Papers by Keyword: Hard Metal

Abstract: Powder injection moulding (PIM) is a cost effective powder metallurgical process for the fabrication of small, complex-shaped components for high performance applications. A binder system, which comprises a major fraction of polyethylene glycol (PEG) and a minor fraction of a very finely dispersed polymethyl methacrylate (PMMA), has been applied for tungsten carbide (WC) – cobalt (Co) hardmetal powders. PEG can be removed rapidly by water leaching and PMMA is removed by subsequent pyrolysis when the components are ramped up to the sintering temperature. In this work, the development of feedstock formulations and of the processing parameters for a successful injection moulding and to achieve high density has been investigated. The present study has demonstrated that the binder can be employed for the production of WC-Co hardmetal components by PIM process. The maximum density achieved thus far is 97% of the theoretical value.

Abstract: When mixtures of Fe, Al, Ti and B powders were heated, the combustion synthesis, or SHS, reaction occurred and produced a TiB2 particle dispersed FeAl-based composite. The TiB2 particle size increased with increasing TiB2 volume fraction from 0.3 to 0.8, which was considered to be due to the fact that the adiabatic temperature of the reaction increases with the increase in TiB2 concentration in the composite due to the large formation enthalpy of TiB2. The TiB2 particle size decreased with increasing preheating time, temperature and pressure before the SHS reaction. It was suggested that partial reaction between elemental powders before the SHS reaction reduced the adiabatic temperature and hence the TiB2 particle size. The Vickers hardness of the composite varied from 500 to 2000 depending on the microstructure. This method was applied to the production of TiC-FeAl, TiC-Fe, TiB2-Fe composites.

Abstract: FeAl-TiB2 composites have been combustion synthesized from mixtures of Fe, Al, Ti and B powders. When the powder mixture was heated in vacuum to approximately 900 K, an abrupt increase in temperature was observed, indicating that the combustion synthesis reactions occurred in the powder mixture. X-ray diffraction analyses revealed that the combustion-synthesized sample consisted of only FeAl and TiB2. Metallographic investigations using a scanning electron microscope revealed that fine TiB2 particles were dispersed in FeAl matrix phase. As the volume fraction of the TiB2 particles increased from 0.3 to 0.8 by controlling the powder mixture composition, the average TiB2 particle size increased to 1 to 7 μm and the average Vickers hardness of the composites increased from 800 to 1600. This method has been applied to the fabrication of some other ceramic particle dispersed metal matrix composites such as Fe-TiC and FeAl-TiC systems.

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: 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: Production scale inert atmosphere microwave sintering has not been successful yet, mainly because of lack of suitable equipment. For sintering in air microwave furnaces are available at different industrial scale, e.g., gas-microwave hybrid heated batch kilns or microwave “adiabatic casket” tunnel kiln [1]. Inert atmosphere furnaces require vacuum and gastight coupling of microwave energy. In the State of the Art technology, microwave-coupling windows represent a heat sink inside the sintering furnace. Although, radiation heat loss at temperatures > 1600 °C can be reduced by using a thermally insulating casket inside the microwave furnace, heat loss and temperature gradients caused by the microwave transparent windows are still not acceptable. Therefore, a new concept was developed assisted heating in inert atmosphere sintering furnaces, enabling high power microwave coupling by means of high temperature resistant antennas [2]. This paper presents microwave sintering results of commercial powder metallurgical (PM)-parts, details of the antenna system and the processing technology.

Abstract: The present work shows the microstructural and mechanical results obtained in joints WC-Co / steel 90MnCrV8 (high strength steel). The joints were carried out using diffusion welding processes and soft interlayers Cu-Ni. The binary Cu-Ni alloys were obtained by electrochemical deposition techniques. The microstructural and mechanical changes provoked in the steel, due to heat treatments, were studied in order to know plastic deformation during the joints. The diffusion welds were obtained in an Edwards vacuum furnace (10-3 - 10-4 Pa), three welding temperatures were used, (825 °C, 850 °C and 875 °C) and 30, 45 and 60 minutes, as welding times. The constant pressure was 5 MPa. The welding interface microstructure was studied by scanning electron microscopy (SEM-EDX). In order to determine the mechanical behaviour of all joints were carried out shear tests. The optimum results were obtained at 850 °C / 45 min and 850 °C / 60 min. Nevertheless, the diffusion welding conditions allowed attaining high quality welding interfaces in all joints of WC-Co / 90MnCrV8

Abstract: The objective of this work was to study the effect of the Ni distribution on the reactivity and densification of WC-(Fe/Ni/Cr) composite powders. For such, stainless steel AISI 304, was used as a binder base composition which was enriched with Ni by three different processing methods: WC sputter deposition using a target of stainless steel with Ni discs, conventional wet milling of commercial powders (WC, stainless steel and Ni powders) and a previous coating of the WC particles with Ni, followed by the conventional mixing of this coated powder with stainless steel powder. The reactive sintering of these composite powders with identical compositions was investigated. The powder compacts were characterized by scanning electron microscopy and X-ray diffraction with Rietveld analysis to quantify de crystalline phases present.

Abstract: Hardmetal is usually processed by the conventional powder technology techniques: mix of WC + Co powders compacted and liquid phase sintering. A new method to process hardmetal parts is hereby described. Parts of WC-15%wt Co were processed by using high pressure – high temperature sintering. It was used the pressure of 5GPa, temperatures of 780-1200-1350-1400oC, and times of 2-4 minutes of sintering. Results are shown as a function of micro-structural evolution, densification, and hardness measurements.