NbC Particles Research Articles

Microstructure and wear behavior of spherical NbC hardmetals with nickel-based binders on AISI 4145H steel

To investigate the effect of spherical NbC particles on the wear resistance of nickel-based coatings, five groups of samples were tested. The microstructure of nickel-based coatings reinforced by spherical NbC particles was examined through X-ray diffraction, scanning electron microscopy, and energy dispersive spectrometry. The wear behavior of samples was analyzed by microhardness, coefficient of friction, 2D profile across the wear track and summary of tribological properties, respectively. The results shows that in the microstructure of nickel-based coatings reinforced by spherical NbC particles, γ-Ni solid solution and Cr23C6 dominated the coating, and complex carbides (NbC, Cr7C3 and a small amount of Cr3C2) and borides (Cr2B) were also detected. The hardness of the nickel-based coating was 400HV0.2. With the increase of the NbC content in the coating, the hardness gradually increased, reaching the maximum when the content was 40% NbC, which was 610HV0.2. The average friction coefficient of AISI 4145H steel was 0.473, and the average friction coefficient of nickel-based coating was 0.573. With the increase of NbC content in the coating, the friction coefficient of the coating gradually decreased, reaching the lowest at a NbC content of 40%, which was 0.470. Although the friction coefficient of the coating changed slightly with the addition of NbC, in the friction and wear of the nickel-based coating, the coating was adhesively worn, and there were many abrasive dust, scratches and grooves on the surface of the coating. By the way, there were only a few scratches on the surface after friction and wear of the nickel-based coating containing 40% NbC. The wear rate of the coating with 40% NbC content was about 1.6% of AISI 4145H steel or one-tenth of the nickel-based coating.

A novel iron matrix composite fabricated by two-step in situ reaction: Microstructure, formation mechanism and mechanical properties

The improvement of comprehensive properties including hardness, toughness, strength, and wear resistance in the steel/iron matrix composites, especially alleviate the inverse relationship between strength and toughness, is strongly required for various applications. Herein, we provide a new strategy, by two-step in situ reaction, to fabricate a novel iron matrix composite with high strength and reasonable toughness. The composite consists of a bundle-shaped Nb–NbC/Fe core-shell structure and cast iron matrix. Predominant features of the Nb–NbC/Fe core-shell structure include a metal Nb core and a NbC–Fe shell layer. The NbC–Fe shell layer is composed of two zones, where zone Ⅰ, near the Nb core, exhibits a NbC/α-Fe/NbC laminated structure; and zone Ⅱ, near the matrix, exhibits a NbC–Fe dense structure. The investigation indicates that the formation of the NbC–Fe shell layer is mainly due to the concentration fluctuation of Nb and C atoms in the Fe–Nb–C ternary system during in situ reaction. The formation of NbC particles is mainly attributed to the in situ reaction of niobium atoms and carbon atoms in the liquid phase system ([Nb] + [C]→[NbC]→NbC), while the formation of Nb2C is attributed to the diffusion-type solid phase transformation driven driven by the diffusion of carbon atoms into the Nb lattice (Nb + 2C→Nb2C). In addition, the fracture toughness of the NbC/α-Fe/NbC laminated structure layer and NbC–Fe dense structure layer is evaluated to be approximately 4.6 ± 0.2 MPa m1/2 and 4.0 ± 0.1 MPa m1/2, respectively. The yield strength, ultimate compression strength, and fracture strain of the Nb–NbC/Fe core-shell rod-reinforced iron-based composite reach 1623 MPa, 1970 MPa, and 11.3%, respectively, showing high strength and reasonable toughness compared to those of the cast iron (420 MPa, 830 MPa and 21.8%, respectively). Thus, this work provides a new strategy for alleviate the inverse relationship between strength and toughness of iron matrix composite.

Microstructures and mechanical properties of in-situ FeCrNiCu high entropy alloy matrix composites reinforced with NbC particles

A series of NbC/FeCrNiCu high entropy alloy matrix composites (2.5, 5, 7.5 and 10 vol% of NbC) were prepared by vacuum induction melting. The microstructures and mechanical properties of the composites were investigated using X-ray electron diffraction, scanning electron microscopy, transmission electron microscopy, tensile and hardness tests. The results show that the FeCrNiCu high entropy alloy matrix composites are composed of FCC solid solution embedded with NbC particles. A coherent relationship was identified between the alloy matrix and reinforcement phase. The formation of NbC particles increases the hardness from 337.6 HV to 591.3 HV. Moreover, compared with the base alloy, the tensile yield strength, ultimate tensile strength and ductility of the new composite first increases and then decreases with the increase of NbC content. The tensile yield strength, ultimate tensile strength and ductility reaches maximum for the composites containing 5 vol% of NbC, which is 458.2 MPa, 691.6 MPa and 24.7%, respectively. The strengthening mechanisms of the composites are discussed and the contributions of dislocation strengthening, load bearing effect and Orowan mechanism are quantified.

Fabrication and characterization of NbC-CoCrFeNiMn high-entropy alloy cermets

NbC based cermets with CoCrFeNiMn high-entropy alloys (HEAs) binders were fabricated by powder metallurgy. The effects of sintering temperatures on the microstructure and mechanical properties of NbC-HEAs cermets were systematically examined. The results show that the relative densities of NbC-HEAs sintered at different temperatures were about 90%. The XRD shows that a brittle M23C6 (M = Cr, Co, Fe, Ni) phase was detected in the cermets. The average particle size of NbC increased with increasing the sintering temperature. The coarsening of NbC particles caused the decrease of hardness and transverse bending strength (TRS) of the cermets. The highest TRS (497 MPa) was obtained for the cermet sintered at 1400 °C. The calculated activation energy was 696.6 kJ/mol, which was much higher than those in single element binders. Large cracks were observed for the cermets sintered at high temperatures, which suggested grain coarsening could reduce the toughness of cermets.

Improving high-temperature mechanical properties of cast CrFeCoNi high-entropy alloy by highly thermostable in-situ precipitated carbides

The CrFeCoNi high-entropy alloy (HEA) exhibits excellent mechanical properties at lower temperatures due to its low stacking-fault energy, however, its medium- and high-temperature strengths are still insufficient. In consideration of the potential diversified applications, more strengthening approaches except for the previously proposed L12 phase hardening deserve further exploration due to its rapid coarsening tendency at high temperatures. Here, we achieved significant high-temperature strengthening of the cast CrFeCoNi HEA by in-situ precipitation of highly thermostable carbides. Alloys with 0.5 at.% and 1 at.% niobium and carbon were prepared by simple casting processes, i.e. drop cast, solute solution and aging. A highly thermostable microstructure was formed, which comprises very coarse grains accompanied with extensive thermostable carbide precipitates embedded, including submicrometer coherent NbC particles in grain interiors and intergranular coherent M23C6 carbides. This high thermostability of microstructure, which is beneficial for the high-temperature loading, is ascribed to the synergy of lacking growth driving force and Zenner pinning effect by the carbides. Tensile properties tested at 673, 873 and 1073 K show that the yield strength and ultimate tensile strength are significantly increased by Nb/C doping, along with the elongation escalation at higher temperatures. The strengthening is mainly due to the precipitation hardening of carbide particles.

Effects of soaking time on the microstructure and mechanical properties of Nb-NbC/Fe core–shell rod-reinforced cast-iron-matrix composite fabricated through two-step in situ solid-phase diffusion

To overcome the disadvantages of low toughness of conventional particle reinforced steel/iron-based composites, a novel niobium-niobium carbide/iron (Nb-NbC/Fe) core–shell rod-reinforced cast-iron-matrix composites were fabricated through two-step in situ solid-phase diffusion at 1172°C for 15min, followed by heat treatment at 1120°C for 1, 4, 7, and 10h (1172°C×15min+1120°C×(1, 4, 7, 10h)). The effects of soaking time on the microstructure and mechanical properties of the composites were investigated. Results indicated that the phase composition of the Nb-NbC/Fe core–shell rod-reinforced cast-iron-matrix composites were NbC, Nb, α-Fe and, graphite (G) phases, where Nb existed as core at the center surrounded by NbC/Fe shell. With the extension of the soaking time, the phase composition of the composites did not change, but the thickness of the NbC/Fe shell increased from 90±3μm to 233±5μm. The average hardness of the NbC/Fe shell was 12.86GPa, which was approximately 2.6 times than that of the cast-iron-matrix due to high volume fraction of NbC particles. The yield strength and strain of the composite prepared at 7h reached the maximum value of 1794.4MPa and 11.6%, respectively. The excellent yield strength was attributed mostly to NbC particles, which induced the load-transfer strengthening and the mismatch of thermal-expansion-coefficient strengthening. Meanwhile, the Nb and α-Fe effectively hindered microcrack propagation, which contributed to the reasonable plasticity of the composite.

On the Strengthening Effects Affecting Tensile and Low Cycle Fatigue Properties of Low-Alloyed Seismic/Fire-Resistant Structural Steels

In the present study, low carbon ferritic and bainitic steels with different contents of Mo, Ti, and Nb were designed for both seismic and fire-resistant applications. The microstructure of steels containing 0.3 wt% Mo–0.02 wt% Nb (‘A’ hereinafter) was mainly composed of bainite. By contrast, the microstructure of steels with 0.2 wt% Mo–0.13 wt% Ti (‘B’ hereinafter) consisted of ferrite with a high density of nano-sized (Ti,Mo)-rich MX precipitates. The results showed that the bainitic microstructure (‘A’ steel) was quite favorable to high-temperature strength and thermal stability. The yield strength of ‘A’ steel at both room and 600 °C temperatures increased consistently with increasing thermal exposure time (600 °C/200–1000 h), since the precipitation of NbC particles occurred while maintaining bainitic ferrite platelets with a high density of dislocations during exposure. In the ‘B’ steel, the formation of nano-sized (Ti,Mo)-rich MX particles was effective to impede dislocation movement, leading to excellent plasticity (lower yield ratio) at room temperature. However, their contribution to precipitation hardening was not so much at 600 °C, as compared to the bainitic strengthening. During low cycle fatigue tests at room temperature, the main different feature between the two steels is that the ‘A’ steel showed cyclic softening while cyclic hardening was evident in the ‘B’ steel. The bainitic microstructure showed a better fatigue life due to increased ductility manifested by cyclic softening, by which dislocation cell was developed.

Use of DICTRA® simulations to support carbide particle growth study in NbC-Ni cemented carbide

Carbide particle growth observed in a NbC-12%Ni (mass percent) sample sintered at 1420 °C was discussed using DICTRA® simulation of spherical particles immersed in a Ni matrix. It is possible to describe the liquid formation during sintering using a model that assumes a spherical region of NbC, with radius equivalent to the NbC particle distribution, surrounded by nickel. NbC volume fraction was obtained for different simulation times allowing the evaluation of the dissolution behavior in different particle sizes. Small carbides (around 1 μm in diameter) suffered total dissolution, while major carbides (10 μm in diameter) did not dissolve during the simulation. Chemical content evidenced that Nb and C from carbide dissolution segregated to liquid phase reaching levels up to 15 and 2%, respectively, showing the availability of this elements to re-precipitate in non-dissolved carbides during cooling from sintering temperature. The simulations indicate that carbide particle growth observed in NbC-12%Ni sintered sample can be a result of dissolution and re-precipitation mechanism.

The effect of subsequent heat treatment on the evolution behavior of second phase particles and mechanical properties of the Inconel 718 superalloy manufactured by selective laser melting

In this work, the influence of subsequent heat treatment on the evolution behavior of Laves phase, δ phase and carbides, and mechanical properties were investigated systematically for the Inconel 718 superalloy manufactured by selective laser melting (SLM). Two different subsequent heat treatment schemes were employed for SLM manufactured Inconel 718 superalloy in our work: 980 °C * 1 h/AC + 720 °C * 8 h/FC to 620 °C * 8 h/AC (the standard heat treatment scheme, SA980) and 1080 °C * 1 h/AC + 720 °C * 8 h/FC to 620 °C * 8 h/AC (the optimized heat treatment scheme, SA1080). The results show that the δ phase can nucleate around the residual Laves phase, and then the composite phase particles are formed at the subgrain boundaries during SA980 heat treatment of SLM manufactured Inconel 718. Moreover, the entangled dislocations around these composite phase particles can promote the initiation of microcrack during the tensile process at elevated temperature, leading to premature failure. On the other hand, two types of carbides were found to exist in the SA1080 heat-treated samples: the nanoscale TiC particles along subgrain boundaries originally formed during the SLM process, and the large-size NbC particles along the grain boundaries formed during the solution heat treatment process. The heat treatment schemes of SA1080 can achieve excellent combination of strength and elongation at room temperature and elevated temperature, which is more suitable for the subsequent heat treatment of SLM manufactured IN718.

Effect of Nitrogen Addition on Microstructure and Mechanical Properties of As-Cast High-Chromium Cast Iron Containing Niobium

This work was conducted to study the effect of four different nitrogen additions on as-cast microstructure, hardness and impact toughness as well as abrasion wear resistance of high-Cr cast iron containing niobium. The results showed that as nitrogen content increased, the austenitic dendrites matrix became less elongated and the eutectic M7C3 carbides were gradually refined in size. EDS analysis demonstrated that N element preferentially accumulated in the NbC particles and substitute part of C to form Nb nitrides (NbN) or Nb cabonitrides Nb(C,N). Such nitrides or carbonitride particles were relatively hard compared to matrix and eutectic carbides resulting in an increase in hardness with increasing N content. The optimum toughness (12 J) was obtained for the iron containing 0.093 wt%N with an enhancement of 33%. The wear resistance increased with increasing N addition, in which the maximum wear resistance was reported for the alloy containing 0.15 wt% N. There was an enhancement in wear resistance of 47% by adding 0.15 wt%N to HCCI at low applied load (30 N), and it decreased to 17.5% at high applied load (60 N). Hence, the highest wear resistance and moderate toughness of HCCI could be achieved by adding 0.15 wt%N.

Development and Characterization of Al7475/NbC Reniforced Metal Matrix Composites

Aluminium metal matrix composites (AMMCs) have considerable applications in aerospace, automotive and military industries due to their high strength to wear ratio, stiffness, light weight, good wear resistance and improved thermal and electrical properties. Ceramic particles such as Al2O3, SiC are the most widely used materials for reinforcement of aluminium. In the present work, an effort is made to enhance the mechanical properties like tensile strength, compression strength and hardness of AMMCs by reinforcing AL7475 matrix with varying NBC particles sizes. By stir casting route (liquid metallurgical technique) in which amount of reinforcement is varied from 2-8 wt% in steps of 2 wt% for varying reinforcement sizes and specimens are artificially aged. The prepared composites of AL7475-Boron Carbide (NBC) are characterized by microstructural studies, SEM and XRD/EDS analysis will be carried out to analyze the microstructure and the dispersion of the reinforced particles in the alloy matrix, mechanical properties such as Tensile strength, Compression Strength, Density, Tribological Properties and Fracture Toughness as per ASTM Standards. Hypothesis of the present work in particularly to the optimum size of reinforcement and also the results of both with and without heat treatment are compared with that of as cast AL7475 Alloy.

Influence of Niobium Content on the Mechanical Properties and Abrasion Wear Resistance of Heat-Treated High-Chromium Cast Iron

The effect of niobium addition up to 3.4 wt% on the microstructure and mechanical properties of heat-treated high-Cr cast iron containing 13.5 wt% Cr was investigated. Niobium addition caused small hard NbC particles to precipitate within the proeutectic austenite which impede the development of austenite dendrite growth resulting in structure refinement. This austenitic matrix upon heat treatment changed to mainly martensitic one with some retained austenite and reinforced with small amounts of secondary carbides of M7C3 type. It was found that the hardness increased with increasing Nb content due to structure refinement and precipitation of hard NbC particles. These particles caused a depletion of carbon in the austenite matrix and thus most of the austenite was transformed to martensite upon heat treatment. The highest impact value was obtained for the base alloy without Nb addition which could be attributed to the high amount of retained austenite. The high-Cr cast iron alloyed with Nb in the range of 1.55–3.4 wt% showed an increase in hardness without any deterioration in toughness. The wear resistance was significantly enhanced by the presence of hard NbC particles up to 2.52 wt% Nb. Exceeding this optimum amount of addition leads to agglomeration of NbC particles and hence deterioration of the wear resistance through three body abrasion wear mechanism.

Improving metal-ceramic systems subjected to sliding contact by reinforcing the metallic counterpart with ceramic particles

The study of sliding wear is important as it occurs in many industrial mechanical systems. In metal-ceramic sliding wear, reinforcing the metallic counterpart with ceramic particles transforms the system from a pure metal-ceramic interaction to one that contains both metal-ceramic and ceramic-ceramic interactions, which may improve the wear performance of both materials involved. This study shows that incorporating NbC particles into a bearing stainless steel reduces its wear rate against SiC, WC and Al2O3 counterparts but its wear rate remained unchanged against ZrO2. For the ceramic counterparts, SiC and WC also experienced reduced wear while Al2O3 showed negligible wear across all tests. ZrO2, on the other hand, experienced a very high level of wear when the stainless steel contained 5 vol% NbC but the wear rate gradually decreased as the volume fraction of NbC increased to 15 vol%. Higher NbC volume fractions are thus expected to yield further improvement.

Influence of Aging Time on Microstructure and Corrosion Behavior of a Cu-Bearing 17Cr–1Si–0.5Nb Ferritic Heat-Resistant Stainless Steel

17Cr–1Si–0.5Nb–1.2Cu ferritic heat-resistant stainless steel was aged at 750 °C from 10 min to 30 h to simulate time aging and study the microstructural evolution and its effect on corrosion behavior by using optical microscopy, scanning electron microscopy, transmission electron microscopy, potentiodynamic polarization, electrochemical impedance spectroscopy, and the Mott–Schottky approach. Four types of precipitates were discovered, including ε-Cu, NbC, Fe3Nb3C, and Fe2Nb-type Laves phase. The nano-sized ε-Cu phase forms first, and its fraction follows the parabolic law change and is the largest. Compared to NbC and Fe3Nb3C particles, the coarsening of the Laves phase is the most pronounced. The aging process is divided into three parts: early-aged (0–5 h), peak-aged (5 h), and over-aged (5–30 h). However, the corrosion resistance is reduced in the early-aged stage of 0–2 h. Further extending the aging time to 30 h, the corrosion resistance is gradually improved. This change may be related to the competitive relationship between the beneficial effects of the Cu-rich phase and the harmful effects of Nb-containing particles. The dissolved Cu on the surface becomes more effective for the suppression of the anodic dissolution by the formation of ionic compounds of chlorine, thereby reducing the deterioration of corrosion resistance caused by Nb-rich precipitation.

Mechanism of NbC as heterogeneous nucleus of M3C in CADI: first principle calculation and experiment research

The phase precipitation curves of carbidic ductile iron with Nb element were simulated by the thermodynamic module in JMatPro software. The lattice mismatch between NbC and M3C was analyzed using Bramfitt two-dimensional mismatch theory, and the bonding strength (adhesive work) and interface stability (interfacial energy) of M3C(100)/NbC(110) interface were calculated by using the first principles method. The microstructure of carbidic austempered ductile iron (CADI) was observed by scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that NbC particles precipitate previously at 1420°C, and the lattice mismatch of M3C(100)/NbC(110) is 3.75 %. Six interface models have been constructed according to different case and termination conditions, in which interface adhesive work of Case I/C interface is the largest (1.35J/m2), interfacial energy of Case I/Fe interface is the smallest. The covalent bond has been formed on the interface, which proves that M3C(100) and NbC(110) can form a stable interface. The experimental results confirm the precipitation of NbC particles. In addition, M3C grows beside NbC particles and they are combined tightly, indicating that NbC can act as an effective heterogeneous nucleation site of M3C.

Evolution behavior of ex-situ NbC and properties of Fe-based laser clad coating

The NbC-reinforced Fe-based laser clad coatings were obtained by ex-situ processing. The evolution behavior of ex-situ NbC was quantitatively researched and the microhardness and wear resistance of laser clad coatings were also investigated. The results show that the ex-situ NbC added in clad powder can decompose and re-precipitate during the laser clad process, which affects significantly the content and morphology of NbC. After the added NbC particles decompose during the heating process of laser beam, Nb and C atoms are released into the molten pool. However, a part of Nb atoms cannot react with C to form NbC, but dissolve into the coating matrix or form Fe2Nb with Fe atoms, which decreases the content in NbC in clad coating. Moreover, Most of re-precipitated NbC phases belong to eutectic microstructure and exist in coatingin the form of network or featherlike structure instead of theoriginal particle shape. As heterogeneous nucleation core, the undecomposed NbC can promote the re-precipitation of new NbC phases. These new NbC can precipitate on the surface of undecomposed NbC particle, and then form the larger block and petaloid NbC phase with core. Both dissolved Nb atom and NbC precipitate can enhancethe microhardness and wear resistance of coating, but the promotion role on the wear resistance is more obvious.

Effect of post-treatments under hot isostatic pressure on microstructural characteristics of EBM-built Alloy 718

Electron beam melting (EBM) has emerged as an important additive manufacturing technique. In this study, Alloy 718 produced by EBM was investigated in as-built and post-treated conditions for microstructural characteristics and hardness. The post-treatments investigated were hot isostatic pressing (HIP) and combined HIP + heat treatment (HIP + HT) carried out as a single cycle inside the HIP vessel. Both the post-treatments resulted in significant decrease in defects inevitably present in the as-built material. The columnar grain structure of the as-built material was found to be maintained after post-treatment, with some sporadic localized grain coarsening noted. Although HIP led to complete dissolution of δ and γ′′ phase, stable NbC and TiN (occasionally present) particles were observed in the post-treated specimens. Significant precipitation of γ′′ phase was observed after HIP + HT, which was attributed to the two-step aging heat treatment carried out during HIP + HT. The presence of γ′′ phase or otherwise was correlated to the hardness of the material. While the HIP treatment resulted in drop in hardness, HIP + HT led to ‘recovery’ of the hardness to values exceeding those exhibited by the as-built material.

Microstructure and Tensile Properties of Ferritic Lightweight Steel Produced by Twin-Roll Casting

Ferritic Fe–8Al–5Mn–0.1Nb–0.1C lightweight steel has been produced by twin-roll casting (TRC) process. The microstructures, in as-cast condition and during subsequent thermomechanical treatments, and tensile properties of the steel have been investigated and compared to those of the similar steel produced with conventional ingot casting (IC). TRC significantly refines the microstructure of the steel in as-cast condition, with a formation of NbC and κ-carbide particles within matrix and along grain boundaries. NbC particles inhibit the grain coarsening during subsequent homogenization treatment, while κ-carbide particles promote recrystallization during final annealing by particle-stimulated nucleation mechanism. Tensile properties of the TRC steel are comparable to those of the IC steel; however, such properties of the TRC steel have been achieved under a much smaller number of processing steps, making TRC as an ideal alternative for the production of ferritic lightweight steels.

Investigation on heterogeneous nucleation substrate of Y2O3 as NbC in hypereutectic Fe–Cr–C hardfacing coating by experiment and first-principles calculation

Three kinds of hypereutectic Fe–Cr–C hardfacing coatings were designed to research the refinement effect and heterogeneous nucleation mechanism of NbC on nano-Y2O3 in the coatings. The microstructure and elemental maps of Fe–Cr–C–Nb–Y2O3 coating were investigated by field emission scanning electron microscope. The phase structures of the coating and heterogeneous nucleation were researched by transmission electron microscope (TEM). The lattice mismatch between Y2O3 and NbC was computed by Bramfitt’s two-dimensional lattice mismatch theory. The adhesive strength, interface energy and electronic properties of Y2O3(111)/NbC(110) interfaces were calculated by a first-principles method. The bonding characteristics of heterogeneous nucleation interfaces were analyzed by charge density difference, electron localization function and Bader charge population. The experimental results show that the primary M7C3 can be refined by NbC, when Nb additive was added into the Fe–Cr–C coating. When nano-Y2O3 and Nb additive were added into the coating simultaneously, the primary M7C3 can be further refined. The SEM results show that NbC can be effective heterogeneous nucleation substrate of the primary M7C3 and there is a compound containing rare earth (RE) element Y in NbC particle. The TEM results verified the RE compound in NbC particle is Y2O3, and they combine together tightly. The calculation results indicate that the two-dimensional lattice mismatch of Y2O3(111)/NbC(110) interface is 6.8%, which reveals that Y2O3 meets the geometric condition to act as a medium-effective heterogeneous nucleation substrate of NbC. In all interface models, the adhesive strength of O-Bridge model is the largest (Wad = 9.75 J/m2) and its stability is the best (γ = − 0.87 J/m2). The major bond type of O-terminated interfaces is covalent one. Actually, the interfacial energy of O-terminated interface is negative, which reveals that their formation process is a process of energy reduction and structure stabilization. It means Y2O3 and NbC can form stable interface structure. It can be predicted that the heterogeneous nucleation occurs preferably on the O-terminated interfaces. Therefore, Y2O3 can serve as an effective heterogeneous nucleation substrate of NbC to refine it.

Influence of NbC particles on microstructure and mechanical properties of AlCoCrFeNi high-entropy alloy coatings prepared by laser cladding

Recently, high-entropy alloys (HEAs) reinforced with ceramic particles have attracted increasing attentions due to their excellent hardness, strength and wear resistance. In this study, AlCoCrFeNi-xNbC high-entropy alloy (HEA) coatings (x = 10, 20, 30 wt%) were prepared by laser cladding. The phase constituents, microstructure and mechanical properties of the HEAs were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), electron back-scatter diffraction (EBSD), transmission electron microscope (TEM), microhardness and wear resistance tests. Due to the high entropy effect, the AlCoCrFeNi HEAs composites comprise only simple BCC and FCC structure phases. The addition of NbC particles results in a decrease in the fraction of the FCC phase. NbC particles are mainly distributed at the grain boundary in the HEAs with the addition of NbC. NbC particles have an advantage on the inhibition of HEA grain growth due to a strong pinning effect. The microhardness and the wear resistance of HEA composite improved significantly with the addition of NbC particles. A good comprehensive mechanical properties was obtained at the HEA with the addition of 20 wt% NbC particles. For the 20 wt% NbC-adding HEA, the average Vickers hardness is 525 HV, the average friction coefficient value is 1.023 and the mass loss is 1.05 mg.