Nickel coating is about holding the grit in place; titanium coating is about protecting the grit and moving heat. Specify nickel for resin bonds, electroplated tools and wire sawing, titanium for metal-bond tools that run hot. Getting this backwards costs tool life and, in wire sawing, whole spools.
What A Coating Is For
Bare diamond does not bond well to anything. It is chemically inert, it does not wet most metals, and in a metal matrix it is held mechanically rather than chemically. A metallic coating changes that: the coating bonds to the diamond on one side and to the matrix on the other, so the particle is anchored instead of merely embedded.
Two coatings dominate the market, and they are not interchangeable. They differ in weight gain, thickness, process and the failure they prevent.
Nickel Coating
Nickel is applied by chemical or electrolytic plating and produces a relatively thick, continuous shell. The famous 56% figure in wire sawing refers to weight gain: one carat of diamond becomes 1.56 carats after coating. Lighter nickel grades at around 30% are used where retention matters but the coating must not dominate the particle size.
Nickel coating suits four situations:
- Resin bond tools. The coating gives the resin something to grip, which raises grit retention and reduces pull-out.
- Electroplated tools. A nickel shell plates more uniformly onto a nickel-coated particle, so the plating layer and the coating form one continuous matrix.
- Wire sawing. The heavy 56% coating is what keeps 6 to 12 micrometre grit attached to a wire running at speed through silicon or sapphire.
- Graphite and carbon cutting. Retention again, in a bond that otherwise releases the grit too early.
Available nickel-coated grades here run from W7 and coarser, with a minimum order of 2000 carats for the coated product.
Titanium Coating
Titanium is applied by chemical plating at a much lower weight gain, typically one to three parts per thousand. It is a thin, reactive layer, not a structural shell.
The job it does is thermal and chemical. Diamond oxidises and graphitises at the temperatures reached during sintering and during dry cutting, and the resulting surface no longer bonds to the matrix. A titanium layer isolates the diamond from oxygen, improves heat transfer away from the cutting edge, and reduces that thermal damage. In practice this shows up as longer life in metal-bond saw segments and drills.
Titanium is the correct choice when the tool is sintered or brazed, when the bond is metallic, and when the failure mode is grit loss after thermal exposure rather than simple pull-out. It is also used in thermal management work, where a titanium-coated powder bonds into a copper or SiC matrix and improves interface conductivity.
Direct Comparison
| Nickel (N) | Titanium (T) | |
|---|---|---|
| Typical weight gain | 30% or 56% | 0.1% – 0.3% |
| Layer character | Thick continuous shell | Thin reactive layer |
| Main function | Mechanical retention | Oxidation protection, heat transfer |
| Bond systems | Resin, electroplated, wire saw | Metal bond, sintered, brazed |
| Effect on particle size | Measurable increase at 56% | Negligible |
| Minimum order | 2000 ct | 2000 ct |
| Grade range | W7 and coarser | W7 and coarser |
What Coating Does Not Fix
Coating is not a substitute for grit quality. A low-toughness particle will still fracture inside a perfect coating, and a wide particle-size distribution will still scratch whether or not the surface is plated. If the problem is surface finish, look at PSD before coating. If the problem is grit pull-out, coating is the right lever.
Coating also changes flow and packing behaviour. Coated powder is heavier and flows differently, which matters in automatic dosing and in resin mixing. Re-check your dosing after switching, even at the same nominal size.
Common Mistakes
- Specifying nickel for a sintered metal bond. Nickel helps retention but does nothing about oxidation at sintering temperature. Titanium is the coating that addresses that.
- Specifying titanium for wire sawing. A 0.2% layer will not hold grit on a wire. Only the heavy nickel route does that.
- Comparing price per carat. A 56% nickel-coated carat contains roughly 0.64 carats of diamond. Compare cost per carat of diamond, not cost per kilogram of coated powder.
How To Verify
Ask for the weight gain percentage, the coating thickness if available, and a cross-section or SEM image showing the layer is continuous rather than patchy. Patchy coating is the most common hidden defect: the average weight gain looks correct while a share of particles is barely covered.
Next Step
Coated products: N nickel-coated diamond and T titanium-coated diamond, both from W7 and coarser. Base grit: HDY for plating grades, HDHR for crushed sharp material.
Application side: electroplated tools, resin and vitrified bond wheels, thermal management composites.