Study On Preparation And Mechanical Property Of Nanodiamond Composite Coatings By Electrodeposition

Due to the high hardness and high wear resistance of diamond, nanodiamond composite coatings have excellent mechanical properties. However, because of the oil-wet hydrophobicity and high surface activity of nanodiamond particles, which makes it difficult to codeposition with matrix metal during the preparation of composite coating. As a result, Ni-diamond composite coating has a poor mechanical properties. Nickel coatings and Ni-nanodiamond composite coatings were electrodeposited on Q235 A steel. We have investigated the parameters and mechanical properties of coatings and made a research on the relationship between microstructure and the parameters and mechanical properties.Through different polishing experiments, we selected mechanical polishing as the pretreatment style of Q235 A at first. The ranges of parameters in the preparation of coatings were determined by the cathodic polarization curves(current density 1.5-3A/dm2, temperature 45?-60?, PH 3.5-5). Based on the parameters above, we conducted a series of orthogonal test to get the best microhardness, elastic modulus, residual stress and surface roughness. The results show that when the nickel coating was electrodeposited under current density 3A/dm2, temperature 45?, PH 3.5, it can have the best mechanical properties: microhardness and elastic modulus reach 3.86 Gpa and 238 Gpa, the surface roughness is 0.182?m. In addition, nickel coatings were electrodeposited with pulse current. As a result, microhardness and elastic modulus of nickel coatings reach 4.04 Gpa and 247.7Gpa.Based on Ni coatings prepared above, Ni-nanodiamond composite coatings were electrodeposited. According to the agglomeration and poor wettability, we added some surfactants in the plating solution. We concluded that when the composite coating was electrodeposited under diamond concentration 8g/L, current density 3A/dm2, the coating has the best properties: the nanodiamond particle content is 14.35%, microhardness and elastic modulus reach 5.302 Gpa and 254.356 Gpa, the tensile stress in the coating is 177.39 MPa. Compared with nickel coatings, Ni-nanodiamond coatings show the better properties. Due to the incorporation of diamond particles, the grain size declined from 30.8nm to 20.4nm, and the composite coatings had a preferred orientation of(200). As a result of the reinforcement of the diamond, the microhardness and elastic modulus of composite coatings increased obviously.