Additive manufacturing of Cu/Ni dissimilar metals, integrating high-thermal conductivity, high strength, high reliability, and low cost, is one of the best choices for the generation of liquid rocket engines, capable of achieving material-structure–function engine integration. Currently, the main challenges faced in the preparation of GH4169 using laser-directed energy deposition (LDED) technology on CuCrZr substrates are the high-laser reflectivity and thermal conductivity of copper alloys, as well as the considerable differences in the physical properties of the two alloys, making it difficult to achieve defect-free metallurgical bonding. Stable process manufacturing and control of microstructural properties are also challenges. Herein, we use surface pretreatment processes followed by additive manufacturing to solve the problems of high reflectivity of Cu alloys and interface metallurgical defects and prepare CuCrZr/GH4169 dissimilar metals.

This study utilizes five processes, namely thermal spraying, cold spraying, electroplating, physical vapor deposition (PVD), and powder spreading, for surface pretreatment of the CuCrZr alloy. On the pretreated surfaces of the CuCrZr substrates, three processes are employed for single-track cladding experiments; Process 1: laser power set at 4.5 kW, and scanning speed set to 1000 mm/min, without powder feeding; Process 2: laser power set at 4.0 kW, scanning speed set at 1000 mm/min, and a powder feeding rate of 35 g/min, and Process 3: laser power set at 4.5 kW, scanning speed set at 1000 mm/min, and powder feeding rate of 40 g/min. The optimal process is selected for overall additive manufacturing of CuCrZr/GH4169 alloy. Microstructural observations are conducted on the interface of single-track cladding specimens (perpendicular to the laser scanning direction) and the interface of overall dissimilar metals specimens. Ultrasonic nondestructive testing and tensile performance testing are performed on the dissimilar metals specimens.

1) Single-track cladding deposition GH4169 experiments are conducted on CuCrZr substrates using different surface pretreatments. The results for thermal spraying (Fig. 6) and cold spraying (Fig. 7) samples are excellent . The thermal spraying samples formed a stable melt pool without microcracks, pores, or local unmelted areas at the interface. In the cold spraying samples, local unmelted areas appeared at the edges of the melt pool when the coating thickness increased to 150 μm. However, the electroplating (Fig. 8) and PVD (Fig. 8) samples did not produce stable melt pools, and there were obvious microcracks and local unmelted areas between the coating and the weld track. The coating prepared by powder spreading process (Fig. 8) showed many unmelted adhesive powders around the weld track, poor continuity of the weld track, unstable melt pool fusion line, and small penetration depth. The thermal spraying experiment yielded the best results. By comparing the main parameters of single-track cladding, the optimal process was selected: thermal spraying was used to deposite the GH4169 alloy coating with 100 μm thickness on CuCrZr substrate, Process 1 was used to remelt the first layer, followed by Process 2 for deposition.

2) The prepared samples exhibited good bonding characteristics between the two materials. Nondestructive testing results did not reveal major defects (Fig. 10). The interface area of the samples along the deposition direction from the bottom to the top parts can be divided into five regions: CuCrZr substrate, columnar crystal, diffusion, Cu element diffusion, and GH4169 regions (Fig. 11). The tensile strength of the laser-directed deposited CuCrZr/GH4169 dissimilar metals along the deposition direction was 280 MPa±4.24 MPa, with the fracture occurring at the interface, slightly toward the copper alloy side, indicating a ductile fracture.

This study primarily investigates the impact of surface modification on the laser reflectivity of copper alloys. Various surface modification processes, including thermal spraying, cold spraying, electroplating, PVD, and powder spreading, were used to prepare nickel-based alloy coatings with different compositions and thicknesses on copper alloy surfaces. After determining the optimal preparation process, coating composition, and thickness, the overall material deposition process was explored. The main conclusions are as follows:

1) The results of the single-track cladding experiments showed that the thermal spraying is the preferred pre-treatment process to achieve defect-free bonding between the CuCrZr alloy and the GH4169 nickel-based high-temperature alloy with a stable melt pool. The GH4169 alloy coating prepared by cold spraying was less effective than that prepared by thermal spraying. The interfaces of single-track deposition after surface modification using PVD, electroplating, and powder spreading processes exhibited defects such as local unmelted areas, microcracks, and poor metallurgical quality.

2) The thermal spraying surface modification process on copper substrates can effectively avoid interface defects and forming difficulties under various process conditions, when the surface GH4169 coating thickness reaches 50?150 μm, resulting in metallurgically bonded interfaces. After comparing the main process parameters using a radar chart, a CuCrZr substrate pretreated with a thermal spray coating (thickness of 100 μm) was selected. Using Process 1 to remelt the first layer and Process 2 for deposition, samples with dense metallurgical bonding and good appearance were obtained. Nondestructive testing confirmed that internal defects met the GJB 1580A—2004 (Class AA) requirements.

3) The interface region of the prepared CuCrZr/GH4169 dissimilar metals is mainly divided into the CuCrZr alloy substrate, columnar crystal, unmelted powder, Cu element diffusion, and GH4169 alloy zones. The columnar crystal zone is formed by remelting the copper alloy. The unmelted powder zone consists of flaky and spherical particles, mainly from insufficiently melted GH4169 coating and powder. The tensile strength of the CuCrZr/GH4169 dissimilar metals along the deposition direction was 280 MPa±4.24 MPa. The fracture of the tensile samples occurred at the interface, slightly toward the copper alloy side, indicating good bonding at the interface, with the fracture surface confirming ductile fracture.