Fe Heavy Alloy Research Articles

Effect of Y2O3, La2O3 and ZrO2 dispersoid addition on ultra-high temperature stability of 95W–3.5Ni–1.5Fe heavy alloy

In this work, the effect of three different oxide dispersoids (Y2O3, La2O3, ZrO2) addition on densification, phase, microstructure evolution and high-temperature stability has been investigated thoroughly and compared with that of 95W-3.5Ni-1.5Fe (wt.%) heavy alloy (WHA). The heavy alloys were prepared by powder metallurgy process and consolidated by conventional sintering at 1500 °C in hydrogen atmosphere. The oxide additives did not improve the densification, however, enhanced the hardness of the sintered heavy alloys. Upon exposure to ultra-high temperature (2300 °C) for 10 s, the base alloy suffered significant damage and experienced mass loss due to evaporation of W-oxide. On the other hand, Y2O3, La2O3 and ZrO2-dispersed heavy alloys exhibit protective oxide layer formation. Furthermore, the XRD and FESEM analyses of the exposed surface affirm that no significant damage has incurred in the oxide dispersed WHAs despite identical experimental condition. Owing to the thermal stability of W-Y-O, W-La-O and W-Zr-O systems, the oxide-dispersed heavy alloys offer better structural stability at ultra-high temperature.

A Tungsten Heavy Alloy with Enhanced Performance Prepared by Spark Plasma Sintering from Fine Spherical Tungsten Powders

Traditional tungsten heavy alloys (WHAs), with a coarse liquid‐phase sintered microstructure, have moderate strength and excellent ductility. Grain refinement is one of the effective methods to improve the strength of these WHAs. The routine spark plasma sintering (SPS) method can refine W grains; however, the obtained typical solid‐state sintered microstructure is detrimental to the performance. Adapted SPS methods such as cyclic SPS and transient liquid‐phase SPS, proposed in the previous study, are capable of modifying W grain morphology to further enhance the performance of parts. They are, however, complex processes, especially when it comes to mass production. In this research, 93W–5.6Ni–1.4Fe heavy alloys (93WHAs) with similar liquid‐phase sintered microstructure are prepared via SPS at solid‐state sintering temperature using fine spherical W powders as raw materials. The influences of the W powder shape and powder mixing condition on the microstructural and mechanical properties of the prepared 93WHAs are investigated. An improved microstructure is obtained in the 93WHA prepared using spherical W powders blended with nano Ni and Fe powders as raw materials, as compared to using the irregular W powders. The alloy thus shows elevated mechanical properties, due to the improved matrix phase distribution and the W grain morphology.

Effect of HfC addition on the microstructure and properties of W–4.9Ni–2.1Fe heavy alloys

In this study, W–4.9Ni–2.1Fe-xHfC mixed alloy powders were prepared by secondary high-energy ball milling and secondary hydrogen annealing, and then sintered and consolidated by spark plasma sintering (SPS) techniques. The microstructure, mechanical properties, wear resistance and corrosion behavior of alloy were obtained by Vickers hardness tester, X-ray diffraction, scanning electron microscopy, reciprocating frictional wear testing machine, CHI 660 E electrochemical workstation and electronic universal testing machine. The results showed that a certain amount of Hafnium carbide (HfC) could effectively inhibit the growth of W particles during sintering process, make the bonding phase disperse more evenly, and effectively improve the hardness, relative density, compression strength, friction and wear properties as well as corrosion resistance of alloy. When the content of HfC was excessive, the inhibition effect of particle growth would be weakened and the bonding phase tended to agglomerate, affecting the strength and hardness, and reducing the abrasion performance and corrosion resistance of alloy. By comparison, the alloy with 0.4 wt% HfC showed the best comprehension performance.

Concurrent Hardening and Toughening of a Tungsten Heavy Alloy via a Novel Carburizing Cyclic Heat Treatment

Tungsten heavy alloys (WHAs), due to the combination of some attractive properties, are used in many engineering applications. Recently conducted researches are however focused on improving the surface properties of these alloys, such as their hardness, wear, and corrosion resistance, by applying different surface treatments. However, the obtained enhanced surface properties are concomitant with the maintenance or even deterioration of the mechanical properties, namely toughness, in the interior regions of these alloys. Herein, a novel carburizing cyclic heat treatment (CCHT)‐integrated technique is used to modify the microstructure of a 93W–4.9Ni–2.1Fe heavy alloy (93WHA). Other than investigating the effect of the applied process on the surface hardness and microstructure of this alloy, the influence of the conducted process on the microstructural and mechanical properties of the interior region of the processed parts is investigated. Due to the application of the CCHT process, the surface hardness of parts increases from 300 HV0.5, as observed in the nontreated samples, to the maximum value of 1049 HV0.5. In addition to the hardening effect observed on the surface of the treated samples, the interior regions of the CCHT‐modified parts are toughened.

Microstructure and mechanical properties of liquid–phase sintered W@NiFe composite powders

W–Ni–Fe heavy alloys were obtained by liquid–phase sintering of W@NiFe composite powders. The face–centered cubic NiFe alloys were deposited as a shell on the core of tungsten particle to form W@NiFe composite powders by intermittently electrodeposition. After liquid–phase sintering, W–Ni–Fe heavy alloys had more gradient morphology and shape distortion as the holding time increased. The bending strength and hardness distributed graded at 1470 °C holding for 0.5 h. Top layer of gradient W–Ni–Fe heavy alloys at 1470 °C holding for 0.5 h showed low WW contiguity, no normal growth of W particle size and high sintered density, which led to excellent bending strength (1245 MPa) and hardness (340 HV0.2). The structure and composition of W@NiFe composite powders and the optimization of sintering process parameters were analyzed and discussed. The sintering behavior of W@NiFe composite powders were also investigated in details.

Correction to: Effect of Y2O3 Addition on the Microstructure, Wear Resistance, and Corrosion Behavior of W-4.9Ni-2.1Fe Heavy Alloy

Correction to: Effect of Y2O3 Addition on the Microstructure, Wear Resistance, and Corrosion Behavior of W-4.9Ni-2.1Fe Heavy Alloy

Effect of Y2O3 Addition on the Microstructure, Wear Resistance, and Corrosion Behavior of W-4.9Ni-2.1Fe Heavy Alloy

Binding and particle phases are the two important parameters influencing materials properties. In this study, a series of novel W-4.9Ni-2.1Fe-xY2O3 (in weight%) alloys with different Y2O3 contents are prepared by secondary ball milling and spark plasma sintering (SPS) techniques to obtain uniformly distributed γ-(Ni, Fe) binding phases and finer grains. The microstructure, mechanical, wear resistance, and corrosion behavior of the sintered bodies with different Y2O3 were obtained by x-ray diffraction, scanning electron microscopy, Rockwell hardness tester, friction wear tester, and three-dimensional profile instruments. The results showed that a certain addition of Y2O3 led to refined grains and uniformed microstructures; but, if excessive, a weak grain refinement would be appeared. Moreover, the grain size tends to be stable with enhancing of the Y2O3 content. Considering properties such as density, hardness, compression yield strength, grain size, and uniform distribution of tungsten hard phase and γ-(Ni, Fe) binding phase, the comprehensive optimal amount of 0.7 wt.% of Y2O3 was attained for the alloy. Meanwhile, the SPS sintered body also exhibited the best friction, wear behavior, and corrosion resistance in 3.5% of NaCl solution.

Microstructure and properties of W–4.9Ni–2.1Fe heavy alloy with Dy2O3 addition

The W–4.9Ni–2.1Fe–xDy2O3 heavy alloy was fabricated by high-energy ball milling and spark plasma sintering (SPS) technique, and the microstructure, mechanical and friction behavior and anti-corrosion ability were investigated by scanning electron microscope (SEM), Rockwell hardness tester, X-ray diffraction (XRD), reciprocating friction and wear tester, electrochemical station, etc. The results show that the trace Dy2O3 particles, which mainly distributes in the W–M (tungsten-matrix) interface and the tungsten matrix phase, can dramatically decrease the tungsten grain size and the amount of O and P impurities aggregating in the interface, promote the γ-(Ni, Fe) bonding phase and tungsten particles uniform distribution, and increase the relative density, hardness, and wear and corrosion resistance properties. But the excessive Dy2O3 addition can make the inhibition effect weaken, resulting in the decrease in the comprehensive performances of the alloy. So, the amount of Dy2O3 should be appropriate. When the adding amount of Dy2O3 particles is 0.7 wt%, the comprehensive performances of the heavy alloy are the best.

Influence of high-energy ball milling on the solid-phase sintering kinetics of ultrafine-grained heavy tungsten alloy

The mechanisms for the sintering of ultrafine-grained 95%W–3.5%Ni–1.5%Fe heavy tungsten alloy powders have been investigated. It has been established that a decrease in the activation energy of grain boundary diffusion and the formation of a nonequilibrium solid solution of nickel and iron in the surface layer of tungsten particles upon high-energy ball milling are responsible for the decrease in optimal sintering temperature.

Effect of high energy ball milling on structure and properties of 95W-3.5Ni-1.5Fe heavy alloys

In this article, an attempt is made to prepare tungsten heavy alloy (WHA) powder by high energy ball milling of 95wt% W, 3.5wt% Ni and 1.5wt% Fe in a dual drive planetary ball mill (DDPBM). The present study mainly focusses on the effect of milling on density, microstructure and mechanical properties of sintered WHAs. The minimum crystallite size of 18nm was observed in 15h milled WHA powder. Sintering of WHAs was carried out at 1500°C for 1h in hydrogen atmosphere. The sintered samples prepared from un-milled and ball milled WHA powders were characterized for microstructure (SEM equipped with EDS) and mechanical properties (Rockwell hardness and nanoindentation). The internal attributes and uniformity in distribution of W spheroids in sintered WHA were investigated with X-ray microcomputed tomography (X-ray μ-CT). All sintered samples exhibited sintered density in the range of 97.1 to 98.6% theoretical. Uniform distribution of W spheroids in Ni-Fe matrix was observed in sintered samples. The mean grain size of sintered WHAs varies in the range of 22.7–31.1μm and W-W contiguity (CWW) ranges from 0.58–0.69. Despite relatively less density (97.1%), the sintered WHA prepared from 15h milled powder offered good combination of bulk hardness ~64.8 HRA and elastic modulus ~431GPa.

Sintering and Cold Swaging of Tungsten Heavy Alloys Prepared from Various Grades of W Powder

In the present work, sintering and cold swaging of 92.5W–5.25Ni–2.25Fe heavy alloys prepared from various grades of W powder were investigated. The mean particle sizes of the W powder grades were 3.4 µm, 10.5 µm, and 28.0 µm. It was observed that linear shrinkage decreased with increasing W particle size. The sintering behavior of the alloys was discussed in terms of liquid capillarity and W particle size. The alloy prepared from the 28.0-µm grade W powder exhibited incomplete densification. This alloy could not be swaged because of the poor mechanical properties. The alloys of the other grades were fully densified. They exhibited better ductility and swageability. The alloy of the 10.5-µm grade W powder had good mechanical properties (e.g., tensile strength 1300 MPa, hardness 38 HRC after 10% cold swaging) that were equivalent to those of the alloy of the fine-grade W powder (3.4 µm).

Densification of SiC Particle Reinforced W–Ni–Fe Heavy Alloy Composites Through Conventional and Spark Plasma Sintering

Silicon carbide particle reinforced W–Ni–Fe heavy alloys were prepared using conventional and spark plasma sintering techniques. Comparative analysis based on the densification response, microstructural and mechanical properties were done. The powder sintered using SPS technique was found to exhibit, good density and mechanical properties over the conventional sintering. Detailed fractography revealed a mixed mode and intergranular fracture. The reinforcement of SiC in W–Ni–Fe, had significantly increased the hardness and other mechanical properties of the heavy alloy composites.

Effect of carburization on microstructure and rolling contact fatigue property of 95W–3.4Ni–1.6Fe heavy alloy

95W–3.4Ni–1.6Fe heavy alloy was carburized by pack carburization. Microstructure and hardness of the carburized alloy were investigated by SEM, EDS XRD. Effect of carburization on the rolling contact fatigue (RCF) property of the alloy was studied. The results showed that the carburized layer was composed of the outer, porous WC layer and the modified subsurface layer with each W grain surrounded by a WC shell. Carburization not only decreased the RCF performance of the alloy but also aggravated the wear of the counter balls. The untreated alloy was damaged by two modes of spalling and delamination under RCF condition. The subsurface main crack of the untreated alloy initiated where the maximum shear stress existed and preferentially propagated along the W–W interfaces. Spalling was the main failure mode of the carburized alloys, and the crumbling WC particles intensified the abrasion of the carburized surface.

Dynamic deformation behavior of 93W-5.6Ni-1.4Fe heavy alloy prepared by spark plasma sintering

In this study, split Hopkinson pressure bar was used to evaluate the dynamic deformation behavior of the 93W–5.6Ni–1.4Fe heavy alloy (93WHA) prepared by spark plasma sintering (SPS) and conventional liquid-phase sintering (CLS). The influence of the microstructural characteristics (such as W grain size, W–W contiguity and volume fraction of the matrix) on the dynamic deformation behavior was investigated. In contrast to the conventional liquid-phase sintered 93WHA, the spark plasma sintered 93WHAs exhibit high yield strength and flow stress during high strain rate compression, due to the decreased mean matrix thickness (the mean matrix thickness is related to the W grain size, W–W contiguity and volume fraction of the matrix). The decreased matrix mean thickness and increased number of grain boundaries in the spark plasma sintered 93WHAs result in an increase of aspect ratio of W grains in the core of the deformed specimen and a decreased width of shear band along the direction of maximum shear stress.

A comparative study of spark plasma sintering and hybrid spark plasma sintering of 93W–4.9Ni–2.1Fe heavy alloy

Mixed 93W–4.9Ni–2.1Fe powders were sintered via the spark plasma sintering (SPS) and hybrid spark plasma sintering (HSPS) techniques with 30mm and 60mm samples in both conditions. After SPS and HSPS, the 30mm and 60mm alloys (except 60mm-SPS) had a relative density (>99.2%) close to the theoretical density. Phase, microstructure and mechanical properties evolution of W–Ni–Fe alloy during SPS and HSPS were studied. The microstructural evolution of the 60mm alloys varied from the edge of the sample to the core of the sample. Results show that the grain size and the hardness vary considerable from the edge to the core of sintered sample of 60mm sintered using conventional SPS compared to hybrid SPS. Similarly, the hardness also increased from the edge to the core. Furthermore, the 60mm-HSPS alloy exhibited improved bending strength of 1115MPa when compared to that of 60mm-SPS, 920MPa. The intergranular fracture along the W/W grain boundary is the main fracture modes of W–Ni–Fe, however in the 60mm-SPS alloy peeling of the grains was also observed which diminished the properties. The mechanical properties of SPS and HSPS 93W–4.9Ni–2.1Fe heavy alloys are dependent on the microstructural parameters such as tungsten grain size and overall homogeneity.

Preparation of W–Ni–Fe heavy alloys by soft chemical method

A facile glycine-nitrate method was developed to prepare superfine W-Ni-Fe powders by using relevant salts as the main raw materials, glycine as an incendiary agent and water as solvent. Phase composition of the composite powders was identified by X-ray diffraction analysis. Morphology of the powder was characterized by transmission electron microscopy and scanning electronic microscopy. Chemical composition of the powders was characterized by energy dispersive spectrometry. The test results indicate that superfine 95 W-3.5Ni-1.5Fe powders with grain sizes of about 150 nm could be obtained with the glycine-nitrate process. The powders showed good sinterability. Relative density higher than 97% with grain sizes of about 2 μm were obtained when the powder compacts were sintered at 1450 °C, and the sintered density reaches 99.3% at a sintering temperature of 1500 °C. The sintered W-Ni-Fe alloys showed good mechanical properties.

Fabrication, characterization, and mechanical properties of 93W–4.9Ni–2.1Fe/95W–2.8Ni–1.2Fe–1Al2O3 heavy alloy composites

In this study, tungsten heavy alloy (WHA) composites were fabricated based on tungsten (W), nickel (Ni), and iron (Fe) system. WHA composites with the composition 93W–4.9Ni–2.1Fe/95W–2.8Ni–1.2Fe–1Al2O3 were prepared by liquid-phase sintering and post-heat treatment to meet the requirement for complex mechanical performance. The relationship between the microstructural characteristics (relative density, W-grain size, and W–W contiguity) and mechanical properties was investigated. Variation in the content of W and addition of Al2O3 resulted in a significant difference in the microstructure of the two parts of W–Ni–Fe heavy alloy composite. The microstructure of the alloy significantly influenced the tensile properties of the two parts of the W–Ni–Fe heavy alloy composite; however, it did not affect their compressive deformation behaviors.

93W-5.6Ni-1.4Fe高比重合金放电等离子主烧结曲线的建立 *

Tungsten heavy alloys are used for a number of applications, including radiation shields, counter weights, electrical contacts, vibration dampeners and kinetic energy penetrators. The most common compositions consist of W along with some combination of Ni, Fe, or Cu. The alloys are usually fabricated by the conventional powder metallurgy technique, in which the elemental blended powders are first compacted and then followed by a high temperature sintering. An important processing goal for this alloy is to obtain a high density with fine grain size. It is therefore desirable to predict its densification behavior and final density. Recently, the master sintering curve (MSC) theory provides a better understanding of whole sintering process. In previous work, the densification and grain growth mechanisms during spark plasma sintering (SPS) of 93W-5.6Ni-1.4Fe heavy alloy were investi-

93W–5.6Ni–1.4Fe heavy alloys with enhanced performance prepared by cyclic spark plasma sintering

Bulk 93W–5.6Ni–1.4Fe heavy alloys were prepared by an optimum sintering schedule and post-heat treatment using spark plasma sintering (SPS) technique. The microstructural parameters of the alloys, including tungsten grain morphology, tungsten grain size and W–W contiguity, are highly related to the heat treatment conditions. After cyclic heat treatment at 1400°C with one cycle, the alloy shows fine near-spherical tungsten grains embedded in the matrix phase with decreased W–W contiguity. The alloy exhibits improved bending strength (about 1700MPa) and yield strength (about 1100MPa at room temperature and about 700MPa at 800°C), due to the microstructural modification. The bending fracture morphology is characterized as tungsten–tungsten intergranular separation, tungsten transgranular cleavage, matrix ductile rupture and local matrix rupture on the separated W–W interfaces. The room temperature yield strength of the spark plasma sintered 93W–5.6Ni–1.4Fe heavy alloys are dependent on the microstructural factors such as tungsten grain size, matrix volume fraction and tungsten–tungsten contiguity.

Gradient structure induced by molybdenum in 90W–Ni–Fe heavy alloy

90W(Mo)–Ni–Fe heavy alloy with gradient structure was fabricated by the diffusion of Mo slice from the alloy's surface at 1480°C. The microstructure and content of binding phase at different regions along the cross section in the samples were investigated by scanning electron microscopy (SEM). The Mo content was determined by energy dispersive analysis (EDS) and the hardness of matrix phase was measured by Vickers' micro-hardness tester. Results show that the grain size, the volume fraction of binding phase and the hardness of matrix phase vary gradually due to the graded distribution of molybdenum. Simultaneously, the interfacial tension gradient induced by the dissolution of molybdenum is the driving force for liquid phase migration during liquid phase sintering.