According to research, the nickel coating weight rate significantly influences both the surface morphology and compressive strength of synthetic diamonds:

1. Effect on Surface Morphology: Roughness Increases with Weight Rate

Morphology Trend: Unplated diamond surfaces are smooth with sharp edges. After nickel plating, the surface turns dark black, with a dense, uniform coating and no bare spots. As the coating weight rate increases, the surface roughness of the diamond increases accordingly.

Mechanism Analysis: During electroplating, the cathode area (exposed diamond surface) is small relative to the large anode plate. As plating time lengthens and the weight rate increases, the dissolution of the anode generates a high concentration of main salt, which is the primary cause of coating surface roughening.

Heat Treatment Effect: Heat treatment at 400 °C does not noticeably alter the surface morphology of the coating.

2. Effect on Compressive Strength: Compressive Strength Increases Substantially with Weight Rate

Strength Trend: Electroplating nickel significantly improves the average single-particle compressive strength, and the average compressive strength increases continuously as the coating weight rate increases.

Experimental Data Comparison (Single-Particle Average Compressive Strength):

Unplated (0% weight rate): 13.975 N (13.5 N after 400 °C heat treatment)

20% weight rate: 26.8 N (27.15 N after heat treatment)

30% weight rate: 28.2 N (29.25 N after heat treatment)

40% weight rate: 28.825 N (33.3 N after heat treatment)

50% weight rate: 32.15 N (34.375 N after heat treatment)

60% weight rate: 33.95 N (36.725 N after heat treatment)

Strengthening Mechanism: Synthetic diamond surfaces naturally contain micro-flaws such as micro-cracks and pores. The nickel coating fills, smooths, and encapsulates these surface flaws, significantly reducing stress concentration under loading. A higher weight rate provides fuller encapsulation and superior flaw healing, leading to greater strength enhancement.

Secondary Strengthening via Heat Treatment: Heat treatment at 400 °C for 30 min eliminates adsorbed hydrogen atoms in the coating, reduces compressive stress and relaxation forces, and homogenizes the coating microstructure, yielding a slight additional increase in compressive strength beyond electroplating alone.