Carbide Network Research Articles

Laser powder bed fusion of a composition-modified IN738 alloy based on thermodynamic calculations

Defects, particularly cracking defects, severely limit the application of Ni-based alloys fabricated via the laser powder bed fusion (LPBF) additive manufacturing process. To address the processability/strength trade-off, in this study a new Ni-based alloy (IN738M) was designed via thermodynamic calculations based on the traditional IN738 alloy. The processability, microstructure, phase precipitation behaviour and mechanical properties were systematically examined. The results demonstrate that the LPBF-fabricated IN738M exhibited excellent LPBF processability, achieving crack-free fabrication even with a high γ′ phase mass fraction. The compositional modifications led to improvements in the microstructure, including the formation of a quasi-continuous carbide network at the interdendritic regions, altered grain orientation and grain refinement. This study also proposes a heat treatment strategy to achieve a bimodal distribution of the γ′ phases for IN738M; the cellular structure was eliminated, with numerous MC-type carbides observed within grains and at the grain boundaries. The IN738M alloy exhibited a superior combination of ultimate tensile strength values (1462 ± 23 MPa) and elongation values (10.2 ± 0.4 %) at room temperature compared to the IN738 alloy (932 ± 35 MPa and 2.6 ± 0.3 %, respectively). These findings will provide valuable guidance for developing Ni-based alloys with enhanced LPBF processability and mechanical properties.

Research Status of Large‐Size Carbides in High‐Carbon Chromium Bearing Steel

Metallurgical quality of bearing steel is an important foundation and guarantees for determining the performance, accuracy, service life, and reliability of bearings. Nowadays, advances in refining technology have led to a significant increase in the cleanliness of bearing steel, and the control of large‐size carbides (primary, banded, and network carbides) has become particularly important. In this article, the recent research on large‐size carbides regarding morphology, precipitation mechanism, and control methods is reviewed. Firstly, the morphological characteristics of carbides are summarized. Primary carbides appear as blocky, lamellar, or irregular shapes, while banded carbides are distributed in bands. Network carbides mainly precipitate along the austenitic grain boundaries and aggregate to form networks. Secondly, the precipitation mechanisms of carbides are summarized. Dendritic segregation is the fundamental cause of the formation of primary and banded carbides, whereas network carbides are the supersaturation precipitation of carbon at austenite grain boundaries. Finally, methods for controlling large‐size carbides are summarized, including improving dendritic segregation, high‐temperature diffusion annealing, improving rolling and cooling processes and using magnesium or rare‐earth treatments. No single method offers sufficient carbide control, and mechanism of rare‐earth refining carbides is unknown. Thus, a comprehensive approach should be used in production to effectively regulate carbides in steel.

Geometric-Quadratic and Quadratic-Geometric Indices-based Entropy Measures of Silicon Carbide Networks

Geometric-Quadratic and Quadratic-Geometric Indices-based Entropy Measures of Silicon Carbide Networks

Evolution of precipitate and its effect on the degradation of impact toughness in a carbon and nitrogen-controlled 316 stainless steel during thermal aging at 650 °C

Impact toughness degradation and microstructure evolution of a carbon and nitrogen-controlled 316 stainless steel during long-term aging at 650 °C for up to 8800 h were investigated. The degradation of impact toughness during aging can be divided into three stages: a rapid decrease during stage I (the first 400 h), a slow decrease during stage II (from 400 to 3200 h), and the stable stage during stage III (up to 8800 h). P enrichment at the M23C6/γ interface is induced by the rejection of P during the formation of M23C6 carbide, and the M23C6/γ interface is preferred location for crack initiation. An increase in the amount of grain boundary M23C6 carbides increases the crack initiation sites, resulting in a rapid decrease of impact toughness during stage I. The ongoing rejection of Ni and Si during the coarsening of M23C6 carbide is beneficial for the nucleation of M6C carbide. The micro-crack initiation at the M23C6/M6C and M6C/γ interfaces is introduced, and a semi-continuous network of M23C6 carbide along grain boundary promotes the crack propagation, leading to a further decrease of impact toughness during stage II. The nearly continuous precipitate morphology is induced through continued growth of grain boundary M23C6 and M6C carbides. The propagation of micro-cracks along the M6C/γ, M23C6/γ, and M23C6/M6C interfaces leads to the mostly intergranular fracture, thus the impact energy tends to be stable during stage III.

The effect of annealing on the microstructure and wear performance of laser-clad high-entropy alloy composite coatings for monorail crane braking systems

Laser cladding was utilized to fabricate WC ceramic particle-reinforced CoCrFeMnNi high-entropy alloy (HEA) composite coatings, with an investigation into the influence of annealing heat treatment on the microstructure and wear behavior of the composite coatings. The HEA composite coatings with a WC particle content of 30 wt% primarily consist of a face-centered cubic (FCC) solid solution phase, various M6C carbides with blocky, fishbone, and dendritic morphologies, and incompletely melted WC ceramic particles. The microstructure of the composite coatings remains stable up to a temperature of 570°C. After annealing at 600°C, the microstructure transforms into a typical dendritic morphology with rod-like carbides precipitating from the solid solution and discontinuously distributed in the interdendritic regions. Due to the annealing softening effect, the microhardness of the coating decreases from 488.1 HV0.3 to 443.1 HV0.3. Following annealing at a high temperature of 800°C, recrystallization leads to a refined equiaxed grain microstructure, with precipitated carbides continuously distributed along the grain boundaries, forming a network. The combined effects of precipitation hardening and fine grain strengthening result in an increase in the microhardness of the coating to 568.6 HV0.3 after annealing at 800°C. As the annealing temperature increases, the wear rate of the WC particle-reinforced CoCrFeMnNi HEA composite coatings also increase. The wear mechanism for the unannealed coating is oxidative wear, and the reduction in hardness leads to adhesive phenomena in the coating after annealing at 600°C. The network of carbides reduces the ductility of the HEA and also the toughness of the oxide film, resulting in the highest wear rate for the coating annealed at 800°C, reaching 38.636×10−6 mm3/(N·m). This study provides valuable insights for the fabrication of advanced wear-resistant coatings.

Topological analysis of entropy measure using regression model for silicon carbide network

Topological analysis of entropy measure using regression model for silicon carbide network

Homogenization Treatment and Plastic Deformation Improve the Carbide Homogeneity of M42 High‐Speed Steel

The mechanical properties of high‐speed steel (HSS) are significantly influenced by the distribution of carbides formed during solidification. Despite extensive research, the nonuniform cooling in large ingots remains an area requiring further investigation. In this study, the microstructure inhomogeneity in M42 HSS with a diameter of 330 mm is examined. Models are developed to predict the dissolution of carbide networks during homogenization, achieving a 39% reduction in hardness variation (Δr) between the center and surface. Further improvements are attained through hot forging and rolling, leading to the fragmentation of the carbide network into a banded structure. Additionally, a detailed carbide tip dissolution model is established, providing a reliable basis for optimizing annealing processes. As a result, the carbide distribution converges significantly, with hardness variations reduced by 88% to only 0.3 hardness Rockwell C scale, showcasing substantial enhancement in material homogeneity.

Effect of the Mn and Cr contents on the oxidation and creep resistance at 1100°C of cast cantor–based HEAs

Cast High Entropy Alloys (HEAs) derived from the Cantor’s composition may represent alternative substitutional solutions to the superalloys which are constituted for more than half of the critical elements nickel and cobalt. Recently, MC–alloyed HEAs constituted by a Cantor’s type matrix associated to an efficient interdendritic network of MC carbides, have demonstrated promising creep resistance at elevated temperatures. Regrettably, they also show poor high temperature oxidation resistance. This bad oxidation behavior is possibly due to the deleterious effect of manganese and to a too low content in chromium. New alloys were elaborated and tested in oxidation at 1100°C with thermogravimetry follow–up and metallographic characterisation, and their creep behavior was controlled. With less Mn and more Cr than the original alloys, these new alloys demonstrated significant progress in oxidation resistance. These changes in chemical compositions did not modify their creep resistances which were globally maintained, for the carbide-free alloy as well as for the MC-containing ones. These Mn-decreased and Cr-increased MC-containing alloys can be considered as low-cost alternative to polycrystalline Ni or Co-based superalloys for working in moderate conditions of corrosive fluids and applied mechanical stresses.

Effects of homogenization and deep cryogenic treatments on microstructure and mechanical property of D2 tool steel fabricated by laser direct energy deposition

The integration of laser direct energy deposition (L-DED) for manufacturing high-hardness D2 tool steel components presents a promising avenue for addressing the increasing complexity of product geometries demanded by modern industry. However, the inherent variability in microstructure and mechanical properties induced by L-DED across the build height necessitates the employment of post-processing techniques to achieve material homogeneity. This study explores the synergistic application of homogenization and deep cryogenic treatment (DCT) as a novel post-processing strategy aimed at mitigating microstructural inhomogeneities and enhancing the mechanical properties of L-DED-fabricated D2 tool steel. Initial analysis of the as-built samples revealed a microstructure characterized by a fine network of eutectic carbides enveloping an FCC matrix, which imposed constraints on martensite transformation during DCT. Homogenization was found to effectively alleviate these constraints, promoting compositional and microstructural uniformity and enabling a more consistent transformation to martensite across the samples upon subsequent DCT. The strategic combination of homogenization and DCT resulted in achieving uniformly distributed high hardness levels exceeding 750 HV throughout the entire sample, regardless of their initial positions within the build. This study demonstrates the potential of combining homogenization with DCT as an effective approach to enhance the structural integrity and mechanical performance of L-DED-fabricated D2 tool steel, offering valuable insights for the development of advanced manufacturing processes for alloyed materials.

Influence of Quenching Conditions on Microstructure Evolution and Hardness of 42CrMo4 Alloy Steel

Evolution of microstructure and hardness in 42CrMo4 steel during quenching under the different cooling conditions were investigated. Mineral oil, polymer solution and water were selected as quenchants to provide different cooling conditions. Quenching experiments were also conducted under magnetic stirring and ultrasonic agitation of polymer solution. Cooling conditions during quenching had significant effect on phase transformation and hardness of 42CrMo4 steel. The quench hardened samples show martensite microstructure along with other micro-constituents. Needle like/acicular ferrite was observed with water quenching due to diffusion less transformation. Sample quenched under ultrasonic agitated medium showed formation of network of carbides. Higher hardness values were obtained with water quenching and ultrasonic agitated polymer quenching.

Preparation and properties of three-dimensional continuous network reinforced Graphite/SiC ceramic composite insulation materials

Addressing the challenge of existing insulation materials struggling to achieve the synergy of lightweight construction, high strength, and low thermal conductivity, this paper presents a method based on multi-material assembly technology to achieve a controlled composite of a three-dimensional continuous silicon carbide network and graphite matrix. Following an examination of the impact of various forming densities and the addition of expandable graphite on the thermal conductivity and compressive strength of graphite/SiC composites, the study explored the effects of different "enhancement network" topologies on the properties of these composites. The investigation demonstrates that adjusting the forming density and incorporating expandable graphite enable regulation of both the porosity and closed porosity of the composites, thereby controlling their compressive strength and thermal conductivity. Additionally, the construction of a three-dimensional continuous SiC network structure within the graphite matrix significantly enhances the compressive strength of the composites, with only a slight increase in thermal conductivity. A graphite/SiC composite thermal insulation material was ultimately developed, boasting a density of merely 1.1 g/cm³, a low thermal conductivity of 1.847 W/m·K, and an impressive compressive strength reaching 15.627 MPa. Its overall performance surpasses that of water-glass sand, making it a promising candidate for various applications in the foundry industry as a thermal insulation material.

How the multi-phase microstructure of a novel tool steel determines its corrosion behaviour in sulphuric acids

The corrosion behaviour of a Fe81Cr15V3C1 steel was analysed compared to commercial X90CrMoV18 (1.4112) in 0.01–1 mol/L H2SO4 solutions. The rapidly cooled steel comprises martensite dendrites, carbide networks (M7C3, MC) and austenite interdendritic areas. Electrochemical measurements with surface analysis (SEM, EDX, AES, GD-OES) revealed the phase impact on corrosion. Active corrosion of austenite occurs at martensite-carbide boundaries leading to narrow bands. A unique oxidation between passivity and transpassivity with dissolution along lamellar carbides and vanadyl(IV) cation release enhances with increasing acid concentration. Both steels exhibit similar corrosion resistance, a superior mechanical performance of Fe81Cr15V3C1 explains its potential for tool manufacturing.

Neighborhood degree sum-based molecular indices and their comparative analysis of some silicon carbide networks

Topological indices of a molecular graph are numeric quantities that characterize its numerous physico-chemical properties, chemical reactivities and biological activities. The neighborhood M-polynomial is productive for discovering neighborhood degree sum-based topological indices. This article deals with computing the neighborhood M-polynomial of silicon carbide networks Si 2 C 3-I[p, q], Si 2 C 3-II[p, q] and Si 2 C 3-III[p, q], and hence examining some standard neighborhood degree sum-based topological indices for the aforementioned networks. The obtained results are analyzed graphically. Moreover, a comparative study of the outcomes with some well-established degree-based topological indices of the silicon carbide networks is executed.

Surveying the Effects of Aging a High C-Containing Co-Based Superalloy From the As-Cast and Solution Heat-Treated Conditions

The microstructure of the high carbon-containing cobalt-based superalloy, Co-101, has been studied in the as-cast state and following a variety of heat treatments. In the as-cast state both M7C3 and Mo-rich M23C6 carbides were observed in the interdendritic regions. After thermal exposure at temperatures between 1000 °C and 1250 °C for 1, 10, and 100 hours, the M7C3 interdendritic carbide network was observed to transform into a Mo-lean M23C6 carbide. These changes were rationalized with thermodynamic calculations. The carbide transformation liberated carbide-forming elements that resulted in the precipitation of intragranular carbides in the dendritic regions at temperatures below 1150 °C. These carbides in the cast-aged material preferentially formed at the dendrite peripheries early during exposure, leading to wide particle size distributions. Peak hardness in the cast-aged material was attained within the first 10 hours of exposure and softening was observed thereafter. After solution heat treating at 1250 °C for 10 hours, the microstructure of Co-101 comprised an M23C6 interdendritic carbide network and solid solution dendrites supersaturated with carbide-forming elements. Subsequent aging of this microstructure for 100 hours at 900 °C led to a high number density and narrow particle size distribution of intragranular carbides. The characteristics of these carbides in the solution-aged material resulted in greater hardness, which was retained for longer durations of exposure, than the cast-aged specimens.

Effect of Ce Addition on Inclusions and Primary Carbide Network in AISI 440C Bearing Steel

The effects of Ce on inclusions and the primary carbide network of AISI 440C bearing steel are experimentally and theoretically investigated. Adding Ce improves the cleanliness and refinement of primary carbide networks in AISI 440C bearing steel ingots. The addition of Ce substantially reduces the contents of total oxygen (T.O) and S in the steel, and MnS and Al2O3 inclusions are modified into finer Ce‐containing inclusions (Ce2O2S and Ce2O3). When Ce is added, the average equivalent diameter of the inclusions decreases from 1.82 to 1.33 μm, and the number of inclusions per unit area (mm2) increases from 59 to 105. Moreover, the addition of Ce reduces the secondary dendrite spacing from 33.82 to 24.2 μm, and the proportion of primary carbide is reduced from 22.08% to 11.17%. The 2D lattice disregistry theory confirms that Ce2O2S and Ce2O3 inclusions can be utilized as effective heterogeneous nucleation cores for γ‐Fe, thus refining the solidification microstructure and also the primary carbide. This study provides theoretical guidelines for the fabrication of domestic AISI 440C bearing steel ingots.

Niobium‐Carbide‐Enhanced Wear Performance of High‐Carbon Steels

In this article, the multifaceted challenges of abrasive wear are explored, delving into its impact on components across diverse industries such as automotive, aerospace, mining, manufacturing, and energy production. The introduction of hard eutectic niobium carbide (NbC) networks into a high C martensitic steel and its effect on abrasive wear properties specifically is investigated. Four ingots are casted with Nb contents of 0.01, 0.25, 0.5, and 1.0 wt% and a base compositions of Fe–1.0C–0.96Mn–0.22Si–0.26Cu–0.11Ni–0.50Cr–0.005V–0.012Nb to determine the influence of eutectic NbC on hardness and wear resistance. Microstructural evaluation performed using scanning electron microscopy, electron dispersive spectroscopy, and X‐ray diffraction reveals that the eutectic NbC networks are broken up and distributed in bands within the microstructure upon hot‐rolling. A general increase in material hardness and wear resistance with an increase in Nb content is observed as measured by dry sand/rubber wheel (DSRW) testing. Nb alloying leads to a 65% decrease in DSRW mass loss between the 0.01 and 1.0 wt% Nb alloys at an approximate rate of 6% per every 0.1 wt% Nb added.

Enhanced toughness-thermal stability synergy and mechanisms of dual-phase Nb alloys by tuning C concentration

Nb alloy has become a promising material in aerospace due to high melting point, low density and excellent processing properties. Nevertheless, the mismatched mechanical properties and thermal stability of single-phase BCC-Nb made the aircraft unable to resist cyclic vibration loads under the action of heat/force/flow. Here, after solid solution, quenching and two-stage aging, an FCC/BCC dual-phase Nb alloy with a discontinuous grain boundary (GB) carbide network skeleton was formed. The results show that interstitial C atoms precipitate from BCC-Nb matrix resulting in volume shrinkage and form discontinuous carbide at GB, which stimulates the phase transition of BCC expansion to FCC near GB. Wherein, discontinuous GB carbides help pin the GB and dislocations, impede grain growth, and change the deformation from local to the entire network skeleton. Meanwhile, the gap provides a channel for the dislocation to pass through the GB. Additionally, the FCC provides the multi-slip system to transfer the dislocation. The results show that the yield strength, tensile strength, elongation, fracture toughness and elastic modulus of Nb alloy are increased by 79.99 %, 34.52 %, 164.22 %, 204.76 % and 1.27 %, respectively. This unique microstructure is expected to guide the design of the next generation of high-performance Nb alloys.

Microstructure and Mechanical Properties of Modified M2 High‐Speed Steel by Adding La2O3 in the Electroslag Casting Process

An electroslag casting method is used to add rare‐earth La to M2 high‐speed steels by adding La2O3 into the molten slag. The effects of the La content on the microstructure and mechanical properties of M2 high‐speed steel are studied. The results show that rare‐earth La is effectively added to steel by taking advantage of the decomposition of La2O3. The rare‐earth La partially modifies the pre‐existing oxide and sulfide inclusions into small and spherical rare‐earth oxysulfide inclusions. By adding an appropriate amount of La, the as‐cast iron dendrite matrix and coarse eutectic carbides can be refined, the carbide content is reduced, the carbide network is broken, and the decomposition of M2C into M6C and MC is promoted. After heat treatment, the network breaking and spheroidalization of the carbides are further facilitated, and the carbide content is reduced. The impact toughness and bending strength of the studied samples are improved by modifying the inclusions and optimizing the microstructure.

Vertex-edge based resolvability parameters of vanadium carbide network with an application

A big amount of vanadium is used in the industry. It is used as a vanadium carbide stabiliser in steel production. Only 0.5 % vanadium in an iron alloy will double the tensile strength. Vanadium salts are used in leather, ink, dye manufacturing and yellow ceramic glaze. On the other hand, vanadium pentoxide is used as a catalyst, in the chemical industry, for the production of sulphuric acid and in the petroleum refinery industry. Resolvability parameter is the most discussed topic in graph theory. This helps to reorganise a network in a unique way, sometimes in terms of atoms (metric dimension) and sometimes bound (edge metric dimension). We studied resolvability parameters of vanadium carbide network in this article i.e. metric, edge metric and partition dimension. Among these metrics resolvability defined by parameters taking a subset from the set of vertices, if it has a unique representation with all the vertices, then it is called a resolving set. The number of elements in the smallest resolving set is called the metric dimension. While the number of elements of the minimal subset of vertices taking from vertex set is called the edge metric dimension, if the representations are unique of all edges and the set is called the edge resolving set. This study can have an effect in many ways in the research, particularly, with the help of some key points such as network structure analysis, material science via material properties, graph theory applications, predictive modelling, material testing and characterisation, as well as in industrial applications.

High Surface Area Metal Carbide Aerogels as Durable Catalyst for the Hydrogen Evolution Reaction

Electrolyzers’ technologies are essential for the Hydrogen Economy scheme, and in order to drive the hydrogen production price down, their lifetime need to be extended. One important parameter that has not been given enough attention in this context is catalyst durability. In this work, a durable platinum-group metal-free catalyst was developed for hydrogen evolution reaction based on porous, high-surface area molybdenum carbide aerogel. Molybdenum oxide aerogel was synthesized by sol–gel method and carburized by methane-treatment. A three-dimensional molybdenum carbide network was obtained by reacting molybdenum oxide aerogel with CH4/H2 mixture at 700°C. Surface area measurement confirmed a substantial increase in the volume of micropores in the transition from oxide to carbide. The carbide aerogel has low density (<0.4 g/ml) with relatively high surface area of 109 m2/g (reduced from 188 m2/g after methane treatment). The molybdenum carbide aerogel shows remarkable durability compared to Pt/C catalyst, with only 10 mV overpotential shift vs. 100 mV for Pt/C after stability test.