The high-temperature oxidation behavior of Ti– (6–36) mass%Al alloys and Ti– (4–15) mass%V alloys have been investigated in a temperature range of 1123 to 1273 K in air. A kinetic study of the oxidation has been also carried out in Ti–6 mass%Al alloy and Ti–4 mass%V alloy. The growth rate of oxides in Ti–V alloys is larger than that in Ti–Al alloys. The oxidation products have been examined by X-ray diffraction (XRD), electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS). The Al₂O₃ layer is probably formed in the Ti–Al/oxides interface of the Ti–6 mass%Al alloy by means of EPMA, although only the rutile TiO₂ is detected by means of XRD in the oxides of surface layer in Ti–6 mass% Al alloy and Ti–4 mass%V alloy at 1273 K. Furthermore, the TiO₂ and Al₂O₃ are observed by XPS in surface of the above both alloys at 1123 K for 3.6 ks, but the V₂O₅ is not observed. It is found that the apparent activation energy (245 kJ/mol) for the oxidation experiment (TG experiment) at a constant heating rate is fairly equal to the activation energy (253 kJ/mol) for the isothermal oxidation in Ti–6 mass%Al alloys.

抄録全体を表示

The process reduction by the forming limit improvement is demanded from the economy of drawn shell. Influence of hydraulic counterpressure on the limiting total drawing ratio in direct redrawing method for forming cylindrical shells is investigated. Thin sheets of A1100-O and A5052-O are applied. Because of the restraining of the material movement at the radius part and side wall of punch and better lubrication between the blank and die surface by hydraulic counterpressure, the limiting drawing ratio is improved. Limiting total drawing ratio improves in all the methods when hydraulic counterpressure is applied to first deep drawing and redrawing. The improvements of the limiting total drawing ratio are 1.25–1.60 times in A1100-O, and 1.22–1.58 times in A5052-O. The improvement ratio of limiting total drawing ratio by intermediate annealing of A5052-O is 1.12 times. Therefore, the effect of hydraulic counterpressure in redrawing is more excellent than that of intermediate annealing.

抄録全体を表示

For a high-purity Al–Zn–Mg–Cu alloy plate with a main composition comparable to 7075 aluminum alloy, the slow strain rate tensile (SSRT) test was carried out in humid air to examine the change of hydrogen embrittlement behavior with temper from underaged (UA) to overaged (OA). The relationship between the fracture response and the processes of hydrogen-transport and -enrichment was discussed. UA material showed a high embrittlement susceptibility accompanied by intergranular cracking (IGC), while OA material revealed a relatively small increase in ductility as a local elongation, leading to transgranular dimple-type fracture. No effect of pre-exposure to enhance the IGC initiation of UA was observed. It is supported that IGC will initiate when a local site along grain boundaries are situated in a hydrogen atmosphere with a given high level of concentration. The hydrogen transport can depend on both lattice diffusion and dislocation transport, and the latter is however assessed to play a determinant contribution to attain the critical concentration. The increased ductility of OA material is attributed to the formation of fine dimples induced by a hydrogen-enrichment at the interface between precipitates and matrix in grains.

抄録全体を表示