| Super-alloys are crucial for the development of aero-engines and gas turbines.The preparation of super-alloy single crystal blades mainly involves two parts of materials and process.At present,the most important process for preparing Ni-based super-alloy blades base on the High Rate Solidification method(HRS)of Bridgeman casting removal or film shell removal.Simulating the solidification process and microstructure of directionally solidified super-alloy are the most important methods to study super-alloy,compared with the experiment,Simulation has the characteristics of short period and low cost,which is the focus and hot topic of domestic and foreign scholars.In this paper,according to the numerical simulation of the directional solidification of nickel based super-alloy DD3,study the influence of different processing conditions on the directional solidification temperature field and microstructure,and to reveal its mechanism,study the grain selector seeding period and grain selection period of grain nucleation/growth behavior,determine the crystallizer design specification.(1)The multicomponent nickel-base super-alloys divide into multi group binary alloys,and the mathematical models and micro-dynamics models were established.The parameters of the model were calculated,including the distribution coefficients of the solute,the liquidus Slope and so on.(2)Study on the two key parameters of directional solidification:the drawing velocity and the temperature of the heating zone,study the effects on solidification process and microstructure of these two parameters by variables control method,simulation results show that with the increase of the drawing velocity,the liquid temperature gradient improve,the dendrite refine.With the increase of the drawing speed,the width of the paste region increase,the position of the paste region is down,the interface concave and the miscrystallization tendency increase;and the dendrite structure refine.Analyze and determine the cause of the formation of the miscellaneous crystals in the paste zone.(3)Study the seeding behavior of the seeding section of the crystallizer.Draw the round rod with the diameter of 15mm and the height of 100mm by UG modeling software.Carry out the solidification simulation and CAFésimulation of the round rod.The grain density in the rod-like pattern decreases with the increase of the distance from the water-cooled copper stage:0-10mm is the exponential decreasing zone,10-40mm is the linear decreasing zone and 40mm is the stable zone.The relationship of the grain orientation and the distance from the Water-cooled copper is similar.In the distance from the water-cooled copper 30~40mm,the grain orientation deviates from the stress axis direction of the average deviation angle of about 10°,the grain density basically no longer change,so the seeding height should be set between 30~40mm.In this paper,the seeding height is set to36mm(4)In this paper,study the selection of the spiral section of the mold selector and draw the mold selector with different helix angle by UG to simulate the casting solidification and CAFéof the different models with different mold selectors.According to the analysis of the research results,the spiral crystal segment is mainly through the impediment to the primary crystal in the longitudinal direction of the spiral segment and the promotion of the secondary crystal in the transverse direction.There is a direct relationship between the elimination of the grains and the position of the crystal selector.The growth of the grains near the lower edge of the spiral selector will be obtained.Pitch h_s and helical diameter h_s and helix angle ? should meet the relation:h_s>d_w tan?.The helix angle has no significant effect on the average deviations of grain orientation from the stress axis(in this paper,the direction of the blade is longitudinal). |
PDF Full Text Request