The application of laser additive manufacturing technology in aerospace field is more and more extensive, some large integral complex structural parts are difficult to be realized by traditional processing technology, but can be produced by different additive manufacturing technology. Selective laser melting (SLM) is a kind of high-energy beam metallurgical forming process. It takes metal powder as raw material, uses high-energy laser as energy source, melts metal powder layer by layer according to the predetermined processing route, rapidly solidifies and deposits layer by layer, and continuously feeds powder and deposits together to finally complete the workpiece forming. Laser deposition manufacturing (LDM) is based on laser cladding technology, and the deposition layer is formed by the interaction of laser, powder and molten pool. LDM technology is characterized by the manufacture of large size parts, especially suitable for the manufacture of advanced large key metal structures for national defense, can be done quickly and reduce the cost. However, the laser deposition technology is limited by its own process characteristics, and compared with the selective laser melting technology, the forming accuracy and surface quality are poor. The main content of this study was laser deposition selective laser melting forming, microstructure and properties of TC4 titanium alloy components and connection mode to carry on the design of connection technology, and the tensile properties of the selective laser melting direct forming a comparison, and to design different connection mode with good testing performance. Titanium alloy had the advantages of low density, high specific strength, low thermal conductivity, high temperature and low temperature resistance, corrosion resistance, non-magnetism, good biocompatibility and so on, and it was widely used in aviation, aerospace, navigation, automotive, chemical, metallurgy, medical and other fields. The chemical activity of titanium alloy enhanced with the increase of temperature, and could be easy to absorb nitrogen, oxygen, hydrogen and other impurities in the air. Titanium was an isomer with a melting point of 1678 ℃ and a densely arranged hexagonal lattice structure (hcp) below 882 ℃, which is called α-Ti. When the temperature was higher than 882 ℃, it exhibited a body-centered cubic (bcc) lattice structure, which was called β-Ti. Due to the different structure of titanium, the titanium alloy with different structure could be obtained by adding appropriate alloying elements to change the phase transition temperature and phase fraction content. TC4 powder was used as raw material, and the selective laser melting parts were connected by laser deposition manufacturing. Large integrated components with complex and fine structures could be obtained. In the first place, the design of the connecting piece was studied, the internal defects of the forming piece were detected by water immersion ultrasonic detection method, and the tensile properties of the connecting piece were tested. The microstructure and fracture morphology of each area were observed by optical microscope (OM) and scanning electron microscope (SEM), and the relationship between the microstructure and properties of the connecting piece was studied. The results showed there was significant differences in the microstructure of the connectors and thus could be divided into SLM, heat affected zone (HAZ), LDM three zones, where SLM zone was composed of α lamina, HAZ consisted of more disorganized α lamina, and LDM zone was composed of long straight α' martensite, the microhardness of the three zones decreased in turn. The strength and plasticity of the tensile samples of the connectors were lower than those of SLM forming parts, the tensile strength and yield strength were more than 1140 and 1050 MPa, respectively, the reduction in elongation reached 48.41% and the reduction in section shrinkage reached 35.14%. The strength decrease was small, and the plasticity decreased significantly. The fracture positions of the connectors occurred in LDM zone, and the fracture mechanism was semi-cleavage semi-ductile fracture. In terms of the connection between the two different deposition directions, for connection of LDM deposition direction perpendicular to SLM deposition direction, its strength and plasticity were higher than LDM deposition direction parallel to SLM deposition direction, which was caused by the relatively good coordination and matching of the performance of each part of the connector. © 2022, Youke Publishing Co., Ltd. All right reserved.
