Effect Of Solution And Aging On Microstructure And Properties Of TC4 Produced By Laser Coaxial Powder Feeding

As one of the most common and widely used titanium alloys,TC4 has important application prospects in the fields of aviation and aerospace.Traditional titanium alloy manufacturing techniques have many shortcomings,such as long production cycle,low material utilization,relatively high manufacturing costs,and difficulties in manufacturing complex structural parts.The laser coaxial powder feeding additive manufacturing technology is a technology for directly forming a digital model into a solid component by layering.This technology provides an effective way to prepare titanium alloys with low cost,short cycle,obvious weight loss and high quality.In this paper,the laser additive manufacturing test of TC4 titanium alloy was carried out by coaxial powder feeding method.The effects of laser power,scanning speed and powder disk rotation speed on the appearance,melting width and melting height of the deposited layer were studied,the deposited layer having a good appearance and satisfying the dimensional requirements and having no defects inside was obtained by orthogonal test.Tensile specimens were prepared using the optimum process parameters and subjected to solution aging treatment.Tensile tests were carried out on the samples in the as-deposited and solution-aging states using the universal tensile tester,the microstructure and phase composition of the as-deposited and solution were analyzed by metallographic microscope,scanning electron microscope and X-ray diffractometry.The effects of solution temperature and time,aging temperature and time on the microstructure and properties of TC4 titanium alloy produced by laser coaxial powder feeding were studied.The test results show that in the single pass test of laser additive manufacturing,as the laser power increases,the melting height increases first and then decreases slightly,and the melting width continues to increase;as the scanning speed increases,the melting height and the melting width continue to decrease;as the rotation speed of the powder disk increases,the melting height continues to increase,and the melting width continues to decrease.The optimum process parameters were determined by orthogonal test as laser power P=2100W,scanning speed V_s=500mm/min,and powder disk speed V_r=1.0r/min.The effect of solution aging on the microstructure of TC4 titanium alloy fabricated by laser additive was studied.With the increase of solution temperature,the coarsening phenomenon of primaryαphase was more obvious.With the increase of solution time,the acicularαphase is blocked by theβphase.With the increase of aging temperature,the change of primaryαphase is small,and the length and width of secondaryαphase increase.With the increase of aging time,both primaryαphase size and volume fraction increase.Comparing the mechanical properties of TC4 titanium alloy after deposition and solution aging,it is found that the strength and hardness of TC4 titanium alloy increase and the plasticity decreases with the increase of solution temperature and solution time.With the increase of aging temperature and aging time,the strength and hardness of TC4 titanium alloy decreased and the plasticity increased.And the best solution aging treatment process is 950℃×1h/WQ+550℃×4h/AC.The microscopic fracture morphology of the as-deposited and solution aged tensile specimens is filled with dimples,which are ductile fractures,but are more uniform and deeper than the dimples in the deposition direction compared with the scanning direction.The microstructure was a typical basket structure with tensile strength of 995MPa,yield strength of 900.3MPa,elongation of 15%,and reduction of area of 35%,the comprehensive performance is significantly better than the national forgings standard,which proves that the production process is relatively reliable.