The orthorhombic 00 martensite was formed in Ti-8 mass%Mo alloy by quenching from 1223 K. The purpose of this study was to investigate phase transformation of the 00 martensite structure by isothermal aging. In differential scanning calorimetry curve of the quenched specimen, an exothermic peak that indicated decomposition from the 00 martensite to and phases was observed near 780 K, so that isothermal aging was performed at 723 K and 923 K for 9.0 ks. Optical microscopy, X-ray diffraction and transmission electron microscopy were performed to these specimens. Band-like products that were composed of the single variant of ! phase were observed in the quenched 00 martensite structure. On the other hand, ð111Þ 00 twins were observed in the 723 K-aged 00 martensite structure. The quenched 00 martensite structure indicated low elastic incline and good ductility, whereas the 723 K-aged 00 martensite structure indicated high yield stress and brittleness. It was pointed out that the ! products were formed to relax the volume expansion from the phase to the 00 martensite, and the ð111Þ 00 twins were formed during the isothermal aging at 723 K with the extinction of the ! products.
The orthorhombic a″martensite was formed in Ti 8 massMo alloy by quenching from 1223 K. The purpose of this study was to investigate phase transformation of the a″martensite structure by isothermal aging. In differential scanning calorimetry curve of the quenched specimen, an exothermic peak that indicated decomposition from the a″martensite to a and b phases was observed near 780 K, so that isothermal aging was performed at 723 K and 923 K for 9.0 ks. Optical microscopy, X ray diffraction and transmission electron microscopy were performed to these specimens. Band like products that were composed of the single variant of v phase were observed in the quenched a″martensite structure. On the other hand, (111)a″twins were observed in the 723 K aged a″martensite structure. The quenched a″martensite structure indicated low elastic incline and good ductility, whereas the 723 K aged a″martensite structure indicated high yield stress and brittleness. It was pointed out that the v products were formed to relax the volume expansion from the b phase to the a″martensite, and the (111)a″twins were formed during the isothermal aging at 723 K with the extinction of the v products.
Three kinds of titanium-molybdenum alloy, Ti-8Mo, Ti-14Mo and Ti-20Mo (mass%), quenched from 1223 K were investigated to clarify the tensile behavior and the cold workability using tensile test and conical cup test. In the quenched state Ti-14Mo showed the superior workability. Ti-20Mo has poor ductility in tensile test, but has relatively good formability in conical cup test. Both Ti-8Mo and Ti-14Mo became brittle through a cold rolling of 50% reduction in thickness; however Ti-20Mo did not change in workability by the cold rolling at all. Hardness remarkably increased with rolling reduction in Ti-8Mo and Ti-14Mo, but was almost constant in Ti-20Mo, especially with Ti-20Mo containing high oxygen. Microstructure of Ti-8Mo and Ti-14Mo rolled until seventy-odd percentage exhibited very fine structure and changed to 0 þ and structure, respectively. On the other hand Ti-20Mo hardly changed in microstructure by a cold rolling besides the formation of some band-like products. The product was composed of single variant of commensurate !-phase, whereas the matrix contained four variants of incommensurate !-phase. It was suggested that the peculiar deformation mechanism of Ti-20Mo was concerned with stress induced transformation of the !-phase.
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