Effect of heat treatment on the microstructure, microhardness and impact toughness of TC11 and TC17 linear friction welded joint

Abstract The service life of whole blisks for the aero-engine compressor is sharply decreased due to the dissimilar linear friction welded (LFWed) joint of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si (TC11) and Ti–4Mo–4Cr–5Al–2Sn–2Zr (TC17) alloys, which have the different microstructure and mechanical properties. To optimize the microstructure and performance of the joint, and improve service life of the whole blisks, the post-weld heat treatment (PWHT) with annealing, solution plus aging were adopted for the welded joint. The results show that the nucleation rate of primary α P phase increases obviously, which are spheres, rods and strips, and orthorhombic martensite α s phases transform into hexagonal martensite α s phases interlaced evenly on the β phase matrix on the WZ of TC17 side; meanwhile, acicular hexagonal martensite α s phases transform into lamellar α s phases on the WZ of TC11 side after solid solution and dual aging. The difference of the microhardness on both sides of the joint is narrowed significantly. The impact toughness of the joint is improved sharply from 9.3 J/cm2 after welding to 27.6 J/cm2 with an increase of 200%. In addition, the dissolution and growth model of primary α p phases were established, which can reasonably predict the nucleation and grow process of α phase. Furthermore, the narrowed discrepancy of the microhardness and increased impact toughness can be attributed to the decreased slice thickness of martensite α s phase, based on the dislocation slip mechanism and distorted discordant model.