Research of Microstructure and Mechanical Properties of Electron Beam Welding Joints for TB18 Titanium Alloy
TB18 titanium alloy is a new type of near-β ultra-high strength titanium alloy,whose high specific strength and high specific stiffness are favored by the aerospace field.Three electron beam welding and heat treatment processes were used to obtain welded joints of TB18 titanium alloy,the relationship between the microstructure and mechanical properties of welded joints are researched through microstructure analysis,tensile and impact property testing,fracture analysis.Results show that TB18 titanium alloy electron beam welded joints consist of the base material,heat-affected zone and fusion zone.In three electron beam welding and heat treatment processes,the fusion zone of solid solution+aging+welding state is composed of the softer β phase,resulting in its mechanical properties show lower strength and higher plasticity.The microstructure of the three regions of solid solution+welding+aging state,welding+solid solution+aging state are β-phase precipitated fine dispersed acicular α-phase.But the former in the fusion zone the ratio of length to diameter of acicular α phase is low,resulting in high strength,poor plasticity and brittle fracture.The ratio of length to diameter of welding+solid solution+aging state in three regions is uniform,so its high strength and good plasticity indicate strength and toughness matching characteristics,hence,it is the optimal electron beam welding and heat treatment process scheme.
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