Since the wear resistance and toughness cemented carbide tool material is not easy to balance, so that the user can select the appropriate tool material according to the specific object to be processed and the processing conditions in many carbide grades, which to choose and carbide tools management inconvenience. To further improve the overall carbide cutting tool materials, current research focus includes the following aspects:
(1) grain refinement
By refining the hard phase grain size, increasing the surface area between the hard phase crystallization and enhance the binding force between the grains, carbide cutting tools can make the material strength and wear resistance are improved. When the WC grain size is reduced to less than submicron, hardness, toughness, strength, wear resistance, etc. can be improved to achieve complete densification temperature required can be reduced. Common carbide grain size 3 ~ 5μm, fine grain carbide grain size of l ~ 1.5μm (micron), ultra-fine grain carbide grain size up to 0.5μm or less (submicron, nanoscale). Ultra-fine grain carbide compared with the same general composition carbide, the hardness can be increased more than 2HRA bending strength can be increased 600 ~ 800MPa.
Commonly used methods include grain refinement process of physical vapor deposition, chemical vapor deposition, plasma deposition method, a mechanical alloying method. Equal lateral extrusion method (ECAE) is a method for grain refinement process promising. The method is that the powder in a mold, and a direction different from the pressing direction (nor vice versa) in the extrusion direction, and the cross-sectional area constant during extrusion. After ECAE powder grain processing technology significantly refined.
Due to the above process for grain refinement is still not mature enough, so in the process of sintering carbide nanocrystals easy soaring into coarse grains, while grains grow will lead to widespread decline in material strength, the individual is often coarse WC grains important factor in causing the fracture. On the other hand, fine grain carbide more expensive, their application constraints also play a role.
(2) coated carbide
The toughness of the cemented carbide substrate by CVD (chemical vapor deposition), PVD (physical vapor deposition), HVOF (High Velocity Oxy-Fuel Thermal Spraying) methods such as coated with a thin wear-resistant metal compound, It allows toughness and abrasion resistance of the coated substrate combination and improve the overall performance of carbide cutting tools.
Coated carbide tools with good wear resistance and heat resistance, especially for high-speed cutting; because of its high durability, versatility, and flexibility for automated processing of small quantity and variety of time can effectively reduce the number of tool changes improve processing efficiency; Coated carbide tool crater wear resistance ability, stable and groove cutter blade, chip breaking effects and other cutting and reliability of the automatic control of the process; Coated carbide tool after passive matrix, refined processing high dimensional accuracy, can meet the automated processing tool change positioning accuracy.
These characteristics determine the coated carbide tools especially suitable for FMS, CIMS (Computer Integrated Manufacturing System) and other automated processing equipment. However, the use of the coating method have not been fundamentally resolved cemented carbide substrate material toughness and poor impact resistance problem.
(3) surface, the overall heat treatment and cyclic heat treatment
Strong toughness of cemented carbide surface nitriding, boronizing and other treatment, can effectively improve the surface abrasion resistance. For better wear resistance but poor toughness cemented carbide overall heat treatment, can change the composition and structure of the bonding material, reducing contiguity WC hard phase, thereby enhancing the strength and toughness of cemented carbide. The cyclic heat treatment process to alleviate or eliminate the stress between the grain boundaries can improve the overall performance of carbide materials.
(4) adding the rare metal
Add carbide material TaC, NbC carbides and other rare metals, can supplement with the original hard phase WC, TiC solid solution combine to form complex structures, thus further strengthening the hard phase structure, and can restrain hard phase grain growth, enhance organizational uniformity and so on, to improve the overall performance of cemented carbide great benefit. In the ISO standard P, K, M carbide grade class, and this has added Ta (Nb) C carbide (especially M class grades in more).
(5) adding rare earth elements
Add a small amount of carbide materials of rare earth elements and yttrium, which can effectively improve the toughness and bending strength, wear resistance also improved. This is because the rare earth elements can enhance the hard phase and binder phase, clean grain boundary carbides and solid solution to improve the wettability of the binder phase. Rare earth element cemented carbide grade most suitable for roughing, semi-finishing grades can also be used. In addition, in such carbide mining tools, anvil, Carbide drawing dies and other tools also have broad application prospects. China is rich in rare earth resources, research and rare earth element in the alloy also has a high level.