Study On Surface Quality And Anisotropy Of Ti6Al4V Fine Components By Selective Laser Melting

Ti6Al4V is a typical ? + ? dual-phase titanium alloy with excellent specific strength,corrosion resistance and biocompatibility.SLMed Ti6Al4 V have been successfully used in injection molds,medical equipment and aerospace.The aerospace complex parts have high standards for the quality and accuracy of forming,and the structure of the components and the principle of anisotropic transformation need to be further investigated.Therefore,first,the RSM method is used to optimize the process parameters to improve the surface quality and reduce defects of Ti6Al4 V components.Second,the typical components are designed for gradient experiments to compensate and correct dimensional errors.Finally,Figure out the relationship between the fine structure and anisotropy transformation.The results are as follows:(1)The roughness and hardness were optimized by RSM,and finally a shaped part with a Vickers hardness of 340.1 HV and a roughness Ra of 2.98 was obtained.The internal defects and porosity of the material were significantly reduced.The optimized process parameters: laser power,scanning speed,and spot pitch are 325 w,1000mm / s,and 120?m,respectively.(2)Divide the dimensional errors of SLM Ti6Al4 V into systematic errors and random errors.Contour-entity,entity-contour and edge remelting three control methods are used,The contour-entity,entity-contour and edge remelting three control methods and appropriate process parameter combinations(Scan power(150w),high Scan speed(5m/s),and border Thickness(100?150?m))are used to correct the above Two kinds of errors thus improve the accuracy and control the edge height of SLMed parts.Finally,the edge remelting method was used to obtain a part having a surface roughness of Ra 6.17.(3)Due to the directional growth of ?,SLMed Ti6Al4 V exhibit anisotropic mechanical properties.High dislocation densities and lamellar twins were observed in the martensite grains,and some twin dislocations formed in the stress concentration area.After the heat treatment,the continuous lamellar twin regions and dislocations in the fine structure region disappeared.During anisotropic transition,high-density dislocations migrate to twin grain boundaries and transform into network dislocations,which accelerates the formation of subgrain boundaries and corresponding grain boundaries.(4)It is found through EBSD that the crystal orientation relationship of the fine structure is random.When the martensite is decomposed,? begins to crack and spheroidize.As a result,fine(? + ?)(L/D: <1?m/<20nm)is uniformly distributed in the gaps of the ? phase(>20?m,3?5nm),and its random crystallographic orientation reduces the anisotropy of the crystallographic distribution.It can be concluded that the heat treatment changes the morphology and type of the structure,and the resulting fine structure can weaken the anisotropy so that it does not affect industrial applications combined with the analysis of mechanical properties.