| 研究実績の概要 |
In this study, the deformation-induced omega-phase transformation during tensile deformation was investigated in the developed spinal-support alloy, Ti-9Cr-0.2O. The results might not only facilitate to interpret the novel “changeable Young’s modulus”-biofunctionality as well as high strength and large elongation of this alloy, but also contribute to clarify when (critical strain) and how (mechanism) the deformation-induced omega-phase transformation undergoes in titanium alloys. A Ti-9Cr-0.2O alloy was prepared by levitation melting, then thermo-mechanical treated, and finally solution treated. Normal tensile test and interrupted tensile tests were performed and the microstructures of the tested specimens were examined. The results show that both preferential single-variant omega transformation along its [0001] direction and growth and/or assembling of uniformly distributed omega particles undergo in the Ti-9Cr-0.2O alloy during tensile deformation. This deformation-induced omega-phase transformation is confirmed to occur in the tensile elastic region, which indicates that it can be triggered by elastic strain or stress without plastic deformation. Under further deformation, this deformation-induced omega-phase transformation can develop to a more extensive level and a re-orientation process works for this transformation; that is, the omega-1 variant may re-orientate into the omega-2 variant via {001}<110> twinning-type mechanism probably related to the external loading condition and the orientations of omega and beta phases.
|
| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
The objective of this study is to clarify when (critical strain) and how (mechanism) the deformation-induced omega-phase transformation undergoes in beta-type titanium alloy in order to control the deformation-induced omega-phase transformation as expected to develop specific properties. In the last year, the deformation-induced omega-phase transformation during tensile deformation was investigated in the developed spinal-support alloy, Ti-9Cr-0.2O. A Ti-9Cr-0.2O alloy was fabricated by cold crucible levitation melting. Normal tensile test and interrupted tensile tests unloading at ~4.7%, ~12%, and ~19% strains, respectively, were performed and the microstructures of the tested specimens were examined by transmission electron microscopy. It is found that the deformation-induced omega-phase transformation can be triggered by elastic strain or stress without plastic deformation. During tensile deformation, preferential single-variant omega transformation along its [0001] direction and growth and/or assembling of uniformly distributed omega particles are both identified in Ti-9Cr-0.2O. During further deformation, a re-orientation process works for the deformation-induced omega-phase transformation; that is, the omega-1 variant may re-orientate into the omega-2 variant via {001}<110> twinning-type mechanism. However, the effects of chromium and oxygen on the deformation-induced omega-phase transformation has not yet been studied as planned. Therefore, based on the abovementioned viewpoints, we judge that the study is progressing rather smoothly.
|
| 今後の研究の推進方策 |
So far, the deformation-induced omega-phase transformation during tensile deformation has been investigated by transmission electron microscopy in the Ti-9Cr-0.2O alloy. For the next step, high-resolution transmission electron microscopy will be utilized to analyze the deformation-induced omega-phase transformation from atomic scale in this alloy. A series of titanium alloys with various chromium and oxygen contents are planned to be prepared. The deformation-induced omega-phase transformation during tensile deformation (such as critical strain, evolution of lattice parameter and volume fraction of omega phase and et al.) is planned to be investigated in these alloys by synchrotron radiation diffraction analysis. The effects of chromium and oxygen on the deformation-induced omega-phase transformation is planned to be discussed. Further, thin film specimens having specific orientations with regards to the loading direction will be sliced from specific-oriented grains in a tensile deformed Ti-9Cr-0.2O specimen by focus ion beam technique, then they are subjected to the transmission electron microscopy analysis. According to the obtained results, the effect of “loading direction-grain orientation”-relationship on the deformation-induced omega-phase transformation in titanium alloys will be clarified.
|
