Effect of hot isostatic pressing process parameters on the organization and properties of TA15 titanium alloy

TA15 titanium alloy is a kind of high-aluminum-equivalent near-alpha titanium alloy independently developed by China, which can be used for long-time service at 540°C. Its nominal composition is Ti-6Al-2Zr-1Mo-1V. The alloy has excellent creep resistance, corrosion resistance and welding performance, and is widely used in the manufacture of structural parts for various types of airplanes, engines and missiles. Powder metallurgy hot isostatic pressing technology can realize the integrated forming of titanium alloy, its fine crystal and no segregation characteristics can make the parts to obtain excellent organizational properties, to avoid melting and pouring, open billet forging and other high-energy processes, through the near-net shaping can significantly improve the utilization rate of titanium alloy.

TA15 titanium alloy hot isostatic pressing research mainly focuses on two aspects, on the one hand, as a means of eliminating the internal metallurgical defects of casting TA15 alloy, the study of different hot isostatic pressing state of ZTA15 alloy properties and organization of the law of change; on the other hand, the use of powder metallurgy method of preparation of TA15 alloy, TA15 powder titanium alloy through hot isostatic pressing process, the study of the organization evolution and the change of performance. The study of its organization evolution and performance changes. At present, there are few reports on the systematic study of the effects of hot isostatic pressing parameters on the organization and properties.

In this study, the controlled variable method is used to carry out high-temperature and high-pressure hot isostatic pressing tests on TA15 titanium alloy powders of the same particle size range, selecting different thermal coupling loading temperatures, holding times and pressure values, and characterizing the microstructure of the alloys and determining the average grain size, to obtain the effects of temperature and pressure coupling on the microstructure evolution and properties of titanium alloy powders, and to obtain the results of the microstructure evolution and properties of the powders under different temperatures, pressures and holding times. The microstructure evolution and performance curves of the powdered titanium alloy under different temperature, pressure and holding time conditions are obtained to provide a reference for the development of hot isostatic forming parts of TA15 alloy for aerospace applications.

The original spherical atomized TA15 titanium alloy powder is used, the specific composition is shown in Table 1, the sphericity is ≥99%, and the carbon steel sleeve is used, the size of which is ϕ60mm×100mm, the powder is filled into the carbon steel sleeve uniformly, and seal welding is carried out on the cylindrical sleeve, the seal welding heating temperature is 600℃, and the vacuum is drawn to 10-3Pa. The seal welded sleeve is subject to the pressing test in hot isostatic pressing furnace, and the temperature, holding time, pressure and three sets of test conditions, such as temperature, pressure and holding time are determined respectively. After sealing and welding, the envelope was pressed in the hot isostatic press furnace, and the test was carried out from temperature, holding time, pressure and three sets of parameters: (1) the temperature was set at 910℃, 930℃ and 950℃, the time was 180min, and the pressure was 130MPa; (2) the pressure was set at 110℃, 130℃ and 150MPa, and the time was 180min; (3) the time was set at 90℃, 180min and 240min, and the temperature was set at 930℃, and the pressure was 130MPa. JSM-6630LV scanning electron microscope was used to observe and characterize the microstructure and morphology of TA15 alloy, and the statistics and analysis of slat spacing and equiaxial α grain content were carried out through the IPP software, and the mechanical properties of the specimens were tested by the 5887-E2-GE mechanical tester with the load greater than 500N and the tensile rate of 0.45-4.5mm/min, and the test results were taken from five specimens with the load greater than 500N and the tensile rate of 0.45-4.5mm/min, and the test results were taken from five specimens with the load greater than 500N. The test results were averaged over 5 specimens.
Conclusion

(1)The tensile strength and yield strength of TA15 alloy show the change of increasing and then decreasing with the increase of furnace pressure, holding time and temperature, while the elongation and section shrinkage show the trend of decreasing and then increasing with the increase of pressure and time, and decreasing with the increase of temperature.

(2)When the hot isostatic pressing process is 930℃×130 MPa×3h, TA15 alloy is a typical net basket organization, with low content of slat spacing and equiaxial α grains, and the room temperature mechanical properties of the billet obtained from TA15 alloy can reach the level of homogeneous forgings, with an average value of tensile strength of up to 952.3MPa, an average value of elongation of up to 17.1%, and a yield strength of 866.3MPa, with a section shrinkage of 47.9%. The average value of tensile strength is up to 952.3MPa, average value of elongation is up to 17.1%, yield strength is 866.3MPa and section shrinkage is 47.9%.