Study On The Residual Stress And Deformation Controlling And Mechanical Properties Of TC4 Parts By Subarea Scanning Strategy In Laser Melting Deposition

As a typical metal additive manufacturing(AM)technology,laser melting deposition(LMD)has become an important means of direct forming of titanium alloy.However,subjected to strong thermal stress,the deformation and residual stress during the forming process will seriously affect the dimensional accuracy and mechanical properties of the parts.At present,subarea scanning strategy is applied in forming large components to reduce thermal stress in the forming process.However,due to the lack of related research and the complexity of subarea scanning strategy,its effects on deformation,residual stress and mechanical properties of components are not very clear so far.For this reason,the subarea scanning strategy is systematically studied in this paper.Based on residual stress and deformation control,the optimization direction of subarea scanning strategy is proposed,and the mechanical performance of forming parts by subarea scanning strategy is also analyzed.The main contents and results are as follows:(1)The effect of subarea scanning on the deformation and residual stress of laser-deposited parts was revealed.Compared with successive scanning strategy,the deformation of substrate was decreased by 71% by applying subarea scanning strategy.According to the temperature simulation model,the consistency of deformation and temperature gradient is demonstrated.Moreover,the residual stress of deposited layers was periodic oscillated and the maximum residual stress is reduced by half compared with successive scanning strategy.(2)The effect of subarea size and subarea scanning order on the deformation and residual stress of large-scaled forming parts was analyzed.The influence of subarea scanning order on residual stress and deformation is far greater than subarea size.Decreasing the subarea size continuously will cause greater deformation.The key to subarea scanning strategy optimization is to optimize subarea scanning order.(3)An outside-in subarea scanning order was proposed.By reducing the temperature gradient in the central deposition area,the warping deformation of the forming part is reduced greatly.(4)A combined subarea scanning strategy was proposed.By using the outside-in subarea scanning order and randomized scanning order in the early and late forming stage separately,the residual stress and deformation of the large-scaled parts can be balanced.A large TC4 titanium alloy component with a size of 500 mm×440 mm×120 mm was successfully formed by this strategy.(5)The mechanical properties of the sample by subarea scanning strategy was studied.Compared with successive scanning strategy,α phase is refined and the coarse growth of β grain is inhibited by subarea scanning strategy.The density of the sample by subarea reaches 98.92%,but the defects of incomplete fusion are easier to occur at the overlap zone.The tensile strength of subarea scanning forming sample is enhanced compared with that of successively scanning strategy,but the plasticity is weakened due to the defects.The sample by subarea scanning strategy basically meets the forming requirements.