The Structure and Mechanical Properties of WC–8 wt.% Co Hardmetal Produced by Cold and Hot Isostatic Pressing

Abstract

The structure and properties of tungsten carbide hardmetal with 8 wt.% Co produced by cold and hot isostatic pressing with the same starting powder mixture and conventional initial pressing of billets in metal dies were studied. The first batch of the samples was prepared by vacuum sintering of the pressed billets. The second batch was prepared by vacuum sintering followed by hot isostatic pressing of the billets at 5 MPa. The third batch was prepared by hot isostatic pressing at 200 MPa followed by vacuum sintering. The sintered samples had a density of 14.57 g/cm 3 in batch 1, 14.60 g/cm 3 in batch 2, and 14.63 g/cm 3 in batch 3. Microstructural analysis showed that cold isostatic pressing promoted more homogeneous and finer structure. According to the coercive force determination and structural analysis performed with scanning electron microscopy and X-ray diffraction, the average size of carbide grains was 1.315 m for the samples in batch 1, 1.396 μm in batch 2, and 1.062 m in batch 3. Determination of residual stresses indicated that they were compressive in both phases (WC and Co) of the batch 3 samples and tensile for the batch 1 and 2 samples. The average values of measured Rockwell hardness were 88, 87, and 90 HRA for the samples in batches 1, 2, and 3. Mechanical tests of the samples indicated that the bending strength and fracture toughness were 1820

Effect of Cold Isostatic Pressing and VC Grain Growth Inhibitor Addition on WC Grain Size and Mechanical Properties of WC-8Co Cemented Carbide

“…As reported in recent publications [12], [19] and which is consistent with the data obtained in this work CIP-ed samples have finer WC grain size compared to those that did not pass CIP. This implies that the Co mean free path in CIP-ed samples was decreased which was accompanied by a rapid increase in specific surface area of WC grains.…”

“…Thus, a significant volume of particles in the range of 1.0-1.6 µm plays a less important role during sintering than the largest ones. However, the high isostatic pressure of CIP primarily acts on the largest particles, possibly destroying them and preliminarily mechanically activating their surfaces, these mechanisms are described in detail elsewhere [12]. By making changes to the sintering processes, CIP significantly reduced the WC grain size in the sintered alloy.…”

“…Obviously, the cycles of formation and destruction are accompanied by the compaction of the green body. Previous research [12] established that the largest WC particles can be crushed with increasing CIP pressure.…”

“…In a recent study [12] which set out to determine the effect of cold isostatic pressing (CIP) on the properties of WC-8Co cemented carbide, it was shown that the CIP of samples before sintering was accompanied by a significant reduction in mean WC grain size compared to unCIP-ed samples.…”