Influence of interstitial elements on micromechanical properties in titanium alloys monitored by in-situ neutron diffraction

Morooka, Satoshi  ; Tsuchiyama, Toshihiro*; Kawasaki, Takuro   ; Harjo, S.   

The interstitial elements such as hydrogen, nitrogen and oxygen have a great influence on the mechanical properties of titanium alloy. In the present work, micromechanical properties such as the phase strains, intergranular strains and dislocation densities for titanium alloys containing such interstitial elements were investigated by means of neutron diffraction (ND) technique. The ND experiments during tensile deformation were carried out using an engineering material diffractometer TAKUMI at J-PARC MLF. Lattice parameters refined by Z-Rietveld code are discussed with an increase of the applied stress. The results show that the phase strains of nitrogen or oxygen-strengthened titanium alloys are partitioned into the grain interface between alpha phase and beta phase. In particular, the strong beta phase leads to a stress value higher than the macro-yield stress, resulting in high strengthening of (alpha + beta) dual phase titanium alloys. On the other hand, the dislocation density of titanium alloy containing hydrogen abnormally increased with an increase of the plastic strain. It is generally thought that hydrogen is trapped in the dislocations. However, our result shows that the dislocation is trapped by hydrogen through the Cottrell effect.