Lamellar kinking in primary hot working of titanium alloy: Cross-scale behavior and mechanism

Lamellar kinking, a complex and significant cross-scale heterogeneous deformation behavior during primary hot working of titanium alloys, affects the microstructure evolution, mechanical response as well as optimization of product performance. However, the essence, development processes, formation condition, and contribution of kinking are still controversial. To address these issues, a two-scale crystal plasticity model is developed to analyze the intra-colony strain partitioning and inter-colony interaction. In-situ laser confocal microscope experiments with detailed microstructure characterization enable to track the origin and evolution of lamellar kinking. Kinking is re-recognized as deformation banding rather than the conventionally claimed instability resulting from elastic or plastic buckling or macro plastic flow. Strain partitioning plays a pivotal role in the driving force of kinking by stimulating the continuous orientation softening and leading to a decrease of strain energy. The dependence of kinking's formation condition on geometrical orientation can be rationalized by the orientation sensitivity of strain partitioning. The formation of kinking contributes to reducing the deformation resistance of colony with initially “hard” orientation and further improve the deformation compatibility among colonies. This work provides new insight into the cross-scale mechanisms of lamellar kinking, which can be utilized to control microstructure homogeneity during hot deformation of titanium alloys aiming at optimizing the performance of forging pieces.