Finite Element Study On The Deformation And Failure Behavior Of Alloy Fabricated By Metal Powder Compression Forming

Hot compression forming and supersonic impact forming of metal powders are important methods to prepare alloys.The powder superalloy prepared by hot compression(hot isostatic pressing)of metal powder has higher temperature bearing capacity and mechanical properties.The metal powder is formed by supersonic impact on the substrate by high-speed gas injection,which can effectively reduce the defects such as oxidation and bad phase transformation.However,cracking caused by defects(carbide,porosity,etc.)in powder metallurgy process Narrows the processing window of powder nickel-based superalloys.At the same time,the residual stress accumulated in the process of supersonic impact of metal powder is easy to cause the phenomenon of coating spalling and cracking.Therefore,it is very important to enlarge the hot working window of powder superalloy and reduce the residual stress in the process of supersonic impact forming.In this paper,the numerical analysis of the hot compression deformation of metal powder superalloy and the supersonic impact forming of metal powder particles is carried out by using finite element method.The stress distribution,failure behavior and residual stress evolution of these two processes were analyzed,and the reliability was compared with the experimental results.The results are as follows:(1)The micromechanical Gurson-Tvergaard-Needleman(GTN)damage model was used to analyze the intergranular fracture caused by holes in superalloy.The deformation temperature is 1050-1150℃ and the strain rate is 0.001-1 s-1.The finite element results are in agreement with the experimental results,and the cracks start to sprout and expand into longitudinal cracks on the outer surface of the specimen.The failure is controlled by strain.The critical failure strain is almost insensitive to the strain rate in this experiment,but increases with the increase of temperature as a third-order polynomial.The failure behavior of P/M(P/M)nickel-based superalloys was studied by isothermal compression experiments,and the processing diagram with failure domain was constructed based on the predicted failure threshold.In order to ensure good hot working performance and avoid flow instability and failure,an optimized processing window for hot deformation of superalloy was proposed.(2)Using copper as the material system,the finite element simulation of twodimensional single particle,three-dimensional single particle and three-dimensional multiparticle is carried out based on Euler method,and the borehole measurement is carried out to study the evolution and distribution law of residual stress.Based on a two-dimensional system,the effects of basic modeling parameters on residual stress are strictly investigated.The results show that the residual stress is affected by the mesh size,matrix size and simulation time.The effect of local failure and material damage is negligible.In addition,thermal softening caused by initial temperature rise and plastic deformation plays an important role in effectively reducing residual stress.(3)In the three-dimensional single-particle simulation,the distribution of regional mean residual stress on penetration depth and thickness shows a tension/compression transition,which is roughly similar to the two-dimensional case.On the other hand,the residual stresses of the coating/substrate in the three-dimensional multi-particle simulation are all compressive stresses,which is due to the wide and continuous dynamic impact of the particles,and is close to the measured values.The simulated compressive stress decreases with the increase of coating thickness,which is due to the increase of thermal softening caused by strong plastic deformation.(4)In this study,two spherical(P1: hard,P3: soft)tantalum powders and one angular(P2)tantalum powder were used as raw materials.Two kinds of mixed powders(20 wt.%P2+P1,20 wt.% P3+P1)were prepared.The results showed that,compared with the other two spherical powders(P1,P3),the angular powder P2 has higher deposition efficiency and lower cost,so it is the first choice for industrial production.