Numerical Simulation And Experimental Investigation On Near Net Shaping Ti6Al4V Parts Under Hot Isostatioc Pressing

Aerospace industry developed rapidly nowadays.A new generation of aerospace engine calls for high thrust-weight ratio.Titanium alloy is suitable for manufacturing of complex key aerospace part.Using traditional manufacturing methods forming titanium alloy parts can't meet the requirements because titanium alloy is difficult to cut.Hot isostatic pressing can produce parts with high performance,especially suitable for producing aerospace titanium part.Numerical simulation technology can analyze shape deformation,densification,stress distribution during HIP.Using HIP technology combined with simulation can cost saving and produce more reliable part.In this study,we analyzed the large deformation,stress distribution,powder flow and densification behavior during HIP.For comparison to the simulation results,the density,shape deformation and residual stress of the specimens were evaluated using Archimedes' principle,3D measuring Technology and Empyrean X ray diffractometer.In the end,we simulated the deformation of the core under three typical HIP processes and optimized the mould.The main conclusions are as follows:(1)A constitutive model based on Perzyna's elastic-viscoplasticity equation was proposed and a lagrangian finite element method was applied to analyze the forming process of the Ti6Al4 V part under HIP.In initial period of HIP the relative density of the powder was low.When the stress exceeded yield limit of the can,the deformation amount of the powder rapidly increased.At the stage of preserving temperature and pressure,the densification increased slowly until the stage of decreasing temperature and pressure,the dramatic contractive thermal strain impelled the powders to compress with each other,corresponding to a sudden promotion of relative density.(2)The Cauchy stress didn't significantly change at the early stag of HIP until the start of decreasing temperature.The stress had a dramatically increase in the powder domain due to inhomogeneous thermal strain till to the end of HIP process.The change of stress in the powder domain closely related to the change of temperature field.The greater the temperature gradient,the greater the stress changed.The stress increased firstly and then decreased from the centre area to the corner area.(3)The deviation of shape deformation between simulation and experiment was less than 6.3%,the average shape deviation was 2.883%.The relative density deviation between simulation and experiment was less than 4.8% and the deviation from the centre area was just about 2%.It suggested that the simulation result was reliable.The relative density in the corner area was low.Because the powder in the corner area difficult to flow.The X ray diffractometer result show the same stress distribution as simulation result but the value deviation was about 100 MPa.The deviations between real and simulation residual stress may come from two factors: one is that the data obtained by X-ray diffraction need numerical approximation;another important factor is that the simulation mentioned above has neglected the phase transition and recrystallization during HIP process which have an effect on final residual stress.(4)The microstructure of the after-HIP part was typical ? and ? structure.In the centre area the morphology of the ? structure was laminated structure and the ? structure was lath structure.The morphology of the ? structure in corner area was equiaxed crystal,the grain size was about 10 um.(5)We simulated the deformation of the core at three typical HIP process conditions including heating after pressuring process,pressuring after heating process and pressuring and heating at the same time process.The maximum displacement variation stages was pressuring and heating stage and unloading stage.The displacement of the core didn't change much in the stage of preserving pressure and temperature.The minimum deformation of the core during HIP process was at pressuring after heating process condition.In this condition,the deformation of blade ab and cd were 1.1047 mm and 0.2650 mm respectively.Using optimized mould can improve accuracy of shape control while the deformation of the core in x and y direction were 0.07 mm and 0.6mm respectively,and the deviation decrease about 71% and 45% in x and y direction.