Effect Of Rare Earth Doping On The Structure And Properties Of Lowcost Cu-Al-Ni High Temperature Shape Memory Alloy

Cu-Al-Ni shape memory alloy has been widely studied due to its low manufacturing cost,good single crystal mechanical and shape memory properties.In addition,as high temperature shape memory alloys,the service temperature of Cu-Al-Ni alloy can exceed 200?.However,the development and application of polycrystalline Cu-Al-Ni alloy are seriously limited due to its coarse grains and brittleness.In this thesis,Cu-Al-Ni-x RE(RE=Nd,Sm,Y,La)four series of alloys were prepared by alloying different rare earth elements with Cu-Al-Ni alloy as the base alloy.The microstructure,phase transformation temperature,mechanical properties,shape memory properties and corrosion resistance of each series alloys were studied by metallographic microscope,X-ray diffraction(XRD),scanning electron microscope(SEM),transmission electron microscope(TEM),differential scanning calorimeter(DSC),electronic universal testing machine and electrochemical workstation.Microstructure observation results show that the microstructure of Cu-13.0Al-4.0Ni-x RE(x=0.2,0.5)alloy is composed of 18R martensite,2H martensite,and the second phase rich in corresponding rare earth elements.Rare earth elements can refine the grain size of Cu-13.0Al-4.0Ni alloy significantly,and the grain size of Cu-13.0Al-4.0Ni alloy decreases by an order of magnitude after doping.The results of martensitic transformation temperature measurement showed that the temperature of M_s,M_f,A_s and A_f decreased after adding rare earth elements to Cu-13.0Al-4.0Ni alloy,especially A_sand A_f.Due to the fine grain strengthening and the second phase strengthening,the addition of rare earth elements greatly improves the mechanical properties of the alloy.Among them,La element has the most obvious effect,the compressive fracture stress and strain values of Cu-13.0Al-4.0Ni-0.5La alloy were 1216 MPa and 19.0%,respectively,which are increased by 636 MPa and 8.5%compared with Cu-13.0Al-4.0Ni alloy.As the plasticity of the alloy is improved,the shape memory effect is also significantly improved.After 8%pre-deformation,the Cu-13.0Al-4.0Ni-0.2Nd alloy can obtain 5.0%reversible strain after heating,which is close to twice of the base alloy,when the pre-strain is 10%,the reversible strain can reach 6.8%.The addition of rare earth elements can also enhance the corrosion resistance of Cu-Al-Ni alloy,Among them,with the increase of Sm and La elements,the corrosion resistance of the alloy is continuously improved,and with the increase of Nd and Y elements,the corrosion resistance of the alloy first increases and then decreases.In general,Cu-13.0Al-4.0Ni-0.5La alloy has the best corrosion resistance.