Spark Plasma Sintering of Fine-Grained WC-Co Composites.

Cemented carbides WC-Co are one of the basic tool materials. They constitute over half of the currently used tools intended for machining. The main advantages of WC-Co cemented carbides are high hardness and abrasion resistance. The properties of WC-Co sinters depend mainly on the content of the binding phase, the sintering method and the grain size of the powder from which the sinters were made. The aim of this study was to produce fine-grained WC-Co composites using SPS (spark plasma sintering) technology, as well as examine the effect of the applied technology on the basic properties of WC-Co sinters: microstructure, hardness, phase composition, compaction degree and tribological properties. In the processes carried out, no additives affecting the reduction in grain growth were used. Sintering was conducted at a temperature of 1200 °C with a holding time of 10 min. The process occurred under a load of 100 MPa. Finally, the samples were cooled in a vacuum of 10-6 mbar. We measured the hardness using a Vickers hardness tester. We took hardness measurements along the diameter of the sintered samples. In order to ascertain the fracture toughness (KIC), we measured the radial crack length around the Vickers indentation and applied Shetty's formula. The tribological tests were carried out with a tribotester using the T-01 ball-on-disc method. The obtained data enabled the characterization of the wear process of the tested materials.

Optimization of Spark Plasma Sintering Technology by Taguchi Method in the Production of a Wide Range of Materials: Review.

This paper reviews the production of sinters using the spark plasma sintering method. SPS (spark plasma sintering) technology has been used for several decades, mainly in laboratories, to consolidate a huge number of both new and traditional materials. However, it is now more often introduced into practical industrial use, with equipment as early as the fifth generation capable of producing larger-size components at competitive costs. Although the mechanism of sintering with the use of this method is not yet understood, the effectiveness of the SPS process for the rapid and efficient consolidation of a wide range of materials with novel micro-structures remains indisputable. With a relatively wide variation in chemical composition, the structure allows the selection of appropriate consolidation parameters for these materials. The influence on the values of apparent density and mechanical properties depends on the parameters of the spark plasma sintering process. In order to achieve a density close to the theoretical density of sinters, optimization of the sintering parameters, i.e., sintering temperature, heating rate, sintering time, pressing pressure and protective atmosphere, should be carried out. In this paper, the optimization of spark plasma sintering of Si3N4-Al2O3-ZrO2 composite was carried out using the Taguchi method. The effects of four sintering factors, namely heating rate, sintering time, sintering temperature and sintering pressure, on the final density were investigated. Optimal sintering conditions were proposed and a confirmation experiment was conducted. The optimal combination of sintering conditions for spark plasma sintering (SPS) of Si3N4-Al2O3-ZrO2 composite for high apparent density was determined as A3-B3-C3-D2. Based on ANOVA analysis, it was found that the apparent density of sintering was significantly influenced by sintering temperature, followed by pressing pressure, sintering time and heating rate. Validation of the developed mathematical model predicting the apparent density of sinters showed close agreement between the predicted response results and experimental results.

Application of U-FAST Technology in Sintering of Submicron WC-Co Carbides.

This article presents the microstructure, hardness, fracture toughness coefficient KIC and phase composition of submicron WC-4Co carbides. The carbides were sintered using the innovative U-FAST (Upgraded Field Assisted Sintering Technology) method, from mixtures of WC-Co powders with an average WC grain size of 0.4 µm and 0.8 µm. The obtained sinters were characterized by a relative density above 99% of the theoretical density. The hardness of the obtained composites was above 2000 HV30, while the KIC coefficient was about 8 MPa m1/2.

Influence of Asymmetric Rolling Process on the Microstructure Properties of Bimetallic Sheet Metals.

This paper presents the results of research on the determination of the influence of kinetic asymmetry of work rolls on structural changes in hot-rolled bimetallic sheet metals. The tests were conducted on bimetallic samples composed of materials 10CrMo9-10 + X2CrNiMo17-12-2. The scope of the research included a comparative analysis for two cooling variants: I in water (freezing the structure immediately after rolling) and II for cooling in air. The research conducted showed that the introduction of asymmetric conditions to the rolling process results in a greater grain fragmentation in the so-called hard layer and does not have a negative effect on microstructural changes in the soft layer.

The Analysis of Erosive Wear Resistance of WC-Co Carbides Obtained by Spark Plasma Sintering Method.

WC-Co (tungsten carbide-cobalt) composites are widely used in industry, wear-resistant parts, and cutting tools. As successful tool materials, WC-Co carbides are widely applied in metal cutting, wear applications, chipless forming, stoneworking, wood, and plastic working. These materials are exposed to severe solid particle erosion by sand particles, such as in the wood industry. During the production of furniture with HDF (High Density Fibreboard), MDF (Medium Density Fibreboard), or OSB (Oriented Strand Board), there are observed problems with tool erosion. Contamination, mainly of the HDF by sand, is quite often, which is why all tools used for the machining of such materials are exposed to erosion by sand particles. Although many studies have been performed on the erosion of various metals, and erosion models exist to predict their erosion behavior, the issue is still relevant. The aim of the study was to determine the effect of grain size (submicron, ultrafine) and the manufacturing technology (SPS-Spark Plasma Sintering, conventional) used on the erosive properties of WC-Co sintered carbides. Sinters produced by the SPS method with different sizes of WC grains and commercial samples were used for the tests. Ten two-hour cycles were carried out under medium conditions of quartz sand and quartz sand with 10% SiC added. Used samples were characterised using scanning electron microscopy (SEM) and roughness was determined. Furthermore, erosion studies allowed individuating a wear mechanism as well as the possibility to foresee cutting performance in prospective application.

Properties of WCCo Composites Produced by the SPS Method Intended for Cutting Tools for Machining of Wood-Based Materials.

This paper presents the possibility of using the Spark Plasma Sintering (SPS) method to obtain WCCo composite materials. Such materials are used as cutting blades for machining wood-based materials. Two series of composites, different in grain size and cobalt content, were analyzed in the paper. The produced materials were characterized using Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), and tribological properties were determined. In addition, preliminary tests were carried out on the durability of the blades made of sintered WCCo composites while machining three-layer chipboard. The results of the microstructure analysis proved that the SPS method makes it possible to obtain solid composites. Phase analysis showed the occurrence of the following phases: WC, Co, and Co3W9C4. The lowest friction coefficient value was found in samples sintered using powder with an average primary particle size of 400 nm (ultrafine).

Shaping Microstructure and Mechanical Properties of High-Carbon Bainitic Steel in Hot-Rolling and Long-Term Low-Temperature Annealing.

Based on the research results, coefficients in constitutive equations, describing the kinetics of dynamic, meta-dynamic, and static recrystallization in high-carbon bainitic steel during hot deformation were determined. The developed mathematical model takes into account the dependence of the changing kinetics in the structural size of the preliminary austenite grains, the value of strain, strain rate, temperature, and time. Physical simulations were carried out on rectangular specimens. Compression tests with a flat state of deformation were carried out using a Gleeble 3800. Based on dilatometric studies, coefficients were determined in constitutive equations, describing the grain growth of the austenite of high-carbon bainite steel under isothermal annealing conditions. The aim of the research was to verify the developed mathematical models in semi-industrial conditions during the hot-rolling process of high-carbon bainite steel. Analysis of the semi-industrial studies of the hot-rolling and long-term annealing process confirmed the correctness of the predicted mathematical models describing the microstructure evolution.