Effect Of Thermomechanical Processing On Microstructure Changes Of Ti600 Titanium Alloy

With the rapid development of the aviation industry, in order to meet the requirements of new aircraft design, countries all over the world are competing to develop titanium alloys for long-term use above 600℃. At present, the development of high-temperature titanium alloys mainly focuses on the Ti-A1-Zr-Sn-Mo-Si system, countries have developed several high-temperature titanium alloys with excellent performance for use at 600 ℃, and this series of alloys has been proved to be the most successful high-temperature titanium alloy system.Ti600 alloy is a kind of near-alpha-type high-temperature titanium alloy developed by Northwest Research Institute of Nonferrous Metals, and it is mainly designed for the application requirements of aviation engines. The Ti600 alloy is a near-alpha type high-temperature titanium alloy developed by the Northwest Nonferrous Metals Research Institute, which is mainly designed for aerospace engine applications. Its composition is based on the above alloy series with the addition of the rare earth element Y, which is in line with the design standard for high-temperature titanium alloys, and is therefore expected to become an aerospace material. For the manufacture of special components shaped like compressor disks and blades, it is considered necessary to optimize the thermomechanical processing conditions to control the microstructure-mechanical property characteristics. Therefore, clarifying the relationship between microstructure and thermomechanical processing parameters is essential for the production of Ti600 titanium alloys.

The material used for the test was Ti600 titanium alloy with a nominal composition of (wt.%) Ti-6Al-2.8Sn-4Zr-0.5Mo-0.4Si-0.1Y, and its β-transition temperature was about 1010°C. The material used for the test was Ti600 titanium alloy with a nominal composition of (wt.%) Ti-6Al-2.8Sn-4Zr-0.5Mo-0.4Si-0.1Y. Ti600 alloy bars in the as-delivered condition were subjected to β-phase zone forging, and the initial microstructure consisted of α lamellae 30-40 μm long × 2 μm wide, and a massive α phase that accounted for about 10% of the fine transformation matrix. Isothermal compression tests were performed on a computer-controlled Gleeble-1500 thermal simulator with a deformation temperature range of 800 to 1100°C, strain rates of 0.001, 0.01, 0.1, 1, and 10 s-1, and a highly compressive specimen of 70%. Immediately after thermal compression, the specimens were water quenched to protect the heat-deformed organization. The test results showed that:
The deformation temperature has a great influence on the microstructure. Processing at temperatures below the β-transition temperature (800 to 950°C), dynamic spheroidization was clearly found in the deformed specimens as the temperature increased. Machining at temperatures higher than the β-transition temperature (1000 to 1100°C), elongation of the β-grains occurred in the plane perpendicular to the forging direction. Some discontinuous acicular martensitic α flakes were found within the transformed β grains.
The strain rate completely influences the deformation of Ti600 alloy. As the strain rate (0.1-10 s-1) increased, the elongated α flakes twisted more, and the fracture of the lamellar organization clearly appeared under α + β processing conditions.
The softening mechanism of Ti600 alloys hot pressed at 1000 to 1100°C is mainly a dynamic restitution, and the formation of subcrystals and dislocation walls are typical microstructural features observed in the β single phase.
Processing in the α + β phase region (800 to 950°C) reduces both the rheological stress with increasing temperature and decreasing strain rate. The softening mechanism is mainly dynamic spheroidization of α-sheets within β-grains.