8%at x=1.5.Due to the fine-grain strengthening,the mechanical properties of Cu-12Al-4Ni-1.5Mn-y Gd alloys were further improved.With the increase of Gd element content,the compressive fracture strength of the alloys increased firstly and then decreased,reaching a maximum of 969MPa at y=0.3.The compressive fracture strain increased all the time,reaching of 15.3%at y=1.The shape memory effect of Cu-12Al-4Ni-1.5Mn and Cu-12Al-4Ni-1.5Mn-0.3Gd alloys under 8%prestrain was 6.4%and 6.6%,respectively.The corrosion behaviour of Cu-12Al-4Ni alloy is slightly damaged by the addition of Mn and Gd,and the effect of Gd was greater than Mn element.