Thermal deformation mechanism of TC11/TC17 linear friction welded joint during isothermal compression

Abstract

Thermal deformation behavior has a significant effect on the microstructure evolution, crystallographic orientation and microhardness of two-phase titanium alloy. In the paper, the evolution rules of microstructure, texture and microhardness of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si (TC11) and Ti–4Mo–4Cr–5Al–2Sn–2Zr (TC17) linear friction welded (LFWed) joint were systematically discussed during the isothermal compression. Comparing with the high microhardness on the welded zone (WZ) after welding, the microhardness value of the whole joint decreases significantly after the pretreatment and isothermal compressions. There is a close relationship between microtexture and plastic deformation. The electron backscattered diffraction (EBSD) analysis method indicates that the distribution of Schmid factor is very uneven, and most of the crystals are aligned to hard orientation on the TC11 WZ; whereas the high Schmid factors occur, and most of the crystals turn to soft orientation on the TC17 WZ, which lead to the plastic deformation of TC17 side more easily than that of TC11 side. With the increasing compression strains, the ratio of low angle grain boundaries (LAGBs) rises, meanwhile, the mean geometrically necessary dislocations (GND) density increases from 2.79 × 10 14 m −2 to 4.30 × 10 14 m −2 , and the fraction of high Schmid factor also goes up slightly. Those can be attributed to the increased deformation energy with the higher compression, which leads to the accumulated driven force and promotes the rotation of grains toward a specific favourable orientation. The relationship between the microhardness and the crystal texture of the TC11/TC17 LFWed joint. • Rules of microstructure, texture and microhardness of LFWed joint were discussed. • Plastic deformation mechanism of the joint was discussed by the Schmid factors. • The ratio of LAGBs and GND density rises with the increasing compression strains. • Microhardness at the joint is more uniform with the higher isothermal compression.