Intrusion features of a high-speed striker of a porous tungsten-based alloy with a strengthening filler in a steel barrier

The complex problem of increasing the penetrating power of strikers based on highly porous tungsten composites is considered by improving their strengthening properties by alloying the hardening components under high-speed collision conditions. Using the method of liquid-phase sintering, we fabricated samples of strikers based on a porous WNiFeCo alloy (tungsten + nickel + iron + cobalt), alloyed with tungsten carbide with cobalt (WCCo8) and titanium-tungsten carbide (TiWC). Dynamic tests of the strikers from the developed alloys were carried out at the collision velocity with a steel barrier of the order of 2800 m/s. The penetration depth of the striker based on a porous WNiFeCo alloy doped with tungsten carbides is 30% higher than the penetration depth of a striker of a monolithic WNiFe-90 alloy (tungsten + nickel + iron with a tungsten content of 90%).     

Effect of tungsten addition on thermal conductivity of graphite/copper composites

Graphite/copper composites with high thermal conductivity were fabricated by tungsten addition, which formed a thin tungsten carbide layer at the interface. The microstructure and thermal conductivity of the composite material were studied. The results indicated that the insertion of tungsten carbide layer obviously suppressed spheroidization of copper coating on the graphite particles during the sintering process, and decreased the interfacial thermal resistance of the composites. Compared with the graphite/copper composites without tungsten, the thermal conductivity of the obtained composites was increased by 43.6%.     

Microstructure of alumina reinforced with tungsten carbide

Carbides and nitrides reinforced alumina based ceramic composites are generally accepted as a competitive technological alternative to cemented carbide (WC-Co). The aim of this work was to investigate the effect of dispersed tungsten carbide (WC) on the microstructure and mechanical properties of alumina (Al₂O₃). Micron size alumina and tungsten carbide powders were mixed in a ball mill and uniaxially pressed at 1600°C under 20 MPa in an inert atmosphere. The hardness of WC reinforced alumina was 19 GPa and fracture toughness attained up to 7 MPa m^1/2. It was demonstrated by TEM analysis that coarse, micrometersized tungsten carbide grains were located at grain boundaries of the alumina matrix grains. Additionally, sub-micrometer tungsten carbide spheres were found inside the alumina particles. Crack deflection triggered by the tungsten carbide at the grain boundaries of the alumina matrix is supposed to increase fracture toughness whereas the presence of intergranular and intragranular hard tungsten carbide particles are responsible for the increase of the hardness values of the investigated composite materials.     

Furnace-melted surface layers from carbide hard alloy powder compounds

No technological difficulties were encountered in the processing of pseudo-hard alloys in the form of powder compounds of conventional nickel-based hard alloys with carbides. The alloy greatly influences the resulting structures of the surface layers. Under some processing conditions tungsten carbide is completely dissolved by the molten alloy matrix. Hard phases based on chromium carbide form on cooling. The induced chromium carbide, Cr₃C₂, retains its structure while absorbing large amounts of iron into its matrix. It can be concluded that not only alloying properties but also to a great extent structural criteria determine the stability of the applied supplementary hard phases.     

Processing and Performance Characteristics of Aluminum-Nano Boron Carbide Metal Matrix Nanocomposites

In this research work, ultrasonic cavitation-assisted casting process was used to fabricate the aluminum alloy-nano boron carbide metal matrix nanocomposites. The optical microscopy results revealed the refined matrix grains in the microstructure of the aluminum alloy-nano boron carbide composites. Boron carbide nanoparticles were uniformly distributed in the aluminum alloy matrix, which can be confirmed by scanning electron microscopic images. The aluminum alloy-nano boron carbide composites show increased dislocation density, compared to the monolithic alloys, which was observed from the transmission electron microscopic images. The addition of nano-boron carbide in aluminum alloy matrix significantly improved its hardness and tensile strength, while the good ductility and impact resistance of the aluminum alloy was almost retained. The results of the dry sliding wear pin-on-disc tests showed improved wear resistance properties of aluminum alloy-nano boron carbide composites compared to the monolithic aluminum alloys.     

Cutting Edge Wear of Tungsten Carbide Tool in Continuous and Interrupted Cutting of a Polymer Composite

An experimental study was conducted to evaluate the performance of C6 tungsten carbide, C2 tungsten carbide, and Polycrystalline Diamond (PCD) inserts in cutting Graphite/Epoxy (Gr/Ep) composites. Continuous and interrupted cutting tests under dry conditions were made to cut woven fabric and tape Gr/Ep composites. It was found that continuous cutting mode and high cutting speeds significantly reduce tool life of carbides. Machining of tape Gr/Ep reduces the tool life more than the machining of fabric work pieces. Also, C2 grade carbide inserts had a longer tool life than C6 carbide inserts despite the type of work piece or machining condition used. It was observed that a PCD insert's life was about 100 times of C2 carbide inserts during continuous cutting and at high speeds.     

The role of silicon in wetting and pressureless infiltration of SiCp preforms by aluminum alloys

Silicon plays an important role in the production of Al/SiC metal matrix composites. As an alloying element in aluminum, silicon retards the kinetics of the chemical reactions that result in the formation of the unwanted intermetallics Al₄C₃ and Al₄SiC₄. As a thin coating on silicon carbide, silicon becomes an active participant in a thermally activated chemical reaction that enhances wetting of silicon carbide by aluminum alloys. Consequently, Al/SiC composites made with siliconized silicon carbide and silicon rich aluminum alloys show mechanical properties that are significantly different from those of similar composites produced with unsiliconized silicon carbide or with aluminum alloys that do not contain silicon. It is shown that a silicon coating on SiC significantly enhances wetting of SiC particles by aluminum alloys, reduces porosity, does not affect the modulus of elasticity, but decreases the modulus of rupture of Al/SiC metal matrix composites.     

Prospects of producing hard alloys based on submicron and nanoscale W and WC powders prepared by a chemical metallurgy process and with the use of self-propagating high-temperature synthesis

We present a brief review of research and design work aimed at producing tungsten-containing hard alloys for various applications. We examine the feasibility and prospects of using a chemical metallurgy method and self-propagating high-temperature synthesis (SHS) for the preparation of submicron and nanoscale hard-alloy powders as a key component of highly efficient state-of-the-art materials and products. Particular examples are presented of the use of submicron and nanoscale powders for the preparation of TVS tungsten-based heavy metallic alloys and VK tungsten carbide hard alloys for various applications. Their application fields are discussed and their properties are compared to those of their analogs produced by conventional powder metallurgy methods. Using the SHS of tungsten carbide as an example, we demonstrate a particular path from research to commercialization (from the discovery of SHS processes to commercialscale production) of key modern engineering materials: tungsten-based heavy alloys and tungsten carbidebased hard alloys.     

A Study of the Influence of Phase Composition of Cutting Inserts Made of Diamond–Tungsten Carbide Nanocomposite on the Process of Finish Turning of Aluminum Alloys and Brass

The effect of phase composition of cutting inserts made of diamond–tungsten carbide nanocomposite on cutting forces, friction coefficient in the cutting zone, and acoustic emission signal in finish turning of aluminum alloys and brass has been studied. It has been found out that the amount of 30 to 40 wt % tungsten in the initial mixture ensures sintering of a tool composite with the most favorable phase composition for turning aluminum alloys and brass.     

The formation of tungsten carbide in cobalt-base wear-resistant coating alloys

Tungsten carbide-cobalt alloys cannot be produced by melting because of a peritectic reaction in the W-C system; they are produced by sintering. Tungsten carbide-cobalt powders (mixed, agglomerated, sintered) can be plasma sprayed or deposited by other techniques but they cannot be fused afterwards without decomposition of the tungsten monocarbide that provides the best mechanical properties for many applications.Wear-resistant cobalt alloys were developed 60 years ago and are based on cobalt-chromium-tungsten-carbon. During studies of the CoCrWC system with various carbon concentrations and at various temperatures we identified MC, M₂C, M₇C₃, M₂₃C₆, M₆C, M₁₂C and M₂₈C carbides. The solidifying M₆C carbide is unstable over a certain concentration range of chromium and decomposes to form tungsten carbide (WC). On heat treatment the tungsten-containing M₆C forms WC in a cobalt-chromium matrix if the chromium content is less than 5 wt.%. It is therefore possible to produce a sprayed and fused or welded layer of WC-cobalt alloy. The rate of WC formation depends on temperature and time. Time-temperature-decomposition diagrams have been established for four alloys. The structures of the heat-treated alloys are similar to those of sintered tungsten carbide-cobalt alloys.     

An easy soft-template route to synthesis of wormhole-like mesoporous tungsten carbide/carbon composites

Wormhole-like mesoporous tungsten carbide/carbon (WC/C) composites can be prepared by an easy method that combines emulsion processing with triblock copolymer self-assembly strategy, followed by a high-temperature carbothermal reduction. X-ray diffraction, transmission electron microscopy, X-ray spectroscopy, thermogravimetric analysis and N₂ sorption techniques were employed to characterize the mesoporous WC/C composites. The results show that the resultant materials have a wormhole-like mesostructure containing nanoscale (∼40 nm) tungsten carbide particles, and high surface areas (up to 314.9 cm²/g). It is proposed that a general assemble procedures are responsible for the wormhole-like mesoporous WC/C composites.     

Wear Behaviour of CTC/FeCrCSi Composite

To bring the excellent abrasion-resistant po-tential of carbide into full play,composites of casttungsten carbide(CTC)grains based on mainlyplate martensite and high Cr,W white cast iron aremade on substrate of grey iron by cast-in-placehardfacing process.Results of high-stresstwo-body and three-body abrasion show that:(1)Base alloy microstructures have overwhelmingdominating effects on abrasion resistances of thecomposites in two-body and especially three-bodyabrasion systems.(2)All composites have very ex-cellent abrasion-resistances which increase drasti-cally with the increase of CTC grain size.In case ofthe same CTC grain size,composite based onmartensite white cast iron is much morewear-resistant than that based on mainly platemartensite although the volume fraction of CTCgrains in the latter is considerably larger than thatin the former.In three-body abrasion system,loadhas little effect on wear rate for composites basedon martensite white cast iron,but wear rate ofconventional wear-resistant materials increaseslinearly in a very steep slope as the nominal stressincreases.     

Novel Flow-Softening and Flow-Anisotropy Approaches to Developing Improved Tungsten Kinetic Energy Penetrator Materials

The penetration performance of uranium alloy kinetic energy (long rod) projectiles are superior to that of equivalent projectiles manufactured from high-density tungsten-based composites. Prior research efforts seeking improvements in the penetration capabilities of tungsten penetrator materials have focussed on increases in the strength, ductility, and toughness of the composites and have not been successful.

Recent studies at the U.S. Army Research Laboratory, however, have established that it is the rate at which the penetrator material softens, under the high-rate, high-pressure deformation it must undergo in the penetration process, not the material's initial strength or ductility, which governs its performance. The rapid flow-softening behavior of uranium alloys, a function of both their mechanical (strain-hardening, strain rate-hardening) and thermal (thermal-softening, etc.) properties, was shown to be responsible for their superior ballistic performances. Other tests demonstrated analogous differences in the performance of different orientations of monocrystal tungsten penetrators, due to the anisotropics in their flow-strengthening and flow-softening behaviors. These results have indicated two novel and promising directions for tungsten penetrator research, broadly categorized as (1) flow-softening and (2) flow-anisotropy approaches. The flow-softening approach seeks to develop an isotropic, plastically unstable behavior, similar to that exhibited by uranium alloys, in new tungsten composites. This approach relies primarily on modifications or replacements of the nickel-based matrix in the currently produced tungsten composites with thermomechanically less stable alloys. Critical issues include the roles and interactions between matrix and tungsten particle phases in the thermomechanical properties of the overall composite, and the nucleation and growth of plastic localizations in these materials. The flow-anisotropy approach seeks to develop directional flow-softening behavior in tungsten-based composites by orienting the tungsten phase.

These efforts to develop tungsten penetrator materials, with performance equalling or surpassing that of depleted uranium, but without the environmental and political concerns associated with producing and fielding uranium ammunition, are reviewed.     

On the structure and properties of wear- and corrosion-resistant nickel-chromium- tungsten-carbon-(silicon) alloys

In some applications, for chemical and physical reasons hard nickel-based alloys have to be used instead of cobalt-based alloys but boron must be avoided. The nickel-chromium-tungsten-carbon system with and without silicon was therefore studied in several concentration ranges at 1050°C with respect to structure, phase, hardness and corrosion and wear resistance. Alloys containing 2% carbon, 10% tungsten and more than 10% chromium are composed of a nickel solid solution and an M₇C₃ carbide in both cast and homogenized (1050°C, 180 h) conditions. On increasing the tungsten content up to 20% the M₂C carbide becomes dominant, and this is associated with a remarkable increase in the hardness of the alloys. Additions of 2% silicon do not change the M₇C₃ and M₂C carbides present. In some cases a carbon-stabilized silicide M₅Si(C) was observed. Silicon additions decrease the liquidus temperature range relatively little, but they affect particle shape and size and the grain size distribution. The relation of various chromium, tungsten and silicon contents to corrosion and wear resistance was studied. The corrosion resistance depends on the chromium content of the nickel solid solution but also on carbide formation (tungsten and carbon content). The silicon content of the nickel solid solution is important too.Because their liquidus temperature is close to 1300°C the alloys cannot be used as self-fluxing and fusing powders for flame spraying but they can be sprayed by plasma torches and they can, of course, be welded.     

Electrokinetic treatment of firing ranges containing tungsten-contaminated soils

Tungsten-based alloys and composites are being used and new formulations are being considered for use in the manufacturing of different types of ammunition. The use of tungsten heavy alloys (WHA) in new munitions systems and tungsten composites in small caliber ammunition could potentially release substantial amounts of this element into the environment. Although tungsten is widely used in industrial and military applications, tungsten's potential environmental and health impacts have not been thoroughly addressed. This necessitates the research and development of remedial technologies to contain and/or remove tungsten from soils that may serve as a source for water contamination. The current work investigates the feasibility of using electrokinetics for the remediation of tungsten-contaminated soils in the presence of other heavy metals of concern such as Cu and Pb with aim to removing W from the soil while stabilizing in situ, Pb and Cu.     

High-temperature mechanical properties of aluminium alloys reinforced with boron carbide particles

The mechanical properties of particulate-reinforced metal-matrix composites based on aluminium alloys (6061 and 7015) at high temperatures were studied. Boron carbide particles were used as reinforcement. All composites were produced by hot extrusion. The tensile properties and fracture analysis of these materials were investigated at room temperature and at high temperature to determine their ultimate strength and strain to failure. The fracture surface was analysed by scanning electron microscopy.     

Investigation of impact behaviour of aluminium based SiC particle reinforced metal–matrix composites

In this paper, the impact behaviour of aluminium and silicon carbide (SiC) particle reinforced aluminium matrix composites under different temperature conditions was determined. Charpy impact tests were performed on as extruded and heat treated specimen at temperatures varying from −176 to 300 °C. Composite specimens based on aluminium alloys of 2124, 5083 and 6063 and reinforced by SiC particles were manufactured. Two different SiC sizes of 157 μm and 511 μm and two different extrusion ratios of 13.63:1 and 19.63:1 were used. The results of instrumented impact tests were compared with the microstructural and fractographic observations. The failure mechanisms and deformation behaviour of unreinforced alloys and composites were assessed. The impact behaviour of composites was affected by clustering of particles, particle cracking and weak matrix-reinforcement bonding. Agglomeration of particles reduced the impact strength of Al 2124 and 6063 based composites. Alumınum 6063 alloys and composites showed a better impact strength. The impact strength of 6063 composites increased with particle size and extrusion ratio. The effects of the test temperature on the impact behaviour of all materials were not very significant.     

Tungsten alloys as radiation protection materials

The radiation shielding effects of some tungsten alloys were evaluated using ¹³³Ba(356 keV) and ¹³⁷Cs(660 keV)γ-ray sources. Tungsten carbide had about the same effect as the commonly used lead, while tungsten-copper alloy gave as good a performance as tungsten. The results of transmittance measurements for these materials, as well as of their Monte-Carlo simulation, are reported.     

Effect of cobalt powder morphology on the properties of WC-Co hard alloys

The effect of cobalt powder morphology on the microstructure of WC-Co hard alloys produced by sintering cobalt + tungsten carbide powder mixtures has been studied using X-ray diffraction, laser diffraction, scanning electron microscopy, density measurements, and Vickers microhardness tests. The results indicate that, under identical sintering conditions, the densest and most homogeneous microstructure is formed in hard alloys sintered using cobalt powders consisting of rounded particles. The use of cobalt powders with dendritic morphologies impedes the homogenization of Co + WC powder mixtures and preparation of pore-free WC-Co hard alloys.     

The Influence of Surface Roughness of Cutting Inserts Made of Diamond–Tungsten Carbide Composite on Cutting Forces and Machining Quality in Turning Aluminum Alloys and Brass

The paper addresses the effect of face roughness of cutting inserts made of diamond–tungsten carbide nanocomposite on cutting forces, vibration, and machined surface quality in finish turning of aluminum alloys and brass. The authors have substantiated the optimal cutting conditions to produce workpiece surfaces with the minimum roughness and waviness.