Abstract
The hot-deformation behavior of an as-cast TiAl alloy with a near-lamellar microstructure was investigated at a deformation temperature within the range of 1020–1200 °C and a strain rate of 0.001–1.0 s−1. A visual three-dimensional diagram of the strain rate sensitivity exponent m was developed based on hot compression data to reflect the correlation between the process parameters and microstructural evolution characteristics. The results showed that the m-value increased with an increase in temperature and a decrease in the strain rate. As the temperature increased, the growth of the m-value at a higher strain rate was faster than the growth of the m-value at a lower strain rate. Moreover, microstructure analysis at different m-values indicated a correlation between the m-value and microstructural evolution characteristics during hot deformation. The mechanism of microstructure evolution during hot deformation can be divided into three evolution modes according to different strain rate sensitivity exponent m-values. At a lower m-value, numerous γ/α2 lamellar colonies appeared similar characteristics to the initial microstructure. At a moderate m-value, broken lamellae in the microstructure formed several chain-like fragments with similar orientations. At a higher m-value, several formed equiaxed α2 and γ phases satisfied the Blackburn orientation relationship in the microstructure.
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