NbC Carbides Research Articles

In-situ synthesis and characterization of Cu/NbC, Cu/NbC-WxC, and Cu/WxC nanocomposites via mechanical alloying

In-situ Cu/NbC, Cu/NbC-WxC, and Cu/ WxC nanocomposites were synthesized by mechanical alloying (MA) at room temperature using high-purity premixed Cu(10-x)NbxW (x = 0, 5, 10 at%) elemental powders. The synthesized powders were then consolidated through Equal Channel Angular Pressing at 700 °C. The microstructure, phase constituent, and hardness of the as-milled and consolidated powders were investigated using scanning and transmission electron microscopy, X-ray diffraction, and microhardness measurements. The 80 h MA resulted in the formation of a Cu/NbC and Cu/NbC-W nanocomposite powder with an average copper matrix crystallite size of 8–11 nm and NbC and W particle sizes mainly less than 100 nm. Refinement of the powders was achieved through cracking at the work-hardened areas in the copper matrix and fracturing of the tungsten and niobium particles. During consolidation, the W converted into W2C and WC phases. Additionally, the Cu matrix crystallite size increased to 41 nm, 43.6 nm, and 65.3 nm for Cu10Nb, Cu5Nb5W, and Cu10W, respectively. While Cu10Nb showed the highest hardness among the as-milled samples, Cu5Nb5W attained the highest hardness value of 462 HV after consolidation, which is due to its smaller Cu matrix crystallite size and finer carbide particles compared to the Cu10Nb and Cu10W alloys and likely due to the synergistic strengthening effect of the NbC and WxC carbide particles. These findings demonstrate the successful synthesis of in-situ Cu-based nanocomposites with tailored microstructures and constituent phases through mechanical alloying.

Creep damage mechanism of 20Cr32Ni1Nb steel at high temperatures

In the petrochemical industry, the centrifugally cast austenitic 20Cr32Ni1Nb stainless steel used in steam reformer furnace's hot outlet manifold experiences creep failure and microstructural degradation, impacting its structural integrity. Understanding the causes of these issues is crucial for addressing the associated challenges. This study examines the creep deformation behaviour, damage mechanisms, and microstructural evolution of 20Cr32Ni1Nb steel under stresses of 22–50 MPa at temperatures of 1163 K (890 °C) and 1223 K (950 °C). Analysis of creep and creep strain rate curves revealed the presence of both primary and tertiary creep stages, with the power law relationship governing the stress-dependent minimum creep rate and rupture life. The variance of creep damage tolerance factor was also analysed, with results showing that in high-stress regimes, loss of section and necking along with cavity growth may initiate tertiary creep, while in low-stress regimes, microstructural degradation, specifically G-phase formation, may initiate tertiary creep. As the duration of creep exposure increases, microstructures were observed to degrade, with the growth and coarseness of NbC and M23C6 carbides. The structure of the space group for the Ni–Nb–Si enriched G-phase in 20Cr32Ni1Nb steel was found to be Fm3‾m, with a lattice parameter of about 1.14 nm.

Effect of aging on secondary phases and properties of an S304H austenitic stainless steel

Effect of aging up to 3000 h at 923 K on the microstructure, the secondary phases, the mechanical properties, and the intergranular corrosion was examined in an S304H-type austenitic stainless steel. The Cu-rich and NbC-type particles with sizes of 1.5 nm and 50 nm, respectively, were uniformly distributed throughout whileM23C6-type carbides with a size of 40 nm precipitated mainly on the grain boundaries after aging for 100 h. Upon further aging a relatively fast coarsening of the boundary M23C6 carbides in accordance to a power law relationship with a particle growth exponent of 4 led to the formation of semi-continuous chains of these carbides along the grain boundaries. These chains diminished the fracture toughness; moreover, the steel became susceptible to intergranular corrosion. On the other hand, the uniform dispersions of NbC carbides and Cu-rich particles were less susceptible to coarsening under aging. The growth behavior of these particles could be expressed with a particle growth exponent of 3. A depletion of solid solution due to precipitate coarsening led to the ferrite appearance primarily along the austenite grain boundaries. The dispersion strengthening by carbide/nitride particles gradually decreased while that from Cu particles increased during annealing, resulting in the tension strength slightly increased with aging duration.

Determination of Corrosion Resistance of High-Silicon Ductile Iron Alloyed with Nb

In this study, the effects of Nb on the microstructural characteristics, hardness, and corrosion resistance of high-silicon ductile cast iron (HSDI)-3.6 wt.% Si were investigated. Samples from different castings with 0–0.9 wt.% Nb were obtained and compared to a commercial ductile iron. Microstructures showed that the amount of ferrite in the matrix increased with increasing Nb content, from 34% for unalloyed HSDI to 88% for HSDI-0.9 wt.% Nb. The presence of randomly distributed NbC carbides was identified by EDX for all the samples alloyed with Nb, and the hardness of the HSDI increased with the Nb content. To evaluate the influence of the Nb content on the corrosion resistance of HSDI, potentiodynamic tests were carried out in a solution of H2SO4. The highest corrosion rate on HSDI was obtained for the HSDI-0.3 wt.% Nb sample, with 2802 mills per year, due to the amount of pearlite present and the lowest presence of NbC carbides, compared to the HSDI-0.9 wt.% Nb, with 986 mills per year. This behavior was attributed to the ferrite matrix obtained because of a high Si content in the DI, which delayed the anodic dissolution of the alloy and suppressed the pearlitizing effect of Nb for contents greater than 0.3 wt.%, as well as to the effect of NbC carbides, which acted as inhibitors.

Ab-Initio Calculation of the Electrical Conductivity, Optical Absorption, and Reflectivity of the 2D Materials SnC and NbC

Using density functional theory (DFT), we performed first-principles calculations of the electrical conductivity, optical absorption, and reflectivity for the 2D carbides SnC and NbC. We calculated the electronic energy band structure of the materials. We performed the calculations without considering the spin–orbit coupling (SOC) term and including it. We determined that 2D SnC is a semiconductor material and 2D NbC is a conductor. We compared the optical absorption and reflectivity with those of graphene. We found that the 2D SnC and graphene optical absorptions in the infrared region are similar and small; the corresponding values for 2D NbC are approximately ten times larger. In the visible range, the absorption values for 2D SnC and 2D NbC are of the same magnitude and much more significant than graphene. We found that the 2D NbC optical absorption for the ultraviolet region was close to zero. Graphene and 2D SnC have similar maximum values for absorption but at different energies. We determined that graphene reflectivity is larger but similar to that of 2D NbC, and that the 2D SnC reflectivity is near zero. Finally, the 2D NbC electrical conductivity value was about ten times larger than the corresponding value for 2D SnC. As expected, when there was a change of dimensionality, the related 3D materials showed a vastly different value for the electrical conductivity. The 2D materials showed conductivities significantly smaller than those of 3D materials in both cases. The results we obtained for 2D SnC and 2D NbC when we included the SOC term showed that the electrical conductivity for 2D SnC increased by 13.18% and 2D NbC by 18.16%. The optical properties changed, particularly the location of the peaks in the optical absorption and reflectivity.

ПОЛУЧЕНИЕ ПОРОШКОВ КАРБИДОВ ТАНТАЛА И НИОБИЯ С ИСПОЛЬЗОВАНИЕМ АЦЕТОНА В КАЧЕСТВЕ ИСТОЧНИКА УГЛЕРОДА

The process of obtaining powders of tantalum and niobium carbides using metal powders of these metals as precursors, and vapors of acetone as a source of carbon has been studied. In the temperature range of 700–850 °C, using magnesium as in situ metal deoxidizers, TaC, Ta2C, and NbC carbide powders were obtained. The specific surface area of the powders is at the level of 8-26 m2/g. The powders are characterized by a mesoporous structure. The average size of crystallites is 10–16 nm.

Tribological performance under abrasive wear of Fe-Cr-C+Nb coating deposited by FCAW process

This paper aims to investigate the abrasion resistance performance of Iron-Crhomium-Carbon + Niobium (Fe-Cr-C + Nb) coatings deposited by Flux-Cored Arc Welding (FCAW) process. Two coatings conditions were prepared in a 1-layer setup, with a selfshielded tubular wire over SAE 1020 carbon steel substrate, varying the FCAW parameterization levels, searching to reproduce different conditions of welding energy and their respective effects on the coatings' properties. Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) were employed in the microstructure and wear micromechanism analysis. X-ray Energy Dispersive Spectroscopy (EDS) was used for chemical composition assessment and Vickers microdurometer for hardness evaluation. In the tribological attempt, it was used the dry/sand rubber wheel apparatus according to ASTM G65. From the results, in neither sample of the two coating conditions, deleterious defects were observed on the surfaces, as well as in the cross-sections, such as lack of fusion and process interruptions. Dilutions were sufficient to ensure metallurgical bond without compromising layer geometry. Cold cracking characteristics of the process and material were observed, which did not significantly influence the performance of the coatings. The microstructure of both coatings showed CrC and NbC carbides dispersed in the Fe-matrix, whose volume fraction and mean free path between them varied as a function of dilution. The greater Nb-content and less intense heat input in the lower dilution coating provided greater refining of the CrC, NbC, and Fe-matrix strength, which was reflected in higher hardness, lower wear rate, and less severe abrasive wear micromechanism.

Microstructure and Mechanical Properties of Spark Plasma Sintered CoCrFeNiNbX High-Entropy Alloys with Si Addition

Three mechanically alloyed (MA) and spark plasma sintered (SPS) CoCrFeNiNbX (X = 5, 20, and 35 at.%) alloys with an addition of 5 at.% of SiC were investigated. The face-centered cubic (FCC) high-entropy solid solution, NbC carbides, and hexagonal Laves phase already developed during MA. In addition, the SPS compacting led to the formation of oxide particles in all alloys, and the Cr7C3 carbides in the Nb5 alloy. The fraction of the FCC solid solution decreased with increasing Nb concentration at the expense of the NbC carbide and the Laves phase. Long-term annealing at 800 °C led to the disappearance of the Cr7C3 carbide in the Nb5 alloy, and new oxides-Ni6Nb6O, Cr2O3, and CrNbO4-were formed. At laboratory temperature, the Nb5 alloy, containing only the FCC matrix and carbide particles, was relatively strong and very ductile. At a higher Nb content (Nb20 and Nb35), the alloys became brittle. After annealing for 100 h at 800 °C, the Nb5 alloy conserved its plasticity and the Nb20 and Nb35 alloys maintained or even increased their brittleness. When tested at 800 °C, the Nb5 and Nb20 alloys deformed almost identically (CYS ~450 MPa, UTS ~500 MPa, plasticity ~18%), whereas the Nb35 alloy was much stronger (CYS of 1695 MPa, UCS of 1817 MPa) and preserved comparable plasticity.

Enhanced strength and plasticity in a Nb2MoWC0.5 alloy via eutectic dilute carbide

Refractory niobium alloys are widely used in aero-engine combustion chambers and rocket propulsion systems. Conventional Nb-based alloys often suffer from insufficient high-temperature strengths or poor room-temperature plasticity. Here we report a strategy to develop a novel Nb2MoWC0.5 niobium alloy with a good strength-plasticity synergy by introducing eutectic NbC carbide. Microstructure characterization reveals that the as-prepared alloy exhibits a hypoeutectic microstructure, in which low-energy eutectic interface remains stable under high-temperature compression up to 1473 K. The stable low-energy metal-carbide interface enables not only a superior high-temperature strength (>1 GPa at 1473 K and 0.61 GPa at 1673 K) but also possesses good room-temperature plasticity (a true plastic strain of 16%) via microcrack tip blunting. The dilute NbC carbide with alloying elements has low stacking fault energy and improved high-temperature plastic deformation. This strategy provides theoretical guidance for designing next-generation high-performance high-temperature alloys to bypass the limitation of alloying elements in conventional refractory alloys.

Nb micro-alloying on enhancing yield strength and hindering intermediate temperature decomposition of a carbon-doped high-entropy alloy

Carbon-doped fine-grained high-entropy alloys (HEA) presented a good combination of yield strength and ductility. However, carbon containing HEAs inherently tend to decompose into intermetallic compounds during thermal exposure at intermediate temperatures. Therefore, selective micro-alloying with 0.2%Nb in CoCrFeMnNi-1.3%C alloy (Nb-HEA) has been attempted to enhance the room temperature mechanical properties as well as for hindering the thermal decomposition at an intermediate temperature. Nb micro-alloying in the carbon-doped high-entropy alloy induces NbC carbides precipitation at 700–900 °C, strengthening the Nb-HEAs. The Nb-HEA shows an excellent combination of yield strength of ∼1096 MPa and elongation of ∼12% after annealing at 700 °C for 1 h. Furthermore, Nb micro-alloying hinders the FCC matrix decomposition at an intermediate temperature (500 °C). Specifically, the brittle σ phase formation at intermediate temperature is dramatically suppressed, while the growth of the L10 and BCC/B2 is inhibited. The results of this work may serve as a guide for designing the Nb alloying HEAs.

Effect of HPHT Sintering on Crystal Structure of NbC and TaC Carbides in PcBN Composites of cBN-NbC-Al and cBN-TaC-Al Systems

Effect of HPHT Sintering on Crystal Structure of NbC and TaC Carbides in PcBN Composites of cBN-NbC-Al and cBN-TaC-Al Systems

First-principles study on CVD growth mechanism of 2D NbC on Cu(1 1 1) surface

Two-dimensional (2D) niobium carbide is a member of the 2D transition metal carbide family. It exhibits properties that are beneficial for various applications. However, fabricating a 2D NbC single crystal with a specific orientation is extremely challenging and its epitaxial growth mechanism is not yet understood. A systematic study on the chemical vapour deposition of 2D NbC on the Cu(111) substrate has been performed in this study using first-principles calculations. The nucleation sites of Nb, C atoms and NbCy (y = 1, 2 and 3) clusters on the Cu(111) surface and the dominant precursor during the initial growth of NbC were determined. The growth kinetics and the epitaxial growth mechanism of a 2D NbC(111) single crystal on Cu(111) were elucidated. The results of this study can serve as a solid theoretical basis for experiments on 2D NbC and other transition metal carbides.

Room temperature compression deformation behavior of a Cr–Nb alloyed high manganese steel

The strain hardening behavior and microstructure evolution of a newly developed Cr–Nb alloyed high manganese steel were investigated in the present study. The investigated steel demonstrated good combination of yield strength (425.6 MPa) and impact toughness (372.5 J/cm2) after solution treatment. Room temperature compression test was conducted to investigate the strain hardening behavior during the practical performance condition. The investigated steel exhibited a long continuous strain hardening stage. The ultimate true stress could be higher than 5000 MPa. No obvious phase transformation was activated during the deformation process. The deformation behavior was dominated by planar dislocation slip, dislocation walls, formation of mechanical twinning and inhabitation of nano size NbC carbide precipitations. The formation of mechanical twinning and dislocation cell played a dyanamic grain refinement effect, which contributed to the upward trend of the strain hardening rate. Precipitation strengthening would also help improving the strain hardening rate.

Fully-gapped superconductivity in single crystalline NbC and TaC probed by point-contact spectroscopy

We report our point-contact spectroscopy (PCS) study on the single-crystalline transition metal carbide NbC and TaC with a superconducting transition temperature = 12.0 and 10.2 K, respectively. The differential conductance curves from both soft-PCS and mechanical-PCS (MPCS) on NbC at 1.9 K can be well fitted by a single-gap s-wave Blonder–Tinkham–Klapwijk model, and the temperature dependent gap follows a standard Bardeen–Cooper–Schrieffer (BCS) behavior, yielding = 2.0 ± 0.3 meV and 2/ = 3.9 ± 0.3 in the intermediate coupling regime. Similarly, our MPCS data on TaC crystals also show its superconducting gap as a function of temperature follows the BCS behavior, yielding = 1.7 ± 0.1 meV and 2/ = 3.9 ± 0.1. Our results thus support that both NbC and TaC are fully gapped s-wave superconductors.

Structural, mechanical, optoelectronic and thermodynamic properties of bulk and film materials in Ti–Nb–C system: First-principles and experimental investigations

Both first-principles study of the random TiC–NbC solid solutions and experimental investigation of the films in Ti–Nb–C system were carried out. The mixing energy, electronic and phonon structures, elastic constants and moduli, hardness, Debye temperature, fracture toughness, dielectric function, electron energy-loss spectra and heat capacity of the random Ti1-xNbxC solid solutions were calculated and analyzed depending on composition. The Ti–C, Nb–C and Ti–Nb–C films were deposited by magnetron sputtering. The deposited films were comprehensively studied with XRD, XPS, AFM, EDS, Raman spectroscopy, indentation and tribological tests. The Ti–Nb–C films with equi-atomic composition are found to exhibit the highest Knoop hardness and lowest friction coefficient as compared to those of the parent TiC and NbC carbides. The results obtained were used to establish the mechanism of the stabilization of the TiC–NbC solid solutions, and to predict their structural, mechanical, optical and thermodynamic properties.

Microstructure and mechanical properties of high-efficiency laser-directed energy deposited 15-5PH stainless steel

Microstructural and mechanical characteristics of 15-5 precipitation hardening (PH) stainless steel fabricated by laser-directed energy deposition (LDED) were investigated thoroughly for high-efficiency deposition. Different from the typical fully martensitic microstructure in wrought counterparts, high-power LDEDed 15-5PH stainless steel in as-deposited condition mainly consists of lath martensite, skeletal δ-ferrite with small amounts of retained austenite and NbC carbides. Formation mechanism of δ-ferrite was proposed based on the combined effects of Cr element segregation and rapid cooling that suppressed the mesothermal austenitic diffusion transformation during LDED process. Besides, the presence of δ-ferrite gives rise to the precipitation of two-scale Cu-rich precipitates after direct aging treatment. The size of CRPs in δ-ferrite (~28.6 nm) is obviously larger than that in martensite (~11.7 nm). The coarsening CRPs in δ-ferrite could be attributed to the surrounding Cu and Ni-depleted conditions. Due to the low original microhardness of δ-ferrite (5.85 ± 0.77 GPa) and the coarsening CRPs inside, relevant tensile tests indicate the yielding and tensile strength of high-efficiency LDEDed 15-5PH stainless steel drops apparently. The present study reveals the possibility of δ-ferrite formation in LDEDed PH stainless steel, which could provide an experimental basis for the optimization of high-efficiency additive process.

Effects of processing parameters on the surface quality of wrought Ni-based superalloy by ultrasonic-assisted electrochemical grinding

Ni-based GH625 superalloy has been widely employed in the aerospace industry due to its high strength, outstanding corrosion resistance, and high-temperature resistance. A novel hybrid processing method of ultrasonic-assisted electrochemical grinding (UAECG) can achieve a high effective removal rate for difficult-to-process materials and thereby avoid stray corrosion during the process. This study systematically investigated the electrochemical dissolution behaviors of GH625 alloy at low current density and the effects of processing parameters on its surface roughness. A qualitative model was proposed to further reveal its removal mechanism for GH625 alloy during the UAECG process. Polarization curves depicted that an efficient and stable electrochemical dissolution was achieved at an appropriate temperature (20 °C) and concentration (10 wt.%) of NaNO3 electrolyte. The findings also revealed that selective corrosion preferentially occurred on the grain boundary or near the NbC carbides under different current density corrosion circumstances. Compared with the ECG process, the excellent surface quality (Ra = 0.37 μm) and taper of the small holes (taper = 0.04 ± 0.005°) are obtained at the optimized condition of a pulse voltage of 5.8 V, feed rate of 0.6 mm/min, cathode speed of 12 kr/min and drive amplitude of 60% by UAECG technology.

Carburization and decarburization behavior of Grade 91 ferritic-martensitic steel in liquid sodium environments

This paper presents a study of carbon transfer and its effect on microstructure and tensile properties of Grade 91 (G91) ferritic-martensitic steel exposed to sodium at 550–650 °C. Sodium exposure tests were conducted in Argonne's forced convection sodium loops up to exposure times of ∼40,000 h. Thermal aging study of G91 steel was conducted in parallel to isolate the thermal aging effect from the sodium effect. It was found that sodium exposures at 650 °C dissolved M23C6 carbides, eliminated the martensite subgrain structure resulting in excessive grain growth and reduced the tensile strength by >50%, while sodium exposures at 550 and 600 °C had an insignificant effect on its microstructure and tensile properties. These effects were attributed to the carburization/decarburization process of G91 steel in sodium environments.Carbon concentrations in sodium were determined by a foil equilibration method. The estimated carbon concentration was in the range of 0.8–1.2 ppm in the SMT-1 loop and 0.3–0.7 ppm in the SMT-2 loop. Thermodynamic analysis of the carburization – decarburization process was conducted for G91 steels exposed in sodium environments. The carbon activity-concentration relationship for G91 was evaluated by considering four phases in G91, i.e. bcc ferrite, M23C6, NbC and VC carbides. It was found that the carburization-decarburization process in G91 steel was dictated by M23C6 carbides at high carbon activities, while NbC and VC carbides dominated the process at low carbon activities. The calculated carburization-decarburization boundary showed that G91 would undergo decarburization at 650 °C and carburization at 550 °C in the sodium loop environments, which was consistent with our experimental observations. This experimental and theoretical analysis provided a basis for predicting the effect of carbon transfer on the integrity of reactor components in sodium environments and for the design of new alloys used in sodium-cooled fast reactors.

Measurement of local creep life of laser cladding coatings by small punch creep test

Examining the creep behavior of materials locally provides important information about material performance. In this study, IN625 powder was layered on GTD-111 superalloy by the laser cladding (LC) method. After LC, the creep behavior of the clad zone (CZ), substrate, and heat affected zone (HAZ) was investigated by the small punch creep test (SPCT) method. The results showed that the CZ has the highest creep life. This was attributed to the widespread presence of equiaxed grains, high volume fraction and fineness of the γ′ phase as well as NbC carbide particles. The HAZ region, on the other hand, had the shortest creep life due to the dissolution of γ′ particles during LC. γ′ phase in the substrate and γ″ phase in CZ, the most important obstacles to dislocations movement during creep were identified, among which γ″ particles were superior to γ′ particles in the substrate due to their high volume fraction and fineness. The results of micro-hardness also confirmed this.

THE INFLUENCE OF Nb, Ta AND Ti MODIFICATION ON HOT-WORK TOOL-STEEL GRAIN GROWTH DURING AUSTENITIZATION

In order to explore the influence of niobium, tantalum and titanium modification on grain growth in high-thermal-conductive hot-work tool steel during austenitisation at high temperatures, three types of modified steels (sample HTCS-130 + 0.06 w/% Nb, sample HTCS-130 + 0.03 w/% Ta, sample HTCS-130 + 0.006 w/% Ti) based on reference (sample HTCS-130 – 0) were prepared. The effect of different austenitisation temperatures (1030, 1060, 1080 and 1100) °C on hardness after quenching and grain size were investigated. The results show that there is a positive effect on the mechanical properties and a decreased grain-growth effect in the modified steel samples. The precipitation behaviour of the carbides was also investigated with electron microscopy. The Mo-W carbides were relatively weak at retaining grain size, but their pinning effect was increased with the incorporation of other carbide-forming elements like Nb and Ta. MC-type carbides on the grain boundary were effective at grain-boundary pinning. Nb even further increased the resistance by forming NbC carbides. The addition of Ti, on the other hand, proved to be ineffective due to the intergranular precipitation of the formed carbonitrides.