Loss of coherency and interphase α/β angular deviation from the Burgers orientation relationship in a Ti-6Al-4V alloy compressed at 800 °C

The mutual relationship between phases in two-phase titanium alloys, alpha(HCP) and beta(BCC), is such that: {0001}(alpha)parallel to{110}(beta); < 11 (2) over bar0 >(alpha)parallel to < 111 >(beta), which in literature are known as Burgers orientation relationships. The coherency of the two phases is controlled by this crystallographic mutual relationship. Loss of coherency between phases during deformation can originate from a non-parallelism between the two boundary crystallographic planes. This study focuses on alpha(HCP)/beta(BCC) interface coherency evolution in a lamellar Ti-6Al-4V alloy subjected to hot compression at 800 degrees C. The strain rate was 10(-3) s(-1) and deformation was carried out to average true strains of epsilon = 0.29, 0.69, and 1.20. Loss of coherency was found at strains epsilon >= 0.50. For these strains, the lamellar alpha + beta microstructure also evolved to a spheroidized morphology. The loss of interface coherency was thus associated with the acceleration of the lamellar microstructure dynamic spheroidization.