Papers by Keyword: Hard Metal

Abstract: Micro EDM (Electrical Discharge Machining) is a known nonconventional process for the machining of hard to cut materials. Due to its ablating nature based on melting and evaporation through heat induced by electrical discharges, it can function independently of the hardness, toughness or brittleness of the workpiece. Thus micro EDM is a possible process to fulfill the requirements of higher precision and high quality in carbide metal machining. Thereby the surface and the roughness of machined carbide metals depend on the discharge energy used. For machining carbide metals with high surface quality pulse generators with ultra-short discharges are required. This paper presents the development of a two-staged pulse generator with the ability to provide ultra-short pulses by using a two-staged pulse. The current and voltage signals of the discharges were recorded and their characteristics were analyzed.

Abstract: Extensive work has been performed on WC-Co hard metals for mining tools, tool inserts and other components. Cobalt is widely used as the binder metal because it’s good wetting behavior and solubility. However, the cost is high. Fe-Cr-Ni alloys show similar characteristics to Cobalt regard to melting temperature and crystal structure. Additionally, Fe-Cr-Ni alloys are a less expensive and nontoxic alternative. The present work analyze sintering characteristics of the WC / Fe-Cr-Ni alloys composite and development of new sintered hard metal composite for mining tools. The composite WC-316L was processed via Powder Metallurgy and sintering was performed at different temperatures: 1200^oC, 1300^oC and 1400^oC rate and 20^oC and isotherm 1hour in vacuum atmosphere. The composite sintered WC-316L was characterized by XRD, SEM and Vickers micro hardness test. The samples processed at temperatures of 1200^oC and 1300^oC showed considerable porosity, heterogeneity microstructure, low density relative and low Micro hardness, 300 HV and 700 HV, respectively. The samples sintered at temperature 1400^oC showed higher homogeneity microstructure compared to the samples sintered at temperatures of 1200⁰C and 1300⁰C, higher density relative, 86%, and micro hardness value compatible with the composite WC-Co, 1890 HV.These analyzes infer that stainless steel can be used instead of cobalt.

Abstract: The main requirements of carbide metal working are higher precision and high quality surface which can be fulfilled by electrical discharge machining. This procedure is accompanied with formation of heat affected zones (white layers) during the discharge process negatively. Therefore, the essential post-processing reduces the efficiency of this process and shows the importance of process energy sources (PES) with ultra short discharge in favor of a clearly differentiated cutting volume. By means of simulations of crater geometry and channel expansion the influence of discharge rise time is defined as determining factor for the cut volume and formation of white layers. The technological section presents two different approaches of realizing ultra-short pulses.

Abstract: t has been established experimentally that irradiating the sample of tungsten carbide hard metal spray-coated by titanium layer 1-2 μm thickness by high-intensity electron beam resulted in generation of a gradient multi-phase nanostructured layer of microhardness higher than that of untreated material by a factor of 2.5.

Abstract: In current research, WC dissolution phenomenon happened in TIG welds was investigated and discussed. And the element diffusion was studied using area-scanning method. The results showed that the WC dissolution phenomenon always happened near WC-Co/Welded seam interface. Moreover, the amount of WC dissolved in welds became less from WC-Co, welds to invar alloys. WC dissolution happened in welded seam induced by tungsten arc led to the WC grain growth (60µm or so) and WC shape changes. The grain boundary (GB) between different WC particles during WC aggregation was also confirmed and WC grain growth was owed to the WC aggregation during the processing of WC dissolution.

Abstract: The experiment of ultrasonic assisted pulse electrochemical compound finishing is carried in this paper. The machining principle of the compound finishing is discussed in this paper. Processing experiments of compound finishing are carried out to study the effects of the main processing para- meters, including the particle size, the ultrasonic vibration amplitude, the minimum gap between the tool head and workpiece and the pulse voltage, on the material removal rate and the surface quality for hard and brittle metal materials. The curves of the corresponding relationships are also obtained. The study indicates that the processing velocity, machining accuracy and surface quality can be improved under the compound finishing, obtaining the processing technology conductions of the compound finishing. Introductions

Abstract: Inserts of drill bits used in perforation of wells are employed to cut many different kinds of stone. The material that shows the best performance on this application is the WC+Co+Diamond composite, obtained via powder metallurgy. However, heterogeneous microstructural aspects in these composites may impair their efficiency. On this work, WC+6%Co-based composites were obtained via high pressure sintering at 5.0 GPa, with diamonds, WC and Co powders. The particle size of the diamond was 400/315 μm, and for the WC and Co, 100/63 μm. Part of the samples also received 2wt%CrB2 as a doping agent. Wear tests were carried out in an abrasimeter with a maximum axial load of 50 kg. Linear and volumetric wear indices achieved values of 821∙10-6 g/m and 10.7 g/m3, that are superior to inserts produced via conventional powder metallurgy.

Abstract: The purpose of this study is to prescribe the influence of Si in WC-Ni Hard Metal. For the manufacture of WC-Ni Hard Metal according to Si content, the researcher manufactured WC-Ni mixed powder which 0wt.%~1.5wt.% of Si was added to after selecting Ni which a fixed amount of B was added to, and then manufactured sintered body by implementing vacuum-sintering to the mixed powder. This study implemented the analysis with HRA, TRS, XRD, SEM, and EPMA to observe densification, alloying reaction, and mechanical properties of the sintered body. In WC-Ni Hard Metal, shrinkage showed a tendency to increase as Si content increased. It is considered that the densification was promoted during liquid phase sintering, because a melting point of binder metal got lower as Si content increased. The hardness of WC-Ni Hard Metal was kept uniformly up to 0.6wt.%Si, and then it showed the tendency to increase from the level of 0.9wt.%Si. It is considered that the hardness of B and Si added to Ni binder metal formed BNi3 phase and Ni3Si phase which had high hardness, and these compound phases restrained the growth of WC particle. It is considered that transverse rupture strength of WC-Ni Hard Metal according to the increase of Si content was increased by the decrease of mean free path of WC particle caused by the improvement of fluidity according to the restrained growth of WC particle by of BNi3 phase and Ni3Si phase, and caused by the improved fluidity according to the decreased melting point of Ni binder metal.

Abstract: The obtained generalized equation for description of a fundamental property of solid crystalline materials i.e. first-order phase transition of the grain boundaries with formation of two-dimensional liquid has been used for calculating of transition temperature of any metals, which value lies in range 0.55 – 086 of melting point. Based on these conclusions to develop strategies for effective forming of coatings by synthesis of nitrides and carbonitrides on surface layers of hard metals and chromium steels have been made. It was shown the hardening of thin surface layer (0.1-0.5mm) due enriched of a nitrides in steels and carbonitrides with diamond like structure and strengthening the following layer by recristallization of W carbides in WC-Co and WC-TiC-Co hard metal. These result to increase of alloys hardness, ductility, and resistance to wear and decrease of sensibility to fragile rupture. Industrial tests have been made.

Abstract: TiC−Fe system cermets and TiC−SUS310L (TiC−SS) system cermets with fully relative density have been produced from elemental powders via self-propagating high-temperature synthesis (SHS) reaction combined with pseudo-hot isostatic pressing. X-ray diffraction (XRD) analysis showed that the SHS products consist of TiC and the binder phase of Fe or SS. Metallographic analysis revealed TiC particles of several micrometer size were homogeneously dispersed in the binder phase. Regardless of differences in the binders, both cermets have similar tendencies: their relative densities increased and their hardness and compressive strengths decreased with increases in the volume fraction of either Fe or SS. In addition, the cermets used stainless steel as the binder had twice superior corrosion resistance to those used iron and also their hardness and compressive strength showed excellent values.