Eutectic Microstructure Research Articles

A simplistic accelerated design methodology for eutectic multi-principal element alloys

In this work, the limitations of the current design strategies of eutectic multi-principal element alloys (EMPEAs) have been investigated and addressed using a novel design approach that utilizes Scheil solidification simulations. The proposed design approach was experimentally verified by demonstrating a eutectic in the Al-Fe-Ti-V-Zr alloy system, in which Fe was identified as the eutectic forming element (EFE). Vacuum-arc-melting was utilized to fabricate the precisely designed Fex(AlTiVZr)100−x (x = 70, 73, and 75) alloys. The alloy, with x = 73, was found to possess a fully eutectic microstructure corroborating the proposed design approach.

Formation of Ln2Si2O7-Mullite eutectic (Ln = Y and Yb) micro-structure by crystallization of glass

The crystallization of the glass with Ln2Si2O7-Al6Si2O13 (Ln = Y, Yb) eutectic composition were examined. In the case of Ln = Yb, both Yb2Si2O7 and Al6Si2O13 phases were crystallized simultaneously. On the other hand, in the case of Ln = Y, two step crystallization occurred. First, Y2Si2O7 phase crystallized at 1000 °C from the glass surface. In the second step, Y2Si2O7 phase and Al6Si2O13 phase crystallized at 1200 °C. Two typical microstructures were formed by a heat treatment at 1250 °C. Y2Si2O7- Al6Si2O13 eutectic microstructure was formed near the bulk surface. In contrast to the formation of eutectic microstructure, facet microstructure was formed at center of the bulk. The activation energy of the crystallization at 1000 °C for Ln = Yb sample was smaller than that of Ln = Y sample. By a heat treatment at 1350 °C for Ln = Yb sample, the sample was completely melted down and a homogeneous eutectic microstructure was formed.

The relation between the glass forming ability and nucleation kinetics of metastable quasicrystals in Mg–Zn–Yb liquid

Bulk metallic glass (BMG), metastable quasicrystals (QCs) and two types of approximant phases concurrently form from the melt during cooling at different rates in a Mg–Zn–Yb model alloy. Such an enriched phase competition between various metastable and stable crystals has also been found during the heating of Mg–Zn–Yb metallic glass between the glass transition and liquidus temperatures. Metastable QC acts as a transient phase that nucleates first from the melt and subsequently transforms into an equilibrium approximant phase. During heating, a metastable approximant phase transforms into the Mg-QC phase mixture which then transforms into the Mg and equilibrium approximant eutectic microstructure. Nucleation kinetics of QCs is critical to analyze for further understanding the relation between QC formation and glass forming ability of the alloy. For this purpose, a metastable phase diagram for QCs has been determined using a novel experimental strategy via fast differential scanning calorimetry (FDSC). Along compositional line binding Mg to Zn17Yb3, one stable eutectic point, i.e. Mg68.6Zn26.7Yb4.7 at 390°C, and one metastable eutectic composition, i.e. Mg64.6Zn30.1Yb5.3 at 350°C, were determined during interrupted heating experiments. We have demonstrated that the glass forming ability of Mg–Zn–Yb alloys strongly depends on the metastable phase diagram of QCs and their nucleation kinetics. Nucleation of metastable QCs limits the metallic glass formation, therefore the bulk metallic glass forming compositional region was found to be below metastable hypoeutectic compositions.

Effects of Si variation and Zr addition on the microstructure, oxidation resistance and mechanical property at 1523 K of Nb-Si-Ti/Zr/Hf-Cr/Al high-entropy superalloys

The present work investigated the influences of the variation of Si content and the minor amount of Zr addition on the microstructure, oxidation resistance and mechanical property at 1523 K of Nb-Si-Ti/Zr/Hf-Cr/Al high-entropy superalloys systematically. Alloy compositions with Nb-21.6(Ti/Zr)-3.1Hf-(9.4–15.6)Si-6.3Cr-3.1Al-1.0B (at. %) were designed using a cluster formula approach to realize the substitution of similar elements, in which these alloys were solid-solutionized at 1573 K for 24 h and then aged at 1273 K for 24 h. It was found that all these aged alloys are mainly composed of BCC-Nb solid solution (Nbss), Nb5Si3 and Cr2Nb phases, where the increase of Si content and the addition of Zr could significantly increase the volume fraction of Nb5Si3 in a form of coarse and primary particles. Consequently, high-Si alloys possess outstanding mechanical property at high temperature, as evidenced by the fact that the yield strength (σYS = 373 MPa) at 1523 K of high-Si/Zr alloy containing 15.6 at. % Si and 1.6 at. % Zr is much higher than that (σYS = 266 MPa) of the low-Si alloy with 9.4 at. % Si and 0 Zr. It is mainly ascribed to the existence of primary Nb5Si3 particles, besides the eutectic microstructure composed of Nbss and Nb5Si3, as well as fine Cr2Nb precipitates in Nbss. Moreover, a minor amount of Zr substitution for the Ti is conducive to the phase transition of α-Nb5Si3 to γ-Nb5Si3. Thus, this high-Si/Zr alloy exhibits an improved oxidation resistance after 50 h-exposure at 1523 K, due to the lowest mass gain of about 80.9 mg/cm2. The constitutions of oxide scales in these alloys were characterized and compared, from which it was found that the better oxidation resistance is closely related to the formation of dense oxide scales. This work will provide a new approach to obtain an optimum combination of mechanical property and oxidation resistance of superalloys through multi-component alloying.

Large-size complex-structure ternary eutectic ceramic fabricated using laser powder bed fusion assisted with finite element analysis

Melt-grown oxide eutectic ceramics are well known for their excellent mechanical properties and microstructural stabilities at ultra-high temperatures. Laser powder bed fusion (LPBF) provides a novel technology for manufacturing materials with large sizes and complex structures. However, crack controlling is a serious challenge in this process owing to the intrinsic brittleness of ceramic materials. In this study, LPBF method is applied to fabricate Al2O3/GdAlO3/ZrO2 ternary eutectic ceramics assisted by a finite element method (FEM) to investigate an optimized process and innovatively reveal the crack formation mechanism and propagation behavior via a single track, a single layer, and multilayers. Temperature and thermal stress distributions under different process parameters are obtained. The maximum tensile stress σy (in front of and behind the edge of the molten pool) perpendicular to the scanning direction induces a longitudinal crack, the tensile stress σx (at the side rim of the molten pool) parallel to the scanning direction induces a transverse crack, and the shearing stress on the XY plane promotes the deflection of the transverse crack on one side of the single track. In the multilayer, the maximum principal stress occurs at the margin zone of the deposition. The maximum principal stress increases at the first three layers and then decreases after the fourth layer. Based on the simulation result, the as-solidified Al2O3/GdAlO3/ZrO2 eutectic ceramics with multiple shapes, such as cylindrical, cubic with round corners, triangular prism, and quadrangular, with dimensions of 30 mm (width or diameter) × 30 mm (length or diameter) × 1 mm (height) and ultra-fine eutectic microstructures (eutectic spacing of approximately 88 nm) are fabricated by LPBF, providing a significant potential to overcome the bottleneck for fabricating large-size and complex-structure ceramics directly in a single-step process. This work provides theoretic foundation and technical support for preparation of ultra-high temperature solidified oxide eutectic ceramics with ultra-fine microstructures and complex structures directly, which has great application potential in fields as aerospace, machinery, and chemical industry.

Exploring the role of indium on the microstructure evolution and interface bonding behavior of brazing diamond abrasive with modified Cu–Sn–Ti

In the brazed joints prepared by Cu-Sn-Ti filler metal, it was found that the filler metal has poor wettability to diamond and diamond abrasive grits are prone to uneven wear resulting in low efficiency of diamond tools and difficulty in achieving the expected processing which are the key factors restricting the performance of brazed diamond tools with Cu based filler. This study aims to improve the wettability of Cu-Sn-Ti filler metal and the brazed joint wear resistance. For this purpose, a new Cu-Sn-Ti-Ga-In composite filler metal was proposed. In this experiment, the subcooling degree and microstructure morphology of the new filler metal were investigated, the microhardness and shear strength of the filler metal were determined, and the shear fracture morphology was analyzed. Wetting tests were conducted on graphite plates to study the effect of indium elements on the wettability of the filler metals. Brazed joints were also prepared, and the crawling morphology of the filler metal on the diamond surface and the wear marks of the diamond abrasive after the frictional wear test were observed. The test results show that Sn3Ti5 is a solid solution is favorable to explain some phenomena. The indium element can increase the subcooling of the filler metal, thus promoting the refinement of Sn3Ti5, and the formation of eutectic microstructure. In brazed joints, indium increases the wettability of the filler metal on the diamond surface thus increasing the climb height and reducing the uneven wear rate, and the brazed joints have the best cutting performance when the filler metal is added with 1 wt% of indium element.

Design of a novel (CoCrNi)84.5Al15.5 eutectic medium-entropy alloy with hierarchically nano-lamellar microstructure through additively manufactured compositionally graded materials

Eutectic medium/high-entropy alloys (E-M/HEAs) exhibit excellent castability and mechanical properties. This present work developed a novel CoCrNiAl based E-MEAs through a high-throughput method based on compositionally graded materials by laser directed energy deposition. The microstructure in the CoCrNiAlx (x ≈ 0−0.8) compositionally graded alloy changed from columnar to equiaxed with increasing Al content, and the fraction of body-centered cubic (BCC) phase increased simultaneously. Especially, a eutectic lamellar microstructure with face-centered cubic (FCC) and ordered BCC (B2) was obtained when the Al content reached 15.5 at%, and it showed a better strength-ductility combination than other reported cast eutectic alloys. The mechanical-property improvement of this novel E-MEA is related to its hierarchically nano-lamellar microstructure, in which the orientation relationship (OR) between FCC and B2 lamellae conforms to the Kurdjumov-Sachs OR, and spherical BCC and ordered FCC phases precipitate from B2 and FCC lamellae, respectively. Furthermore, the fracture mechanisms of this novel E-MEA were also investigated by in-situ tensile test and transmission electron microscope, indicating that the crack modes were closely related to the eutectic lamellar direction relative to the tensile axis, and the considerable ductility stemmed from the cooperative deformation between FCC and B2 phases caused by various deformation mechanisms.

Preliminary Study of New Low-Temperature Hard Abrasion Resistant Fe-P and Fe-P-X (X = C or/and B) Casting Alloys.

This article analyses the as-cast state of practically unknown Fe-P-based cast alloys with or without an addition of carbon and/or boron, cast into a grey cast iron mould. The melting intervals of the alloys were determined by DSC analysis, and the microstructure was characterized by optical and scanning electron microscopy with an EDXS detector. The hardness and microhardness of the alloys were also measured. Their hardness reached values between 52 and 65 HRC depending on chemical composition and microstructure, showing their high abrasion resistance. The high hardness is a consequence of the eutectic and primary intermetallic phases of Fe3P, Fe3C, Fe2B or mixed type. By increasing the concentration of metalloids and combining them, the hardness and brittleness of the alloys were increased. The alloys with predominantly eutectic microstructures were the least brittle. Depending on the chemical composition, the solidus and liquidus temperatures ranged from 954 °C to 1220 °C and were lower than those of the well-known wear-resistant white cast irons.

Microstructure and mechanical properties of Al0.4Co0.5V0.6FeNi high-entropy alloys processed by homogenization treatment

Al0.4Co0.5V0.6FeNi high-entropy alloys (HEAs) are fabricated by the vacuum arc melting method and homogenization treatment (HT) at 1000, 1100 and 1200 °C for 5 h (samples denoted as HT-1000, HT-1100 and HT-1200, respectively), followed by water quenching. The microstructural characteristics and mechanical properties of the HEAs are investigated by a combination of optical, scanning and transmission electron microscopy, X-ray diffraction and tension tests. The solidification of the Al0.4Co0.5V0.6FeNi HEAs is calculated using Pandat software to show that the FCC phase forms in the liquid phase, which then undergoes a eutectic reaction to form the FCC and BCC/B2 phases. The Al0.4Co0.5V0.6FeNi HEAs exhibit a typical eutectic microstructure with an alternating lamellar structure. Compared with that in the as-cast state, the volume fraction of the FCC phase in the HT state increases from 53.16% to 60.75% and the yield strength of the HT-1200 alloy increases by ∼27.5% with increasing homogenization temperature. Fine small spherical and ellipsoidal nanoprecipitates are uniformly distributed within the FCC matrix. These FCC phase nanoprecipitates become the most important factor contributing to the yield strength.

Tribological considerations for failure restoration and maintenance of radial plunger pump against friction and abrasive wear behavior by microwave cladding of Ni-Graphene

Clean and efficient manufacturing techniques are in great demand in modern industrial facilities. New methods are being developed which are cleaner, environment-friendly, economical, and have better mechanical properties, among others. Due to hot corrosion, Tribological components are often subjected to wear and tear. Graphene (Gr) is a promising material with microwave absorption performance due to its self-lubricating properties, low density, and cementite (Fe3C) formation capabilities with iron. This work examined the effect of self-lubricating behavior and surface hardening of plungers of Austenite alloy by Ni-Gr cladding and glazing. Using silicon carbide abrasive media, a pin-on-disc wear tester was utilized for abrasion testing. Scanning Electron Microscopy (SEM), and X-ray diffraction (XRD) analysis supplemented with a microhardness test were performed to measure the improvement in the properties of clad samples. The results showed that temperature variation influences phase change and mechanical properties. The Ni-Gr cladding showed dense eutectic microstructure at 750° C. XRD’s results revealed that the disintegration of the cladding layer is reduced due to heat treatment along with the generation of the Fe3C phase. In addition, the deposited specimen confirmations maximum wear resistance and hardness characteristics with a minimum wear rate at 750 °C, just above the steel's first critical temperature.

Evolution of microstructure in nickel-based C-HRA-2 alloy during welding thermal simulation

The welding heat-affected zone (HAZ) of C-HRA-2 nickel-based alloy at different welding peak temperatures (Tp) (850 to 1450 °C) was obtained through welding thermal simulation. The microstructure of the different simulated HAZs was characterized by an optical microscope (OM), a scanning electron microscope (SEM), and a transmission electron microscope (TEM). The microhardness of simulated HAZs was examined using a microhardness tester. The results indicated that fine and dispersed M23C6 carbides were identified along the grain boundaries in the simulated HAZs at 1050 and 1150 °C. In the simulated HAZs above 1250 °C, eutectic microstructure of γ matrix bonded with M23C6 carbides was identified close to the grain boundaries due to constitutional liquation. The liquefaction of γ matrix and M23C6 carbides primarily accounted for the simulated HAZ liquation of C-HRA-2 alloy during continuous welding heating. The content of the liquefied phase was increased as Tp was increased. The liquefied phase was converted into the eutectic microstructure of γ matrix and M23C6 carbides in the cooling process. Besides 1050, 1150, and 1450 °C, the microstructures under other Tp were similar to the microstructure of the Base Metal (BM). The microhardness distribution of simulated HAZs tended to be higher in the middle and lower at both ends with the increase of Tp. Furthermore, the result indicated that the microhardness of the simulated HAZ was the closest to BM at 1050 °C.

Microstructure and mechanical properties of hypoeutectic Al–6Ce–3Ni-0.7Fe (wt.%) alloy

A hypoeutectic, Fe-modified Al–Ce–Ni alloy (Al–6Ce–3Ni-0.7Fe, wt.%) is studied in terms of microstructure, thermal stability, ambient temperature strengthening, and creep resistance. The as-cast microstructure consists of primary Al dendrites and interdendritic binary eutectic regions (Al–Al11Ce3 and/or Al–Al9(Fe,Ni)2), with micron/submicron lamellar spacing, depending on the location along the height of the ingot. The cast alloy exhibits excellent coarsening resistance at 400 °C, with mostly unchanged microstructure and microhardness after 6 weeks of aging, indicating good thermal stability of Al11Ce3 and Al9(Fe,Ni)2. Orowan strengthening and load transfer are identified as strengthening mechanisms at ambient and elevated temperature. A high volume fraction of the intermetallic phases (providing load transfer) and relatively coarse eutectic spacing (for modest Orowan strengthening) result in a moderate as-cast microhardness of 566 ± 32 MPa. Creep resistance at 300 and 350 °C is similar to a binary Al-12.5Ce eutectic alloy (with twice the Ce content) because of two countering effects: Al–6Ce–3Ni-0.7Fe shows a higher volume fraction of strengthening intermetallic phases, but it also exhibits a large fraction of primary Al dendrites which weaken the alloy. By contrast, the alloy, when laser-remelted at the surface, has a fully eutectic microstructure without primary aluminum dendrites achieved by high undercooling on solidification, with a refined network of eutectic phases that doubles the microhardness as compared to the cast alloy. Whereas coarsening is faster due to the shorter diffusion distances between the eutectic phases, hardness remains ∼30% higher than the as-cast alloy after ∼6 weeks aging at 400 °C.

Microstructural verification of the theoretically designed novel eutectic multi-principal element alloy

This letter proposes the theoretical design methodology based on the proportional mixing of binary eutectics for predicting novel eutectic multi-principal element alloys (EMPEAs). It was then experimentally verified by manufacturing a dual-phase eutectic Zr61.9AlTiVCr alloy having a density of 6.04 g/cc. Zirconium was identified as the eutectic forming element in this system, notably having only 3 binary eutectics in a quinary system. The alloy developed by vacuum arc melting revealed the formation of an irregular lamellar eutectic microstructure consisting of cubic and hexagonal Laves phases. The as-cast alloy had a superior hardness of HV527, with 780 MPa compressive strength. This study paves the way for designing new EMPEAs without depending on any simulation software.

Microstructure and phase evolution in the U-10Zr fuel investigated by in situ TEM heating experiments.

The development of U-Zr metallic nuclear fuel for fast spectrum reactors is impacted by a lack of mechanistic understanding of the fuel behavior evolution under thermal irradiation conditions, despite previous works providing substantial fuel performance data. This work uses in-situ transmission electron microscopy heating experiments to study phase and microstructural evolution in several unirradiated U-10Zr specimens during rapid heating ramps (from room temperature to 1000 °C). The starting α-U + bcc-(Zr, U) eutectic microstructure began to decompose above 600 °C. The decomposition initiated from the bcc (U,Zr) phase. Similar results were observed for all specimens even when fabricated by different routes (e.g., cold rolled or annealed). The impact of observed microstructure and phase evolutions at high temperatures on fuel fabrication and in-pile fuel transient test was also discussed.

Three-dimensional morphology of an ultrafine Al-Si eutectic produced via laser rapid solidification

Al-Si alloys processed by laser rapid solidification yield eutectic microstructures with ultrafine and interconnected fibers. Such fibrous structures have long been thought to bear resemblance to those formed in impurity-doped alloys upon conventional casting. Here, we show that any similarity is purely superficial. By harnessing high-throughput characterization and computer vision techniques, we perform a three-dimensional analysis of the branching behavior of the ultrafine eutectic and compare it against an impurity-modified eutectic as well as a random fractal (as a benchmark). Differences in the branching statistics point to different microstructural origins of the impurity- and quench-modified eutectic. Our quantitative approach is not limited to the data presented here but can be used to extract abstract information from other volumetric datasets, without customization.

Theoretical model of yield strength for eutectic colony microstructure materials

Eutectic alloys have a wide range of applications and have been studied in numerous experiments and simulations. However, there is no model available to describe the contribution from the morphology on strength of the eutectic structure. The model for eutectic strengthening σsp = kspf λ−1/2 is derived from the Brown model and Taylor-Orowan's equation. The equation reveals the relationship between yield strength and eutectic features including slip parameter, effective shear modulus, second phase volume fraction and eutectic spacing. The equation predictions agree well with the experimental measurements for both Al-Ce and Fe28Ni18Mn33Al21 alloys. The model may effectively predict the yield strength of eutectic alloys and provide insights for eutectic strengthening.

Design, microstructure, and mechanical property of negative Poisson's ratio porous structure fabricated by LPBF of AlCoCrFeNi2.1 eutectic high-entropy-alloy

Negative Poisson's ratio (NPR) materials are a type of structural materials that show an atypical deformation response. In general, metal-based porous materials with NPR do not have good mechanical properties due to the substrate's limited yield strength and plasticity, as the NPR behavior is unlikely to play a continuous role in the deformation. AlCoCrFeNi2.1, a eutectic high-entropy alloy (EHEA) with high yield strength and high ductility was used to fabricate the NPR structures by laser powder bed fusion (LPBF) to enhance the structures mechanical properties and NPR behavior. Structures with four different sets of structural parameters were designed for this study. The microstructure and mechanical properties of AlCoCrFeNi2.1 EHEA, synthesized by LPBF were studied, and the strength and energy absorption effect of NPR porous structure materials were investigated by static and dynamic compression experiments. Research showed the large number of inter-phase interfaces provided by the nano-scale cellular eutectic microstructure effectively restrict dislocation movement, thereby enhancing the strength and toughness of this EHEA alloy, endowing it with superior impact resistance, fracture resistance, and mechanical energy absorption. The compressive performance and the mechanical energy absorption capacity of the 3D EHEA-based NPR porous structure strongly depend on the inclination angle Ф between the thick rod and the horizontal direction in the 2D single-body model design. The strength and energy absorption of the structure with a high inclination angle of 75° material are both higher than those of the structure with a low inclination angle of 45° by almost a factor of two.

Comprehensive microstructure regularization mechanism and microstructure–property stability at 1773 K of directionally solidified Al2O3/GdAlO3 eutectic ceramic composite

Melt grown Al2O3/GdAlO3(GAP) eutectic ceramic composite is considered as a promising ultra–high temperature structural material in fields as aerospace, power generation and so on. In order to tune the properties of directionally solidified Al2O3/GAP eutectic ceramic composite, its microstructure evolution is investigated over a wide range of compositions and solidification rates by laser floating zone melting method (LFZM). With the increase of solidification rate and the enrichment of Al2O3 phase, the eutectic microstructure undergoes a transformation from “Chinese script” irregular morphology to rod–like regular and complex regular morphology. The synergistic effects of composition and solidification rate on the microstructure regularization have been quantitatively characterized by the proportion of regular eutectic. High solidification rate (>200 μm/s) is beneficial to the formation of isothermal interface, partly inhibiting the anisotropic growth of Al2O3 faceted phase, which further promotes the coupling growth of the eutectic phases at the front of the interface and facilitates the microstructure regularization. The stability of eutectic spacing is verified to coincide with the Ostwald ripening relationship when the eutectic ceramic composite is thermally exposed at 1773 K for long–term (250 h). The microstructure coarsening rate is less than 0.003 μm/h, and the hardness slightly decreases about 4%, and the fracture toughness remains almost unchanged, which indicates excellent thermal stability of microstructure and property for the Al2O3/GAP eutectic ceramic composite at high temperature.

A sunflower-like eutectic microstructure in the AlCrFeMnNi2 high-entropy alloy with excellent compressive mechanical properties

Although most BCC-based high-entropy alloys have high strength and excellent high temperature mechanical properties, their low plasticity greatly limit their application. It is a new challenge to develop new BCC-based high-entropy alloys with excellent combination of high strength and plasticity. In this study, we prepare a new BCC/B2 AlCrFeMnNi2 high-entropy alloy with a unique sunflower-like eutectic microstructure. This alloy has a high yield strength of 1206 MPa, a high fracture strength of 3437 MPa and large compressive plastic strain of 37.5%. The excellent compressive mechanical properties are superior to many other BCC/B2 high-entropy alloys. These properties can be attributed to its unique microstructure consisting of coherent interface between BCC and B2 phase and the bimodal distribution of the B2 precipitates. Our results can provide a meaningful reference for improving the plasticity of BCC-based high entropy alloys.

Novel nano-lamellar AlCoCrFeMn0.5Mo0.1Nbx eutectic high-entropy alloy coatings by ultrasonic assisted laser cladding: Microstructure and tribological behaviors

Eutectic high-entropy alloys (EHEAs) possess in-situ composite structure, which provides a novel strategy for developing wear-resistant alloys or coatings. In this work, a new-type AlCoCrFeMn0.5Mo0.1Nbx (x = 0.4 hypoeutectic, 0.65 eutectic and 0.8 hypereutectic) EHEA coatings were designed and prepared by ultrasonic assisted laser cladding. The design strategy, microstructure and tribological behaviors of the EHEA coatings were studied in detail. The Nb0.4, Nb0.65 and Nb0.8 coatings were all composed of BCC solid solution and Laves phase. The Nb0.65 coating showed typical nano-lamellar/nano-granular eutectic microstructure, while the Nb0.4 and Nb0.8 coatings had hypoeutectic and hypereutectic microstructures, respectively. The wear rates of the EHEA coatings (5.5 × 10−6 mm3/N·m for Nb0.4 coating, 5.3 × 10−6 mm3/N·m for Nb0.65 coating and 8 × 10−6 mm3/N·m for Nb0.8 coating) were significantly lower than those of most metallic and metal-ceramic composite materials. The wear mechanisms of Nb0.4, Nb0.65 and Nb0.8 coatings were slight adhesive wear and oxidation wear. Numerous regular rolling structures formed on the wear scar of Nb0.65 coating, which provides an anti-friction effect for the coating. The good carrying capacities and high hardness of the BCC, Laves and eutectic microstructures contributed to the excellent wear resistance of the EHEA coatings.