EFFECTS OF Si-ADDITION ON MECHANICAL PROPERTIES OF HOT-ROLLED SHEET AND HOT WORKABILITY IN Ti-5Al-1Fe

摘要

Addition of a small amount of Si to Ti-5Al-1Fe, coil sheet reliable high strength α+β titanium alloy, was investigated with focusing on hot workability and mechanical properties. Si addition degrades hot workability of Ti-5Al-Fe with the coarse Widmanstatten colony microstructure in a certain range of the high α+β temperature region. This is considered to be attributed to the hardness difference between the α and the β phases which increased by solid solution Si, especially between the grain boundary α and the film-like β phase adjacent to that. The ductility loss is improved once the materials are heated to the β region and deformed on the way of cooling. Strength of the hot-rolled sheets increases from 1020 to 1220 MPa by 0.3% Si with keeping enough ductility. Based on the fundamental studies, a 7-ton hot-rolled coil sheet of 4.5 mm in thickness was successfully manufactured and the excellent mechanical properties were confirmed.