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

中性子回折その場測定によるチタン合金の微視的力学特性に及ぼす侵入型元素の影響

諸岡 聡  ; Harjo, S.   

Morooka, Satoshi; 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 technique. In-situ neutron diffraction during tensile deformation was performed with TAKUMI, a high-resolution and high-intensity TOF neutron diffractometer for engineering materials science at MLF of the J-PARC. 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.