Alloy Carbides Research Articles

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.

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.

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.

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.

Hydrogen Trapping and Precipitation of Alloy Carbides in Molybdenum Added Steels and Vanadium Added Steels

Hydrogen Trapping and Precipitation of Alloy Carbides in Molybdenum Added Steels and Vanadium Added Steels

Thermal fatigue performance enhancement of new high-Cr martensitic die steels based on overall microstructure manipulation by trace TiC–TiB2 nanoparticles

Thermal fatigue failure is one of the main factors affecting the service life of hot work die steel. Achieving excellent thermal fatigue resistance for hot working die steels can benefit the industry economically. In this work, (TiC + TiB2)/Al master alloys were used to add TiC–TiB2 nanoparticles into high-Cr die steels, which achieves microstructure manipulation and obtains excellent thermal fatigue resistance and strength-plastic combination. The results showed that after being manipulated by 0.02 wt% TiC–TiB2 nanoparticles, the surface oxidation zone of the high-Cr die steel after different thermal fatigue cycles is reduced than high-Cr die steel without manipulation. TiC–TiB2 nanoparticles effectively refined the heat-treated microstructure of high-Cr die steel, promoting the Cr element and alloy carbides being more uniformly distributed in the matrix, which prevents the occurrence of oxidative pitting and conducive to the formation of a dense and uniform Cr2O3 oxide layer, and further preventing the initiation of thermal fatigue cracks. Moreover, these finer and more uniformly distributed precipitates in TiC–TiB2 nanoparticles manipulated high-Cr die steels will promote stress dispersion and hinder thermal fatigue crack propagation. This work provides a promising avenue for the design of low-cost, high-performance, and long-life die steels for industrial applications.

Microstructure, Tensile Properties, and Fracture Toughness of an In Situ Rolling Hybrid with Wire Arc Additive Manufacturing AerMet100 Steel.

As a type of ultra-high strength steel, AerMet100 steel is used in the aerospace and military industries. Due to the fact that AerMet100 steel is difficult to machine, people have been exploring the process of additive manufacturing to fabricate AerMet100 steel. In this study, AerMet100 steel was produced using an in situ rolling hybrid with wire arc additive manufacturing. Microstructure, tensile properties, and fracture toughness of as-deposited and heat-treated AerMet100 steel were evaluated in different directions. The results reveal that the manufacturing process leads to grain fragmentation and obvious microstructural refinement of the AerMet100 steel, and weakens the anisotropy of the mechanical properties. After heat treatment, the microstructure of the AerMet100 steel is mainly composed of lath martensite and reversed austenite. Alloy carbides are precipitated within the martensitic matrix, and a high density of dislocations is the primary strengthening mechanism. The existence of film-like austenite among the martensite matrix enhances the toughness of AerMet100 steel, which coordinates stress distribution and restrains crack propagation, resulting in an excellent balance between strength and toughness. The AerMet100 steel with in situ rolling is isotropy and achieves the following values: an average ultimate strength of 1747.7 ± 16.3 MPa, yield strength of 1615 ± 40.6 MPa, elongation of 8.3 ± 0.2% in deposition direction, and corresponding values in the building direction are 1821.3 ± 22.1 MPa, 1624 ± 84.5 MPa, and 7.6 ± 1.7%, and the KIC value up to 70.6 MPa/m0.5.

Potential solution to the sustainable ethanol production from industrial tail gas: An integrated life cycle and techno-economic analysis

Utilising industrial tail gas for ethanol production is a viable pathway to significantly mitigate CO2 emissions whilst simultaneously producing value-added fuels and chemicals, which has received great attention in recent years. While some technologies have been commercial deployed, new technological concepts continue to emerge in order to improve the life cycle and techno-economic performance. In this investigation, a novel ethanol production technology integrating tail gas-based ethanol (TG-ethanol) with electro-catalytic CO2 reduction (ECR), called TGEE technology, was first proposed to address the energy and carbon efficiency issues associated with the state-of-the-art TG-ethanol technologies. The process was modularly modelled for to accommodate different ECR integration scenarios for three typical industrial tail gas streams (steel, iron alloy and calcium carbide). In addition, life cycle & techno-economic analysis based on Monte Carlo simulation were employed to evaluate the environmental and economic performance of the TGEE process. Results show that ethanol capacity can be increased by 1.3–2.9 times with carbon efficiency up to 36–82%. Life cycle carbon footprints of TGEE-ethanol were estimated to be 1.77–3.93 t CO2eq/t ethanol, with a carbon reduction potential of 32–63% higher than the TG-ethanol. Minimum ethanol selling price is estimated to be 428–962 $/t ethanol, which is lower than the current ethanol market price (900–1080 $/t). Overall, the comprehensive analysis suggests that the TGEE process emerges as a more economically and environmentally benign next-generation technology for ethanol production from industrial tail gas.

Secondary hardening in an Cr-Mo-V steel: Effect of thermal cycle tempering

Secondary hardening by precipitation of alloy carbides during tempering in an experimental Cr-Mo-V alloy steel was studied under continuous and isothermal conditions. Measurements of microhardness and nanohardness analysed the hardening behaviour during stage IV as a function of time, temperature, and heating rate. Scanning electron microscopy and scanning probe evidenced the carbides precipitated during stage IV. It was observed that hardening is a function of not only tempering temperature and time but also of the heating rate according to the Hollomon–Jaffe parameter. The parameter increases as the heating rate increases due to the effect on the temperature, showing a clear softening. The hardening behaviour, evaluated with the Hollomon–Jaffe parameter, was very similar regardless of the test, micro- or nanoindentation.