Numerical Simulation And Experiment Of Near Net Shaping Inconel625Turbine Disk Under Hot Isostatic Pressing

The near-net-shape hot isostatic pressing (NNS-HIP) can produce nickel-basedsuperalloy turbine disc parts with complex structure, and has advantages such as highdensity, excellent mechanical properties and saving materials. In NNS-HIP process,powder shrinks with irregular large deformation. It is important to use the numericalsimulation to predict powder densification and container deformation law, thus optimizethe container structure. However, due to the powder compressibility, large deformationand variable boundary in HIP process, accurate simulation needs further and systemsresearch in the constitutive model, material parameters and the finite element solution. Inthis paper, numerical simulation is used to optimize the container structure, and a complexturbine disk parts is produced using NNS-HIP. Specific content and conclusions are asfollows:The powder constitutive model is studied based on the continuum plasticity theory.Shima’s constitutive model modified by Abouaf is used to describe the rheologicalbehavior in HIP. This model introduces the stress deviator tensor correction factor andhydrostatic pressure correction factor to describe the porosity effects on constitutiveequations. To consider the creep, the modified Raboin’s hyperbolic sine power law creepmodel is used to describe the viscoplastic rheological behavior of powder in hightemperature.To determine the constitutive equation of Inconel625, interrupted HIP experimentsare done and different density samples are got. Zener-Hollomon parameter, temperaturecompensated strain rate, is determined using the least squares through high temperaturecompression tests, the relationship between equivalent strain rate and equivalent stress onhigh temperature is established; the powder density, densification rate and hydrostaticpressure curves in HIP are got, and parameter is deduced; parameter is deducedthrough the porous body compression experiments.Two NNS-HIP turbine disc container schemes are simulated using MSC.Marc. Thesimulation results show that: core deformation is large and powder density is low in theshape follow-up scheme; the vertically symmetrical scheme has good shape with high powder density; the container compressive deformation drives powder densification, andthe core is not substantially deformed in vertically symmetrical program; the containerdeformation include elastic deformation, plastic yielding, aging strengthening, hightemperature yield and residual stress stage; powder expands first and then compacts in amulti-stage mode. The good agreement between simulation and experiment results showthat the numerical simulation can accurately predict the container deformation and powderdensification law, and guide NNS-HIP container design.Room temperature tensile test results of HIP forming sample show that: the tensilestrength of the annealed samples is264MPa higher than ASTM forgings standard, butpercentage elongation after fracture is only16%. SEM images of microstructure show thatHIP forming Inconel625alloy has fine grain size about30μm, mainly composed with thematrix phase, strengthening phase ’’and MC carbides. To improve the plasticity,solution and aging treatment is done. The results show that the plasticity improves by52.5%after solution treatment, tensile strength decreases161MPa. SEM images offracture show that: the strengthening phase is all dissolved in the matrix in solutionstate, and the hard and brittle carbides distribution changes from catenulate to dispersed,leading to uniformity and good plasticity. The percentage elongation after fractureincreases by12.5%after aging treatment, tensile strength decreases35MPa. SEM imagesof fracture show that: in the aging process, Nb and Mo precipitate form the matrix, formacicular phase, while large quantity of brittle carbides precipitate in grain boundaries,resulting in limited improvement of the plasticity.In summary, this paper chooses a suitable powder constitutive model, determines theconstitutive equation of Inconel625powder through experiments, uses MSC.Marc tosimulate NNS-HIP complex turbine disc process, selects a better container scheme andpredicts container deformation and powder densification law in HIP process, and studiesthe impact of solution and aging on the performance of Inconel625alloy HIP parts.