Numerical Simulation Of Solidification Structure Evolution Of Titanium Alloy Hydrogenated In Liquid Satate

With good mechanical properties, together with high specific strength and high temperature creep resistance, titanium alloys become more and more popular in the astronavigation and navigation now. The technology of Thermo-Hydrogen Processing (THP) is a particular method of heat treating which can improve the workability and mechanical properties of titanium alloy. Up to now, the main method of THP is hydrogen penetration under the solid states, and the research on alloy ingots usually starts with solidification. With the help of grain structure formation and evolution simulation, we can not only predict the solidification structure and mechanical properties of casting, but also obtain the fixed quantity relationship between process parameters and solidification structure. So the numerical simulation is becoming an effective research method of microstructure evolution during solidification of hydrogenated titanium alloy.Mathematical model of the structure evolution and the fixed relationship between hydrogen content and the of hydrogenated Ti-6Al-4V alloy are established. and the structure evolution of hydrogenated Ti-6Al-4V alloy during its solidification with/without convection or in different superheat are simulated based on a finite differential method (FDM) for macroscopic field calculation and a cellular automaton technique (CA) for microscopic modeling of grain nucleation and growth according to the established mathematical model. The simulation results indicate that a larger and finer equiaxed region is formed by increasing the hydrogen content in the Ti-6Al-4V melt or by considerate the convection. With lower superheat,the main structure of Ti-6Al-4V is coarse and large columnar region which will become much larger in higher superheat. Titanium alloy hydrogenated in liquid state would enlarge the equiaxed region. nmaxThe experiments of titanium alloy hydrogenated in liquid state with use of Induction Skull Melting and Vacuum Un-consume Electrode Arc Furnace are designed and the experimental results are investigated in detail by which we obtained two groups of experimental ingots with 1.28at% hydrogen, one group with the same heating times but different heating electrical currents, that is, I=100A,150A,200A and 250A.and The other with the same heating electrical current but different heating times, that is, t=20s,25s and 30s. In addition, we also obtained an experimental ingot that heating time is 20s and heating electrical current is 100A, but with no hydrogen. The experimental results indicated that coarse and large columnar structures are observed in high superheat hydrogenated Ti-6Al-4V alloy. And the structures will become finer with a higher superheat. A larger equiaxed region is formed under the condition of increasing the low superheat. Besides, in a same condition the coarser equiaxed region can be converted to finer columnar region by hydrogenating in liquid state.The simulated results show a good agreement with the experimental observations, indicating that the validity and the efficiency of the models developed.