冷喷涂 Ti-Al 复合材料的搅拌摩擦加工改性研究

Titanium-aluminum alloys are prone to cracks and oxidative inclusions when prepared by the thermal processing-type additive manufacturing technologies. With solid-phase additive manufacturing, the problems of cold spraying (CS) direct deposition of titanium-aluminum intermetallic compounds can be solved, but the metal particles are hard and brittle, resulting in a very low deposition rate or deposition failure, etc. In response to the needs of additive manufacturing of titanium-aluminum alloys, the combination of cold spraying and friction stir processing (FSP) method for the in-situ preparation of the titanium-aluminum is adopted. In order to meet the demand for additive manufacturing of titanium-aluminum alloys, the alloys are prepared in situ by combining cold spraying and friction stir processing. The test materials were pure Ti powder (15-53 μm) and pure Al powder (13-38 μm), which were mixed and processed by a planetary ball mill for 3 hours (no grinding ball was required) according to the ratio of 35% Ti and 65% Al, to obtain the mixed powder for cold spraying. Pure 1060 aluminum plate was used as the substrate for cold spraying. Before the cold spraying, the surface of the aluminum plate was ultrasonically cleaned by acetone immersion and then sandblasted with Al₂O₃. The pre-deposited body was obtained after the deposition of pure Ti and Al by cold spraying, and the deposited Ti-Al composite was processed by friction stir processing at the same traveling speed and rotational speeds of 800 r/min, 1 000 r/min, and 1 200 r/min. The cold spraying system was developed by Northwestern Polytechnical University, with a Laval nozzle with a throat diameter of 2.5 mm and an outlet diameter of 5 mm, and the accelerating gas and powder feeding gas in the cold spraying process were N₂. The friction stir processing was carried out with a Computer Numerical Control friction (CNC) stir processing welding machine, FSE-SD3020T, from Beijing Solidweld Co. In the heat treatment (HT) experiment, the protective gas was argon. The cold sprayed deposit was subject to the heat treatment at a temperature of 650 ℃for 8 hours and 650 ℃ for 8 hours + 900 ℃ for 3 hours respectively and subsequently cooled to room temperature in the furnace. The samples were cut along the face of the Gaussian curve superposition of the cold spraying, which had a size 15 mm×15 mm×10 mm after electric spark cutting. The microstructure of the cross section after cold spraying, the cross section after heat treatment and the cross section after friction stir processing were observed by scanning electron microscope (SEM). X-ray diffraction (XRD) was used to examine the phases and phase contents contained in the samples following different treatments. Additionally, the microhardness of the samples after friction stir processing was measured by microhardness test. A comparative study of the microstructure and properties of the titanium-aluminum compounds after heat treatment and friction stir processing was also conducted. The results demonstrated that the Ti-Al intermetallic compounds were not formed in the cold spraying state of the deposited body, and the porosity in the cold sprayed deposit was less than 0.7%. The formation of Ti and Ti-Al intermetallic compound composite microstructure containing fine grains in the deposited body was a consequence of FSP. An increase in rotational speed resulted in a reduction of porosity and an increase in the content of the formed titanium-aluminum intermetallic compounds. The highest microhardness of the deposit was 256HV0.1. XRD results demonstrated that the intermetallic compound generated after FSP was TiAl₃ and there were unreacted primary Ti particles present in the composite. Through the comparison of the cold sprayed deposit with heat-treated deposit, the deposit after HT exhibited a significant increase in porosity due to the Kirkendall effect. In contrast, the deposit after FSP demonstrated a dense microstructure with minimal observable pores and a refined composite structure. The titanium-aluminum intermetallic compounds were prepared in situ by high-pressure cold spraying technology and friction stir processing, showing a uniform and dense microstructure and excellent internal bonding. The optimized friction stir processing parameters can be used to complete the additive manufacturing of these titanium-aluminum intermetallic compounds, which meets the expected requirements of the test.