This study investigated the hot deformation behavior of Ti-4Al-1Sn-2Zr-5Mo-8V-2.5Cr alloy through isothermal compression tests at temperatures from 780 to 930 • C with strain rates ranging from 0.001 to 1 s −1 . The flow stress decreases with a decreased strain rate and an increased temperature. A constitutive equation was established for this alloy and the dependence of activation energy on temperature and strain rate is discussed. We further proposed a processing map using the dynamic materials model. On the processing map various domains of flow stability and flow instability can be identified. The deformation mechanisms associated with flow stability regions are mainly dynamic recrystallization (DRX) and dynamic recovery (DRV). The flow instability is manifested in the form of the band of flow localizations. The optimum processing conditions are suggested such that the temperature range is from 780 to 880 • C and the strain rate ranges from 0.001 to 0.01 s −1 .

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Abstract:In this study, a Ti composite reinforced with 5 vol. % (TiB w + TiC p ) was fabricated by an in situ casting route. Open die forging in (α + β) phase region was conducted on the composite casting. The microstructures of the as-forged composite pancake are inhomogeneous in terms of matrix microstructure and distribution of reinforcements. The matrix grains are gradually refined from the periphery to centre of the pancake. The reinforcements TiB w and TiC p tend to be uniformly distributed in the centre region. It is suggested that the microstructure difference can be mainly ascribed to the temperature variation from the periphery to the centre. The tensile testing results show that the centre region of the composite pancake exhibits higher strength than the peripheral region. The mechanical behaviour of the composite pancake with the temperature is discussed.

In this study, hot deformation behavior and microstructure evolution of a new near beta titanium alloy reinforced with trace TiCp (2 vol%) are investigated by isothermal compression test. The flow stress curves present various characteristics based on the deformation parameters. The hot deformation activation energy is determined to be 507.1 KJ mol−1, which is lower than that of the matrix alloy. Based on the dynamic material model (DMM), processing map at the strain of 0.6 indicates that flow instability mainly concentrates at 780–820 °C and strain rate higher than 0.22 s−1. Results of microstructure evolution illustrate that flow instability is characterized by the cracking, localized plastic flow, and bending of TiC particles. In the safety region, the morphology and fraction of α and β phases are closely depended on deformation conditions. At α/β field, dynamic recrystallization (DRX) of β grains dominants the deformation mechanism due to the existence of TiC particles by providing nucleation sites. Meanwhile, the DRX degree of β grains is enhanced markedly compared with that of the matrix alloy in β phase field. Finally, deformation mechanism evolution under the given processing conditions is illuminated.

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