Martensitic Transformation and Internal Structure of the TiPd and TiPd-Fe Alloys

The crystal structures, internal structure and shape memory effect of the TiPd and TiPd-Fe martensitic alloys were investigated by electron microscopy and tensile testing. The B19(2H) martensite which was found in the earlier X-ray investigation was found to exist in both the TiPd alloy and the TiPd-Fe alloys. The internal structure of this martensite was found to be (111)2H twin. By substituting palladium by iron (the content of titanium is fixed at 54 at%), the Ms temperature decreases with increasing iron content. In the iron added alloys with 4, 5 and 6 at%Fe, a new martensite phase with 9R structure was found to exist in addition to the twinned B19(2H) martensite. In the alloys with 7 and 8 at%Fe, an "intermediate phase" which is very similar to the "incommensurate phase" in TiNi alloys was found to exist. Additional "superlattice" diffraction spots of this phase lie on 0.3n {110} B2 (7at%Fe), and 0.28n {110} B2 (8 at%- Fe), (n: integer). The shape memory effect and pseudoelastic behaviour of the polycrystalline specimens of the 54Ti-39Pd-7Fe and 54Ti-38Pd-8Fe alloys were investigated by tensile testing. Recoverable strain by shape memory effect was about 1% (percentage of recovery 100%) and pseudoelastic strain 3%, in both the alloys.