Tungsten Heavy Alloys Research Articles

Heterogeneous phase deformation in a dual-phase tungsten alloy mediated by the tungsten/matrix interface: insights from compression experiments and crystal plasticity modeling

Tungsten heavy alloy (WHA) is a typical multiphase alloy material consisting of hard tungsten (W) and soft matrix (γ) phases. When loaded, the two phases deform quite differently due to the large difference in their mechanical properties. At present, our understanding of phase deformation and behavior in the multiphase context is relatively poor compared to the single phase case. Such insight is necessary, however, for the design of multiphase alloys having optimal phase microstructure and corresponding material behavior. By combining mechanical testing and crystal plasticity modeling, the relationship between phase microstructure and multiphase alloy deformation behavior is systematically investigated in this work. The results demonstrate that deformation in the W and γ phases is quite different and related to the contrast in material properties between the two phases. Deformation heterogeneity in the multiphase alloy is characterized by the strain gradient near/across the W/γ interface and differences in phase deformation states in relation to the contrast in phase material properties and phase volume fraction. It is found that dislocation pile-up and twinning are the main mechanisms mediating heterogeneous deformation in the region around W/γ interfaces. Based on this insight, a novel design strategy for multiphase alloys is proposed based on optimization of the contrast in phase mechanical properties and the phase volume fractions. This strategy can be employed to design new tungsten alloys and other multi-phase alloys.

Microstructure evolution and mechanical properties of tungsten alloy prepared by laser directed energy deposition

Tungsten heavy alloys (WHAs) are widely applied across military, medical, and other advanced industries. Laser-directed energy deposition (LDED) is an innovative approach to fabricate WHAs with intricate microstructures. This study explored the manufacturing processes and forming characteristics of three distinct tungsten alloy compositions to elucidate the microstructural formation mechanisms and performance evolution of WHAs prepared by LDED. Electron backscatter diffraction analysis revealed the occurrence of heterogeneous nucleation and dendritic precipitation in supersaturated solid phases across different alloy compositions. By applying the drag force equation derived from the two-phase flow theory, the Gaussian energy distribution inherent to the LDED process, and the low flowability of WHAs, this study reveals the microstructural layering mechanisms within LDED-produced samples. Through process optimization, 90W samples that exhibited an ultimate tensile strength of 1093MPa and elongation of 16.8% were obtained. In situ mechanical testing revealed that the reduced elongation of the WHAs produced by LDED is due to their unique fracture mechanism driven by the interconnection of cracks between fractured tungsten particles. However, by incorporating smaller W particles and optimizing the gap ratio, the stress concentration can be effectively mitigated and crack propagation can be curtailed, thereby significantly enhancing elongation.

Manufacturing of heavy tungsten alloys from nano-sized metal oxides via simultaneous reduction-sintering powder treatments

Heavy tungsten alloys are of great importance in the engineering and mining industries as well as the military and medical applications because of their stability at high temperatures, high strength and dense structures. The present study develops a novel technology for the production of heavy tungsten alloys via thermal treatment of nano-sized metal oxides based on simultaneous reduction and sintering processes. Heavy tungsten alloy (95W-3Ni-2Fe) was produced from the reduction of mixed nano-sized metal oxides precursor in H2 at 1000 o C followed by sintering at 1350–1450 o C for 30–90 min. The reduced and sintered samples were characterized by XRD to follow up the crystallinity, total porosity measurement was used to find out the densification properties, the grain structure and morphology were examined by RLM and SEM attached with EDAX. Micro-hardness tester was also used to investigate the influence of sintering conditions on the grain densification. A fundamental study on the kinetics of reduction of mixed nano-sized metal oxides precursor was performed by isothermal and non-isothermal techniques. Both results from isothermal and non-isothermal tests were used to calculate the activation energy which was correlated with macro- and micro-structures to predict the corresponding reduction mechanism. However, the influence of sintering temperature and time on the crystallinity of the produced phases, grain structure, morphology, total porosity, pore-size distribution, bulk and apparent densities, and the hardness of sintered compacts was extensively investigated. The results revealed that the presence of NiO and/or Fe2O3 in the mixed metal oxides precursor was very important to ease the reducibility of WO3 as the metallic phases of Ni and/or Fe act as a catalyst for the reduction of WO3. The rate of reduction proceeds faster in the following order: NiO > Fe2O3 > mixed oxide > WO3. In non-isothermal experiments, it was found that the heating rate has a considerable effect on the reduction of precursor, i.e., the lower the heating rate, the higher the degree of reduction. It might be reported that the use of nano-sized metal oxides particles in the fabrication of heavy tungsten alloys greatly affects the main properties of the produced alloy. With the increase in sintering time, larger sizes of dense grains were developed, and the matrix became denser as a result of sintering and re-crystallization effects. The higher the sintering time, the higher the grain densification and the less pores formed in the matrix. On the other hand, with the increase in the sintering temperature, the grain boundaries were well defined in which the grains were composed of tungsten metal and surrounded by inter-metallics. The higher the temperature, the higher the XRD peak intensities of metallic tungsten and intermetallics as a result of sintering and re-crystallization.

Transient liquid phase sintering in spark plasma sintered tungsten heavy alloys with Nb and Mo additives

In the present investigation spark plasma sintered tungsten heavy alloys of composition 90W-7Ni-3Fe, 84W-7Ni-3Fe-6Mo, and 84W-7Ni-3Fe-6Nb were analyzed to determine the effect of Mo and Nb addition on microstructure and phase formation. The alloys were sintered at temperatures ranging from 1150 °C to 1275 °C and at a fixed sintering pressure of 30 MPa. Nb added alloy exhibited a maximum relative density of 99% at sintering temperature of 1200 °C. Whereas the base alloy and Mo added alloy, exhibited a maximum relative density of 97.9% and 95.9% at 1150 °C respectively. Transient liquid phase sintering was found to play a crucial role in the base alloy and Mo added alloy whereas the Nb added alloy was found to undergo persistent liquid phase sintering. Microstructure characterisation by SEM revealed formation of finer tungsten grains with average grain size ranging from 1 μm to 4.3 μm. Mo addition restricted the tungsten grain growth while Nb addition promoted the tungsten grain growth compared to the base alloy. Phase analysis by XRD revealed the formation of Ni4W intermetallic (at lower temperatures) for the base alloy, NbO2 and NbW intermetallics for Nb added alloy and MoNi rich phase for Mo added alloys. Hardness measured by Vickers hardness method revealed a declining trend in hardness with increase in sintering temperature, owing to tungsten grain growth in all the alloys and along with Kirkendall pore formation and growth for the base alloy and Mo added alloy. Nb addition resulted in maximum hardness of 678 HV1 which is highest ever reported for SPSd WHA with 90 wt% concentration of W.

Microstructures and mechanical properties of W-Co-Al tungsten heavy alloy prepared by different formation processing

High density, high strength and high susceptibility to adiabatic shear banding (ASB) have always been pursued by tungsten heavy alloys (WHAs) for kinetic energy armor-piercing projectiles. To meet the demand, this work reported a novel tungsten heavy alloy with high-density L12 precipitation-strengthened Co9Al9W binder (WCAW). WCAWs were prepared by liquid phase sintering (LPS) and laser ultrashort-time liquid phase sintering (LULPS) respectively. Experimental results show that LULPS technique with large molten pool convection and rapid solidification can produce WCAWs with uniform W distribution, low W-W contiguity and fine W particles. Conversely, W particles in LPS WCAWs were excessively connected and segregated. The uniform distribution, low W-W contiguity and fine W particles enable LULPS WCAW to exhibit better mechanical properties. The ultimate compressive strength of the LULPS WCAWs is ∼2442 MPa, 16.4 % higher than that of the LPS WCAWs. As well, the dynamic yield strength of LULPS WCAWs is high, which is ∼2281 MPa and 37.4 % higher than that of LPS WCAWs.

Tungsten heavy alloys for kinetic energy penetrators: a review

Tungsten heavy alloys are preferred materials for kinetic energy penetrators owing to the combination of high density, tensile strength, good impact strength and inert nature. The factors affecting shear band formation in the material and strategies to aid their early emergence by various alloy and process modifications to sustain a self-sharpened head during penetration are the main focus of this review article. Changes in the microstructural features such as tungsten grain size, dihedral angle and contiguity and mechanical properties by the addition of various alloying constituents and post-processing are critically discussed, along with high strain rate deformation behaviour analysis. This article also captures recent developments in the last decade and future prospects in the field of tungsten heavy alloys.

The effect of pressure and temperature on the properties of 88 W-10Ni-2Mn tungsten heavy alloy produced by cold press method

This research explored the impact of pressure and temperature to determine the optimal conditions for producing an 88 W-10Ni-2Mn tungsten heavy alloy (WHA) suitable for industrial purposes. To achieve this objective, tungsten, nickel, and manganese powders with predetermined ratios underwent wet milling in a two-step process. Subsequently, the powder mixture underwent compression at two pressures, namely 200 MPa and 250 MPa, employing the cold press method. The compressed mixture was then subjected to sintering in a tubular furnace at temperatures of 1200 °C, 1250 °C, 1350 °C, and 1400 °C. Microstructural characterization was conducted using optical and scanning electron microscopes (SEM). The findings indicated that increasing both pressure and temperature resulted in an enhancement of the sintering density in the samples. The optimum value was achieved at 1400 °C and 250 MPa, reaching 90.11 g/cm3. Furthermore, in the quenching sintering process, the carburization of 88 W-10Ni-2Mn WHA contributed to an increase in the micro hardness of the samples, reaching a maximum of 529 HV. The hardness exhibited an increase from 355 HV to 529 HV with a temperature rise from 1200 °C to 1250 °C. However, it decreased from 377 HV to 352 HV when the temperature increased from 1350 °C to 1400 °C. The increase of sintering temperature also led to slightly increases the continuity of tungsten‑tungsten due to the growth of tungsten particles. By increasing the temperature from 1350 °C to 1400 °C, ductile fracture was observed in WHA.

Improvement of Mechanical and Wear Properties of Tungsten Heavy Alloy Using Two-Stage Sintering and Carburizing Processes

Improvement of Mechanical and Wear Properties of Tungsten Heavy Alloy Using Two-Stage Sintering and Carburizing Processes

Tensile behaviors of rolled and annealed 90W7Ni3Fe alloy

Tungsten heavy alloys (WHAs) with two-phase composite structures display unique mechanical properties. Here, we explore the effects of rolling strain and annealing temperature on tensile behaviors of 90W7Ni3Fe WHAs. Cold rolling followed by low-temperature annealing (<1000 °C) induces an increase in yield strength at the expense of ductility. The ductility of WHAs can only be restored by raising the annealing temperature to 1000 °C. Keep the annealing at 1000 °C while gradually increasing the rolling strain not only improves the strength of WHAs but also maintain a good ductility. Once exceeding a critical rolling strain of 60 %, the yield strength of WHAs increases to 1480 MPa, while result in a substantial decrease in ductility. The evolutions of two-phase composite structures with rolling and annealing induces the alterations of the tensile properties of WHAs. These results provide a reference for designing thermal-mechanical processing recipes for WHAs.

Systematic investigation of microstructure, distortion, mechanical and thermal properties of NiB and ZrB2-modified 90W-6Ni-4Co alloys

The present work focuses on the role of NiB and ZrB2 addition on density, structural evolution, mechanical and thermal properties of 90W-6Ni-4Co (wt%) heavy alloys. The investigated tungsten heavy alloys were sintered at 1485 °C and 1500 °C with a holding time of 75 min in H2 atmosphere. Compared to the base alloy 90W-6Ni-4Co, the NiB-substituted alloys showed improved densification at both sintering temperatures. An in-depth study of the phase and microstructure of the 1500 °C sintered samples was carried out. X-ray diffraction analysis confirmed the presence of ZrO2 in ZrB2 containing WHAs. Microstructural analysis affirms that ZrB2 incorporation attributes for grain size refinement in sintered alloys. Furthermore, the elephant foot formation in the sintered samples was avoided by incorporating NiB individually or in combination with ZrB2 dispersoids. The distortion parameter (δ) of the samples sintered at 1500 °C was found to be decreased from 24.83 (0 wt% ZrB2) to 6.36 (2 wt% ZrB2). On the other hand, the combined addition of NiB and ZrB2 provides better shape retention with δ=2.82 for the tungsten heavy alloys with 3 wt% NiB and 2 wt% ZrB2. The maximum compressive stress of ∼2000 MPa was obtained in the 89W-6Ni-4Co-1ZrB2 samples. The maximum and minimum bulk hardness of 432 ± 5 HV3 and 365 ± 9 HV3 was obtained for 88W-3Ni-3NiB-4Co-2ZrB2 and 90W-6Ni-4Co heavy alloys. The coefficient of thermal expansion of the 90W-6Ni-4Co alloy was found to be the highest (7.65 × 10−6 /°C), which was reduced to 7.1 × 10−6 /°C and 6.8 × 10−6 /°C with the incorporation of 1 and 2 wt% ZrB2 respectively. W-rich channels were noticed in the microstructure of 1500 °C sintered samples. Overall, W-Ni/NiB-Co-ZrB2 alloys are very effective in enhancing the mechanical properties and distortion behavior compared to W-Ni-Co alloys.

Effect of dispersed particles on microstructure evolution and mechanical properties of 93W–4.6Ni–2.1Fe–0.3Co alloys

93W–4.6Ni–2.1Fe–0.3Co alloys reinforced by ZrC particles were prepared by the two-step sintering method in this article. The conventional sintering process conducted at a temperature of 1485 °C resulted in the formation of microvoids between the larger dispersed particles and the matrix, thereby leading to a degradation in the tensile property (959 MPa/11.5%). Through controlling the sintering temperature at 1440 °C, a dispersion-strengthened tungsten heavy alloys (WHAs) with excellent comprehensive tensile properties (974 MPa/27.0%) was obtained, mainly attributed to the synergistic effect of homogeneous dispersion strengthening and grain boundary purification. Under high compressive strain rates, dispersion-strengthened WHA demonstrates a superior yield strength compared to WHA, suggesting that dispersion-strengthened WHAs have potential applications in the armour-piercing field.

Sintering behaviour of liquid phase sintered 90Mo-10(Ni–Cu) alloys

Molybdenum (Mo), a refractory material, boasts an elevated melting point of 2610 °C and is predominantly synthesised through powder metallurgy at high temperatures reaching 2000 °C, necessitating the use of liquid phase sintering (LPS) technique. This study investigates the LPS of Mo with varying proportions of Ni–Cu binders, aiming to understand the mechanism of intermetallic formation and to manufacture low-cost, dense, intermetallic-free and near-net-shape Mo-base alloys. Employing the manufacturing design paradigm for 90W-10(Ni–Cu) tungsten heavy alloys (WHAs) and utilising conventional powder metallurgy techniques, Mo-based 90Mo10(Ni–Cu) alloys were synthesised. Initial findings indicate that the densification of Mo-compacts increases with increasing the Ni–Cu ratio in the binder phase. However, an excess of Ni results in the loss of structural rigidity and geometric distortion during sintering. In Ni-rich alloys, two distinct liquid phases, Ni-rich and Cu-rich, emerge at sintering temperatures. These phases exhibit different solubilities for Mo and solidify into a dual-phase matrix. Intriguingly, in contrast to WHAs, 90Mo-10(Ni–Cu) alloys with a Ni-rich composition manifested irregular Mo particles, a dual-phase matrix, and δ-MoNi intermetallic compound formation. The formation of the intermetallic compound can be avoided by reducing the solubility of Mo in the Ni-rich liquid during sintering. Microstructural evolution and distortion are analysed using stereological quantification of various microstructural parameters. It reveals that alloys with low Mo solubility, high connectivity and high dihedral angle maintain their structural rigidity and resist distortion. Both micro-hardness and bulk hardness increased with increasing Ni–Cu ratios in the binder phase. Based on the present results, a mechanism for liquid phase sintering in the 90Mo-10(Ni–Cu) system in the presence of two liquid phases is postulated.

Undeformed chip thickness models for precise vertical - spindle face grinding of tungsten heavy alloy

Tungsten heavy alloys (WHAs) have superior usage performance in various applications and are expected to be used as key components in nuclear energy, aerospace and precision instruments. As a strain-rate sensitive material, the material properties of WHA will change greatly with different grinding parameters during processing. However, most of the existing material removal models are established based on the static properties of the material. The precision grinding of WHA still lacks theoretical guidance. In this research, the effects of strain, strain rate, and temperature on the dynamic properties of WHA under high temperature and high pressure during face grinding are considered. The maximum undeformed chip thickness model for vertical-spindle face grinding with cup wheels is established. The relationship between the undeformed chip thickness, grinding quality, and grinding parameters was investigated. Experimental results show that the maximum undeformed chip thickness under the same conditions is 3.16 times smaller than conventional grinding, and the critical strain rate for ductile-brittle transformation is about 1.46 × 107 s−1. The grinding specific energy of WHA decreases with the increase of the maximum undeformed chip thickness and decreases with the increase of the material removal rate, reaching a minimum of 121.6 J/mm3. This study not only provides a new method for predicting the grinding condition of WHAs but also enhances the understanding of the cup wheel face grinding process and provides theoretical guidance for reducing the machining damage of WHA.

Metallographic and Extraction Replica Methods for Characterization of Tungsten Heavy Alloy: H13 Clads

Tungsten heavy alloys are used in demanding high pressure die casting applications due to their high temperature strength, high thermal conductivity, and low thermal expansion. High cost limits applications to small sintered die inserts and manual gas tungsten arc weld repairs. A new tungsten heavy alloy consumable, Anviloy wire, was developed for automated cladding of hot work tool steel dies. Literature regarding characterization of tungsten heavy alloy die steel clads was lacking. Understanding base metal dilution effect on clad microstructure is critical but required new sample preparation methods. An Anviloy wire-H13 clad was made using hot wire gas tungsten arc cladding and analyzed with metallography. Samples were found to have grain boundary M6C carbide phase as-welded with the help of an alkaline sodium picrate etchant. An isothermally aged arc crucible melted sample of the same composition was characterized using metallography, scanning electron microscopy, and transmission electron diffraction. The clad representative arc crucible melted sample was subjected to isothermal aging at 725°C for 100 hours. Isothermal aging resulted in precipitation of a high volume fraction of intermetallic platelets. Using a new carbon extraction replica sample preparation method involving two chemical polishing steps, transmission electron diffraction of precipitates indicated they were mu phase intermetallic.

Interfacial structure and formation mechanism of 90 W-7Ni-3Fe/steel using co-sintering method

In this study, we proposed a powder metallurgy method to develop an interlocking interface in tungsten heavy alloy/steel composites, which is achieved by co-sintering technology using tungsten heavy alloy and steel powders with a large difference in particle size. The interfacial microstructure evolution and mechanical properties of the co-sintered joint as a function of co-sintering temperature were investigated systematically. Results showed that a well-bonded interlocking interface was formed along the steel particles as a result of the tungsten heavy alloy particles filling in the gaps between two neighboring steel particles. The co-sintered joint contains four regions: the W alloy matrix, the Fe3W3C layer, the Ni-affected layer, and the steel matrix. Based on the microstructural characterization, the interface formation mechanism and reaction layer growth behavior are discussed in depth. Benefitting from the interlocking structure, the highest tensile strength of the co-sintered specimen is 265 MPa, which is 66% higher than that of the non-interlayer joint obtained by diffusion bonding method. Moreover, its performance is better than that of some W alloy/steel with an interlayer. This technique offers a potential method for the efficient preparation of a W alloy/steel composite structure with outstanding properties.

Crack self-healing by high-temperature annealing of a 90W7Ni3Fe tungsten heavy alloy

WNiFe tungsten heavy alloys (WHAs) are leading candidates for fusion plasma-facing components, since they are toughened by embedding brittle W-particles in a ductile phase honeycomb matrix. We show that fatigue cracks in a 90W7Ni3Fe WHA, up to ≈ 1.3 mm long, are completely healed by vacuum annealing at 1300 °C for 24 h, as confirmed by microstructural observations and locating the healed crack initiation site, by both re-loading and re-precracking. Annealing also improves WHA toughness. Healing is not due to previously postulated mechanisms. We hypothesize that it derives from internal annealing stresses that extrude the ductile phase into adjacent cracks.

Hardness-guided machine learning for tungsten alloy strength prediction

Yield strength determines the material's resistance to permanent deformation. However, the traditional estimation method based on the triple relationship of Vickers hardness exhibits limited accuracy when applied to tungsten heavy alloys (WHA) with two-phase structure. This study presents a novel approach using machine learning and hardness data to predict the yield strength of tungsten heavy alloy efficiently and accurately. Among the eight machine learning models used, Gradient boosting decision tree model (GBDT) was the most effective model. The results demonstrate a strong agreement between the GBDT-based predictions and experimental results, with an average error of 6.7 %. We also gave the hardness versus yield strength relationship for the 90WNiFe alloy system. This finding highlights the potential of the GBDT regression model in conjunction with hardness measurements for predicting yield strength with high precision.

The bifunctional low mismatch nano strengthening phase leads to a high strength-ductility W-Ta-Ni-Fe-Cu alloy

As a typical tungsten-based composite consisting of tungsten (W) particles and matrix phase, tungsten heavy alloys (WHAs) are extensively utilized in the military due to their exceptional strength and high density. However, the large grain size (>30 µm) of powder metallurgy liquid phase sintered (LPS) WHAs and the low strength of the matrix phase limit the further improvement of the alloy. In this work, high-density ultrafine WHAs were fabricated by two-step low-temperature sintering, and the density of the alloy reached 17 g/cm3 with an average W particle size of 7.81 µm. Additionally, the eutectic reaction between Ni and Ta was controlled to generate dispersed nano-Ni3Ta phases in situ in the matrix phase, further improving the strength of the alloy. Under the synergistic strengthening effect of fine-grain strengthening, dispersion strengthening, and solid solution strengthening, the average ultimate tensile strength of the alloy reached 1190.39 MPa. At the same time, the alloy maintained good elongation with a total elongation of 20.8 % due to the good co-grid interface orientation between the Ni3Ta phase and the matrix phase. This study provides a new idea for developing high-strength WHAs and has a guiding significance for developing Ni-based alloys.

Crystallographic texture evolution in hot-press sintered tungsten heavy alloy with the effect of niobium (Nb) addition

This study examines the impact of niobium on the crystallographic texture evolution and grain boundary distribution of hot press sintered tungsten heavy alloy (W-4.9Ni-2.1Cu). EBSD analysis was used to examine the evolution of crystallographic texture and grain boundary character distribution in sintered compacts. The important findings of this study depict that cubic texture component {001} <111> were evolved in niobium unalloyed compacts due to the solidification of atoms aligned in a specified preferred orientation. Besides, it reveals the weakness in the cubic texture in niobium alloyed compacts due to the recrystallization followed by sub structural recovery occurrence during sintering. In addition, an increase in CSL fraction in niobium alloyed compacts illustrates the dominance of surface diffusion during sintering caused by the grain refinement attributed from the niobium enrichment at the tungsten-binder interface. Metallographic studies showed that the niobium concentration increment in WHAs has concomitant effect with sintered compacts' properties. A W-4.9Ni-2.1Cu-1 Nb alloy achieved the highest values for micro-hardness (432 HV0.5), electrical conductivity (23.74 % of IACS), and relative density (99.90 %).

Co-sintering characteristics of W-Re pre-alloyed powder and Ni, Fe

Tungsten (W) heavy alloys (WHAs) have unique mechanical properties and are widely used in the national defence and military industries. Adding Re to WHAs can produce a good “Re effect” and improve their performance. However, the solid solubility of Re in W particles was limited in traditional sintering processes, which limited its application. This study prepared W-Re solid solution powder by pre-alloying (mechanical ball milling) and W-Re-Ni-Fe alloy with an ultimate tensile strength of 1.05 GPa by co-sintering W-Re solid solution powder with Ni and Fe powders. At the same time, the diffusion path of the Re element in WHAs and its influence on the properties of W particles and matrix phase were determined. The addition of Re can improve the strength and hardness of the alloys but hinder the dissolution and precipitation process of W in the matrix phase, weakening the W-matrix interface, and the ductility of the alloy ultimately decreases. Therefore, it is expected to enhance the interdiffusion reaction between W particles and the matrix phase by regulating the composition of the matrix phase, thereby achieving a synergistic improvement in the strength and toughness of WHAs.