Alloy Carbides Research Articles

Optimization of cutting temperature and surface roughness in CNC turning of Ti-6Al-4V alloy using response surface methodology.

This study investigates the optimization of cutting conditions for machining titanium alloy (Ti-6Al-4V) using Response Surface Methodology (RSM), with the goal of minimizing tool-chip interface temperature and surface roughness. The research focuses on key cutting parameters to investigate the most effective combinations for enhancing surface finish and reducing thermal impact during machining. The present study deals with the dry turning of Ti-6Al-4V alloy with carbide alloy inserts in a way to utilize the Analysis of Variance (ANOVA) to develop predictive models for minimum surface roughness and optimum temperature. The findings reveal that both cutting speed and depth of cut are critical in determining machining outcomes. Specifically, a low cutting speed of 88m/min coupled with a high depth of cut of 0.20mm was found to elevate the cutting temperature to approximately 835°C, resulting a surface roughness of 0.59μm. Conversely, increasing the cutting speed to 120m/min while reducing the depth of cut to 0.10mm significantly lowered the temperature to around 607°C, resulting a surface roughness of 0.19μm; thus, thereby improving surface finish and reducing thermal stress on the tool. Additionally, a 27% reduction in cutting temperature and a minimum surface roughness of 0.19μm were achieved with optimal settings of 120m/min cutting speed, 0.08 mm/rev feed rate, and 0.10mm depth of cut. The study demonstrates the effectiveness of RSM in optimizing machining parameters for optimum temperature and better surface finish in the titanium alloy machining.

Pre-deformation induced precipitation of alloy carbides and its effect on residual stress

The plasticity generated by carbide precipitation during tempering can relax the residual stress. For low-carbon micro alloyed steel 700L. The plastic behavior resulting from carbide precipitation leads to low stress relaxation. And it is prone to plate shape problems such as warping and edge waves. How to enhance carbide precipitation to relax stress has always been the goal pursued by researchers. In this paper, I discussed the effect of carbide precipitation on stress relaxation by applying pre-deformation to intervene the precipitation law of carbides. It is found that pre-deformation can interfere with the precipitation behavior of carbides during tempering, which in turn affects the relaxation degree of residual stress. Applying pre-deformation can inhibit the precipitation of cementite, improve the dispersion degree and precipitation size of alloy carbides, and improve the relaxation degree of residual stress in the tempering process. With the increase of deformation, the precipitation of cementite during tempering is inhibited, the precipitation of cementite decreases, the precipitation of alloy carbides increases and distributes more dispersed, and the size of alloy carbides decreases from 11.4 nm to 8.6 nm. After pre-deformation tempering, the residual stress is greatly relaxed, up to 85.09%.

Fine-Tuning the Active Phases of CoFe Alloy Carbides for Boosting Olefin Synthesis from CO2 Hydrogenation

Fine-Tuning the Active Phases of CoFe Alloy Carbides for Boosting Olefin Synthesis from CO₂ Hydrogenation

Neutronic Analysis of the AP1000 Fuel Assembly with Accident Tolerant Cladding Materials

An alternative material for fuel cladding was required to prevent oxidation caused by interacting with steam, leading to improvement in core integrity. This study analyzes reactor physics parameters of various cladding material candidates for Pressurized Water Reactor (PWR) such as SS-304 austenitic stainless steel, FeCrAl alloy, APMT alloy, and silicon carbide (SiC) ceramic, as candidate Accident Tolerant Fuel (ATF). The neutronic parameters such as infinite multiplication factor (k-inf), and neutron spectrum, while temperature reactivity coefficient related to fuel temperature (DTC) and moderator temperature (MTC) is also considered, followed by a void coefficient of reactivity (VCR) of each candidate material were then compared with ZIRLO as a standard cladding material of AP1000. k-inf calculated by SRAC2006 is also compared to MCNP for various fuel assembly types. At the beginning of cycle (BOC), the 2.35% UO2 using SiC gives a higher kinf than ZIRLO at 937 pcm, while 4.45% UO2 with 88 IFBA & 9 PYREX at 796 pcm. FeCrAl, APMT, and SS-304 cladding gave a smaller k-inf compared to ZIRLO in the range of 11000-14000 pcm at 2.35% UO2 fuel assembly. The values of DTC, MTC, and VCR were still negative throughout the reactor operation which indicates that the inherent safety feature of alternative cladding was possible for this type of fuel assembly, especially for iron-based cladding material followed by an increase in fuel enrichment.

Functionally graded material for improved wear resistance manufactured by directed energy deposition

AbstractProtecting components against wear and corrosion is a common way to improve their lifetime. This can be achieved by coating them with a hardfacing material. Common coatings consist of materials such as tungsten carbide or cobalt-chromium alloys, also known as Stellite. Hardfacing materials can be deposited by welding methods like plasma welding or laser cladding. The discrete change of the base material to the hardfacing layer can lead to cracks and chipping. Studies showed a reduced risk of cracking when a functionally graded material is used to create a smooth transition between the base and the hardfacing. Gradings from austenitic steel to cobalt-chromium alloys are already known in the literature. However, there is no knowledge about austenitic- ferritic duplex steels as base material. Therefore, this study aims to demonstrate the feasibility of a functionally graded material from duplex steel to cobalt-chromium alloy with a new approach. By using powder-based directed energy deposition, a graded material with smooth material transition is manufactured additively. Cracking and porosity are examined through metallography. Microhardness measurements as well as the analysis of the chemical composition by energy dispersive X-ray spectroscopy and X-ray fluorescence are used to validate the build-up strategy.

Precious Metal-Free Electrocatalysts for Anion-Exchange Membrane Fuel Cell Cathodes via Magnesium-Based Template-Assisted Synthesis

Anion-exchange membrane fuel cells (AEMFCs) represent a viable alternative to proton-exchange membrane fuel cells, as they allow for the utilization of less expensive cell components and non-precious metal electrocatalysts on the electrodes. Transition metal-containing nitrogen-doped carbon materials (M-N-C catalysts) have shown very high activity toward the oxygen reduction reaction (ORR) in alkaline solution and promising performance as cathodes in AEMFC tests.1 Such materials are often prepared via high-temperature pyrolysis of carbon precursors in the presence of nitrogen and metal sources, in which nitrogen doping occurs during the carbonization. For the fuel cell application, hierarchical porous structure of the catalysts is desirable. To tailor the porous structure of carbon materials, hard templates are often used in the pyrolysis, typically silica nanoparticles, which need harsh conditions for removal. More sustainable alternatives to these are various other inorganic nanoparticles, e.g. some salts or oxides, which can be dissolved in dilute acids or water. These nanoparticles can also be derived in situ during the pyrolysis from thermally unstable precursors, for instance, MgO particles can be obtained from Mg acetate or citrate.2 This study introduces a simple method for preparing mesoporous M-N-C catalysts (M= Fe or both Fe and Co) for the ORR by pyrolysis of organic precursors, dicyandiamide and transition metal salts.3 Lignin, mixture of alkylresorcinols, and rapeseed press cake were used as sustainable carbon sources, whereas Mg acetate served as a precursor for a sacrificial template and was leached post-pyrolysis in a dilute acid solution.The physicochemical analyses of the catalyst materials revealed that these consisted of porous sheet-like carbon structures. The presence of the template precursor in the synthesis significantly increased the specific surface area of the catalysts and the amount of smaller pores (d<10 nm). Nitrogen was uniformly distributed on the catalyst, while transition metal was partly distributed, presumably as atomically dispersed metal centers, and partly forming metal-rich nanoparticles. These particles consisted of Fe carbide or FeCo alloy and were encapsulated in carbon layers. Rotating disc electrode (RDE) tests conducted in alkaline solution indicated slightly higher ORR activity for the catalysts prepared with the template. The activity of both Fe-containing and bimetallic (FeCo) catalysts was similar to that of a commercial Pt/C catalyst. In addition, the ORR activity of catalysts derived from different organic precursors was also rather similar. In short-time stability tests the catalysts showed promising durability. In the membrane-electrode assembly tests at AEMFC conditions, the bimetallic catalyst derived from lignin surpassed the Fe-containing counterpart, achieving a promising peak power density of 833 mW cm-2 at 80 °C. These findings underscore the potential to produce highly active precious metal-free cathode catalysts for AEMFCs by a straightforward high-temperature pyrolysis from various sustainable carbon sources. Acknowledgments This work was financially supported by the Estonian Research Council (grants PRG4, PRG723, PRG753, and PRG1509) and by the Estonian Ministry of Education and Research (TK141 and TK210). References A. Sarapuu, J. Lilloja, S. Akula, J. H. Zagal, S. Specchia and K. Tammeveski, ChemCatChem, 2023, 15, e202300849. T. Morishita, Y. Soneda, T. Tsumura, and M. Inagaki, Carbon, 2006, 44, 2360-2367. K. Kisand, A. Sarapuu, J. C. Douglin, A. Kikas, A. Treshchalov, M. Käärik, H. M. Piirsoo, P. Paiste, J. Aruväli, J. Leis, V. Kisand, A. Tamm, D. R. Dekel, and K. Tammeveski, ACS Catal., 2022, 12, 14050-14061. Figure 1

Low-temperature CO2 Hydrogenation to Olefins on Anorthic NaCoFe Alloy Carbides.

The hydrogenation of carbon dioxide to olefins (CTO) represents an ideal pathway towards carbon neutrality. However, most current CTO catalysts require a high-temperature condition of 300-450 °C, resulting in high energy consumption and possible aggregation among active sites. Herein, we developed an efficient iron-based catalyst modified with high-sodium content (7 %) and low-cobalt content (2 %), achieving a CO2 conversion of 22.0 % and an olefin selectivity of 55.9 % at 240 °C and 1000 mL/g/h, and it is even active at 180 °C and 4000 mL/g/h with more than 25 % olefins in hydrocarbons. The catalyst was kept stable under continuous operating conditions of 500 hours. Numerous characterizations and calculations reveal high content of sodium as an electronic promoter enhances the stability of the active anorthic Fe5C2 phase at low temperatures. Further incorporating the above catalyst with cobalt, as a structural promoter, causes Fe species to form a FexCoy alloying phase, which in turn facilitates the formation of higher active anorthic (FexCoy)5C2 phase, different from the conventional carbides and alloy carbides. An in-depth investigation of the synergistic effects of structural and electronic promoters can improve catalyst performance, increase reaction efficiency and cost-effectiveness, and provide profound insights for understanding and optimizing CO2 hydrogenation reactions.

Dissolution of Primary Carbides and Formation and Healing of Kirkendall Voids in Bearing Steel under Pulsed Electric Current

The alloying elements in 8Cr4Mo4V bearing steel tend to form large primary carbides with carbon, which not only causes element segregation but also becomes the primary source of fatigue crack initiation, thereby decreasing the material's usability and machinability. Owing to the excellent thermal stability of primary carbides, traditional homogenization annealing requires high temperatures, which is both time‐ and energy‐intensive. Excessively high heat treatment temperatures can also result in “overburning” of the sample. Herein, primary carbides are rapidly dissolved at low temperatures using pulsed electric current treatment. The additional free energy introduced by the pulsed electric current lowers the thermodynamic barrier for carbide dissolution. During the second‐phase dissolution process, the unbalanced diffusion of elements may cause the formation of Kirkendall voids. Due to the difference in electrical conductivity between the voids and the matrix, the pulsed electric current generates thermal compressive stress on the voids, promoting rapid atom migration to these voids and accelerating their healing. This pulse‐current treatment technology offers a novel method for the rapid dissolution of carbides in alloys at low temperatures and for the rapid healing of related voids.

Synthesis of (Ti, Cr)xCy Carbides in VT6 Alloy by Direct Laser Deposition

Synthesis of (Ti, Cr)xCy Carbides in VT6 Alloy by Direct Laser Deposition

Manganese Partitioning and its Effect on Residual Stress

The residual stress in low‐carbon high‐strength steel is not effectively relaxed during alloy carbide precipitation but is fully relaxed during manganese partitioning. The specific microscopic mechanisms responsible for this observed phenomenon have yet to be fully elucidated. This study employs first‐principles calculations in conjunction with experiments to demonstrate that alloy carbide precipitation leads to the formation of dense dislocation tangles that hinder carbon diffusion and carbide precipitation. Conversely, manganese partitioning aids carbon diffusion by altering dislocation morphology while also causing plastic deformation. The simultaneous occurrence of partitioning plasticity and precipitation plasticity during manganese partitioning results in a more significant relaxation of residual stress compared to alloy carbides precipitation: The plasticity coefficient for alloy carbide precipitation is 1.303 × 10−5, while the plasticity coefficient for manganese partition is 2.691 × 10−5. During alloy carbide precipitation, the elastic strain energy decreases to 43.48% of its initial value, whereas it can be further reduced to 25.29% after manganese partitioning.

Structure and properties features of CA-PVD Ti-Al-Ni-N coatings deposited on carbide alloys and tool steel substrates

The results of studies of the properties of CA-PVD Ti-Al-Ni-N coatings deposited on widely used carbide alloys of the WC-Co, WC-TiC-Co, WC-TiC-TaC-Co groups and carbon steel are presented. It has been shown that the hardness and Young's modulus of the coatings on different substrates differ by up to 1.5 times, even though there is no significant difference in composition. The formation of globular aggregations on cell ridges, which is a characteristic feature of the morphology of coatings on steel substrates, and the presence of multilevel (stepped) structure were observed. The difference in CSR, microstrain and lattice period values for the nitride phase in the coatings on the substrates has been established. From the point of view of differences in thermal diffusivity of substrates, features of morphology and substructure of coatings are explained. The differences in the properties of coatings are also associated with the implementation of tensile macrostresses on steel in comparison with compressive stresses on carbide substrates. Tensile macrostresses and macrolayering are the reasons for the relatively low level of strength (2–3 times) of adhesion of the coating to tool steel compared to coatings on carbide substrates. At the same time, a decrease in the shear strength of the coating material on a steel substrate due to macro-layering may be the reason for the relatively low friction coefficient of this coating (~0.5) compared to coatings on a carbide base (0.69–0.53). The work provides recommendations for the most effective use of Ti-Ni-Al-N coating on carbide alloys and carbon steel.

Coarsening of alloy carbides during a cyclic heat treatment for grain refinement in ultrahigh-strength steels

Strength–ductility trade-off dilemma is acute in materials science, especially for ultrahigh-strength steels. The improvement of toughness requires careful tuning of grains and precipitates. Thermal cyclic treatment and annealing before quenching are two effective ways of microstructural refinement for steels. However, a combination of the two methods has never been studied. Complex alloy carbides form in the process of annealing, but their effects on grain refinement in the subsequent quenching are unclear. Here, a systematic comparison of microstructure and mechanical properties is established between a thermal cyclic treatment with annealing (CHT) and traditional quench-temper treatment (QT). The results indicate that the CHT treatment leads to the coarsening of alloy carbides and subgrains, and the decrease in strength and toughness.

A biomimetic micro-texture based on shark surface for tool wear reduction and wettability change

Aiming at the problems of severe tool wear and difficulty in ensuring machining surface quality during the cutting process of Ni-base superalloy, a micro-texture design method resembling a shark surface is proposed, which simplifies the skin teeth on the shark surface into a diamond shaped structure with ribs. Different micro-textured samples were prepared using femtosecond laser, and surface wettability characterization and friction and wear experiments were conducted to study the wear reduction and anti wear effects of micro-texture. The parameter combinations with the maximum contact angle and the minimum coefficient of friction were selected. The wear mechanism of YG8 carbide alloy and GH4742, as well as the wear reduction mechanism of microstructure were revealed. Biomimetic cutting tools were prepared and their effectiveness in controlling tool wear, reducing cutting forces, and improving machining quality was verified through milling experiments.

The dual effects of phosphorus on the hot deformation behavior in an as-cast Ni-Fe-Cr based alloy

The effect of phosphorus on dynamic recrystallization (DRX) and hot deformation behavior of an as-cast Ni-Fe-Cr based was investigated by performing hot compression deformation. The results indicate that phosphorus can play dual roles during hot deformation. The phosphorus dissolving in matrix and segregating to the dislocation can hinder the dislocation motion and DRX nucleation, which acts as the solute drag effect. And phosphorus-addition can increase the size and number of MC carbides. MC carbides increase the local dislocation density around them and promote the DRX nucleation and exhibit the particle stimulated nucleation effect. Influenced by the dual effects of phosphorus, the DRX fraction and grain size decrease first and then increase with the increase of phosphorus content. The solute drag effect of the substitutional phosphorus atoms on dislocation motion decreases the DRX nucleation rate and increase the possibility of instability at low deformation temperature in phosphorus-addition alloys. In the early stage of deformation, more MC carbides in the high-phosphorus alloy hinder the motion of dislocation and result in the stress concentration, which leads to the intergranular cracks at high temperature and high strain rate.

Acoustic Features of the Impact of Laser Pulses on Metal-Ceramic Carbide Alloy Surface.

Technologies associated with using concentrated energy flows are increasingly used in industry due to the need to manufacture products made of hard alloys and other difficult-to-process materials. This work is devoted to expanding knowledge about the processes accompanying the impact of laser pulses on material surfaces. The features of these processes are reflected in the acoustic emission signals, the parameters of which were used as a tool for understanding the accompanying phenomena. The influence of plasma formations above the material surface on self-oscillatory phenomena and the self-regulation process that affects pulse productivity were examined. The stability of plasma formation over time, its influence on the pulse performance, and changes in the heat flux power density were considered. Experimental data show the change in the power density transmitted by laser pulses to the surface when the focal plane is shifted. Experiments on the impact of laser pulses of different powers and durations on the surface of a hard alloy showed a relationship between the amplitude of acoustic emission and the pulse performance. This work shows the data content of acoustic emission signals and the possibility of expanding the research of concentrated energy flow technologies.

Empirical Investigation of Properties for Additive Manufactured Aluminum Metal Matrix Composites

Laser additive manufacturing with mixed powders of aluminum alloy and silicon carbide (SiC) or boron carbide (B4C) is investigated in this experiment. With various mixing ratios of SiC/Al to form metal matrix composites (MMC), their mechanical and physical properties are empirically investigated. Parameters such as laser power, scan speed, scan pattern, and hatching space are optimized to obtain the highest density for each mixing ratio of SiC/Al. The mechanical and thermal properties are systematically investigated and compared with and without heat treatment. It shows that 2 wt% of SiC obtained the highest strength and Young’s modulus. Graded composite additive manufacturing (AM) of MMC is also fabricated and characterized. Various types of MMC devices, such as heat sink using graded SiC MMC and grid type three-dimensional (3D) neutron collimators using boron carbide (B4C), were also fabricated to demonstrate their feasibility for applications.

Enhanced microwave absorption in graphene-based composites: A study on the synergistic effect of ferrite integration and electromagnetic coupling

Graphene integration with magnetic particles demonstrates a synergistic enhancement in dielectric and magnetic loss properties, facilitating the realization of absorbing materials that are strong, broadband, lightweight, and thin. This study achieved uniform dispersion of ferrite on the surface of in-situ synthesized high-conductivity graphene, utilizing an economical liquid glucose precursor and cobalt ferrite sintering process. An interface consisting of iron carbide and cobalt-iron alloy forms between the graphene and cobalt ferrite, significantly enhancing the samples’ microwave absorption performance. Furthermore, the magnetic loss is notably enhanced through the coupling of soft and hard magnetic materials. Consequently, a composite material consisting of Graphene/Fe3C/CoFe2/CoFe2O4, with a minimal thickness of 1.85 mm, demonstrated an impressive minimum reflection loss of −48.8 dB and a notable absorption bandwidth extending over 4.04 GHz. This research will offer an effective approach for developing high-performance microwave absorption materials using graphene-based composite magnetic materials.

Construction of superhydrophobic tungsten carbide via laser processing and its thermal, chemical and mechanical properties

Designing microscale microstructures on superhard materials and achieving superhydrophobic surfaces through wettability adjustment have promising application prospects. However, current popular methods for preparing superhydrophobic surfaces have not designed and optimized the microstructures, and achieving superhydrophobicity on superhard materials using conventional industrial methods remains a tremendously challenge. Here, we propose a novel multiscale microstructure design on superhard tungsten carbide (WC) alloy material, achieved through laser processing, which exhibits superhydrophobicity after low surface energy modification. To ensure the designed microstructures possesses excellent mechanical strength and wettability, the influence of size parameters on mechanical strength and their relationship with wettability through finite element analysis (Abaqus) and characterization techniques were conducted. Based on the optimized robust multiscale structure, we also investigated the comprehensive properties of the superhydrophobic surface. The thermal, chemical, and mechanical stability of the WC superhydrophobic surface were explored through experiments involving temperature exposure, immersion in acid-base solutions, friction and wear tests. Our findings demonstrate that the superhydrophobic WC surface exhibits excellent temperature resistance over a wide range, maintaining superior water repellency even after prolonged exposure to chemical solutions and mechanical abrasion tests. In addition, the substrate's microstructure and SiO2 nanoparticles successfully replicated on the optical glass surface through molding technology, creating a consistently superhydrophobic glass microstructure. This work provides a new perspective for designing superhard alloy materials with robust microstructures and offers potential for a series of applications, such as mold, semiconductor and solar cell.

WC nanoparticles and NiFe alloy co-encapsulated in N-doped carbon nanocage for exceptional OER and ORR bifunctional electrocatalysis

Developing earth-abundant electrocatalysts with optimized intrinsic active sites is crucial for enhancing bifunctional oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) performance. In this study, we fabricated a hollow structured carbon framework utilizing NiFe Prussian Blue analogs (PBAs) as templates, while polypyrrole (PPy) and phosphotungstic acid (PW12). Pyrrole monomer underwent polymerization on the nanocubic PBA surface in the presence of PW12 (PBA@PPy-PW12). Subsequent carbothermal reduction created an N-doped carbon shell with embedded NiFe alloy and tungsten carbide (WC) nanoparticles. The polymeric PPy-PW12 nature can not only prevent the aggregation of PBA and WC structures but also enhance electrical conductivity by connecting neighboring nanospheres. Moreover, the introduction of WC can significantly enhance the bifunctional electrocatalytic activity of the carbon-based catalyst, which is attributed to synergism between the WC and NiFe materials within the NC layer. Consequently, NiFe/W0.3C@NC exhibited outstanding OER (overpotential = 290 mV for 10 mA/cm2; Tafel slope = 57 mV/dec) and ORR (half wave potential = 0.81 V; Tafel slope = 61 mV/dec) performances. This work presents a promising avenue for developing high-performance electrocatalysts for energy conversion systems that showcase remarkable efficiency, stability, and potential practicability.

General investigations on the heat treatment and thermal fatigue behavior of an experimental hot work tool steel tailored for laser powder bed fusion

An experimental hot work tool steel with a leaner chemistry compared to the standard AISI-H13 grade, aimed at enhanced processability, was gas atomized and processed using laser powder bed fusion (L-PBF) to >99.8 % relative density. The lower carbon content (∼0.25 wt% vs. ∼0.4 wt% in H13) resulted in a softer as-built (AB), and quenched martensite (∼485 HV1 vs. 625 HV1 in H13), higher martensite-start temperature (∼360 °C vs. 280–320 °C), and about ∼18 % reduction in dilatation, ascribed to the volume expansive martensitic transformation. Charpy V-notch impact toughness in AB condition (>30 J) was higher than those reported for AB H13. These features account for the improved L-PBF processability. The tempering response in comparison with a wrought H13, was characterized by a larger precipitation of thermally stable Mo- and V-rich secondary hardening alloy carbides at the expense of the easy-to-coarsen Cr-rich ones, attributed to the higher Mo and lower Cr content in experimental alloy. The combination of lower C- and V-contents in experimental alloy, reduced the driving force for the precipitation of coarse vanadium rich carbides during austenitization, as confirmed by electron diffraction spectroscopy (EDS) and synchrotron X ray diffraction. This led to a stronger fine secondary hardening alloy carbide precipitation during tempering, and enhanced temper resistance. As elaborated by isochronal tempering, as well as tempering curves, reduction of the elements Si, and Cr shifted the secondary hardness peak to higher tempering temperatures. Consequently, tempering, and thermomechanical softening resistance was significantly enhanced in the new steel with a maximum hardness of ∼550 HV1 in over-tempered condition (i.e., slightly above secondary hardness peak). Thermal fatigue (TF) tests revealed a denser and finer TF crack network with a larger oxidation in experimental steel. Thereby, the TF crack penetration depth scaling with the local plastic yielding of the matrix was evidently shorter in the new steel compared with wrought H13, thanks to significantly improved hot hardness, thermal conductivity, and enhanced thermomechanical softening resistance. Finally, a proof of concept is demonstrated by processing a relatively large injection molding die (150 mm × 110 mm × 30 mm) with promising tensile and impact toughness properties after direct double tempering to 51 HRC, and 45 HRC hardness levels.