Comparison of mechanical and microstructure properties of tungsten alloys for special purposes (original) (raw)
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Damage Mechanisms for 93W and 97W Tungsten-Based Alloys
Rare Metal Materials and Engineering, 2010
Dynamic compression and in-situ tensile tests were carried out for two kinds of W-Ni-Fe alloys with 93wt% and 97wt% tungsten contents fabricated by P/M technique; their microstructures and damage model were examined and discussed. The damage mechanisms for 93wt% W alloy belongs to ductile separation of W-W interface, and that for 97wt% W alloy belongs to initiation and propagation of microcracks inside tungsten grains. On the base of Ostwald ripening theory for the sintering process, the microstructures of the two kinds of alloys with different tungsten volume fractions under various sintering conditions were predicted, and the results agreed with the tests very well. With the help of Ostwald ripening and micromechanical theory, we set up a relationship for sintering condition, volume fraction of tungsten and mechanical properties to help material design, production and mechanical property prediction.
Materials, 2021
The paper presents the results of studies on the effects of heat treatment and cold-work parameters on the mechanical properties and microstructure of the tungsten heavy alloy (WHA) with the composition W91-6Ni-3Co. Tungsten heavy alloy (WHA) is used in conditions where strength, high density, and weight are required. The material for testing as rod-shaped samples was produced by the method of powder metallurgy and sintering with the participation of the liquid phase and then subjected to heat treatment and cold swaging. The study compares the effect of degree deformation on the strength, hardness, microhardness, and microstructure of WHA rods. The conducted tests showed that heat treatment and cold-work allowed to gradually increase the strength parameters, i.e., tensile strength σuts, yield strength σys, elongation ε, hardness, and microhardness. These processes made it possible to increase the tensile strength by over 800 MPa (from the initial 600 MPa after sintering to the final...
Mechanical Properties of Forged Tungsten Heavy Alloys
Acta Polytechnica CTU Proceedings
Tungsten heavy alloys are composite materials containing spherical tungsten particles embedded in binder matrix. Their excellent mechanical properties can be further improved by rotary forging. This paper aims to gain deeper understanding of the forging process by investigating the local elastic modulus, hardness, and residual stress of individual phases in W6Ni3Co pseudo-alloy. The resulting global properties of the composite material such as stress-strain behavior, fracture toughness and fatigue crack growth rate behavior are also studied. The results show that sintered and quenched material consists of highly textured matrix containing nearly perfect single crystal spheres of pure W. The rotary forging leads to significant lattice deformations destroying the texture and significantly increasing the hardness of both WNiCo matrix and W particles and making residual stresses in W particles anisotropic with increased compression along the longitudinal axis of the forged part.
Materials Today: Proceedings, 2018
In the present study, a 90W-6Ni-2Fe-2Co (Wt.%) tungsten heavy alloy was processed through liquid phase sintering route, followed by vacuum heat treatment and swaging. Further, ageing was carried out at 700° C for three different time period, in order to improve mechanical properties. Microstructural analysis showed decrease in contiguity levels from sintered to swaged condition. Swaging improved the tensile strength of the alloy at the expense of ductility and impact. Aging of the swaged alloys showed further improvement in yield, tensile strength and hardness of the alloy with concomitant loss of ductility and impact toughness. The fracture surface of sintered alloy exhibited brittle failure features consisting of tungsten-matrix and tungstentungsten failure. However, the heat treated alloy showed lesser intergranular failure indicating higher ductility. The swaged alloy exhibited relatively higher fraction of transgranular cleavage features. The study shows that the heat treatment (that includes solution heat treatment and ageing) and swaging can be used judiciously to tailor the final mechanical properties of the tungsten heavy alloys.
Physica Scripta, 2017
The mechanical properties of tungsten produced in different forms before and after neutron irradiation are of considerable interest for their application in fusion devices such as ITER. In this work the mechanical properties and the microstructure of two tungsten (W) products with different microstructures are investigated using depth sensing nano/micro-indentation and transmission electron microscopy, respectively. Neutron irradiation of these materials for different doses, in the temperature range 600 °C–1200 °C, is underway within the EUROfusion project in order to progress our basic understanding of neutron irradiation effects on W. The hardness and elastic modulus are determined as a function of the penetration depth, loading/ unloading rate, holding time at maximum load and the final surface treatment. The results are correlated with the microstructure as investigated by SEM and TEM measurements. Supplementary material for this article is available online
Materials, 2021
Tungsten heavy alloys are two-phase metal matrix composites that include W–Ni–Fe and W–Ni–Cu. The significant feature of these alloys is their ability to acquire both strength and ductility. In order to improve the mechanical properties of the basic alloy and to limit or avoid the need for post-processing techniques, other elements are doped with the alloy and performance studies are carried out. This work focuses on the developments through the years in improving the performance of the classical tungsten heavy alloy of W–Ni–Fe through doping of other elements. The influence of the percentage addition of rare earth elements of yttrium, lanthanum, and their oxides and refractory metals such as rhenium, tantalum, and molybdenum on the mechanical properties of the heavy alloy is critically analyzed. Based on the microstructural and property evaluation, the effects of adding the elements at various proportions are discussed. The addition of molybdenum and rhenium to the heavy alloy give...
Effect of Mn/Ni ratio variation on microstructure of W–Ni–Mn alloy
Powder Metallurgy, 2008
Tungsten heavy alloys (WHA) such as W-Ni-Cu and W-Ni-Fe are usually used as kinetic energy penetrators (KEP). However, the amount of penetration of these alloys is not sufficient due to their mushrooming effect that occurs as they impact their targets. On the other hand, KEP made of depleted uranium (DU) in spite of their excellent penetrating properties are not a very good substitute for WHA due to their environmental problems. Therefore, in order to increase the penetration depth of WHA penetrators, a new brand of WHA namely W-Ni-Mn alloys have been developed. The present paper deals with the microstructural improvement of such an alloy system, so that it can provide a potential candidate material to be used as KEP, having sufficient penetration depth. For developing this material, various ratios of Mn/Ni powder were mixed with 90 wt-% pure tungsten powder before compaction and sintering in order to investigate the amount of solubility of W in Ni-Mn matrix. In addition to study the effect of this ratio on the re precipitation and growth of W particles within the matrix after being subjected to sintering process, the results of the present study indicated that the grain refinement of W grains is possible by addition of Mn to W-Ni heavy alloys, so that the higher the amount of Mn/Ni ratio up to certain amount, the smaller will become the W grain size after sintering process. Worth mentioning that according to the results obtained by other researchers for WHA penetrators, the finer W grain size, the deeper the penetration of KEP would be. In addition, the results of the present study show that by selecting a suitable sintering cycle, one may obtain a dense microstructure having a density of ,100%, i.e. 99?6%. 7 EDS Profiles of W-Ni-Mn matrix a Mn/Ni51/9; b Mn/Ni58/2 8 Microstructure of samples having 90 (wt-%)W but different Mn/Ni ratio a 1/9; b 2/8; c 4/6; d 5/5; e 6/4; f 8/2 Zahraee et al. Effect of Mn/Ni ratio variation on microstructure of W-Ni-Mn alloy Powder Metallurgy 2008 VOL 51 NO 4 Zahraee et al. Effect of Mn/Ni ratio variation on microstructure of W-Ni-Mn alloy Powder Metallurgy 2008 VOL 51 NO 4
Microstructure effects on tensile properties of tungsten-Nickel-Iron composites
Metallurgical Transactions A, 1988
Controlled processing of heavy alloys containing 88 to 97 pct W resulted in high sintered densities and excellent bonding between the tungsten grains and matrix. For these alloys, deformation and fracture behavior were studied via slow strain rate tensile testing at room temperature. The flow stress increased and the fracture strain decreased with increasing tungsten content. The tradeoff between strength and ductility resulted in a maximum in the ultimate tensile strength at 93 pct W. Microstructure variations, notably grain size, explain sintering temperature and time effects on the properties. During tensile testing, cracks formed on the surface of the specimens at tungsten-tungsten grain boundaries. The crack density increased with plastic strain and tungsten content. The surface cracks, though initially blunted by the matrix, eventually increased in density until catastrophic failure occurred. An empirical failure criterion was developed relating fracture to a critical value of the surface crack tip separation distance. Application of the model explains the effects of microstructural variables on tensile properties.
Recent Progress in Processing of Tungsten Heavy Alloys
Journal of Powder Technology
Tungsten heavy alloys (WHAs) belong to a group of two-phase composites, based on W-Ni-Cu and W-Ni-Fe alloys. Due to their combinations of high density, strength, and ductility, WHAs are used as radiation shields, vibration dampers, kinetic energy penetrators and heavy-duty electrical contacts. This paper presents recent progresses in processing, microstructure, and mechanical properties of WHAs. Various processing techniques for the fabrication of WHAs such as conventional powder metallurgy (PM), advent of powder injection molding (PIM), high-energy ball milling (MA), microwave sintering (MW), and spark-plasma sintering (SPS) are reviewed for alloys. This review reveals that key factors affecting the performance of WHAs are the microstructural factors such as tungsten and matrix composition, chemistry, shape, size and distributions of tungsten particles in matrix, and interface-bonding strength between the tungsten particle and matrix in addition to processing factors. SPS approach ...
Effect of matrix alloy and cold swaging on micro-tensile properties of tungsten heavy alloys
Materials Letters, 2006
The tensile properties of two types of tungsten heavy alloys, W -5.6% Ni -1.4% Fe and W -4.7% Ni -2.2% Co, were investigated as a function of matrix alloy (Ni -Fe vs. Ni -Co) and specimen orientation with respect to the cold swaging axis. Orientation dependent rod properties were measured using a micro-tensile testing unit developed at LLNL. Tungsten particles were slightly oblong in the swage direction in both alloys and particle -particle bonding was also apparent in both alloys. In the W -Ni -Fe alloy separation between W particles and the Ni -Fe matrix was observed, as well as Ni -Fe matrix cracking. The W -Ni -Co alloy showed no evidence of separation between W and the matrix alloy or Ni -Co matrix cracking. Differences in the matrix material condition appear to manifest themselves in the observed tensile properties and fracture surfaces. The ultimate tensile strength and elongation at failure values of the W -Ni -Co alloy were larger than those of the W -Ni -Fe alloy. D