The Formation and Elastic Behavior of TiNi Intermetallic Sintered From a TiH₂–Ni Powder Mixture

The phase formation and consolidation processes in TiH₂–Ni powder mixtures resulting in TiNi intermetallic were studied. The use of titanium hydride as a precursor in optimal sintering conditions (900–1000°C) allowed a material with optimum porosity to be produced and a liquid phase to be avoided during sintering. The phase formation processes were found to occur rapidly in the sintering of TiH₂–Ni mixtures. At sintering temperatures of 900–1000°C, 70–82% TiNi formed. Intermetallic Ti₂Ni compound was an additional phase that emerged in the material in all sintering conditions. The stability of this phase was attributed to its affinity for oxygen and thus formation of stable complex oxides. The superfine mixture and highly active titanium resulting from the decomposition of titanium hydride accelerated the oxidation process. Moreover, the interaction with oxygen began sooner than with nickel. The samples produced from the finest mixture were less homogeneous than the samples produced from a coarser mixture. The high-speed interaction between titanium and nickel and rapid oxygen absorption were due to the hydride powder with significantly finer particles. In these sintering conditions, the material had 12–15% porosity and was thus optimum for medical applications. Studies of the mechanical behavior of TiNi alloys revealed an abnormally low elastic modulus of 40 GPa. Experiments on cyclic loading–unloading showed that the initial elastic strain was 1.1% and reversible transformation strain 0.7%. When the strain reached 4%, the elastic modulus decreased to E ~ 32.7 GPa, the total elastic strain increased to ε_el ~ 2.6%, and damping capability Q^–1 became equal to 0.036. The mechanical characteristics of the materials were close to those of human bones. The experimental results demonstrate that the sintered TiN materials exhibit the structure and mechanical properties that make them promising for the design of human bone implants.