Formation of abnormal structure in ZTA15 titanium alloy casting and its impact mechanism on tensile behavior

Abstract

Partial block-dropping phenomenon was existed during the precision process of TA15 titanium alloy casting. In view of multiple means of microscopic physical characterization analysis such as OM/SEM/EDS/XRD and by considering the tensile performance results, the microstructure and mechanical properties between block-dropping area and the regular areahad been investigated. This article focused on the impact mechanism on tensile behavior that generated from the abnormal structure of block-dropping area. The results reveal that both the block-dropping area and the regular area show bi-modal microstructure, whereas the β phase concentration of the block-dropping area is far beyond the regular area and emerges as β spot. Microanalysis shows that the segregation of Fe is the major factor causing the abnormal structure and β spot, as well as the sharp plasticity decreases of alloy. The segregated Fe alters the microstructure and properties of the alloy, mainly because the saturation of Fe in α-Ti is only 0.1%, which leads to the formation of brittle TiFe eutectic phase. The increase of strength reduces the plasticity of the alloy casting, and further lead to the block-dropping during the process.

Keywords

• titanium alloy casting
• β spot
• tensile performance
• tife eutectic phase
• intergranular fracture