Carbide Mechanism Research Articles

Quantitative control of interfacial structure and thermal conductivity between diamond and copper via thermal diffusion of alloying element

The thermal property of diamond/metal composites mainly depends on the chemical bonding and structure of interfacial layers between two heterogeneous materials. To improve the thermal property of the diamond/metal composites, a metallic carbide layer that bridging both crystal structure and thermal transport of heterogeneous interfaces is required, though the formation mechanism of such carbide interfaces during powder sintering remains under debate, particularly for the scenario of varying thermal diffusion. Here, systematic experiments of diamond/Cu–Cr composites have been conducted to unravel the effects of two important variables for thermal diffusion, temperature (800–1025 °C) and holding time (5–60 min), on the growth of chromium carbide interfaces and the resulting thermal conductivity. It is found that the main characteristics of chromium carbide layer is more related to the holding time, that is, prolonged thermal diffusion. The extraction of diamonds in as-sintered composites allows a detailed quantification of coating efficiency and crystallographic-facet-dependence of chromium carbide interfaces during diamond/metal reaction at varying temperature and holding times. It is found that the prolonged thermal diffusion is not as expected to deteriorate the thermal conductivity, and leads to a more densified structure with highest thermal conductivity instead (∼577 W/(m·K)). Furthermore, thermal diffusion of diamond/metal reaction is discussed based on theoretical models. We theoretically demonstrate that long thermal diffusion could enhance the thermal diffusivity for the composites and achieve ∼90.8% of theoretical thermal conductivity predicted by the Maxwell-Eucken model.

Atomistic understanding on the surface formation mechanism of nanoscale scratches along different crystal orientations of silicon carbide

Single crystal silicon carbide has been widely used in many fields due to its excellent physical and chemical properties. However, these special properties of silicon carbide can lead to surface defects and subsurface damage in precision machining processes. In this research, high-speed scratching experiments and molecular dynamics simulations were used to study the surface formation mechanism of nanoscale scratches along the [1-210] and [1-100] crystal orientations of silicon carbide. For both the simulations and experiments, different scratching crystal orientations result in the formation of different amorphous patterns. The angle between the scratching orientation [1-210] and the amorphous pattern is 60°, while the angle between scratching orientation [1-100] and the amorphous pattern is 30°. The stress concentration during the scratching process along the orientations [1-210] and [1-100] is mainly located at the two edges and one edge of the amorphous patterns, respectively. The amorphous patterns along the < 1-210 > directions on the (0001) plane are caused by dislocations and slips on the {10-10} plane. This study reveals the material deformation mechanism and removal mechanism of silicon carbide along different crystal orientations scratching, providing theoretical guidance for the nanoscale machining of silicon carbide.

Temperature-Dependent Oxidation Behavior of Silicon Carbide Surface: Reactive Molecular Dynamics Simulations.

The high-temperature oxidation mechanism of silicon carbide (SiC) is crucial for designing thermal protection systems in aircraft. This study explored the oxidative chemical reaction processes and mechanism on SiC surface and interfaces within the temperature range of 300-2300 K by using reactive molecular dynamics simulation. The oxygen impact on the silica (SiOx) growth of the SiC surface was analyzed, which shows a progressive increase of silica thickness. The simulation results indicated that the oxidation process of SiC was a typical passive oxidation mechanism. With the environmental temperature rising and oxygen impact, the increase of oxidation thickness on the SiC surface undergoes three oxidizing reaction processes: little chemical adsorption of oxygen molecules on the initial surface, rapid oxidation of silicon and carbon, and dramatic oxidation of the interface between the oxidation layer and SiC. Additionally, this work studied the mechanism of oxidation thickness growth and chemical diffusion of oxygen. The oxidation rate is weakened according to the oxygen atom diffusion barrier effect of silica repulsion. Moreover, the kinetic parameters were statistically calculated by fitting the growth of Si-O bonds and their reaction rate constants. Subsequently, the activation energy and pre-exponential factors were derived by using the Arrhenius equation to model the chemical reaction kinetics of the thermal oxidation process. The chemical reaction behaviors of the two stages could be concluded as follows: (i) in stage I, the initial oxidation is reaction rate limiting; (ii) in stage II, SiC oxidation is limited by both the oxidation reaction rate and the oxygen diffusion coefficient of the oxidation layer. The activation energy of stage II increased compared with stage I due to the oxygen atoms diffusion barrier between the oxidation layers. This study on the oxidation and ablation mechanism of the SiC surface at the atomic scale would provide insight into understanding thermal oxidation behavior and the design of ceramic materials.

Cutting mechanism of reaction-bonded silicon carbide in laser-assisted ultra-precision machining

Reaction-bonded silicon carbide (RB-SiC) is an important material used in aerospace optical systems. Due to the property mismatch between Si and SiC phases, the underlying cutting mechanism in ultra-precision machining of RB-SiC remains relatively unclear. Recently, laser-assisted machining (LAM) has emerged as an effective technique to improve the machinability of hard and brittle materials, which brings the question that how the high temperature affects the machining mechanism of RB-SiC. To elucidate these aspects, a series of grooving experiments and MD simulations were conducted in this study. The interaction mechanism between phases on material removal and subsurface damage was revealed and the effect of cutting temperature on Si-SiC interaction was explored. The results indicate that in conventional ultra-precision machining, SiC grains could affect the deformation of Si phase, whereas the influence of Si phase on SiC deformation is limited. As the cutting temperature increases, the Si-SiC interaction is less apparent and the deformation of Si and SiC becomes more independent. Meanwhile, the prominence of phase property mismatch on subsurface damage are reduced while the extension of disordered phases into boundaries merges as an important mechanism in subsurface damage formation. This research helps to understand the thermal effect on material interaction between phases during machining and aid to improve the performance of LAM on RB-SiC.

Impact of CO hydrogenation diffusion limitation and cluster size on Fischer-Tropsch synthesis mechanism: An integrated experimental and theoretical study

This research examines how varying cobalt particle sizes and support pore sizes affect CO diffusion in Fischer-Tropsch synthesis (FTS). It explores cobalt catalysts deposited on perlite (P) and its modified version (S) with weight loadings ranging from 5% to 20%. N2 adsorption-desorption, BET analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H2-TPR), hydrogen temperature-programmed desorption (H2-TPD), transmission electron microscopy (TEM), and Fourier-transform infrared spectroscopy (FT-IR) analyses were utilized for characterization. The results designate that higher cobalt loading on the modified support (S) decreases CH4 selectivity while enhancing selectivity towards C5+ hydrocarbons. Despite larger cobalt particles in 15CP compared to 15CS, 15CP exhibits higher CH4 selectivity and reduced C5+ selectivity because of CO diffusion limitations and smaller pore size. DFT calculations reveal product selectivity depends on FTS mechanism and cobalt cluster size influences reaction pathways, with smaller clusters favoring CO insertion and larger clusters favoring carbide mechanisms.

Conversion mechanism of pyrolysis humic substances of cotton stalks and carbide slag and its excellent repair performance in Cd-contaminated soil

Unlike traditional biomass composting humification, pyrolysis humification can rapidly convert waste biomass into humic substances (HSs) at lower temperatures and in an alkaline environment for soil remediation. This study utilized the strong alkaline solid waste carbide slag (CARBIDE) and cotton stalk (CS) for pyrolysis humification. The pyrolysis humification mechanism and effect of CARBIDE and CS were investigated using FT-IR, NMR, and Py-GC/MS. Furthermore, the ability of HSs to remediate cadmium-contaminated soil (Cd-soil) was assessed through soil property analysis, pot tests, and microbial diversity studies. The results showed that humic acid (HA) and fulvic acid (FA) had the highest yield of 19 % and 5 %, respectively, among the humic substances (HS-CS&CA) produced under the conditions of 250 ℃, reaction time of 2 h and mass ratio of CS to CARBIDE of 5: 1. At 250 ℃, CARBIDE changed the heat transfer mechanism of biomass, promoted the decomposition of more hemicellulose and protein, promoted the Deamination, Ketonization and Maillard reaction, and synthesized more HAs. HS-CS&CA had a significant remediation effect on Cd-soil. The immobilization rate of Cd was as high as 23 %, and the accumulation of Cd in maize was reduced by 65 %. At the same time, the relative abundance of beneficial bacteria such as Xanthomonadaceae and Bacillaceae for immobilizing Cd was increased, and the cycling effect of N and P was also enhanced. This study provides an innovative technical route for the rapid humification of CARBIDE and CS and its application in Cd-soil remediation.

Study on material removal mechanism and surface formation characteristics of reaction-bonded silicon carbide by electrical discharge grinding technology

Study on material removal mechanism and surface formation characteristics of reaction-bonded silicon carbide by electrical discharge grinding technology

Temperature-dependent water corrosion mechanism of silicon carbide: Atomic insights from reactive molecular dynamics simulation

Silicon carbide (SiC) is an ideal material for both aeronautics and space industries, but SiC is highly susceptible to water corrosion at high temperature. A clear understanding of water corrosion mechanism of SiC is still lacking because the complex interaction dynamics are extremely difficult to be investigated experimentally. In this study, the temperature-dependent of water corrosion mechanism of SiC was investigated by reactive molecular dynamics simulation, and three different corrosion regimes were observed with the increase of the ambient temperature. In regime I (below 1000 K), only Si–H and Si–OH terminations were formed on SiC surface and almost no corrosion occurred; in regime II (1000–1500 K), the same number of carbon and silicon atoms were corroded in the form of gaseous molecules, and the relation between the number of atoms lost and temperature was in good agreement with the Arrhenius expectation; lastly, in regime III (above 1500 K), the number of Si–O–Si groups formed exceeded the volatilized number, leading to the obvious retention of the Si–O–Si network structures. These results can guide the design and preparation of SiC materials for aerospace applications by providing an atomic insight into the mechanisms of water corrosion on SiC.

The Importance of Sintering-Induced Grain Boundaries in Copper Catalysis to Improve Carbon-Carbon Coupling.

Syngas conversion serves as a gas-to-liquid technology to produce liquid fuels and valuable chemicals from coal, natural gas, or biomass. During syngas conversion, sintering is known to deactivate the catalyst owing to the loss of active surface area. However, the growth of nanoparticles might induce the formation of new active sites such as grain boundaries (GBs) which perform differently from the original nanoparticles. Herein, we reported a unique Cu-based catalyst, Cu nanoparticles with in situ generated GBs confined in zeolite Y (denoted as activated Cu/Y), which exhibited a high selectivity for C5+ hydrocarbons (65.3 C%) during syngas conversion. Such high selectivity for long-chain products distinguished activated Cu/Y from typical copper-based catalysts which mainly catalyze methanol synthesis. This unique performance was attributed to the GBs, while the zeolite assisted the stabilization through spatial confinement. Specifically, the GBs enabled H-assisted dissociation of CO and subsequent hydrogenation into CHx*. CHx* species not only serve as the initiator but also directly polymerize on Cu GBs, known as the carbide mechanism. Meanwhile, the synergy of GBs and their vicinal low-index facets led to the CO insertion where non-dissociative adsorbed CO on low-index facets migrated to GBs and inserted into the metal-alkyl bond for the chain growth.

Insights into Fischer–Tropsch catalysis: current perspectives, mechanisms, and emerging trends in energy research

Fischer–Tropsch (FT) synthesis is an important module for the production of clean and sustainable fuels and chemicals, making it a topic of considerable interest in energy research. This mini-review covers the current literature on FT catalysis and offers insights into the primary products, the nuances of the FT reaction, and the product distribution, with particular attention to the Anderson–Schulz–Flory distribution (ASFD) and known deviations from this fundamental concept. Conventional FT catalysts, particularly Fe- and Co-based catalysis systems, are reviewed, highlighting their central role and the influence of water and water–gas shift (WGS) activity on their catalytic behavior. Various mechanisms of catalyst deactivation are also investigated, and the high methanation activity of Co-based catalysts is illustrated. To make this complex field accessible to a broader audience, we explain conjectured reaction mechanisms, namely, the carbide mechanism and CO insertion. We discuss the complex formation of a wide range of products, including olefins, kerosenes, branched hydrocarbons, and by-products such as alcohols and oxygenates. The article goes beyond the traditional scope of FT catalysis by addressing topics of current interest, including the direct hydrogenation of CO2 for power-to-X applications and the use of bifunctional catalysts to produce tailored FT products, most notably for the production of sustainable aviation fuel (SAF). This mini-review provides a holistic overview of the evolving landscape of FT catalysts and is aimed at both experienced researchers and those new to the field while covering current and emerging trends in this important area of energy research.

Investigation of tool wear and energy consumption in machining Ti6Al4V alloy with uncoated tools

This research studies the energy consumption and wear mechanism of carbide cutting tools in dry machining of Ti6Al4V alloy. In the first phase of experiments, full factorial design experiments were employed to study the tool wear rate (R) and specific cutting energy (SCE) with respect to the machining conditions (cutting speed and feed rate). Results showed that machining responses such as tool wear and energy consumption are affected by cutting conditions, thus requiring investigation to understand the wear mechanisms. Therefore, in the second phase, additional experiments were performed to investigate the tool-workpiece interactions at the cutting conditions reported to have low, moderate, and high tool wear. It was revealed that strong adhesion and material transfer between the tool and workpiece caused high wear. Electron dispersive X-ray spectroscopy (EDX) analysis of worn tools showed that the transfer of tungsten (W) and cobalt (Co) to the workpiece and titanium to the tool surface is the primary cause of tool deterioration. As a result, diffusion and dissolution have degraded cutting performance and weakened the tool edge, leading to rapid wear. Furthermore, worn tools resulted in relatively higher energy consumption per unit volume of material removed at the tooltip. The degradation of cutting performance and weakening of the tool edge results in rapid wear and higher energy consumption. The study suggests that minimizing tool wear is crucial for energy reduction, improved sustainability, and cleaner production goals in dry machining of titanium-based alloys.

Insights into refinement mechanism of primary M7C3 carbide by La2O3 via experiments and first-principles calculations

This study is dedicated to summarize refinement mechanism of the primary M7C3 carbide by rare earth oxide La2O3. The La2O3 was added into hypereutectic Fe–27Cr–4C alloy, and its microstructure was observed and analyzed by optical microscope (OM), X-ray diffractometer (XRD) and scanning electron microscope (SEM). The lattice mismatch degrees of La2O3//M7C3 interfaces were calculated. The interface properties of La2O3//M7C3 were calculated by the first principles. The effectiveness of La2O3 as the heterogeneous nucleus of the primary M7C3 carbide in the alloy was analyzed. The results show that the primary M7C3 carbide can be refined by La2O3 in this alloy. The lattice mismatch degree between La2O3(111) plane and M7C3(0001) plane is 2.36%, which indicates that La2O3 as the heterogeneous nucleus of M7C3 is the most effective. La2O3(111) plane and M7C3(0001) plane were chosen to construct the interface models. Two surface models, such as La-termination and O1-termination on La2O3(111) plane were constructed, which converge to 26 and 21 layers, and their surface energies are 5.256 J/m2 and 2.029 J/m2, respectively. The surface model of M7C3(0001) plane converges to 17 layers, and its surface energy is 3.199 J/m2. Among La-M7C3 and O1-M7C3 interfaces, the adhesion work (16.162 J/m2) of O1-M7C3 is larger than that (1.731 J/m2) of La-M7C3. However, the interface energy (−10.910 J/m2) of O1-M7C3 is smaller than that (6.725 J/m2) of La-M7C3, which indicates that O1-M7C3 interface has the best interface bonding property and the lowest interface nucleation resistance. Therefore, La2O3 can serve as the heterogeneous nucleus of M7C3 and tends to form an O1-M7C3 heterogeneous nucleation interface.

ReaxFF molecular dynamics simulation and experimental validation about chemical reactions of water and alcohols on SiC surface

The high chemical inertness of silicon carbide (SiC) makes it difficult for surface chemical reactions to occur. Surface oxidation reactions are crucial for improving the processing efficiency and surface quality of SiC wafers. Extensive research has been conducted on conventional aqueous polishing slurries, while investigations on non-aqueous solvent-based polishing slurries have emerged as alternative options for enhancing SiC surface processing, as evidenced by recent scholarly reports. However, the surface chemical reaction mechanism of silicon carbide in either water or other hydroxyl groups containing solvents remains still unclear and is not well understood. In this work, ReaxFF molecular dynamics simulation was used to study the dynamic reaction processes between solvents and 6H SiC (001) surfaces. The oxidation of SiC surface in water and alcohol solvent is found to go through three stages: in the first stage, the solvent molecules move towards the SiC surface and react with the uncoordinated Si atoms and C atoms on the surface; in the second stage, the solvent molecules adsorbed on the surface of SiC reduces the Si–C bonding energy and promotes the breaking of Si–C bonds; in the third final stage, the migration of OH and H on the SiC surface induces the formation of Si–O–Si bonds, which promotes the continuous oxidation of the SiC surface. The order of simulated chemical reactivity between solvent and silicon carbide surface is consistent with experimental polishing removal rates. The reaction mechanism of solvent on silicon carbide surface was proposed by combining ReaxFF simulation results with polishing experiments, AFM, and XPS data analysis, shedding new insights on better understanding the mechanism of SiC chemical mechanical polishing.

Precipitation mechanism of dispersed carbide in a gear carburizing layer and its effect on properties

AbstractHeat treatment is carried out on 20MnCr5 gear steel using a cycle carburizing process. The dispersed carbide precipitation mechanism in the carburized layer of 20MnCr5 gear steel is revealed, and the metallographic organization, microhardness, wear resistance, and fatigue properties are tested. The precipitation mechanism of two kinds of dispersed carbides at grain boundary and inside grain in carburized layer of gear steel was observed by experiment. The size of dispersed carbide particles is 0–5 μm, and 90% of the dispersed carbide is appropriately smaller than 1 μm. Compared to gears without dispersed carbide, gears with dispersed carbide have high microhardness within a 0.4 mm depth below the surface and a low friction coefficient. It has been verified by bench test that the presence of diffuse carbides dramatically improves the fatigue life of the gears after shot blasting and shot peening.

Analysis of wear mechanism and sawing performance of carbide and PCD circular saw blades in machining hard aluminum alloy

High-efficiency sawing is widely applied in primary and secondary machining sectors, but it faces limitations due to saw tooth life and manufacturing constraints. This research investigates the wear mechanism, wear characteristics, and sawing performance of carbide and polycrystalline diamond (PCD) saw teeth when machining hard aluminum alloy. The results show that the sawing forces with PCD saw teeth are less than those of carbide teeth, yielding better surface quality and longer tool life. The wear mechanisms of saw teeth of two materials with different tooth types are classified and characterized finely. Carbide teeth are subject mainly to abrasion and adhesion at the cutting edges, while adhesion, corrosion, and diffusion primarily contribute to flank face wear. PCD teeth mainly suffer from abrasion and micro-chipping on the cutting edges and faces. A comprehensive description of the wear evolution of carbide and PCD teeth is presented, with the cutting heat being the primary cause of carbide tooth wear and the presence of hard particles in the workpiece causing PCD tooth wear by SEM and EDS analysis. The friction coefficient of the PCD teeth is considerably lower than that of the carbide teeth by sliding friction and wear tests, which also proves its more superior thermal stability and wear resistance during wear evolution analysis. Systematic research analyzes and discusses the wear mechanism and wear characteristics of saw teeth in high-speed sawing process, which can further enhance the understanding of the saw tooth wear to provide theoretical guidance for saw tooth design and manufacturing.

Elucidation of the synergistic mechanism of nano silicon carbide and titanium nitride as highly efficient additives of polyalphaolefin on strengthening the lubrication performance of movable contact interface

This study comprehensively investigated physicochemical and tribological performance of polyalphaolefin (PAO4) oil introducing oleic acid (OA)-functionalized SiC/TiN hybrid nanomaterials. The dispersion stability, wettability, thermal stability, and friction properties of the nanolubricants (NL) system were greatly improved following the application of hybrid NL. Additionally, the anti-wear and reducing-friction behavior were assessed via a four-ball tribometer. The results showed that the COF and WSD values of wear scar lubricated by hybrid NL were greatly reduced by approximately 32.7% and 35.1%, respectively, compared with the base oil. Finally, it is strongly confirmed that the significant improvement of friction performance is mainly due to improved interfacial effect of NL, the stable chemical tribo-film generated onto the friction surface, and the synergistic effect among SiC, TiN nanoparticles, and OA surfactant.

Continuous SiC Skeleton-Reinforced Reaction-Bonded Boron Carbide Composites with High Flexural Strength.

Reaction-bonded boron carbide (RBBC) composites have broad application prospects due to their low cost and net size sintering. The microstructure, reaction mechanism of boron carbide with molten silicon (Si), and mechanical properties have been substantially studied. However, the mechanical properties strengthening mechanism of reaction-bonded boron carbide composites are still pending question. In this study, dense boron carbide ceramics were fabricated by liquid Si infiltration of B4C-C preforms with dispersed carbon black (CB) as the carbon source. Polyethyleneimine (PEI) with a molecular weight of 1800 was used as the dispersant. CB powders uniformly distributed around boron carbide particles and efficiently protected them from reacting with molten Si. The uniformly distributed CB powders in situ reacted with molten Si and formed uniformly distributed SiC grains, thus forming a continuous boron carbide-SiC ceramic skeleton. Meanwhile, the Si content of the composites was reduced. Using PEI-dispersed CB powders as additional carbon source, the composites' flexural strength, fracture toughness, and Vickers hardness reach up to 470 MPa, 4.6 MPa·m1/2, and 22 GPa, which were increased by 44%, 15%, and 10%, respectively. The mechanisms of mechanical properties strengthening were also discussed.

Tailoring Ni3ZnC0.7/graphite heterostructure in N-rich laminated porous carbon nanosheets for highly efficient microwave absorption

Bimetallic transition carbide nanoparticles (Ni3ZnC0.7) encapsulated with graphitic shells were successfully embedded into N-rich laminated porous carbon nanosheets (NC–ZnNi1.5) by one-step pyrolysis of bimetallic organic frameworks. It was found that C atoms penetrated octahedral interstitial spaces of the Ni lattice to form Ni3ZnC0.7. The charge states and distribution of metal atoms were influenced by the interstitial C atoms, which promoted polarization relaxation and facilitated dielectric loss. Simultaneously, the volatilization of Zn influenced recrystallization and rearrangement of the crystalline domains, facilitated graphitization and established a 3D conductive network to optimize the conductive loss. Besides, multi-level heterogeneous interface and nitrogen doping also further optimized the impedance matching. Benefiting from these advantages, the minimum reflection loss of NC-ZnNi1.5 was −69.1 dB at 12.7 GHz, and the effective absorption bandwidth was 6.5 GHz. The mechanism of bimetallic carbide's dielectric loss was explained in detail, providing a new pathway for the development of multi-component carbon-based microwave absorbers in the future.

Atomistic simulation on the removal mechanism of monocrystal silicon carbide with textured surface nano-machining in water lubrication

A new machining method that combines textured surface and water lubrication is proposed in this paper to improve the friction characteristics of ground silicon carbide (SiC). The effects of water film thickness and grinding speed on the nano-machining behavior of monocrystal cubic SiC are revealed using molecular dynamics simulation. Moreover, a Rayleigh chip thickness model is employed to predict surface roughness. According to the obtained results, friction characteristics and machinability of textured samples are strengthened compared with the non-textured sample. Behavior characteristics are further improved in water-lubricated conditions, which show that the temperature, grinding force, and friction coefficient decrease, while the hydrostatic stress and the von Mises stress increase. Therefore, tool wear and sub-surface damage are improved. Furthermore, an improved material removal performance is also achieved under high-speed grinding. Lastly, it is observed that surface roughness of ground SiC is improved in water lubrication and under high-speed grinding.

Microstructure and bond strength of niobium carbide coating on GCr15 prepared by in-situ hot press sintering

The hardness and adhesion of protective hard coatings to the substrate are the most important parameters that influence the performance of the tool. Herein, we propose an effective strategy, by in-situ hot press sintering, to fabricate a novel niobium carbide coating with high hardness and excellent interfacial bond strength on GCr15. The coating is composed of Nb2C, NbC, and α-Fe phases. The volume fraction of niobium carbide (Nb2C and NbC) phases reaches 93%. Along the direction of coating thickness, the grain morphology of niobium carbide changes from equiaxed (Nb2C) to columnar (NbC), and then to equiaxed (NbC), presenting a gradient microstructure. The coating/substrate interface displays an excellent macro/micro interface. The formation of the gradient microstructure is attributed to the nucleation-growth process controlled by the carbon concentration gradient diffusion. The novel gradient coating can simultaneously achieve superhardness (20.2 ± 0.3 GPa) and excellent bond strength (>210 ± 20 MPa). The excellent bond strength is mainly attributed to the in-situ formation of the coating and the gradient microstructures. The tensile test results show that the fracture mechanism of the niobium carbide coating on GCr15 is mainly a brittle fracture of niobium carbide coating and a small amount of coating debonding.