Why Add Nickel to Diamond Tools?

The performance of diamond tools depends not only on the diamond abrasives themselves but also to a large extent on the metal bond (matrix) that holds the diamonds. Nickel, as an important transition metal, is often added to copper-based, cobalt-based, and iron-based bonds. It plays a unique role in improving sintering behavior, interfacial bonding, mechanical properties, and high-temperature performance.

 

1. Improving Sintering and Alloying Behavior

Nickel has a relatively high melting point of 1455°C, and the sintering behavior of nickel powder alone is only moderate. However, nickel is mutually soluble with copper and can alloy well with copper-based bonding phases. Therefore, adding nickel to copper-based bonds can form uniform solid solutions or alloy phases, optimize the matrix microstructure, and avoid segregation of low-melting components, thereby improving the density and uniformity of the sintered body. This is very important for ensuring the overall quality of the diamond tool matrix.

2. Enhancing Wettability of the Bond to Diamond and Skeleton Materials

A certain amount of nickel can improve the wettability of copper-based bonding phases to skeleton materials and diamond. Better wettability means that the molten bonding phase can spread more effectively over the diamond surfaces and skeleton particles, forming tighter interfacial bonding upon cooling. This enhances the holding force of the matrix on the diamonds and reduces premature diamond pull-out.

It is worth noting that nickel itself does not readily react with the carbon on the diamond surface, and at high temperatures nickel has relatively weak erosion on diamond. This means that while improving wettability, nickel does not excessively damage the diamond, which helps maintain the integrity and cutting ability of the diamond.

3. Reducing Matrix Loss During Sintering

Nickel can effectively "absorb" molten tin and other liquid alloys, reducing matrix loss during sintering. In bonds containing low-melting metals such as tin, liquid phase may exude during sintering, causing composition segregation, porosity, and a less dense matrix. Nickel can dissolve or adsorb these liquid phases, keeping them within the matrix and maintaining the integrity and compositional stability of the bond. Therefore, nickel is often added to cobalt-based and iron-based bonds to improve sintering behavior.

4. Providing High Strength, High Toughness, and High-Temperature Performance

Nickel has particularly high toughness, relatively high strength and hardness, as well as good oxidation resistance and a certain degree of "red hardness." These properties make nickel-based bonds suitable for diamond tools used under heavy load conditions, such as heavy grinding, drilling, and cutting. Nickel can effectively improve the impact resistance of the matrix, making it less prone to fracture or deformation.

However, nickel-based bonds tend to have poor sharpness. This is because the high toughness of nickel leads to relatively slow matrix wear, so worn diamond grits do not fall off easily, thus reducing the self-sharpening ability of the tool. Therefore, nickel is usually combined with other elements to balance sharpness and tool life.

5. Optimizing Overall Performance by Combining with Cobalt and Iron

When nickel is properly combined with cobalt and iron, satisfactory comprehensive properties can be obtained, such as high toughness, low deformation, and moderate wear resistance. Adding nickel to cobalt-based bonds can improve sintering behavior and toughness, while adding nickel to iron-based bonds can improve toughness and oxidation resistance, and also reduce cost. By adjusting the Ni/Co/Fe ratio, a good balance among sharpness, service life, and cost can be achieved to meet the needs of different machining applications.

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Conclusion

The addition of nickel to diamond tools mainly takes advantage of its ability to alloy with copper, improve the wettability of the bond to diamond and skeleton materials, reduce liquid phase loss during sintering, and provide high toughness, high strength, and high-temperature stability. These effects collectively enhance the holding force of the matrix on diamonds and the impact resistance of the tool. Although nickel may reduce the sharpness of the matrix, reasonable combination with elements such as cobalt and iron can achieve optimized overall performance, enabling diamond tools to adapt to a wider range of machining conditions.