Titanium-aluminum alloy vacuum diffusion welding test method
Tue May 17 18:41:46 CST 2022
The atomic ratio of Ti3Al used in the experiment is Ti-23Al-17Nb, which is composed of primary α2 phase, primary flaky O phase and matrix B2 phase, and the density is 4. 5 g/cm3, the tensile properties of the base metal at room temperature and 650 °C in the rolling direction are 966 and 698 MPa, respectively. The composition of Ti2AlNb alloy is Ti-17Al-25Nb, which is composed of two phases of O + B2 phase, and the density is 4. 9 g/cm3 ． The average tensile strength of the base metal along the rolling direction at room temperature and 650 ℃ are 1 096 and 809 MPa, respectively.
Before the test, the Ti2AlNb alloy was processed into 6 mm × 4. 5 mm × 3 mm size specimen. The Ti3Al alloy was processed into 8 mm × 8 mm × 3 mm size specimens for metallographic observation and 15 mm × 8 mm × 3 mm size specimens for mechanical property testing. The surface of the Ti2AlNb base metal to be welded was polished step by step, the intermediate layer foil was polished with 1200-grit sandpaper on the surface oxide film, and then the base metal and the intermediate layer were ultrasonically cleaned in acetone solution for 10 min to remove the surface oil. After assembly, it was placed in a Centorr CVI M60 vacuum furnace (vacuum degree of about 5 × 10 - 3 Pa) for diffusion bonding. The bonding temperature used for solid-phase diffusion bonding of Ti3Al and Ti2AlNb alloys was 800-950 °C, the holding time was 30-180 min, and the bonding pressure was 5 MPa. The prepared samples were cut by wire electric discharge, polished, polished and corroded with sandpaper, the microstructure and fracture morphology of the joints were observed by scanning electron microscopy, and the components of the joints were analyzed by means of energy dispersive spectroscopy and XRD. Use INSTRON MODEL 1186 electronic universal testing machine to test the shear strength and tensile strength of the connecting joint, and the loading speed is 0. 5 mm/s, the joint strength is obtained by calculating the average value of 5 effective strengths to obtain the diffusion concentration gradient, which is related to whether the diffusion is fully and smoothly carried out. Under the process parameters of connection temperature T = 900 °C, holding time t = 90 min, and connection pressure p = 5 MPa, Ti3Al and Ti2AlNb were diffusion bonded with titanium foils with thicknesses of 10, 30, 50, and 100 μm in turn. The microstructure of the joint interface is shown in Fig. The thickness of the titanium foil is 10 and 30 μm, and the α + β dual-phase structure is formed at the interface, which is consistent with 2. Section 1 has the same conclusion. As the thickness of the titanium foil increases, the intermediate diffusion region gradually thickens. From Fig. 2c and Fig. 2d, it was observed that coarse α and β structures remained in the joint, which would adversely affect the mechanical properties of the joint. Therefore, the thickness of the intermediate layer should not be too thick