Ti-7Mo-3Nb-3Cr-3Al: A NEW NEAR β TITANIUM ALLOY COMBINED HIGH STRENGTH AND IMPROVED FRACTURE TOUGHNESS

摘要

The near β titanium alloys with remarkably less β-stabilizers contents than mctastable β titanium alloys, have been a subject of intensive interests for high strength applications due to their deeper hardenability and adjustable mechanical properties compared to the α+β and metastable β Ti alloys. Here, a new near β titanium alloy with nominal composition of Ti-7Mo-3Nb-3Cr-3Al (wt.%) were developed to get a combination of high strength and improved fracture toughness. Two typical processing routes, α/β solution treated & aged (STA) and β-annealed with subsequent slow cooling and aging (BASCA) were introduced to investigate the microstructure characteristics and microstructure-performances relationships. The results show that the STA can lead to tunable high strength, 1300MPa～1450MPa, with a large plasticity, 6%～20%. The BASCA can result in outstanding fatigue properties and damage tolerance, 120～150 MPa-m~(1/2). The microstrucutre evolution that govern distinct types of performances, particularly the strength, plasticity and damage tolerance are addressed in more details for the Ti-7333 alloy, thus providing rational explanations for the microstrucrure control or design of near β titanium alloys.