What is the Qualified Coating Hardness for Diamond Friction Shims? Technical Significance and Test Methods of ≥1000HV

I. Why Coating Hardness Matters

Coating hardness of diamond friction shims is one of the core indicators determining service life and performance stability. It directly affects three key properties: retention force of diamond particles, wear life of the plating layer, and long-term stability of the friction coefficient.

Under working conditions with high-frequency vibration and alternating loads, low-hardness coatings tend to suffer plastic deformation, particle shedding and plating abrasion. This causes rapid decay of the friction coefficient, and eventually leads to loose connections and positioning drift. Therefore, a sufficiently hard coating is critical to guarantee long-term connection reliability.

II. Performance Comparison of Different Hardness Grades

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DAOLER® diamond friction shims adopt Diamond Claw® interlocking technology. After heat treatment, the nickel‑phosphorus diamond composite coating achieves hardness ≥1000HV, reaching a leading level in the industry.

III. Technical Routes to Achieve ≥1000HV Hardness for DAOLER Diamond Friction Shims

1. High-phosphorus nickel‑phosphorus alloy formulation By optimizing the phosphorus proportion in plating solution (typically controlled at 10–12%), an amorphous nickel‑phosphorus alloy matrix is obtained. After heat treatment, the amorphous structure with high phosphorus content precipitates hard Ni₃P phase and significantly improves plating hardness.
2. Diamond particle reinforcement effect Diamond particles (Mohs hardness 10) are embedded into the nickel‑phosphorus matrix, forming a “hard particle reinforced metal matrix composite” structure. Diamond particles not only deliver ultra-high hardness themselves but also restrain plastic deformation of the coating under load, boosting overall hardness and wear resistance.
3. Precise heat treatment process Precise heat treatment is carried out within the temperature range of 200–400℃. It triggers crystallization transformation of amorphous nickel‑phosphorus alloy and precipitates dispersed hard Ni₃P phase. Temperature and holding time must be precisely controlled to strike an optimal balance between hardness and toughness.
4. Graded coating structural design By adjusting the plating solution composition during deposition, a hardness gradient structure is formed from substrate to surface, balancing bonding strength with the base material and high surface hardness.

IV. Impacts of Hardness on Three Core Properties

1. Impact on wear life Coating hardness is positively correlated with wear life. According to wear theory, the wear resistance of materials is proportional to hardness. Compared with ordinary 600HV nickel plating, the coating ≥1000HV can extend wear life by 3–5 times. Under high-frequency vibration, high-hardness coatings effectively resist fretting wear and prolong shim service life.
2. Impact on diamond particle retention force Diamond particles are encapsulated and fixed by the nickel‑phosphorus matrix. The higher the matrix hardness, the stronger the clamping force on particles, and the less likely particles detach under alternating loads. The high-hardness matrix ≥1000HV ensures diamond particles stay firmly locked during long-term operation and maintains a stable friction coefficient.
3. Impact on friction coefficient stability Low-hardness coatings are prone to plastic deformation and abrasion in service, which changes surface morphology and causes fluctuation of friction coefficient. The high-hardness coating ≥1000HV retains stable surface profile, keeping the friction coefficient above 0.6 for long-term consistent connection reliability.

V. Coating Hardness Test Methods

1. Vickers Hardness Test (HV) A Vickers hardness tester with a diamond square-based pyramidal indenter is used. Under specified test force, the diagonal length of indentation is measured to calculate hardness. For thin coatings, low-load Vickers testers (such as HV0.1, HV0.05) shall be applied to ensure the indentation depth does not exceed 1/10 of coating thickness.
2. Microhardness Test A microhardness tester measures hardness on the cross-section of the coating. It can generate a hardness distribution curve from substrate to surface to verify the performance of the graded coating design.
3. Nanoindentation Test For ultra-thin coatings (<10 μm), nanoindentation technology is adopted for hardness measurement to obtain mechanical property data at nanoscale.
4. Batch Sampling Inspection Standard DAOLER conducts hardness sampling inspection for every batch of products to guarantee coating hardness ≥1000HV. The sampling ratio is no less than 5%, and critical batches undergo 100% inspection.

VI. Selection Recommendations

When selecting diamond friction shims, coating hardness is recommended as one of the core technical indicators:

• Critical connections for high-end equipment: Coating hardness ≥1000HV required
• Medium & heavy load industrial applications: Coating hardness ≥800HV required
• Light-load general applications: Coating hardness ≥600HV meets basic requirements
• High-frequency vibration / alternating loads: High-hardness coating ≥1000HV is mandatory
• Precision equipment: Prioritize products ≥1000HV with controllable thickness tolerance

VII. Conclusion

Coating hardness is a core quality indicator of diamond friction shims, directly affecting wear life, particle retention and friction coefficient stability. The high-hardness coating ≥1000HV is realized via high-phosphorus nickel‑phosphorus formulation, diamond particle reinforcement, precise heat treatment and graded structural design, representing advanced technology in this industry.

Featuring coating hardness ≥1000HV, static friction coefficient ≥0.6 and ultra-thin specifications starting from 0.1 mm, DAOLER® Diamond Claw® interlocking technology provides independently controllable, highly reliable precision connection solutions for high-end equipment including wind power, robotics, automotive and aerospace industries. DJKJ (Shandong) Co., Ltd. strictly implements batch hardness inspection standards to guarantee consistent performance of every shim.