Microstructural characterization on martensitic α″ phase in Ti-Nb-Pd alloys

The alloying effect of Pd on the martensitic transformation behavior in Ti-Nb alloys has been systematically investigated using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The composition field of the orthorhombic α″ martensite is determined on the Ti-Nb-Pd isothermal section, and appears close to the Ti-Nb edge. The addition of small amounts of Pd affects the lattice parameters of the α″ significantly. It was noticed that increasing Pd content will increase a but decrease b value of the α″ while c remain almost constant. Such variations could make the martensitic transformation easier and a fully martensitic structure containing single α″ has been detected by XRD and TEM in a Ti-18.2Nb-0.5Pd (at.%) alloy. Transformation twinning of the (1 1 0)α″ type was observed in the transformed martensite although the density is low.