Shin-ya Komatsu

Effect of two phase warm rolling on aging behavior and mechanical properties of Ti–15Mo–5Zr–3Al alloy

Abstract The isothermal aging behavior and change in tensile and mechanical properties of Ti–15Mo–5Zr–3Al alloy have been studied after three different pre-treatments, i.e. PR (rolling at partial solution temperature), PRP (PR+partial solution treatment) and C (complete solution treatment) by hardness and resistivity measurements, tensile and Charpy impact tests. After the PR and the PRP treatment, almost all of the plate-like primary α particles which were left in as-received specimens became granular, furthermore age-hardening was observed in that α+β bi-phased specimens. Plate-like α is always formed by the aging. Sub-grain size of β phase in the PR and the PRP specimens is 1–2 μm, and no grain growth is observed during the aging. Tensile properties after 673 K-600 ks or 773 K-60 ks aging are improved by the PR or the PRP than the C pre-treatment. The fracture surface of the aged and tensile tested PR and PRP specimens shows dimples, whereas that of the C specimen shows flat surface, area fraction of 40–50%, due to grain boundary fracture. Deflection–load curve shows practically no change in its shape with variation in the pre-treatment, however maximum load is highest in the PRP specimen and decreases in order of the PR and the C. Total absorbed energy is also larger in the PR and the PRP specimens than in the C specimen in age-hardened state. The best strength–ductility balance is attained by the PRP specimen aged at 773 K for 60 ks.

Effect of chromium content on electrical resistivity and tensile properties of Ti–Fe–Cr alloys

Abstract The effects of substituting chromium for iron and the use of low cost ferrochromium alloys in the production of β-Ti–Fe–Cr alloys have been studied with respect to phase constitution, stability, and mechanical properties, in solution treated and quenched states using resistivity, hardness measurement, X-ray diffraction, and tensile testing. Resistivity at room and liquid nitrogen temperatures, and hardness decreased while the ratio of resistivity at liquid nitrogen temperature to that at room temperature increased with increases in chromium content. Alloys of Ti–Fe–Cr, with almost the same electron per atom value, with higher chromium content have smaller volume fractions of athermal omega than alloys with higher iron content. There is less solution hardening in the former alloys than in the latter alloys. Tensile strength decreased with increases in chromium content, while elongation and reduction in area significantly increased. The balance between tensile strength and ductility (elongation and reduction in area) improved in the alloys with added chromium as a substitute for iron. Therefore, no negative influences of ferrochromium alloying on mechanical properties was observed in this study.

Aging behaviour of Ti15Mo5Zr and Ti15Mo5Zr3Al alloy up to 573 K

Abstract Aging behavior of Ti 15Mo 5Zr (15-5) and Ti 15Mo 5Zr 3Al (15-5-3) alloys isothermally aged below 573 K has been investigated mainly through resistometry. In the 15-5 alloy, resistivity at 77 K (ϱLN) increases only slightly, whereas the resistivity at room temperature (ϱRT) increases greatly. The ϱ of the 15-5-3 alloy shows the same tendency as that of the 15-5, but the increase in ϱ continues for a longer period and the increment is larger than in the 15-5 alloy. X-ray diffraction and hardness of the 15-5-3 suggest a long incubation period for the precipitation of the aged ω phase, in contrast to that of a 15-5 alloy aged between 623 K and 723 K. The increase in ϱRT of these alloys might be best interpreted as the concentration separation of β matrix, like GP zones in Al alloys, which contributes to a significant increase in ϱ but to only a minor increase in hardness. Also with α precipitation at high aging temperature, a slight increase is observed in ϱLN during an apparent incubation period. These results suggest that the concentration separation of β occurs at both high and low aging temperatures and that suppression of aged ω by Al addition makes the ϱ increase conspicuous.

Effect of Scandium Addition on Aging Behavior of 6061 Aluminum Alloy

It has been reported that scandium addition improved various properties of aluminum alloys. However, present authors can not find any reports about the addition of Sc to 6000 series alloys. In this study, Sc was added to 6061 alloy and various effects of the Sc addition on aging behavior were examined, comparing with Al-Sc binary alloy. In the STQ state, resistivity at 77K, ρD77, of 0.2%Sc added alloy (6061+Sc) was about 2.0n-m higher than the alloy of no addition (6061). The ρD77 increased in initial stage of isothermal aging up to 473K, then decreased. Though ρD77 of binary Al-0.176%Sc alloy began to decrease from 1.8Ms at 448K and 18ks at 523K, excess decrease in ρD77 of 6061+Sc corresponding to precipitation of Sc compounds was not clear. Peak value of the HV0.1 was decreased and peak aging time delayed by the Sc addition in aging up to 498K. However, softening by overaging was retarded by the Sc addition. These effects of the Sc addition are considered to come from vacancy trap by solute Sc atoms or interface between particles of Sc compound and matrix acting as vacancy sinks.

Change of Thermal Conductivity of Ti-20V and Ti-15V-3Cr-3Sn-3Al Alloys Below Room Temperature with Isochronal Aging

Thermal conductivity, K near liquid nitrogen temperature and electrical resistivity, p at liquid nitrogen temperature were measured on Ti-20V and Ti-15V-3Cr-3Sn-3Al (Ti-15-3) alloys. K of both alloys after solution treatment and water quenching was lower than that of 18Cr-8Ni stainless steel. With isochronal aging, isothermal ω and α precipitated in Ti20V alloy and only a precipitated in Ti-15-3 alloy. Both species of precipitates increased the K and decreased the ρ. Relation between K and T K/ρLN, which were changed by isochronal aging, was almost linear in both alloys though gave different gradients for each precipitates and alloys. Maximum K values of present β Ti alloys range from 4 to 6 Wm−1K−1 near liquid nitrogen temperature, which are about a half or two thirds of 18Cr-8Ni stainless steel.