Heavy Alloys Research Articles

Comparative studies of the constitutive models for tungsten heavy alloy (95W-3.5Ni-1.5Fe) at high strain rates

The plastic behaviors’ description of a tungsten heavy alloy (95W-3.5Ni-1.5Fe) at temperatures of 298–773 K and strain rates of 0.001–11,000 s−1 is systematically studied based on four constitutive models, that is, Zerilli-Armstrong model, modified Zerilli-Armstrong model, Mechanical Threshold Stress model, and modified Mechanical Threshold Stress model. The quasi-static compression experiments using an electronic universal testing machine and the dynamic compression experiments using a split Hopkinson pressure bar apparatus are employed to obtain the true stress–strain curves at a total of three temperatures (298 K, 573 K, and 773 K) and a wide range of strain rates (0.001–11,000 s−1). The parameters of the four constitutive models are obtained by the above fundamental experimental data and Grey Wolf Optimizer. The correlation coefficient and average absolute relative error are used to evaluate the predicted performance of these models. Modified Mechanical Threshold Stress model is found to have the highest predicted performance in describing the flow stress of the 95W-3.5Ni-1.5Fe alloy. Eventually, two compression experiments whose loading conditions are not in the fundamental experiments are conducted to validate the four models.

Investigation of tungsten heavy alloys using powder metallurgy technique

Recently, developing new alloys of Tungsten heavy (WHA) is the most important issue that researchers considered due to their wide applications of radiation protectors, vibration absorber, kinetic energy penetrators and heavy-duty electrical contacts. The present work shows 9 different Tungsten alloys with a variety of weight percent’s from "Graphene" as a Nano- particle additive. The proposed alloys produced by minimizing manufacturing parameters by applying the Taguchi technique. In addition, this work used to relate the Powder-Metallurgy (PM) parameters such as Sintering Temperature (ST) level, the weight % of the added Nano-particle of Graphene (Gw) and the type of Process Control Agent (PCA) with the mechanical characteristics such as Young’s modulus, modulus of Bulk, modulus of Shear, Poisson's number, Vickers hardness, Grain size , Relative Density. The results showed that specimen number 8 is given higher values of modulus of elasticity, reached 326.2 GPa, bulk value of 255.64 GPa, and shear value of 126.7 GPa with PM preparation condition at 15000C sintering temperature, stearic acid as a process control agent (PCA) and 0.0 %Wt. of Graphene.

Получение микродисперсного железо-никелевого порошка в процессе электрохимической переработки тяжелых вольфрамовых сплавов типа ВНЖ

The process of electrochemical processing of the VNZh type heavy tungsten alloy (wt. %: 80 W, 16 Ni, 4 Fe) under the action of direct and alternating current of industrial frequency in an ammonia-alkaline solution has been investigated. It was found, that the process is accompanied by the transition of tungsten from the alloy to the solution and the formation of a microdispersed powder, based on iron and nickel.

Quantitative characterization of frank loops and their effects on the plastic degradation in heavy ion irradiated alloy 800H

Alloy 800H has recently received significant attention owing to its potential applications in molten salt reactors. However, its irradiation tolerance and plastic degradation after irradiation are not well understood. In this study, Alloy 800H was irradiated by 3 MeV Cu+ ions with irradiation damage up to 10 dpa. The microstructure changes were characterized using two Rel-rods cases and weak beam dark field technology by performing transmission electron microscopy. The plastic mechanical properties before and after the irradiation were extracted from P-h curves derived by performing nanoindentation at loading rates of 0.05, 0.1, and 0.5 nm/s. The microscopy studies demonstrate that the characterization and evolution of the two variations of Frank loops are distinct and the 13⟨1‾11⟩ Frank loops firstly nucleate and coarsening. The nanoindentation results demonstrate that the measured yield stress increases with the increasing irradiation damage and decreasing loading rate. The good agreement on yield stress between the calculated and measured values suggests that using the characteristics of two variations of Frank loops to calculate the contribution of yield stress is appropriate. In addition, the decreasing measured values with increasing loading rate are attributed to the increased geometrically necessary dislocations, which are correlated with the indent size effect.

Microstructure and mechanical properties of novel tungsten heavy alloys prepared using FeNiCoCrCu HEA as binder

In the present work, novel tungsten heavy alloys (WHAs) have been developed using FeNiCoCrCu high entropy alloy (HEA) as binder through conventional sintering process. The composition of the alloy is 90 wt% W-10 wt% HEA. FeNiCoCrCu HEA was prepared by mechanical milling of elemental Fe, Ni, Co, Cr, and Cu powders in an equiatomic ratio for 60 h. XRD analyses revealed that HEA contains predominant FCC phase along with BCC minor phase. In order to evaluate the effectiveness of FeNiCoCrCu HEA as a binder of WHA, in this study, W and HEA were mixed in the ratio of 9:1, pressed and sintered at temperatures of 1470 and 1500 °C for dwell time of 1 h 30 min under hydrogen atmosphere. These sintered samples are mentioned as WHEAs (W-High Entropy Alloys). The evolution of phases, microstructures, and mechanical properties was investigated as a function of sintering temperature vis-á-vis those prepared by mixing of W and Fe, Ni, Co, Cr, Cu in the same proportion as in HEA (W-EleMental: WEM). The effect of hydrogen treatment (HyT) prior to the sintering of WHEAs on above mentioned characteristics was studied. Structural investigation of WEMs and WHEAs showed high intense W-peaks. Micrographs of these sintered samples showed typical liquid phase sintered microstructures having three distinct phases: bright W-phase, gray matrix phase, and black Cr-oxide phase. With the increase of sintering temperature and introduction of HyT step, the volume fraction of solid W-grain has been increased and W-content in the matrix of WHEAs is reduced. Upon sintering, WHEAs yield better densification, higher compressive strength, and higher bulk hardness. This increase of strength from WEMs to WHEAs was attributed to better densification of WHEAs compared to the former. The maximum values of compressive strength (1912 ± 14 MPa) and bulk hardness (479 ± 16 VHN) were achieved in the case of hydrogen treated W-HEA powder sintered at 1500 °C.

Neutron activation and radiation damage assessment for W-Ni-Fe tungsten heavy alloys with variable Ni content

A challenging issue for the magnetic fusion concept of generating nuclear power is the performance of plasma-facing components, particularly in the divertor within the fusion power plant. Tungsten alloys, such as W-TiC, W-La2O3, etc., are the prime candidate structural materials for advanced He-cooled divertors in next-step devices beyond ITER. In recent years, W-Ni-Fe heavy alloys (WHAs) have emerged as more promising alternatives than the above-mentioned alloys. WHAs exhibit superior fracture toughness and better fabricability. However, Ni raises concerns because it may generate an unsafe level of radioactive waste (radwaste). Given the significant promise of WHAs, neutron activation assessment is critically needed, particularly to determine the limit of Ni that can be employed. This is the main purpose of this study. The assessment is provided for disposal option and for recycling alternative of divertors made of WHAs. Additional calculations are performed to obtain the neutron flux and spectrum, transmutation products, and He/H gas production data for a typical divertor design. These additional data are generated to inform future multiscale simulations of microstructure evolution and radiation damage accumulation in WHAs. Furthermore, estimation of atomic displacement damage dose is presented. In the future, the estimated dose should be compared with the more accurate data from the multiscale simulations and revised accordingly.

Unsupervised machine learning in fractography: Evaluation and interpretation

Modern computer vision and machine learning techniques, when applied in Fractography bare the potential to automate much of the failure analysis process and remove human induced ambiguity or bias. Given the complex interaction between intrinsic (e.g. microstructure) and extrinsic (e.g. environment, loading history) factors leading to failure, deep learning methods, which exhibit very high efficiency in establishing complex interconnections between the input data, may end up revealing new correlations and information that is encoded onto the complex geometries of fracture surfaces and remained hidden from us so far. In this work, we examine the potential use of an unsupervised learning pipeline to classify fracture surfaces of five tungsten heavy alloys following their chemical content (i.e. Tungsten percentage). Encouraged by the success of the algorithms, we move on and analyze the features on the fracture surfaces which are governing the decision process of the algorithms. The fractographic interpretation of these features shows that the extent of plasticity on the fracture surface serves as a measure for the classification process. The examined pipeline can be used to identify failures originating from erroneous manufacturing processes, leading to locally varying Tungsten concentrations and ultimately premature failure.

Preliminary Study of the Rhenium Addition on the Structure and Mechanical Properties of Tungsten Heavy Alloy.

The results of structure and mechanical property investigations of tungsten heavy alloy (THA) with small additions of rhenium powder are presented. The material for the study was prepared using liquid phase sintering (LPS) of mixed and compacted powders in a hydrogen atmosphere. From the specimens, the samples for mechanical testing and structure investigations were prepared. It follows from the results of the microstructure observations and mechanical studies, that the addition of rhenium led to tungsten grain size decreasing and influencing the mechanical properties of W-Ni-Fe-Co base heavy alloy.

The Effect of Cold Swaging of Tungsten Heavy Alloy with the Composition W91-6Ni-3Co on the Mechanical Properties

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 , yield strength , 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 value of over 1470 MPa after heat treatment with cold swaging deformation with reduction of 30%) and the hardness from 32 to 46 HRC.

Appearance of textures with a c-axis parallel to the extrusion direction in Mg alloys

The appearance of an unusual texture with the crystallographic c-axis parallel to the extrusion direction (‘C-texture’) occurs in bands in extruded and fully recrystallized Mg-6.5Zn alloy. This texture was previously only reported in rare-earth-containing Mg alloys. Based on our results and the available literature, it seems that this texture requires heavy alloying, and it is not linked exclusively to the presence of second phase particles. Moreover, it appears to be associated with higher extrusion ratios. Also, the starting texture seems not essential for its formation. The most likely mechanism would be the promoted pyramidal <c+a> slip stimulated by high solute levels that provides the necessary lattice rotation, along with the easy activation of prismatic <a> slip.

The Deformation Behaviors and Mechanism of the High-Temperature Mechanical Properties of a Ni48W35Co17 Alloy

Investigations of the plastic deformation mechanisms of Ni-W-based heavy alloys varying with increasing temperatures are very important for the development of hot forming processes and applications at elevated temperatures. In this study, the continuous variation of strength and plasticity of a novel Ni-W-based heavy alloy with increasing temperatures was investigated. The tensile strength of a Ni48W35Co17 sample at 600 °C was 471 MPa, which was 47% lower than that at 100 °C. A variation in an abnormal decrease in elongations at temperatures from 400 °C to 800 °C was found in this alloy. The elongation rate of the sample tensile at 600 °C was 19%, which was 73% lower than that at 100 °C. A microstructural analysis revealed that the number of twins in the sample tensile at a temperature higher than 600 °C increased considerably compared with the sample tensile at lower temperatures, indicating that the dislocation slips were suppressed during the high-temperature stretching process. The precipitates of the NiW phase were found in the 600 °C tensile sample, which was not clearly observed in the 400 °C tensile sample, suggesting that dislocation slips were affected by the formation of these precipitates. Moreover, the orientation relationship between the matrix and NiW phase was (200)Ni//(240)NiW and [001]Ni//[001]NiW. The tiny precipitated phase was the main reason for the plasticity decrease of the alloy with the temperature increase.

Effect of Heat Treatment Process and Composition on Deformation and Damage Behavior of WHA under Detonation Loading

The excellent material properties of tungsten heavy alloy (WHA) make it widely used in the military field. When used as killing elements of weapons, its dynamic mechanical properties under detonation loading directly determine the damage effect of weapons, which makes the research on its mechanical behaviors under high pressure and high strain rate loads such as detonation loading of great significance. In this paper, several WHAs with different compositions and processes are selected, and the mechanical properties and deformation and damage behavior under static explosion test are analyzed by combining macro and micro study, so as to provide guidance for the subsequent optimization of the performance design of WHA.

Effect of carbon addition on microstructure and mechanical properties of as-cast nickel-based heavy density matrix alloy reinforced by high tungsten content

In present work, a novel carbon-doped interstitial strengthening nickel-based heavy density matrix alloy reinforced by high tungsten content (Ni-W-Co) was prepared by conventional casting technology using a laboratory vacuum induction melting (VIM) furnace. The effects of carbon addition on as-cast microstructure and phase constituents were characterized by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). And the tensile properties and microhardness were tested as well. Results demonstrated that the present heavy density alloy has a single-phase FCC structure and exhibits typical dendrite characteristics. The carbon content (0–0.021 wt%) presents little influence on as-cast microstructure and phase constituents, but significantly improves the mechanical properties. Both tensile strength and ductility of the matrix alloy were increased synchronously with the addition of interstitial carbon atoms on account of the interstitial strengthening. The tensile fracture morphology revealed the transition from complete ductile dominated features to a mixed fracture mode consisting of quasi cleavage and ductile fractures. Minor carbon addition can trigger an obvious increase for lattice parameters and thus contribute to the strength improvement, and the increase in lattice friction stress enhanced the work-hardening rate and postponed the necking of C-addition alloy compared with C-free alloy.

Antibiotics- and Heavy Metals-Based Titanium Alloy Surface Modifications for Local Prosthetic Joint Infections.

Prosthetic joint infection (PJI) is the second most common cause of arthroplasty failure. Though infrequent, it is one of the most devastating complications since it is associated with great personal cost for the patient and a high economic burden for health systems. Due to the high number of patients that will eventually receive a prosthesis, PJI incidence is increasing exponentially. As these infections are provoked by microorganisms, mainly bacteria, and as such can develop a biofilm, which is in turn resistant to both antibiotics and the immune system, prevention is the ideal approach. However, conventional preventative strategies seem to have reached their limit. Novel prevention strategies fall within two broad categories: (1) antibiotic- and (2) heavy metal-based surface modifications of titanium alloy prostheses. This review examines research on the most relevant titanium alloy surface modifications that use antibiotics to locally prevent primary PJI.

Latent heat of crystallization and precursor film induced superior wettability of tungsten heavy alloy by Cu[sbnd]Ti based amorphous alloys

We synthesized a series of CuTi based crystalline and amorphous brazing filler metals (BFMs) and further investigated the microstructure characteristics and melting features for comparison. The presence of precursor film together with latent heat of crystallization showed a significant effect on the enhanced wettability of amorphous BFMs/tungsten heavy alloy (WHA) system. The wetting and spreading mechanism were addressed in a view of atomic adsorption and diffusion. The brazed joints showed effective interface bonding and high shear strength, especially at elevated temperature (up to 364 MPa at 400 °C). This study demonstrates the great superiority and feasibility of amorphous brazing filler metals in the joining of WHAs.

Experimental and numerical investigation of model I dynamic fracture toughness of 95W-3.5Ni-1.5Fe alloy using the semi-circular bend specimens

Semi-circular bend specimens are used to measure the brittle materials' fracture toughness, such as brittle metals, rocks, and ceramic materials. The quasi-static and dynamic model I fracture toughness of tungsten heavy alloy, a typical brittle metal material, are measured using the semi-circular bend specimens under quasi-static compression and dynamic impact loadings. For quasi-static cases, the specimens are loaded on a universal testing machine with a constant loading speed. While for dynamic cases, the specimens are executed on a modified split Hopkinson pressure bar system with the impact pressures from 0.2 to 0.4 MPa. The results show that the dynamic fracture toughness of tungsten alloy increases with the increase of the loading rate. Further, a rate-dependent bilinear traction-separation law is introduced to explain the dynamic fracture behaviors of tungsten alloy. The parameters of the rate-dependent law are obtained from the experiments and the finite element simulations. Finally, the dynamic simi-circular bend simulations using the cohesive element with rate-dependent cohesive law are established to simulate the crack propagation, and the simulation results are in good agreement with the test data.

Powder Metallurgical Processing and Characterization of Molybdenum Addition to Tungsten Heavy Alloys by Spark Plasma Sintering.

The effect of adding molybdenum to the heavy tungsten alloy of W-Ni-Fe on its material characteristics was examined in the current study. The elemental powders of tungsten, iron, nickel, and molybdenum, with a composition analogous to W-3Fe-7Ni-xMo (x = 0, 22.5, 45, 67.5 wt.%), were fabricated using the spark plasma sintering (SPS) technique at a sintering temperature of 1400 °C and under pressure of 50 MPa. The sintered samples were subjected to microstructural characterization and tested for mechanical strength. The smallest grain size of 9.99 microns was observed for the 45W-45Mo alloy. This alloy also gave the highest tensile and yield strengths of 1140 MPa and 763 MPa, respectively. The hardness increased with the increased addition of molybdenum. The high level of hardness was observed for 67.5Mo with a 10.8% increase in the base alloy’s hardness. The investigation resulted in the alloy of 45W-7Ni-3Fe-45Mo, observed to provide optimum mechanical properties among all the analyzed samples.

The simultaneous improvement of strength and ductility of the 93W-4.6Ni-2.4Fe prepared by additive manufacturing via optimizing sintering post-treatment

The influence of sintering post-treatment temperature on the microstructure and mechanical properties of 93 W-4.6Ni-2.4Fe (wt%) tungsten heavy alloy prepared by powder extrusion 3D printing has been examined. The density of the specimen gradually increases to over 99.5% with the increase of the sintering temperature. The contiguity first decreases with increasing temperature and then increases, which is mainly related to the evolution of the distribution of γ phase and the tungsten particle size. The fracture mode of the 93W-4.6Ni-2.4Fe specimen changes from brittle fracture for the sintering temperature of 1430 °C to ductile fracture for the sintering temperature range of 1450–1480 °C. The sintering temperature of the 93 W-4.6Ni-2.4Fe specimen with the highest tensile strength (1040 ± 6 MPa) and elongation (20.7 ± 0.4%) is determined to be 1480 °C. The high ductility of the specimen sintered at 1480 °C can be attributed to the formation of high-density uniformly distributed dimples in the network γ phase and the bridging effect of γ phase on the cracks. The high strength is related to the high density of specimen, moderate contiguity, suitable tungsten particle size and solid solution strengthening effect.

Stress-Strain Distribution Within Rotary Swaged Tungsten Heavy Alloy

This study deals with thorough investigation of stress-strain parameters within an innovatively processed tungsten heavy alloy (THA). THAs are challenging materials featuring exceptional mechanical and physical properties and they are applicable in various demanding industrial fields, such as in the aeronautics, medicine, or military. The herein studied material is a WNiCo alloy prepared from original powders via powder metallurgy. The pre-sintered material was processed via plastic deformation, in particular hot rotary swaging with the usage of induction heating directly before a swaging pass. The experimental study was supplemented with numerical simulation of the deformation process, which was performed via the finite element method (FEM). The simulation was primarily focused on prediction of the development of effective imposed strain during the swaging process performed in multiple steps, and its correlation with stress distribution during swaging. The numerically predicted effective imposed strain development was subsequently verified via Vickers microhardness measurements, whereas the predicted results of stress distribution were validated via experimental observation of residual stress distribution performed via analysing scans acquired by scanning electron microscopy (SEM, electron backscatter diffraction analysis). The results showed that the deformation technology consisting of induction heating and hot rotary swaging was well optimized as the swaged billets featured satisfactory surface roughness and no surface cracks. Also, the tungsten agglomerates within the structure exhibited deformation in the direction of the main acting swaging force, especially in the locations the effective imposed strain in which was the highest. The values of predicted effective imposed strain and microhardness correlated reliably with the experimentally acquired and predicted results of residual stress distribution. In other words, the locations the effective strain in which was the highest also exhibited a more significant presence of residual stress.

Low temperature study of phase equilibria in the Co–Ni–W ternary system: Evidence of a new intermetallic phase Co3W-D0a

Tungsten heavy alloys (Co–Ni–W) of different compositions were prepared by powder metallurgy (solid sintering), heat treated at 800 °C and 1000 °C and subsequently analyzed. The experimental phase identifications and composition measurements emphasized discrepancies compared to the isothermal ternary sections simulated with commercial thermodynamic databases. The isothermal sections at 800 °C and 1000 °C were found more complex than expected since a new intermetallic phase appeared to be stable (D0a structure - Cu3Ti prototype). Likewise, an interpretation of phase equilibria evolution with temperature was established to reach agreement with high temperature data. Formation enthalpies associated with the new phase were obtained through first-principles calculations and supported experimental results as they confirmed the stabilizing role of Ni addition for the D0a structure.