Research On Dimensional Deviation Of TC4 Alloy Fabricated By Selective Laser Melting

Selective laser melting(SLM)is a common additive manufacturing(AM)technique that is based on powder-bed fusion(PBF)to process metallic components with complex shapes,good mechanical properties,and high dimensional accuracy.Owing to the numerous advantages of SLM compared to conventional manufacturing technologies,SLM has been used in aerospace industry.TC4(Ti6Al4V)is an ? + ? titanium alloy,has been widely used in the manufacture of aircraft structures,compressor disks and blades of aircraft engines due to its excellent mechanical properties.However,due to the poor thermal conductivity,strain hardening tendency,high hardness,and high chemical reaction activity of oxygen,TC4 titanium alloy is difficult to meet the processing requirements of TC4 alloy.Therefore,the emergence of SLM technology provides a wider prospect for the application of TC4 titanium alloy in the aerospace field.The structure of components in the aerospace field is complex and requires high precision.At present,there are few studies on the dimensional accuracy of SLM process.Therefore,in this paper,a series of TC4 blade features were manufactured by SLM process.The distribution rule of dimensional deviation of blade samples and the influence of thermal stress generated during SLM process on dimensional deviation were studied.A series of TC4 blade samples were fabricated by SLM process.The range of blade body height was 27.5 mm ? 45 mm,and the height difference between each two blades was 2.5 mm.The distribution of dimensional deviation exhibits a parabolic law at the trailing edge of blade.The overall deformation tendency of the blade is that the thicker portion deformed toward the pressure side,and the edges deformed toward the suction side.The dimensional deviation of the blade samples becomes larger as the height of the blade body increases.The thermal stress analysis of different parts of the TC4 blade during the SLM process found that the maximum blade stress was concentrated at the tenon and where the blade body and the tenon were connected.The stress along the Z direction(building direction)during SLM process was larger than the other two directions.There are large tensile stresses on both sides of the blade body.The part near the thicker leading edge of the blade body is mainly a tensile stress resisting the tendency of thermal compression deformation,and the part near the thinner trailing edge is mainly a compressive stress resisting the tendency of thermal expansion deformation.The X-ray diffraction measurement of the residual stress on the surface of the SLMed TC4 blade showed that after the substrate was removed,the stress released,and caused the trailing edge to deform to the side of the pressure surface.The microstructure observation results showed that Widmanstatten Microstructure was formed in the SLMed TC4 components.A large number of acicular ?' martensitic colonies exist in the columnar primary ? grains.The wall thickness at the trailing edge of the SLMed TC4 blade is thinner than at the leading edge,and the cooling rate is faster.Therefore,the width of the columnar original ? grains at the trailing edge is narrower than that at the leading edge,and the percentage of small-sized ?' grains and small angle grain boundaries(LAGBs,<10 °)is also higher,making the measured hardness at the trailing edge is higher than that of other parts of the blade.The tensile property test results show that the yield strength of SLMed TC4 alloy is about 1100 MPa,the tensile strength is about 1223 MPa,and the elongation is about 7.83%.The compressive property of the SLMed TC4 decreased with increasing temperature.