Heavy Alloys Research Articles

Study on Removal Mechanism of Ultrasonic Elliptical Vibration Cutting of Tungsten Heavy Alloy

Study on Removal Mechanism of Ultrasonic Elliptical Vibration Cutting of Tungsten Heavy Alloy

Effects of Laser Scan Strategies on Densification, Residual Stress, and Mechanical Properties of W-Ti Heavy Alloy Fabricated by Laser Powder Bed Fusion

Effects of Laser Scan Strategies on Densification, Residual Stress, and Mechanical Properties of W-Ti Heavy Alloy Fabricated by Laser Powder Bed Fusion

Study on tool wear mechanism of single-crystal diamond in ultrasonic vibration elliptical cutting of tungsten heavy alloy

Tungsten heavy alloy has been widely used in the nuclear industry, military, and other fields due to its excellent material properties. In this paper, the wear of single crystal diamond tool and its influence on surface roughness were studied by ultrasonic elliptical vibration cutting experiment of tungsten heavy alloy and compared with conventional cutting. The experimental results show that under ultrasonic elliptical vibration cutting, the flank wear of a single crystal diamond cutter is reduced by 74.5%, and the retreat of the cutting edge is reduced by 70.6%. After the cutting experiment, the elements on the cutting surface, chip surface, and diamond tool adhesion were detected and analyzed by Raman spectroscopy and X-ray photoelectron spectroscopy. The results show that compared with conventional cutting, ultrasonic elliptical vibration cutting can effectively inhibit the graphitization of single-crystal diamond tools and avoid chemical wear. This is an essential reason why single-crystal diamond tools can be used for tungsten heavy alloy processing under ultrasonic elliptical vibration cutting.

Microstructure and mechanical properties of hot isostatic pressed tungsten heavy alloy with FeNiCoCrMn high entropy alloy binder

Microstructural development and mechanical properties of tungsten heavy alloy, WHA, with FeNiCoCrMn high entropy alloy, HEA, binder were investigated and compared to conventional WHA using Fe–Ni binder. Both WHAs, with HEA and conventional Fe–Ni binders, were fabricated by hot isostatic pressing at a temperature of 1450 °C in an argon environment. Scanning electron microscopy revealed that WHA with HEA and conventional binders possessed uniform and well-refined microstructures. Energy dispersive spectroscopy and X-ray diffraction, XRD, spectroscopy validated the formation and composition of HEA, existing as a skeletal network surrounding tungsten grains. HEA binder exhibited an overall increase of 42% in micro Vickers hardness values. Furthermore, hardness values of the tungsten heavy alloy were also seen to rise when fabricated with HEA binder. However, WHA sample with HEA binder was seen to undergo faster strain hardening and a premature failure, leading to lower values of ultimate strength and reduced ductility.

The Influence of Co Addition on the Structure and Mechanical Properties of Tungsten Heavy Alloys.

This study shows the results of Ni replacement with Co in a W-Ni-Co-type tungsten heavy alloy (WHA) in terms of the structure and mechanical properties. Five alloys containing 92 wt. % of tungsten plus Ni and Co changing in the proportions (Co:Ni) of 1:9, 2:8, 3:7, 4:6, and 5:5 were prepared using liquid phase sintering (LPS). The specimens were studied directly after sintering and after solution heat treatment. The tensile strength, yield strength, and elongation were evaluated. The results of tensile tests were supplemented with microhardness measurements of tungsten grains and matrix. Light microscopy was used for the microstructure, and a scanning electron microscope (SEM) equipped with an EDS attachment was applied for the assessment of the fracture mode and chemical microanalysis. It was concluded that the replacement of Ni with Co led to a tensile property increase that was accompanied by a gradual decrease in elongation that started to be critical for a Co:Ni ratio higher than 4:6.

Reduction Behavior and Characteristics of Metal Oxides in the Nanoscale

The development of nanomaterials and nanotechnology enables the production of nanosized metallic alloys with advanced characteristics from their oxides via a thermal reduction technique. The aim of the present work was to produce metallic iron, nickel, and tungsten through the gaseous reduction of nanosized metal oxide powders as a preliminary step towards the fabrication of nanosized heavy tungsten alloys with unique properties. Nanosized NiO, Fe2O3, and WO3 were isothermally and non-isothermally reduced with H2, and the oxygen weight loss was continuously recorded as a function of time. The Thermogravimetric TG-DTA technique was applied in the non-isothermal reduction up to 1000 °C. The reduction extents were calculated from the TG curve, whereas the accompanying heat of the reaction was measured from the DTA curve. The results revealed that NiO was reduced at <420 °C, Fe2O3 was reduced at <600 °C, and WO3 was reduced at >950 °C. In the isothermal process, metal oxides were reduced with H2 at 700–1000 °C; a micro-force balance was used and the O2 weight loss was continuously recorded. At a given temperature, the rate of reduction increased in the order NiO > Fe2O3 > WO3. The nano-oxide powders and the reduced products were physically and chemically characterized. The activation energy (Ea) values were computed from the isothermal reduction in the initial and later stages to elucidate the corresponding reduction mechanism. The Ea values indicated that the reduction of metal oxides was controlled by the gas diffusion mechanism at both the initial and later stages of reduction. The results of the present study determined the optimal operation parameters at which the thermal gaseous reduction technique could be applied for preparing metallic alloys from nanosized metal oxides.

Comparison of mechanical and microstructure properties of tungsten alloys for special purposes

Tungsten belongs to group of refractory metal that possess extraordinary resistance to heat and wear and it is the heaviest engineering material. Because of its properties tungsten is used for special purposes. This paper presents the results of mechanical and microstructure research on the example of the characteristic heavy tungsten alloys 91W-6Ni-1.8Fe-1Co and 93W-5Ni-1.6Fe-0.3Co with different Ni/Co ratios. The proper Ni/Co ratio is important to obtain a favorable microstructure and mechanical properties of these materials. The distribution of the W, Ni, Co and Fe elements in tungsten phase and binder phase, which can influence on mechanical properties of tungsten alloys. The SEM analysis and mechanical results show that the alloy, which has Ni/Co within the given limits, posses a finer microstructure and better mechanical properties that is very important for the maintenance of the quality of tungsten alloys for special purposes.

Investigation of powder bed laser fusion additive manufacturing of 93W, 5.6Ni, 1.4Fe tungsten heavy alloys

Tungsten exhibits a variety of interesting properties with significant potential for advanced applications but is currently limited by the difficulty of forming complex shapes for end-use parts. Additive manufacturing using powder bed laser fusion techniques may offer an alternative method of forming tungsten parts with greater design flexibility. To investigate this potential, two 93W, 5.6Ni, 1.4Fe tungsten heavy alloy (WHA) powders were densified using a Renishaw AM 400 laser melting system to >99.8% theoretical density and the resulting microstructures assessed. High densification was possible utilizing long exposure times to maximize melting at low laser powers, low to moderate laser powers to avoid overheating the FeNi phase, and small point distances, hatch distances, and layer heights to maximize remelting. SEM investigation of the resulting microstructure revealed two distinct phases: nearly pure W and ∼ 90% W-rich W-Ni-Fe. This was believed to be the result of complete melting of the NiFe powder and either dissolution of tungsten within the liquid NiFe matrix or partial melting of the tungsten powder. High cooling rates in the additive manufacturing process resulted in a tungsten-rich W-Ni-Fe matrix phase compared to traditional liquid phase sintered WHA alloys. Microhardness testing was conducted to begin assessment of resulting mechanical properties, with extremely high hardness values being measured when compared with expected literature values. Fine microstructure and high W content in the matrix phase contribute to these high hardness values, but further investigation is needed.

Proper (Nb,Fe) co-alloyed TiAl-based alloy with good hot deformation processing capability

In order to develop a proper (Nb,Fe) co-alloyed TiAl-based alloy with excellent hot deformation processing capability, avoiding the heavy alloying induced damage of service properties, the Ti–44Al–4Nb-0.5Fe-0.1B and Ti–44Al–2Nb–2Fe-0.1B alloys are designed and prepared. This paper mainly focuses on whether and why the hot deformation processing capability of the new alloys are improved. In view of this, thermo-compression experiments are carried out, hot deformation behavior is studied, constitutive equations are derived, hot processing maps are drawn, and hot deformation microstructure is studied. The results show that the Ti–44Al–2Nb–2Fe-0.1B alloy has lower true stress, moderate diffusion activation energy, lower stress exponent and larger hot processing window. Especially, the large hot processing window of Ti–44Al–2Nb–2Fe-0.1B alloy covers almost all the tested range of 1100 °C–1250 °C and 0.001 s−1-1.0 s−1, and meanwhile, the its power dissipation factor is higher. At lower temperatures of 1100 °C and 1150 °C, relatively more B2 phase in the Ti–44Al–2Nb–2Fe-0.1B alloy plays a good stress-strain coordination effect in the hot deformation process. At higher temperatures of 1200 °C and 1250 °C, the Ti–44Al–2Nb–2Fe-0.1B alloy is in the higher temperature phase region. Moreover, the compressed Ti–44Al–2Nb–2Fe-0.1B alloy has relatively lower dislocation density and more adequate dynamic recrystallization. In conclusion, all these results demonstrate that the Ti–44Al–2Nb–2Fe-0.1B alloy meets the design expectations, that is, this alloy with a proper (Nb,Fe) addition still has a very good hot deformation processing capability. At the same time, the Ti–44Al–2Nb–2Fe-0.1B alloy has a typical near-lamellar structure, rather than containing too much B2 phase or even containing lots of τ2 phase, so the good service properties can be expected.

Effect of W particle size on mechanical properties of a tungsten heavy alloy

Preparing fine tungsten particles tungsten heavy alloys (WHAs) is a method to improve the susceptibility to adiabatic shear of WHAs. In this paper, W-AlCrFeNiV alloy (W-HEA) with different size W particles were prepared by laser ultrashort-time liquid phase sintering (LULPS) and liquid phase sintering (LPS). The effects of W particle size of W-HEA on mechanical property and susceptibility to adiabatic shear are studied. The results show that W-HEA with 3 μm W particles has excellent mechanical properties-tensile strength nearly 1500 MPa. The tensile strength is 58% higher than that W-HEA with 20 μm W particle. W-HEA with 3 μm W particle dynamic compression strength is 2200 MPa under 4000 s-1. The dynamic strength is 22% higher than that tungsten heavy alloy with 20 μm W particle. And the smaller W particles are, the stronger susceptibility to adiabatic shear is. The adiabatic shear band width of W-HEA with 3 μm W particles is 10 μm after dynamic compression.

Design of ultrasonic elliptical vibration cutting system for tungsten heavy alloy

Design of ultrasonic elliptical vibration cutting system for tungsten heavy alloy

Medium heavy alloy fabrication with ultrafine grain and high performance via spark plasma sintering

• Medium heavy alloys were successfully fabricated for the first time using the spark plasma sintering technique. • Nearest theoretical density achieved for the Ni-37W-5Co alloy. • Σ3 boundaries are formed in the Ni matrix. • The Ni-37W-5Co alloy has the highest UTS of 740 MPa. W-Ni-Co, W-Ni-Co-Ta, and W-Ni-Co-B 4 C medium-heavy alloys and alloy composites are developed using the spark plasma sintering technique in the current study. This work aims to investigate the structure–property correlations of the three different compositions mentioned above. The compacts are subjected to extensive metallurgical and mechanical testing. Annealing twins are formed in the Ni matrix phase, and the density of the twins revealed a difference in material strength. The densification response and tensile tests showed that the base alloy W-Ni-Co has the highest tensile strength (740 MPa), an elongation of 4.5%, and a relative sintered density of 96%.

Effect of Ta addition on the sinterability of spark plasma sintered W-Ni-Fe alloy

The purpose of this research is to investigate and characterize the W-Ni-Fe-Ta compositions by solid-state sintering using the Spark Plasma Sintering (SPS) technique at a relatively lower temperature. The sinterability of W-Ni-Fe ternary tungsten heavy alloy (WHA) with the addition of Tantalum in predetermined compositions was sintered using SPS at 1100°C under 30 MPa pressure. The effect of Ta addition on WHA densification, microstructure, and mechanical properties was studied. Ni was found to act as an activator in the sintering of tungsten. SEM and energy dispersive spectroscopy revealed an even distribution of Ta in the W and Ni-Fe matrix. The data of hardness and ultimate tensile strength were explained using grain size, contiguity, and the formation of brittle intermetallic phases. W-7Ni-3Fe-5Ta alloy composition has the highest ultimate tensile strength of 870 MPa, 189.2 HV0.5kgf hardness, and 83.42% relative sintered density. During the tensile test, W grain cleavage fracture, W-W decohesion, matrix tearing, and W matrix intergranular types of fracture surface were observed.

Theoretical and numerical studies of surface microstructural transformation in ultrasonic elliptical vibration cutting tungsten heavy alloys

Theoretical and numerical studies of surface microstructural transformation in ultrasonic elliptical vibration cutting tungsten heavy alloys

Effect of Sintering Temperatures on Grain Coarsening Behaviors and Mechanical Properties of W-NiTi Heavy Tungsten Alloys.

W-NiTi tungsten heavy alloys were prepared by an infiltration process using submicron W powders, and the effect of sintering temperatures on grain-coarsening behaviors and the mechanical properties of W-NiTi tungsten heavy alloys were investigated. The microstructures and mechanical properties were investigated using scanning electron microscopy, X-ray diffraction and compression tests. The results showed that tungsten particles were uniformly distributed in the NiTi binder. The W-NiTi tungsten heavy alloys consisted of B19'-NiTi and body-centered cubic W phases. The average tungsten particle sizes of W-NiTi tungsten heavy alloys sintered at 1400 °C, 1480 °C and 1560 °C were 2.62 μm, 4.04 μm and 5.20 μm, respectively. The average tungsten particle size increased with sintering temperatures, while the densities decreased at higher temperatures. The cavities retained in the W-NiTi tungsten heavy alloy sintered at 1560 °C, which degraded the mechanical properties. The calculated grain growth activation energy of W particles in the NiTi binder was 330 kJ/mol, which was higher than those in conventional W-NiFe and W-NiCo tungsten heavy alloys. The higher activation energy means more difficult diffusion process of W atoms in NiTi binders during sintering. Therefore, finer-grained heavy tungsten alloys were more easily obtained by using NiTi binders. Yield strength of W-NiTi tungsten heavy alloys decreased with increasing sintering temperatures due to coarsened tungsten particles.

Bimodal grained Mg–0.5Gd–xMn alloys with high strength and low-cost fabricated by low-temperature extrusion

Obtaining high strength in Mg alloys generally requires a high alloying content, especially rare earth elements. However, as a lightweight alloy, the heavy rare-earth content has a negative impact on the density of Mg alloys and the related cost, which increases the exploration need of low rare-earth and low-cost Mg alloy. In this work, a new low-cost and high mechanical strength Mg–0.5Gd–xMn (x = 0, 0.5, 1.0, 1.5, 2.0 wt.%) alloys system was developed by the low-temperature extrusion at 250 °C. A typical bimodal grain structure was formed in as-extruded Mg-0.5Gd-xMn alloys. The results presented a gradually increased yield strength and ultimate tensile strength with the increment of the Mn content from 0 to 1.5 wt.%. The tensile yield strength and ultimate tensile strength reached 357 MPa and 364 MPa in Mg–0.5Gd–1.5Mn alloy, which was 62 MPa and 63 MPa higher than that of the Mg–0.5Gd alloy. The high performance was mainly due to the bimodal grain structure, which produced a good Hall-Petch strengthening and the back stress strengthening. The Mg–0.5Gd–xMn alloys possessed a feature of comparable high mechanical strength with heavy rare-earth content traditional Mg alloys but a much lower cost, which promotes the future application.

Effect of rotary swaging on microstructure evolution and adiabatic shear sensitivity of 90W–7Ni–3Fe alloy under dynamic loading

Tungsten heavy alloys (WHAs) are widely used in the preparation of kinetic penetrators. However, the penetrating performance of alloys, measured by the “self-sharpening effect”, is often limited by the low sensitivity of the adiabatic shear band (ASB). To address this issue, the 90W–7Ni–3Fe rods with deformation degrees of 20% and 40% were prepared by rotary swaging (RS) at high strain rates (4000 s−1 and 6000 s−1, respectively). The deformation and ASB behavior of RS-treated alloys were compared to those of undeformed samples. According to the results, RS pretreatment significantly increased the dynamic penetration strength and ASB sensitivity of the alloys. Besides, the characterization of the recrystallized microstructure within ASB and the calculation of the adiabatic temperature rise indicated that microstructure softening could be the primary cause for the initiation of ASB, which was consistent with the rotational dynamic recrystallization (RDR) mechanism. Moreover, the higher strain energy of the 40% RS deformation sample with high densities of dislocations and twins promoted the subgrain rotation and RDR initiation, providing a recrystallization prerequisite for the propagation and proliferation of ASB. The recrystallized twins formed after the completion of the RDR in the 40% RS deformation sample in order to adapt to the reloading impeded the movement of dislocations, which became a stress concentration site promoting microdamage more likely to nucleate and expand, making the ASB more prone to fracture. Therefore, this study is of great significance for the development of self-sharpening WHA kinetic penetrators.

Tungsten Heavy Alloys Processing via Microwave Sintering, Spark Plasma Sintering, and Additive Manufacturing: A Review

Tungsten-heavy alloys (WHA) are a pseudo-alloy in which tungsten is the primary phase and remains filled with additives such as Ni–Fe and Ni–Cu. These alloys are widely used to make their applications’ structural, electrical, and electronic components. According to this study, in addition to processing factors, the prime factors affecting the performance of WHAs are microstructural features such as tungsten and matrix composition, powders shapes and sizes, and distributions of tungsten particles in the matrix, as well as interface-bonding strength between the tungsten particle and matrix. This study summarises current developments in WHA processing, microstructure, and mechanical characteristics. For the manufacture of WHAs, various processing methods are discussed, including traditional powder metallurgy (PM), microwave sintering (MW), spark plasma sintering (SPS), and additive manufacturing (AM). SPS process depicts better results when compared with conventional sintering. This review will also hint at the effects of some additives in tungsten and their advantages.

Effects of laser printing parameters on molten pool formation, microstructure evolution and mechanical properties of laser directed energy deposition of difficult-to-process tungsten heavy-alloy

Laser directed energy deposition (LDED) additive manufacturing is promising in the fabrication of high-performance W-based heavy-alloys which are normally difficult-to-process due to their unique nature such as the extremely high melting point and high ductile-brittle transition temperature. In this work, a novel 95 W heavy alloy modified by nanosized Ni and Fe particles was manufactured by LDED process. The effects of laser power on the formation mechanisms of molten pool were investigated. It was found that a relatively high laser power could promote the complete melting of W powder and formation of regular molten pool morphology. The microstructures of laser-processed W heavy alloy showed columnar grains, cellular grains and equiaxed grains from bottom to top within the molten pool along the building direction. The three-dimensional finite element simulation revealed the temperature gradient ( G ), cooling rate ( C ) and solidification velocity ( S ) within the molten pool were different, which was responsible for the microstructural development. The bulk-form 95 W heavy-alloy part free of defects was produced at the laser power of 1400 W. The optimally processed 95 W heavy-alloy by LDED showed a high average nanohardness of 8.6 GPa and a sound wear performance with a low coefficient of friction (COF) of 0.5. The tensile tests also revealed the achievement of a combination of an excellent tensile strength of 541 MPa and an elongation of 0.99%. This work demonstrated that LDED was able to manufacture high-performance tungsten heavy-alloys in bulk form with outstanding mechanical properties.

Influence of microstructure on crack initiation and propagation behavior in swaged tungsten heavy alloy during Charpy impact process

In this study, microstructure evolution and mechanical properties of 90W–7Ni–3Fe alloy under different swaging levels were systematically examined, with an emphasis on the relationship between the deformed microstructure and impact failure behavior. The deformed microstructure was characterized by scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM), and the impact toughness of specimens were tested using an instrumental Charpy impact machine. Microstructure observations showed that swaging significantly changed shape of W grains and increased the W contiguity. With increasing of deformation levels, microstructure changed from high density dislocations to subgrain structures. Furthermore, pronounced <101> texture is also found in the W phase at the highest deformation level. With increasing of deformation level, the tensile strength sharply increased from 950 to 1313 MPa and the tensile strain decreased from 27% to 9%. The impact test results indicate that the total impact absorbed energy consists of crack initiation energy and crack propagation energy. As deformation level increases, crack initiation energy decreased from 81 J to 23 J, while crack propagation energy first increased to 23 J and then decreased to 10 J. The decrease in crack initiation energy is mainly caused by the increase in dislocation density and W contiguity. The variation of crack propagation energy is relatively complex and influenced by several factors, such as W contiguity, the ability of the matrix phase to resist crack extension, the increased W cleavage event, and so on. Our study provides a deep insight into the relationships between microstructure and impact toughness of swaged tungsten heavy alloys.