Scaling up the application process of “Ni–SiC” metal-matrix composite coating

Introduction. Today, metal-matrix composite coatings are widely in demand due to the possibility of combining the properties of both the metal base and their reinforcing particles. The simplest and most technologically advanced method of coating is electrodeposition. One of the key parameters that determines the quality of the coating formed and the electrodeposition rate is current density. The literature presents opposing views on how current density affects the quality of composite coatings. The primary criterion is the volume fraction of reinforcing particles. The use of nanoparticles (less than 100 nm in size) as a hardener makes it possible to significantly increase the hardness and wear resistance of the matrix due to dispersion hardening, however, they have a high tendency to agglomeration and require more careful control of electrodeposition modes. It is important during electrodeposition to form a coating with a uniform distribution of particles in the metal matrix over the entire working area of the workpiece to ensure stability of mechanical and functional properties, which will subsequently determine the durability of the parts. From this point of view, it is of interest to scale the electrodeposition process and switch to model samples, the long size of which imitates the maximum height of a real axisymmetric part, for example, a cylinder, which will allow reproducing coating conditions close to production ones. The aim of the research is to study the homogeneity of the structure and properties of the Ni–SiC coating containing a fraction of particles larger than 2 μm and formed on long workpieces (with an area of 0.2 dm2) in the process of electrodeposition depending on the current density. Methods and materials. Cast aluminum alloy AK7 was used as the substrate material for forming the Ni–SiC composite coating. The dimensions of the substrate samples were 70×20×4 mm. Electrodeposition mode: current density of 0.5 A/dm2, 10 A/dm2, 20 A/dm2; duration 60 minutes; temperature 60 °C. The microstructure of the coatings was examined using a JSM-6490 LV scanning electron microscope at a magnification of ×500. Microhardness was estimated using a TBM Tochline microhardness tester at a load of 50 g. Wear resistance tests were performed on a Nanovea tribometer using the ball-on-disk method. Results and discussion. The technology of electrodeposition of the matrix composite coating “Ni–SiC” on long flat samples (0.2 dm2) of aluminum alloy AK7 was developed and the optimal process parameters were selected. The possibility of forming a homogeneous coating based on a nickel matrix containing large SiC particles on flat long samples (0.2 dm2) of aluminum alloy AK7, simulating a sector of an axisymmetric part, was demonstrated. Conclusion. The metal-matrix composite coating “Ni–SiC”, formed on flat long samples (with an area of 0.2 dm2) of aluminum alloy AK7 as a result of electrodeposition, is characterized by uniformity of thickness, volume fraction of silicon carbide particles and microhardness in three control zones for each current density. The higher the current density during electrodeposition, the higher the thickness of the formed Ni–SiC metal matrix composite coating, the volume fraction of reinforcing particles and the microhardness.