Identification of Stable Processing Parameters in Ti-6Al-4V Alloy from a Wide Temperature Range Across β Transus and a Large Strain Rate Range

摘要

The hot workability of Ti-6Al-4V alloy was investigated according to the measured stress-strain data and their derived forms from a series of hot compressions at the temperatures of 1,023-1,323 K and strain rates of 0.01-10 s~(-1) with a height reduction of 60%. As the true strain was 0.3, 0.5,0.7 and 0.9, respectively, the response maps of strain rate sensitivity (m-value), power dissipation efficiency (η-value) and instability parameter (ξ-value) to temperature and strain rate were developed on the basis of dynamic material model (DMM). Then the processing map was obtained by super-imposition of the power dissipation and the instability maps. According to the processing map, the stable regions (η ＞ 0 and ξ ＞ 0) and unstable regions (η ＜ 0 or ξ ＜ 0) were clarified clearly. Further, the stable regions (temperatures of 1,198-1,248 K and strain rates of 0.01-0.1 s~(-1)) with higher η value (＞0.3) corresponding to the ideal deformation mechanisms involving globularization and superplasticity were identified and recommended. The microstructures of the deformed samples were then observed by microscopy. And homogeneous microstructures with refined grains were found in the recommended parameter domains. The optimal working parameter domains identified by processing map and validated by microstructure observations contribute to the design in reasonable hot forming process of Ti-6Al-4V alloy without resorting to expensive and time-consuming trial-and-error methods.