The phase stability and hardness of Ti–30Zr–M(M=Nb,V,Cr,Mo,Fe,Ni and Al)shape memory alloys were investigated by structural observations,d-electron alloy design and microhardness tests.Optical microscopy and X-ray diffraction results show that Nb,V,Cr,Mo and Fe are allβ-stability elements in Ti–30Zr–M alloys with the effect enhanced by the presence of Zr.The composition of the least stableβ-phase alloy values of Nb,V,Cr,Mo and Fe in Ti–30Zr alloys are 12%,9%,5%,3%and 2%,respectively,indicating an increasing sequence of theβ-stability ability.Ni and Al showα-stability or moderate effects and the addition of Ni induces the appearance of(Ti,Zr)_(2)Ni phase in Ti–30Zr–5/15Ni alloys.Based on the d-electron alloy design method,the bond order of Ti and alloying atoms(Bo)and the metal d-orbital energy level(Md)are calculated to build the Bo–Md diagram of Ti–30Zr–M alloys associated with the phase structure identification.The microhardness of Ti–30Zr alloy is increased by addition of a small amount of the alloying element,except for Nb.There is a drop of the microhardness of each Ti–30Zr–M alloys whenβphase appears by the addition of more alloying elements.
