Advances in alloy design aspects of cemented carbides

A coated cemented carbide alloy composed of the base material comprising a WC-base cemented carbide alloy containing 4-10 wt.% of cobalt as the binder phase and the coating layer with the overall thickness of 5-100 mu m formed on the surface of the alloy. The alloy as the base material has a cross section, after being mirror-finished, wherein at least 70 % of the WC crystals as the hard phase comprise either fine particles A with a diameter of 0.1-1 mu m or fine particles B with a diameter of 3-10 mu m and the areal ratio (SA/SB) of the particles A and B ranges from 0.22 to 0.45. The coating layer is composed of at least one layer containing at least a carbide, nitride, carbonitride, carbonate or boronitride of titanium, zirconium and/or hafnium and at least one layer containing at least an oxide of titanium, zirconium or hafnium or Al2O3.

Cemented carbide alloy for cutting tool and coated cemented carbide alloy

The effects of compaction pressure on properties of carbide cutting tools containing 80·5 wt-%WC, 5 wt-%TiC, 5 wt-%TaC–NbC and 9·5 wt-%Co were studied. These tools were formed by powder metallurgy with different compacting pressures ranging from 77 to 231 MPa (5–15 tons in−2) and sintered in a vacuum furnace at a constant sintering temperature (1450°C) and at a constant heating and cooling rate of 5°C min−1. Green and bulk densities, shrinkage and hardness of the produced compacts were measured. Tool cutting performance has been assessed based on machining a medium alloyed steel workpiece under different cutting conditions and measuring the tool flank wear and the workpiece surface roughness. The microstructure of the compacts was metallographically examined using scanning electron microscopy. The results have revealed that both densities and hardness figures increase with increasing compaction pressures, while shrinkage decreases. Cutting performance has not demonstrated a substantial improvement...

Effect of compacting pressure on microstructure and mechanical properties of carbide cutting tools

In the present study, WC-10Co with TiC, VC and (Ta, Nb)C as the inhibitors to the grain growth was prepared using high energy ball milling and the subsequent HIP process at various temperatures. Phase evolution and microstructural studies were performed for the milled and sintered samples by x-ray diffraction, vibrating sample magnetometry, field emission scanning electron microscopy and transmission electron microscopy. Also, the density and microhardness of the sintered samples were measured. It was found that densification and grain-growth rate were sensitive to the sintering temperature, type and overall content of the additives. The samples sintered at the higher temperature showed better densification and hardness, with lower porosities. The additives were found to have significant influence on the microstructure and properties of the sintered products. Sintered samples containing additives had considerably improved microhardness, but densification was lowered up to 4.8%. However, the highest microhardness was 1920 HV for the sample with the three types of additives sintered at 1480 °C.

Sintering Behavior of WC-Co with Additives of TiC, VC, and (Ta, Nb)C: Microstructural and Mechanical Features

Specimens of TT7K12 alloy with a combined carbon content of 0.92-0.97 and of TT20K9 alloy of 0.91-0.95 of stoichiometric have a WC+(Ti,W,Ta)C+Co three-phase structure. The width of the WC+(Ti, W, Ta)C+Co three-phase area is 0.26-0.25% C. With a reduction in carbon content the grain size of the WC and (Ti, W, Ta)C phases decreases. An increase in carbon content in the alloy within the limits of the area of three-phase equilibrium leads to a decrease in the lattice parameter of the cobalt phase caused by the decrease in the content of tungsten and titanium dissolved in it, which corresponds to the results of earlier investigations of the WC-Co, TiC-WC-Co, and TiC-WC-TaC-Co systems. Alloys with a combined carbon content of 0.92-0.95 of stoichiometric possess the best combination of properties with the maximum coefficient of life and high bend strength.

Influence of carbon on the structure and properties of TiC-WC-TaC-Co sintered carbides

An investigation was conducted to study the variation of properties of a WC–TiC–TaC–NbC–Co alloy with carbon content. Carbon content was varied by adding tungsten and/or carbon black to the powder mixture. Lattice parameter measurements by X-ray diffraction showed the maximum solubility of tungsten in cobalt to be ∼10%. Besides α-cobalt, the presence of e-cobalt was also observed. There is little change in cobalt lattice parameters, hardness, and coercive force outside the region where three phases are present. Although toughness reaches a maximum above the stoichiometric carbon content, optimum machining performance is obtained at a rather lower carbon content. With 5–8% tungsten in solution in the binder, the binder strength is improved, which explains the satisfactory machining results. PM/0193

F. Zeman

Papers

Influence of Carbon Content on WC–TiC–(TaNb)C Cemented Carbides