Research On Deformation Mechanism And Fracture Criterion Of Ti40 Burn Resistant Titanium Alloy In Hot Metal Forming

In the field of metal forming, the study of workability or formability of material and defects during metal forming is the focus of researchers. Workability is generally determined by the occurrence of ductile fracture and therefore limitations are set by the appearance of surface or internal cracks within regions that are highly strained due to extensive material flow. The advent of numerical methods to handle large deformation plasticity has made it possible to analyze the occurrence of cracks during the metalworking process. In order to predict the occurrence of defects, it is necessary to establish a reliable fracture criterion in hot forming. Ti40 burn resistant titanium alloy, which was easily to crack during the ingot cogging procedure, was used to systematically research its deformation mechanism and fracture behavior based on various fracture criteria. Zener-Hollomon parameter, which considered the influence of both temperature and strain rate, was introduced to establish a new criterion in hot forming. The research method and main conclusions of this paper as follows:The flow stress-strain curves were used to study the flow softening and discontinuous yielding phenomenon. Flow softening of Ti40 alloy arises as a result of structural instabilities such as adiabatic heating, generation of a softer texture during deformation and flow localization. The discontinuous yielding phenomenon has been related to the rapid generation of mobile dislocations from grain boundary sources, leading to hot deformation proceeding from the grain boundary region inward.The deformation mechanism at high temperature was investigated. It was found that dynamic recovery appears at temperatures less than 950℃ and dynamic recrystallization zone appears at temperatures higher than 950℃. The appearances of dynamic recrystallization varied with the strain rates: 'necklace' recrystallization which was associated with Ti₅Si₃ particles precipitating along beta grain boundaries occurred at higher strain rates (>1s^-1), and a typical continuous recrystallization with serrated grain boundaries which was attributed to substructure occurred at lower strain rates (<0. 1s^-1).The fracture behaviors and mechanism of Ti40 alloy were disclosed. It was found that shear cracking along 45° orientation with respect to the compression axis...