In-situ Study Of Phase Transformation During Heating And High Temperature Mechanical Property Of Laser Additive Manufacturing Ti-6Al-4V Alloy

Ti-6Al-4V alloy is a typical ? + ? titanium alloy.Because of its advantages of low density,high specific strength,and good corrosion resistance,it is widely used in the aerospace field.However,the forming and processing of titanium alloys are difficult.When manufacturing complex parts,it will face with problems such as long cycle time,high cost.Laser additive manufacturing is an advanced near-net-shape manufacturing process.It can directly build parts based on CAD models,without dies or substantial machining.Laser additive manufacturing Ti-6Al-4V alloy is the hotspot of current research.During high temperature applications,high temperature will cause low temperature ? phase in Ti-6Al-4V alloy to transform into high temperature ? phase.Therefore,microstructure will change,which in turn will effect the high temperature mechanical properties.Therefore,it is very meaningful to study phase transformation during heating from ? to ?,and the effect of microstructure on high temperature mechanical properties in laser additive manufacturing Ti-6Al-4V alloy.This article combines scanning electron microscopy(SEM)and in-situ hightemperature tensile testing techniques.The in-situ phase transformation experiment was performed to analyze the phase transformation mechanism of Ti-6Al-4V alloy.Subsequently,the relationship between microstructure and mechanical properties with temperature changes was established by performing in-situ high temperature and room temperature tensile test.The results show that the microstructure of the laser additive manufacturing Ti-6Al-4V sample is composed of coarse columnar ? grain growing parallel to the direction of the build macroscopically.Within the ? grain,basket-weave structures and? colonies with the same orientation were observed.In the high temperature of holding stage,the residual ? phase decreases continuously with the holding time increasing.And ? colonies were destroyed and disappeared.The high-temperature ?-phase passes through ? plates and grows in parallel lines.As the holding time further increasing,the high-temperature microstructure grows like a step-twisted manner.The mechanical properties and fracture behavior of Ti-6Al-4V alloy at room temperature and 650 ? were compared by in-situ SEM tensile test.When the specimen was stretched at room temperature,it exhibits the shear deformation process with short extension of ? plates.The slip systems opened in a small amount and slip bands propagate by cutting off ? and ? phases.Therefore,the specimen shows high stress and low elongation.When tensile at 650 ?,the specimen exhibits the necking deformation with long stretching and bending of ? plates.The slip systems opened in a large number,and the propagation of slip bands along grain boundaries.Thus,the specimen shows low stress and high elongation.