The microstructural evolution of near beta alloy Ti-10V-2Fe-3Al during subtransus forging

Abstract

The microstructural evolution of titanium alloys during subtransus isothermal forging (IF) has been effectively demonstrated using a testing methodology developed at Imperial College London. Double truncated cone specimen geometries were isothermally deformed at near ␤ transus temperatures to obtain microstructural information for a range of strains within a single specimen. The methodology was applied to the near ␤ alloy, Ti-10V-2Fe-3Al, to determine the effect of strain, strain rate, and IF subtransus temperature on microstructural evolution.

Microstructure evolution during warm working of Ti–5Al–5Mo–5V–1Cr–1Fe at 600 and 800 °C

“…7c). This behavior mirrors typical changes associated with dynamic fragmentation and spheroidization of a lamellae [23]. At the lower temperature (600 1C), the length of a lamellae did not change until e$0.69, but decreased rather rapidly at larger strain almost attaining the value of the lamella length at 800 1C after e¼1.2.…”

“…Such a relationship may be expected to be weak especially since the bulk of the imposed deformation was accommodated by the bcc b phase, which tends to exhibit limited plastic anisotropy compared to the hcp a phase in titanium alloys. Hence, as noted above, it is likely that the observed flow softening may be ascribed primarily to slip transfer [10] and fragmentation of the b matrix [23]. The latter effect would reduce the constraint imposed on the deformation of b and hence the stress required to bring about its deformation.…”

“…Such behavior in single-phase metallic materials is often associated with discontinuous dynamic recrystallization [24]. For two-phase titanium alloys, on the other hand, mechanisms such as slip transfer [10], dynamic fragmentation [23], and texture softening have been suggested. An analysis of the results in [23] reveals that the fractional softening of Ti-10V-2Fe-3Al with a Widmanstatten-a preform microstructure was of the order of 50% for a strain of $0.7 in the temperature range between 760 and 790 1C and a strain rate of 10 À 3 s À 1 .…”

“…For two-phase titanium alloys, on the other hand, mechanisms such as slip transfer [10], dynamic fragmentation [23], and texture softening have been suggested. An analysis of the results in [23] reveals that the fractional softening of Ti-10V-2Fe-3Al with a Widmanstatten-a preform microstructure was of the order of 50% for a strain of $0.7 in the temperature range between 760 and 790 1C and a strain rate of 10 À 3 s À 1 . The slightly lower level of fractional softening found at 600 1C in the present work may be due to the small amount of dynamic precipitation of fine a phase within the b layers (noted above) which would provide an increment of strengthening.…”

The Flow Behavior and Microstructural Evolution of Ti-5Al-5Mo-5V-3Cr during Subtransus Isothermal Forging

“…[11][12][13] As a result, several deformation mechanisms have been proposed to explain the behavior of Ti-6-4 and therefore facilitate more accurate process modeling. Unfortunately, the larger a phase volume fraction (50 pct in Ti-6-4 compared to 13 pct in Ti-10-2-3) present in a + b alloys at typical industrial processing temperatures has been shown to affect the deformation mechanisms, preventing the simple adoption of mechanisms from one alloy type to another.…”