Tensile-stress-induced growth of ellipsoidal ω-precipitates in a Ti–20wt%Mo alloy

Abstract

The effects of applied tensile stress on the growth of ellipsoidal ω phase precipitates have been investigated for a Ti−20wt%Mo alloy aged at 300 °C. The application of tensile stress accelerates the growth of ω-precipitates when the misfit strain ε Μ of the precipitates along the loading direction is greater than 0; however, it does not significantly affect the growth of precipitates in cases where ε Μ < 0. Whereas the growth of precipitates under no stress or in the case where ε Μ < 0 under tensile stress is governed by the diffusion of

Growth kinetics of ellipsoidal ω-precipitates in a Ti–20 wt%Mo alloy under compressive stress

“…As in our previous study [9], we often observed grains in which the (113) β plane was nearly parallel to the surfaces of TEM thin foils. The grains in which the (113) β plane was parallel to the specimen surfaces were used to estimate the misfit strains of the variants I and II, among the four possible ω-variants, along the LD on (113) β (see Fig.…”

“…We have observed the compressivestress-induced growth of ω-precipitates in the case ε Μ < 0, which is in contrast with the tensile-stress-induced growth of the precipitates in the case ε Μ > 0 [9], and further found the lower velocity of the interface-controlled growth of ω-precipitates in the case ε Μ < 0 under a compressive stress of 450 − 550 MPa than the velocity of the interface-controlled growth of ω-precipitates in the case ε Μ > 0 under the same tensile stress, as will be shown later.…”

“…The solution-treated specimens were then aged at 300 °C for 3 h under no stress (free aging). Free aging at 300 °C for 3 h induced complete nucleation of the ω-precipitates [9]. The aged specimens were further aged at 300 °C for various times under an applied compressive stress of 400, 450, 500, and 550 MPa using a creep testing device.…”

“…Specimens aged under a compressive stress of X MPa, a tensile stress of X MPa, and no stress are hereafter referred to as XC, XT, and 0F. The maximum applied stress of 550 MPa was approximately four-fifths the yield strength of the solution-treated specimen at 300 °C [9].…”

“…Subsequently, Monzen et al [9] examined the effects of applied tensile stress on the growth of ellipsoidal ω-phase precipitates in a Ti−20Mo alloy aged at 300 °C. The application 4 of tensile stress promotes the growth of ω-precipitates when the misfit strain ε Μ of the precipitates along the LD is greater than 0; however, it does not significantly affect the growth of precipitates in the case ε Μ < 0.…”