Evolution Mechanism of Lamellar α in Tri-Modal Microstructure of TA15 Ti-Alloy during Near β Deformation

Abstract:

Near-β deformation combined with subsequent heat treatment process provides a possible way to obtain the tri-modal microstructure for TA15 Ti-alloy. As an important component of tri-modal microstructure, the evolution of lamellar α, which determines damage tolerance properties, is complex and difficult to control in the process of near β deformation and subsequent heat treatment. At the same time, the tri-modal microstructure has strict requirements on the composition and morphology of final microstructure, especially on lamellar α. In this paper the microstructure evolution behavior of TA15 Ti-alloy after deformation and 950 °C, 100 min, WQ+800 °C, 8 h, AC under different deformation conditions (deformation temperature, deformation degree and strain rate) were investigated via the thermal simulation test and metallographic test. The evolution mechanism of lamellar α in tri-modal microstructure was revealed. Based on the obtained results, taking high damage tolerance as target, the reasonable range of near β deformation condition were determined to obtain lamellar α possessing excellent fracture toughness and microstructure meeting requirement of tri-modal microstructure. Experimental and theoretical analyses show that for TA15 Ti-alloy the tri-modal microstructure of excellent performance could be obtained within the deformation condition range. The results can provide a guide for obtaining the tri-modal microstructure and excellent lamellar α via near-β deformation processing.

Key words:TA15 alloy; tri-modal microstructure; near β forging; heat treatment; lamellar α