| TiAl alloy is recognized as the most development potential of lightweight superalloy,and has a broad application prospects,because of its low density,high modulus and excellent oxidation resistance,high temperature strength,creep resistance,flame resistance and other excellent performance.The metallurgical method is an important forming method of TiAl alloy which has obvious advantages in eliminating macroscopic composition segregation,looseness,shrinkage and near net forming.in this way the microstructure of TiAl alloy.However,TiAl alloy is very unstable and in high chemical activity at high temperature,and reacts with the crucible base material and air seriously,which makes the alloy contaminated,so usually vacuum melting and inert gas atomization method are taken use to prepare TiAl alloy powder.The melting and diversion are important processes of atomization,but melting and diversion are carried out in high temperature closed environment,it is not easy to carry out direct experimental observation.In this article,numerical simulation technology is taken to simulate the various stages of alloy atomization milling process,which is of great significance for the preparation of high performance TiAl alloy powder.The results show that magnetic induction,induced current,and electromagnetic force are only distributed in the Ti Al alloy's and copper crucible's surface,and inward attenuate quickly.Besides,the direction of the induced current is opposite to that of the coil current,and the induced current in the copper crucible is much larger than the induced current in the TiAl alloy.The direction of the electromagnetic force points to the inside of the TiAl alloy.There is contact resistance between crucible and metal melt.The contact resistance consists of micro-contact thermal resistance and thermal micro-gap resistance.The smaller the contact pressure,the greater the micro hardness,the greater the surface roughness,the smaller the rough slope of the surface,the greater the contact resistance is.When the parameters are set to: surface roughness 4um,surface roughness average slope 0.3,contact pressure 25 KPa and micro-hardness 300 MPa,micro-contact thermal resistance R_s= 1.7257K/W WW,thermal micro-gap resistance is R_g= 0.2703K/W,and contact heat resistance is R_c= 0.2352K/W).Melting starts on the side of the ingot and once there is sufficient molten metal the fluid flow and surface deformation procedures switch on.The molten metal tends to first fill the space between the ingot and the crucible due to gravity.Since the electromagnetic force acts radially inwards in the liquid layer the melt is also squeezed upwards to cover the top of the ingot.As more metal melts,then a dome of liquid is formed,within which strong turbulent convection takes place.When the catheter is clogged,the solidified TIAl alloy is heated by an induction coil,the place near the inlet is melted at first,affected by the inlet's temperature.With heating,two melt zones are combined,the liquidus continues to move down until it reaches the outlet.When the melt flow in the catheter is stable,there is little effect on the temperature of the catheter and the melt as a whole.When the frequency is 3000 Hz,the maximum temperature of the outlet temperature is 2.5? higher than that of the non-magnetic field,and the different of the melt's temperature from inside to outside is reduced from 13? to 7.5??The velocity of the melt in the conduit varies considerably from the inlet to the outlet,but the axial velocity of the outlet has no significant effect and the greater the frequency,the greater the radial inward velocity of the outlet,the better the convergence effect is. |
PDF Full Text Request