Study On Stress And Deformation And Microstructure Properties Of Titanium Alloy In Laser Metal Deposition Based On Island Scanning Strategy

Laser metal deposition technology has great advantages in the field of near net shape forming large titanium alloy parts due to its high deposition efficiency and good component properties.However,the local periodic thermal cycle in the process produces a steep thermal gradient,which easily leads to severe local residual stress,deformation and even cracking.It greatly limits the application of this technology.The island scanning method divides the layer into multiple regions for depositing,which improves the influence of thermal stress to a certain extent.It is the development trend of laser metal deposition for large-scale components.However,due to the complex island mode,more island variables,and fewer related reports,its influence on the stress evolution mechanism,deformation and microstructure performance during is still unclear,and its application in engineering is restricted.Therefore,in this paper,the influence of scanning strategy on the residual stress,deformation and microstructure properties was systematically studied through the combination of experiment and simulation.The optimization direction of island scanning strategy was proposed,which provides a reference for laser metal deposition of large-scale high-performance titanium alloy components.The main contents are as follows:(1)The effect of the island scanning strategy on the depositing temperature field is explored.The island scanning strategy reduces the temperature gradient and improves the local temperature distribution effect and heat accumulation during consecutive scanning process.(2)The influences of the shape and size of the sub-island,jump sequence and interlayer cooling time on the residual stress and deformation are revealed.Compared with residual stress,island scanning can reduce deformation more obviously,and the reduction of stress is more obvious in a certain direction.At the same time,whether it is rectangular or square island there is a lower limit to reduce the stress and deformation.Too small size may lead to greater stress and deformation.For the rectangular island method,the difference of residual stress is determined by the jump sequence and the direction of the scanning vector in the sub-island.With the increase of interlayer interval time,the residual stress and substrate deformation show an overall increasing trend.(3)An optimal partition scanning strategy is obtained,namely,the one-way rectangular4 sub-island successive jump strategy without interlayer interval time.Compared with consecutive process,the deformation of substrate is reduced by 23%,the residual stress in the Y direction is reduced by 42%.The low value of the residual tensile stress in the X direction was equivalent to that in the consecutive scanning,and the peak residual stress is larger.(4)An island scanning method with interlayer variable sub-island size is proposed,which increases the density of rectangular 4 sub-island deposited part from 93.6% to 97.9%.The unfused defects in the overlap location of sub-island are improved.The grain size is smaller and the average hardness is higher under the strategy of interlayer variable subisland size process.Due to the existence of hole defects in all island scanning deposited parts,the plasticity is weakened.The mechanical properties of the interlayer variable subisland size scanning deposited parts are equivalent to the consecutive scanning process,which is a very promising scanning method.