Abstract
Recently lower costly alloy, Ti-Cr(Fe)-0(N) which shows strength as high as Ti-6A1-4V alloy has been in common use. Both nitrogen (N) strengthened (Ti-4Cr-0.2N (mass%)) and oxygen (O) strengthened (Ti-4Cr-0.20) titanium alloys have been studied for their utilization on the structural materials. Their tensile deformation behavior was investigated by in-situ neutron diffractmeter "TAKUMI". Lattice spacing was measured with increase of the applied stress. The internal stress was partitioned into the grain interface between alpha phase and beta phase, which was called as phase stresses. Phase strains were measured in the axial and transverse direction determined lattice parameters by Reitveld refinement. Beyond the onset of plastic flow, micro-yielding, almost no change of the phase strain in alpha phase was detected with increase of the applied stress. On the other hand, phase strain in beta phase was continuously increased. Furthermore, the N (O) adjunction increased the yield stress and tensile strength. These results show good agreement with the predictions by a simple two-phase model: the strong beta phase yields higher stress than macro-yield stress, resulting in high strengthening of (alpha + beta) dual phase titanium alloys.
