Materials Science Forum Vols. 534-536

Abstract: Nano-grained WC-10Co hardmetal can be made by doping a new invented VC-based multi-grain-growth-inhibitor and suitable technical processing. The specifications for quantitative measurement of the grain size of WC in the alloy were investigated. It is very important to obtain the SE images of the alloy with good contrast and clear profile of WC grains by FESEM; then the linear intercept (LI) method was used to quantitatively measure the intercepts of WC grains. When the surveyed intercept numbers of WC grain exceeded 200, the statistic data for the mean grain size of WC were reproduced. The discriminative minimal grain size of used LI method was 12 nm; the maximum intercept of WC grain was 109 nm; the average intercept of WC grains was 45 nm and the corresponding 3D mean grain size of WC was 70 nm which is agreeable with the XRD outcome.

Abstract: Cr-C-Ni composites were synthesized in situ from elemental powders of Cr, Ni and C by high energy milling followed by reactive sintering. The milled powders with the grain size in nano-scale were pressed to compacts and sintered. During the thermal treatment that was performed after the pressing the chromium carbide was formed first and then the Cr3C2-Ni cermets were sintered in one cycle. The interface between the binder phase and the carbide grains of the in situ composite has a good bonding strength as it is not contaminated with oxidation films or other detrimental surface reactions. The microstructure of such cermets is fine-grained and more homogeneous than that of cermets produced by conventional method. As a result the cermets have higher hardness, transverse rupture strength and 1.2-2 times higher wear and erosion resistance.

Abstract: This paper presents a detailed study of large grains carried out by transmission electron microscopy in two WC-Co alloys, one W rich and the other C rich. In the W rich alloy, some large grains are found in contact with the η phase while no connection of the large grains with graphite particles can be pointed out in the C rich alloy. The C content greatly influences the morphology of large grains: they are flatter in the C rich alloy with smoother interfaces. Whatever the C content, they contain few dislocations compared to matrix grains except in a small area where a dense network is often present. One or even several small WC grains with a small angle misorientation or with a Σ=2 coincidence relationship are often found inside the large grains. They have likely been engulfed during the growth of the large grains owing to the low boundary energy.

Abstract: The present study describes the wear and mechanical behaviour of some carbide composites (TiC-base cermets and WC-base hardmetals) in cyclic loading applications (blanking of sheet metal). Adhesive wear as well as fatigue endurance were tested, followed by XRD measurements. The results show that the blanking performance of a carbide composite is dependent on its level of resistance to adhesion wear and fatigue sensitivity. XRD measurement revealed that fatigue damage is preceded by plastic strain in both the ductile binder and the brittle carbide phase.

Abstract: Magnetron sputtered TiN, (Ti, Al)N and TiN/(Ti, Al)N multilayer coatings grown on cemented carbide substrates have been characterized by using electron probe microanalysis (EPMA), X-ray diffraction (XRD), scanning electron spectroscopy (SEM), nanoindentation, scratcher and cutting tests. Results show that TiN coating is bell mouth columnar structures, (Ti, Al)N coating is straight columnar structures and the modulation structure has been formed in the TiN/(Ti, Al)N multilayer coating. TiN/(Ti, Al)N multilayer coating exhibited higher hardness, better adhesion with substrate and excellent cutting performance compared with TiN and (Ti, Al)N coating.

Abstract: WC-10Co-0.8VC nanocrystalline powders were sintered by spark plasma sintering (SPS) and hot pressing sintering (HPS), and the microstructure and properties were compared. Results show that, sintered at 1300°C, the sample prepared by SPS for only 3 minutes has higher density than that prepared by HPS for 60 minutes. SEM and SPM observation shows SPS at 1200°C has a more uniform and finer microstructure, and most of the WC grains are smaller than 100nm. It has a relative density of 95.1%, HV30 of 1887, and KIC of 11.5 MPam1/2. If a suitable sintering parameter is chosen, SPS is a promising consolidation technique to prepare nanocrystalline WC-10Co-0.8VC with improved properties.

Abstract: Multilayered coatings on tungsten carbide cutting tools are widely used for enhancing cutting performance. In this paper, we review the CVD TiC/TiCN multilayer as a function of the multilayer period. The TiC/TiCN multilayers in initial stage show preferred (220) orientation but shifts to (200) orientation with decreasing multilayer period. The nanohardness of TiC/TiCN multilayers were found to increase with decreasing multilayer period and shows a maximum of 23.8 GPa at a period = 33.5 nm.

Abstract: To improve the fracture strength and wear resistance of WC-Co cemented carbide, various technologies have been developed related producing the nano crystalline. There have been extensive studied conducted to retard grain growth during liquid phase sintering. However, when this inhibitor is added by simple mixing, a micro-pores forms during sintering In this study, WC-Co nanocrystalline powders with grain growth inhibitor in the site were prepared by MTP (Mechano-Thermic carburizing Process) to minimize this formation of micro pores and to retard grain growth effectively during sintering. In addition, then the phase and grain size of WC-Co nanocrystalline powders were evaluated according to the condition of MTP.

Abstract: The effects of substrate surface treatment on TiAlN PVD coating on submicron cemented carbide was investigated. Surface roughness and morphology were improved by physical treatment such as micro blasting, brush lapping and plasma etching with decreased Co content in the surface layer. The Co content in the surface does not seem to affect coating adhesion or the quality considerably. The smoother surface induced by the surface treatment improved TiAlN adhesion and surface roughness. The insert treated by blasting and lapping before coating showed a better cutting performance than those with ultrasonic treatment. It was concluded that the substrate surface characteristics are closely related to the performance of the TiAlN coated inserts.