The Characteristics of Refined Grain and Coating of Cemented Carbide Tool Materials

Because the wear resistance and toughness of cemented carbide tool materials are not easy to take into account at the same time, users can only choose suitable tool materials from many cemented carbide grades according to the specific processing objects and processing conditions. This brings the choice and management many inconveniences. In order to further improve the comprehensive cutting performance of cemented carbide tool materials, current research hotspots mainly include:

Ⅰ. Refined grain cemented carbide tools

By refining the grain size of the hard phase, increasing the surface area between the hard phase crystals, and enhancing the bonding force between the grains, the strength and wear resistance of the cemented carbide tool materials can be improved. When the WC grain size is reduced to sub-micron or less, the hardness, toughness, strength, and wear resistance of the material can be improved, and the temperature required to achieve complete densification can also be reduced.

The grain size of ordinary cemented carbide is 3-5μm, the grain size of fine-grained cemented carbide is 1-1.5μm (micron level), and the grain size of ultra-fine-grained cemented carbide can reach 0.5μm or less (subs-micron, nano-level). Compared with ordinary cemented carbide with the same composition, ultra-fine grained cemented carbide can increase its hardness by more than 2HRA, and its bending strength can be increased by 600-800MPa.

Commonly used methods of grain refinement mainly include physical vapor deposition, chemical vapor deposition, plasma deposition, and mechanical alloying. Equal Channel Angular Extrusion (ECAE) is a very promising method of grain refinement, which is to put the powder in a mold and extrude it in a direction different from (not opposite to) the extrusion direction, and the cross-sectional area during extrusion is unchanged. The powder crystal grains processed by the ECAE process can be significantly refined.

Because the above-mentioned grain refining process method is still not mature enough, the nano grains are easy to grow into coarse grains during the cemented carbide sintering process, and the general growth of the grains will cause the material strength to decrease. A single coarse WC grain is often An important factor causing material fracture. On the other hand, the price of fine-grained cemented carbide cutting tools is relatively expensive, which also restricts its popularization and application.

Ⅱ. Coated cemented carbide tools

On the cemented carbide substrate with better toughness, by CVD (chemical vapor deposition), PVD (physical vapor deposition), HVOF (high velocity oxy-fuel thermal spraying) and other methods, a thin layer of wear-resistant metal compound can be applied. Combine the strength and toughness of the substrate with the wear resistance of the coating, thereby improving the overall performance of cemented carbide tools.

1. Coated cemented carbide tools have good wear resistance and heat resistance, and are especially suitable for high-speed cutting; due to their high durability and good versatility, they can be effectively reduced when used in small batches and multi-variety flexible automated processing. The number of tool changes improves the processing efficiency.

2. The coated carbide tool has strong anti-crescent wear resistance, stable cutting edge and groove shape, reliable chip breaking effect and other cutting performance, which is beneficial to the automatic control of the machining process.

3. The body of the coated cemented carbide tool has high dimensional accuracy after passivation and refinement treatment, which can meet the requirements of automatic machining for tool change positioning accuracy.

The above characteristics determine that the coated carbide cutting tools are particularly suitable for automatic processing equipment such as FMS and CIMS (Computer Integrated Manufacturing System). However, the use of coating methods still fails to fundamentally solve the problem of poor toughness and impact resistance of cemented carbide base materials.