Fundamental Study On Spray Forming Of Ti-51Al Alloy

According to the analysis of the heat distortion, HIP densification process and the related microstructure, the forming technology manufacturing route of Ti-51Al alloy was studied by experiments, FLUENT numerical simulation and theoretical analysis.In this paper, a BN-black lead composite atomizer used safely within 2000℃was designed for the spray forming of TiAl alloy. Further, the gas flow field and pressure field in the front of the atomizer was simulated by gas dynamics software-FLUENT. The result shows that the extension elongation is 5mm when the inside diameter of the catheter is 5.5mm, and the mercury pull in the front of the catheter will increase firstly, and decrease later with the atomization pressure changing from 0.5MPa to 2.0MP; when the atomization pressure is 1.5MPa, the negative pressure effect is the best so it is suitable to the spray forming of TiAl alloy. Under this process condition, a ?180×50mm TiAl alloy ingots was produced. Further SEM,XRD,EDS analyses show the ingots contain typical DP microstructure which is constituted byγ-TiAl base andα2+γlamellar-structure. The later lamellar-structure is about 10μm and takes 20% volume fraction.Under 1250℃, 160MPa and pressure holding time of 4h, the deposited ingots were densified by HIP technique. The maximum density can reach 98% and the microstructure is almost single-phaseγ-TiAl, the grain size becomes 100-200μm which is bigger than that of SP ingots. A Gleeble-1500D thermal simulation machine was used to simulate the hot compress processing. It is shown that the deformed sample did not obviously recrystallized before 1150℃, with the rising of temperature and the increase of the strain rate, the recrystallization will be intense dramatically. When the temperature is 1200℃, the deformed microstructure is almost recrystallizaiton. Further calculation shown that the hot activation energy is 457.24kJ/mol based on which the constitutive equation and hot processing chart were founded, and the best hot deformation process was obtained that is 1150℃and a strain rate of 0.01s-1.