Microstructural response at the interface and its effect on the fatigue fracture behavior of rotary friction welded dissimilar titanium alloys: Ti–5Al–2Sn–2Zr–4Mo–4Cr (Ti17) and Ti–6Al–2Sn–4Zr–2Mo (Ti6242)

Abstract

Ti17 and Ti6242 tubes were subjected to rotary friction welding to fully understand the microstructural response and its effect on the fatigue fracture behavior of the dissimilar joint. Experiment was conducted using friction linear speed 1 m s ^−1 , friction pressure 80 MPa, burn-off length 5 mm and forging pressure 120 MPa as welding parameters. Electron backscattered diffraction was utilized to systematically examine the microstructures and microtextures across the Ti17/Ti6242 friction welded interface. Thereafter, two fatigue tests were conducted to characterize the fatigue performance of Ti17/Ti6242 joint, one of which is used to identify the fatigue fracture location of the joint and another one to analyze the fatigue fracture behavior. Results clinched that the formation of joint exhibited 600 μ m thick weld interface comprises of thermal-mechanical affected zone (TMAZ), heat affected zone (HAZ) and welding zone (WZ) with varying thicknesses (i.e. 100 μ m to 200 μ m). It was also observed that Ti17 WZ is occupied by equiaxed β grains (mean size of 10 μ m) with only one texture which was closely similar to {110} . Whereas, Ti6242 WZ contained acicular α ’ laths (1 μ m) with two types of α texture. Ti17 HAZ + TMAZ were consisted of acicular α ’ laths within refined equiaxed β grains and three types of texture of α and β , were respectively found in Ti17 HAZ + TMAZ zone. Whereas, Ti6242 HAZ + TMAZ zone was developed by elongated equiaxed α , acicular α ’ laths and few β phases and only two types of texture of α and one type texture of β were found in this zone. The microstructural response across the joint concentrates plastic deformation in Ti6242 HAZ + TMAZ during fatigue cycle, which causes the fatigue fracture occurs at a radial distance of 150 μ m from the boundary between the Ti6242 TMAZ + HAZ and Ti6242 base metal.

Keywords

• titanium alloy
• rotary friction welding
• microstructure
• microtexture
• fatigue fracture behavior
• electron backscattered diffraction