Effect of Mn/Ni ratio variation on microstructure of W–Ni–Mn alloy

Abstract

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%.     

Investigation of deformation and heat treatment effects on properties of PM 92.5W–5Ni–2.5Fe heavy alloys

Abstract

This paper presents the effects of vacuum heat treatment under different cooling conditions on mechanical and structural properties of forged heavy alloys, such as 92.5W–5Ni–2.5Fe and 92.5W–5Ni–25Fe microalloyed with Co. The tungsten composition in the c phase has proved to be higher and more homogenous in the rapidly cooled alloys than in the slowly cooled ones. The effects of chemical composition inhomogeneity on mechanical and structural properties of alloys were also analysed and discussed. The results of tensile and toughness testing have shown an increase in ductility and toughness, while the strength of heat treated alloys decreased in comparison with the strength of forged alloys. The fracture analysis has shown that in the sintered and rotary forged alloys, intergranular fracture of the tungsten phase and transgranular fracture of the γ phase occurred, respectively. The fracture of these phases after heat treatment was characterised by transgranular morphology.     

Features of the Sintering of Fe–Cu–Sn–Ni and Cu–Ti–Sn–Ni Powders during Hot Pressing

Powder Metallurgy and Metal Ceramics - The efficiency and durability of a diamond tool fabricated using powder metallurgy methods depend on several factors. These are the quality of diamond...     

Effects of wet and dry milling conditions on properties of mechanically alloyed and sintered W–C and W–B4C–C composites

Abstract

Tungsten based W–1C and W–2B₄C–1C (wt-%) powders synthesised by mechanical alloying (MA) for milling durations of 10, 20 and 30 h, in wet (ethanol) and dry conditions, were characterised. X-ray fluorescence spectroscopy investigations revealed Co contamination which increased with increasing milling time during wet milling. X-ray diffraction investigations revealed the presence of W and WC phases in all powders, Co₃C intermetallic in the wet milled W–1C powders and W₂B intermetallic phase in both wet and dry milled W–2B₄C–1C powders. As blended and MA processed powders were consolidated into green compacts by uniaxial cold pressing at 500 MPa and solid phase sintered at 1680°C under hydrogen and argon atmospheres for 1 h. X-ray diffraction investigations revealed the presence of W₂C intermetallic phase in sintered composites produced from both wet and dry milled W–1C powders and the W₂B intermetallic phase in sintered material from the wet milled W–2B₄C–1C powder. Sintered composites from wet milled powders showed relative densities >91%, with the maximum density of 99·5% measured for the sintered 30 h wet milled W–2B₄C–1C composites. Microhardness values for the wet milled W–1C and W–2B₄C–1C composites were 2–2·5 times higher than those for dry milled composite powders. A maximum hardness value of 23·7±2·1 GPa was measured for the sintered W–2B₄C–1C composite wet milled for 20 h.     

Research on the preparation and shielding properties of W–Ni–Fe alloy material by liquid phase sintering

Traditional and single shielding material has not satisfied the demand for radiation protection. Shielding materials with a good comprehensive performance have attracted attention. W–Ni–Fe alloys with different Ni/Fe ratios have been prepared through liquid phase sintering using W, Ni and Fe elementary powders. The microstructure, morphology and fracture appearance of such prepared W–Ni–Fe alloys with different Ni/Fe ratios were analysed with the SEM and metallographic test. The effects of the Ni/Fe ratio on the density, microhardness, tensile strength and shielding efficiency were investigated. The results show that for W–Ni–Fe alloys with different Ni/Fe ratios, the alloy surfaces are composed of ellipsoidal W particles on a Ni–Fe substrate. However, when the Ni/Fe ratio is 7:3, uniform and spherical W crystals are embedded in the Ni–Fe substrate and evidently form dense boundaries, which contribute to the good mechanical properties and shielding effect of the alloy.     

Regularities of the contact interaction of titanium carbide with Ni and Ni–Mo melts

Regularities of the dissolution, the phase formation, and the structure formation implemented under the contact interaction conditions of titanium carbide of various compositions with Ni and Ni–(5–25%)Mo melts are investigated. It is originally established that the dissolution of carbide TiC_x in nickel-based melts is incongruent. Preferentially, carbon transfers into the melt at x ≥ 0.9 and titanium at x ≤ 0.8. The limiting stage of the dissolution is diffusion of metal atoms in the liquid phase. The formation regularities of carbide Ti_1–nMo_nC_x (K-phase)—the main product of the contact interaction in the TiC/Ni–Mo system—are revealed. It is established that the K-phase is formed under the relative excess conditions of the Ni–Mo melt preferentially according to the dissolution–isolation mechanism. The composition of autonomous isolations of the K-phase depending on the experimental conditions (1450°C, 0–25 h) varies in limits from Ti_0.4Mo_0.6C_0.7 (a = 4.27 Å) to Ti_0.7Mo_0.3C_0.6 (a = 4.29 Å). It is determined by the molybdenum concentration in the melt at the unsteady dissolution stage and by the concentration ratio between titanium and carbon in it at the steady-state dissolution stage.     

Deposition,Characterization and Evaluation of Monolayer and Multilayer Ni,Ni–P and Ni–P–Nano ZnO<Subscript>p</Subscript> Coatings

Ni, Ni–P and Ni–P–ZnO_p monolayer films along with multilayer coatings containing different arrangements of these layers were produced on steel substrates by electrodeposition and electroless deposition techniques. Co-deposition of ZnO nano-particles, as well as morphology, cross-section, microstructure and microhardness of coatings were investigated. Corrosion behaviors of monolayer coatings were studied by potentiodynamic polarization and electrochemical impedance spectroscopy techniques, and the results were compared to multilayer films. Results revealed that, Ni–P–1.5 vol% ZnO_p monolayer film obtained from a bath with 4 g L^?1 of these particles had the highest hardness between all samples. Further addition of nano-particles to the bath lead to the formation of discontinuous films. Most of the multilayer coatings with different arrangements exhibited higher corrosion resistance as compared to monolayer films. Corrosion current density of three-layer Ni–P–ZnO_p/Ni/Ni–P coating, considered as the most corrosion resistant film, was about 538 times lower than monolayer Ni–P coating.     

Simultaneous reduction nitridation for the synthesis of tungsten nitrides from Ni–W–O precursors

Abstract

Tungsten nitrides were synthesised from NiO–WO₃ and NiWO₄ precursors at 973–1273 K in a flow of H₂–N₂ gas mixture. The reduction–nitridation reactions were carried out isothermally in fluidised bed reactor, and the off-gas from the reactions was continuously analysed by gas chromatography. The effect of reaction temperature and precursor composition on the rate of formation of Ni–W nitrides was studied. The different phases developed during the reduction–nitridation reactions were identified by X-ray diffraction analysis technique. The morphology and the grain structure of the precursors were examined by SEM, and the elemental composition in the structure was analysed by electron dispersive spectrometry. The results showed that the reduction of Ni–W–O precursors proceeded in a stepwise manner (NiWO₄→Ni–WO₃→Ni–WO₂→Ni–W). Tungsten nitrides (WN and WN₂) were formed from the reaction of the freshly reduced W metal with N₂ gas and WN was the predominant phase detected at higher temperatures. The reaction mechanisms were elucidated from the apparent activation energy values and the application of different formulations derived from the gas–solid reaction model at early and later stages of reactions. It was concluded that the interfacial chemical reaction is the rate determining step at initial stages, while a combined effect of gaseous diffusion and interfacial chemical reaction controlled the reaction at later stages. At final stages, the nitridation reactions contributed to the reaction mechanism leading to produce tungsten nitrides.     

On development of press and sinter Al–Ni–Mg powder metallurgy alloys

Abstract

The objective of this research was to initiate the development of powder metallurgy alloys based on the Al–Ni–Mg system. In doing so, binary (Al–Mg) and ternary (Al–Ni–Mg) blends were prepared, compacted and sintered using elemental and master alloy feedstock powders. Research began with fundamental studies on the sintering response of the base aluminium powder with additions of magnesium. This element proved essential to the development of a well sintered microstructure while promoting the formation of a small nodular phase that appeared to be AlN. In Al–Ni–Mg systems a well sintered structure comprised of α aluminium plus NiAl₃ was produced at the higher sintering temperatures investigated. Of these ternary alloys studied, Al–15Ni–1Mg exhibited mechanical properties that were comparable with existing commercial 'press and sinter' alloys. The processing, reaction sintering and tensile properties of this alloy were also found to be reproducible in an industrial production environment.     

Effects of strain aging on the structure and mechanical properties of PM 92·5W–5Ni–2·5Fe heavy alloys

Abstract

This paper describes the effects of strain aging on the mechanical properties and the microstructure of forged 92·5W–5Ni–2·5Fe and its heavy alloys microalloyed with cobalt. The investigation was performed on cold rotary forged rods deformed 15, 20 and 30% and strain aged at temperatures from 673 to 1273 K for 1·8–32·4 ks. The results show that for these alloys, there is a temperature range from 773 to 873 K in which maximum ultimate strength and hardness can be attained. Furthermore, the strain aged alloys have shown strength and hardness increase at a temperature of 973 K in a time period of 10·8 ks. The fracture analysis has shown the presence of predominant transgranular fracture of the tungsten phase and γ-phase in the strain-aged alloys in comparison with the forged alloys. The results indicate that interface and tungsten phase strengthening are predominant mechanisms of strain aging.     

China Limits the Mining Quantity of Tungsten and Rare Earth

Based on a notice issued by the Ministry of Land Resources, China's tungsten mining quantity in 2006 will be controlled to 59,060 tons in concentrates form, which include 4,250 tons of recycled tungsten. And the rare earth mining quantity in 2006 will also be controlled to 86,620 tons (REO) including 8,320 tons of heavy rare earth and 78,200 tons of light rare earth.     

Microstructural Features and Mechanical and Tribological Properties of Fe–Cu–Ni–Sn Composites Precipitation-Hardened with CrB2 Additions

Powder Metallurgy and Metal Ceramics - The structural features, hardness, elastic modulus, and wear resistance of Fe–Cu–Ni–Sn composites with different CrB2 contents, produced by...     

Simulation and verification of core–shell MC carbide design in Fe–C–Ni–V–Ti steel

Thermodynamic theory was used to calculate the formation temperature and site fraction of MC carbides in Fe–C–Ni–V–Ti system. The calculation results showed the...     

Morphological development during ageing of NiW alloys

The ageing response of a NiW alloy has been studied by electron microscopy. Two particle morphologies develop on ageing: a semi-coherent lath shaped particle and a coherent multi-variant domain (MVD) plate-shaped particle composed of two perpendicular twin variants. The factors responsible for the evolution of these shapes on coarsening are discussed. A comparison of the energies associated with the two morphologies suggests that the MVD particles will be more stable.     

Changing Conditions of Supply and Demand in the Tungsten Concentrate Market

In January 2004,when Jiangxi Tungsten Indus-try Group,one of the major tungsten producersin China,made a quote of RMB 25,500 yuanper ton,the actual domestic market quotes hadalready risen above RMB 28,000 yuan per ton.In February,when the major tungsten produc-ers negotiated a quote of RMB 28,500 yuan perton,the actual domestic market quotes had     

Effects of Trace Additions of Magnesium on Microstructure and Properties of Fe–36Ni Invar Alloy

Low-thermal-expansion alloys play a crucial role in high-precision instruments and devices. Simultaneously improving mechanical performance and keeping or even decreasing low thermal expansion behavior are urgently required for their industrial application. Herein, a new attempt to treat Fe–36Ni Invar alloy by adding trace magnesium (Mg) in a concentration ranging from 0 wt% to 0.0030 wt% (similarly hereinafter) is conducted. The introduction of Mg results in grain refinement and an increase in the volume fraction of the annealing twins. Compared with the Mg-free sample, the coefficient of thermal expansion (CTE) of 0.0030% Mg alloy is significantly decreased by more than 20%, which is mainly related to lattice distortion and matrix purification. The yield strength of 0.0030% Mg alloy improves by 10% with respect to Mg-free alloy, because of grain boundary strengthening and solid-solution strengthening. The study may lay the basis for a better understanding of the application of Mg in low-thermal-expansion alloys.     

Effect of Vacuum Hot Pressing Temperature on the Mechanical and Tribological Properties of the Fe–Cu–Ni–Sn–VN Composites

Powder Metallurgy and Metal Ceramics - The mechanical (hardness and elastic modulus) and tribological (friction force and wear rate) properties of the Fe–Cu–Ni–Sn–VN...