Research on the thermal deformation behavior and mechanism of monophasic TC18 alloy above the β-transus temperature

The thermal-deformation behavior and mechanism for TC18 alloy in the the monophasic zone under temperatures of 890−1040 °C, strain rates of 0.001−10 s -1 , and deformation quantities of 20−60% were studied. The flow stress curves present significant flow softening (FS) under high strain rates and low temperatures. From power-dissipation-efficiency ( η ) diagram combined with microstructural analysis, the peak η does not always appear under high temperatures and low strain rates, as traditionally believed. There are obvious dynamic recovery (DRV), discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) in the relatively high η zone. The deformation mechanisms are related to η , while η reduces with rising strain rate, but exhibits a nonlinear variation with elevated deformation temperature. The predominant deformation mechanisms under the large strains shift from the synergistic effect of CDRX and DDRX below the inflection-point temperature and under lower strain rates, and the inhibitory effect of DDRX on CDRX above the inflection-point temperature and under lower strain rates, to the strong DRV under higher strain rates. The fiber, fiber, fiber, fiber, and fiber are the main microtexture components of the deformed alloy. The deformation microtexture is weakened owing to the stochastic orientation distribution for DRX grains. The weakening degree of deformation microtexture rises with elevating the DRX volume fraction. This provides a new idea for eliminating or weakening the anisotropic deformation microtexture generated during the actually upsetting and drawing processes of the alloy by increasing DRX volume fraction through regulating thermal-deformation parameters.