Papers by Keyword: Isochronal Heat Treatment

Abstract: Although titanium is considered to be a ubiquitous element since it has the tenth highest Clarke number of all elements, it is classified as a rare metal because the current refinement process is more environmentally damaging than the processes used to refine iron and aluminum. Furthermore, the beta stabilizing elements of titanium alloys (e.g., V, Mo, Nb, and Ta) are very expensive due to their low crustal abundances. Manganese is also considered to be a ubiquitous element, since it has the 12th highest Clarke number of all elements. Therefore, manganese is a promising alloying element for titanium, especially as a beta-stabilizer. In order to develop beta titanium alloys as ubiquitous metallic materials, it is very important to investigate the properties of Ti-Mn alloys. In this study, the phase constitution of and the effect of heat treatment on Ti-3.3 to 8.7 mass% Mn alloys were investigated by electrical resistivity and Vickers hardness (HV) measurements and by X-ray diffraction (XRD) analysis and optical microscopy. In 3.3, 5.1, and 6.0 mass% Mn alloys quenched from 1173 K, ’ martensite and  phase were identified by XRD, whereas in the 8.7 mass% alloy, only the  phase was detected. The resistivities at both temperatures increased with increasing Mn content up to 6.0 mass% Mn and the positive temperature dependence of resistivity became negative at 6.0 mass% Mn. LN increased gradually with increasing Mn content up to 8.7 mass% Mn, whereasRT decreased considerably at a Mn content of 8.7 mass% Mn. HV increased with increasing Mn content up to 5.1 mass%, after which it began to decrease. In Ti-3.3 mass%Mn and 5.1 mass%Mn alloys, the resistivity and the resistivity ratio decreased with increasing temperature of isochronal heat treatment because of decomposition of ’ martensite. In 6.0Mn and 8.7Mn alloys, the resistivity and the resistivity ratio decreased, while Vickers hardness increased with increasing temperature of isochronal heat treatment because of isothermal  precipitation. Furthermore, the temperature for the onset of precipitation increased with higher Mn content.

Abstract: To develop new shape memory and super-elastic alloys for medical applications, titanium alloys using non-toxic metallic elements, such as Ta and Nb, are being actively investigated. In this study, aimed at developing new shape memory Ti alloys, we investigate the effect of oxygen, a powerful alpha stabilizing interstitial element, on the heat treatment behavior of Ti-50mass%Ta-5mass%Zr through electrical resistivity and Vickers hardness measurements and shape-recovery tests. Ti-50Ta-5Zr-0.14Ox and 0.33Ox alloys, and the β and α” bi-phase was confirmed by XRD. Only the β phase was identified in the Ti-50Ta-5Zr-0.62Ox alloy. Upon isochronal heat treatment, the resistivity at LN and resistivity ratio of Zr-0.33 and 0.62Ox alloys decreased up to around 523 K. In the 5Zr-0.62Ox alloy, orthorhombic martensite and the α” and β phases were identified in the specimens heat-treated at 473 and 523 K. The decreases in resistivity at liquid nitrogen temperature and resistivity ratio are due to the formation of α” during isochronal heat treatment. The formation of α” was confirmed by X-ray diffraction in the 5Zr-0.62Ox alloy. The shape memory effect was observed in 5Zr-0.14 and 0.33Ox alloys and the shape recovery ratio of both alloys was about 40% at 673 K.