Plasma Transferred Arc Welding Research Articles

Microstructure and high-temperature tribological behaviours of nano-HfC reinforced Inconel 625 composite coating by Plasma-transferred arc welding

The study involved plasma arc transfer welding (PTAW) for preparing coatings of Inconel 625 alloys that contained different amounts of nano-sized hafnium carbide (nano-HfC) particles. The impact of nano-HfC on the microstructure evolution and mechanical properties of PTAWed Inconel 625 were investigated. The research reveals that nano-HfC decomposes during the high-temperature plasma arc process and then react with O element to generate nano-HfO2. These HfO2 can serve as nucleation sites for MC carbides, which restricts the growth of secondary dendrite arms, leading to a more disordered grain growth direction. Simultaneously, the decomposition of HfC can increase the C/Nb ratio of the matrix, effectively suppressing Laves phase formation while encouraging the development of MC carbides. Compared with IN625, the wear rate of composites at room temperature and 600°C were decreased. Notably, at 600°C, the wear rate of the coating with 0.5 wt% HfC is the lowest among all the samples, as reflected by a noteworthy reduction in wear rate of 50%. This is mainly attributed to the refinement of γ matrix, reduction of Laves phase as well as precipitation of the fine-sized MC carbides. This work illustrates that adding nano-HfC is an effective way to improve the wear resistance of the PTAWed Inconel 625.

Microstructure and high-temperature tribological behaviours of nano-HfC reinforced Inconel 625 composite coating by plasma-transferred arc welding

The study involved plasma arc transfer welding (PTAW) for preparing coatings of Inconel 625 alloys that contained different amounts of nano-sized hafnium carbide (nano-HfC) particles. The impact of nano-HfC on the microstructure evolution and mechanical properties of PTAWed Inconel 625 were investigated. The research reveals that nano-HfC decomposes during the high-temperature plasma arc process and then react with O element to generate nano-HfO2. These HfO2 can serve as nucleation sites for MC carbides, which restricts the growth of secondary dendrite arms, leading to a more disordered grain growth direction. Simultaneously, the decomposition of HfC can increase the C/Nb ratio of the matrix, effectively suppressing Laves phase formation while encouraging the development of MC carbides. Compared with IN625, the wear rate of composites at room temperature and 600 °C were decreased. Notably, at 600 °C, the wear rate of the coating with 0.5 wt% HfC is the lowest among all the samples, as reflected by a noteworthy reduction in wear rate of 50 %. This is mainly attributed to the refinement of γ matrix, reduction of Laves phase as well as precipitation of the fine-sized MC carbides. This work illustrates that adding nano-HfC is an effective way to improve the wear resistance of the PTAWed Inconel 625.

Thermal-induced evolution of microstructure as a plasma arc coating Direction-Dependent phenomenon

This study elucidates the effects of different directed energy deposition trajectories on the microstructure and properties of powder plasma transferred arc welding (PPTAW) fabricated coatings. Two trajectories, straight (STT) and complex (CXT), were explored to deposit NiCrBSi powders onto a low alloy steel substrate. Finite element thermal analysis revealed distinct heat distribution zones, the middle zone (MZ) and transition zone (TZ), showing temperature variations between the STT and CXT coatings. Microstructural examination indicated lower dendrite arm spacing (DAS) in the STT coating (11 μm) than in the CXT coating (16 μm). Electron backscatter diffraction (EBSD) analysis demonstrated significant grain refinement in the STT coating (17.4 μm) versus the CXT coating (68.7 μm). X-ray diffraction phase analysis identified three reinforcing phases − γ-Ni, Cr23C6, and Cr3C2 – enhancing corrosion resistance and tribological properties. The STT coating exhibited superior corrosion resistance with a corrosion current density (icorr) of 12.8 µA/cm2, while the CXT coating showed icorr of 34.3 µA/cm2. Additionally, the STT coating exhibited higher hardness (832 ± 33 HV1.0) and better wear resistance with a wear rate of 10.46 ± 0.29 × 10-3 m3/m, over the CXT coating (hardness: 450 ± 36 HV1.0; wear rate: 12.67 ± 0.54 × 10-3 m3/m).

Effect of pool temperature on microstructure and corrosion resistance of PTAW Ni layer

In plasma transferred arc welding (PTAW), the weld pool temperature often fluctuates. The spray weld layer is prone to overheating, leading to adverse effect on its performance. This study investigated the influence of spray welding current on the weld pool temperature and in turn on the microstructure, microhardness and corrosion resistance of the PTAW-Ni layer on a steel substrate. Weld pool temperature increased with increasing spray welding current and varied along the welding gun path before reaching the steady state. With increasing pool temperature, more Fe diffused from the substrate into the spray weld layer, leading to a widened fusion zone, an increased dilution rate and a decreased microhardness. The spray weld layer has a dendritic microstructure. The dendrites have a higher Cr content, while the interdendritic regions have a higher Ni content. Increasing weld pool temperature increased diffusion, resulting in reduced enrichment of the Cr and Ni elements. The increase of Fe and decrease of Cr in the spray weld layer caused the decreasing corrosion resistance.

Effect of HVOF spray coating on the tribological surface of onshore gate valves

Gate valve is one of the most common design concepts in onshore Oil & Gas installations. This equipment is composed of a wedge-shaped obturator that performs linear sliding movements during activation. Fluid sealing is achieved through metallic contact between the surfaces of the gate and seat components. Metal surfaces are commonly hardened by heat treatment or coated with Stellite 6 alloy by plasma-transferred arc welding (PTAW). The application of high-velocity oxygen fuel (HVOF) coatings on these surfaces for wedge-gate valves has not yet been foreseen. In addition, comparative studies on the tribological performance of technical surfaces used in onshore wedge-gate valves are also scarce. Therefore, this study presents the results of tests performed on specimens using a ball-on-flat tribometer with linear reciprocating sliding, simulating a gate valve tribosystem in operation: flat (gate) and ball (seat). Martensitic stainless steel 13Cr was used with the contact interfaces under the following conditions: (A) heat treated, (B) Stellite 6 coating by PTAW, (C) Stellite 6 coating by HVOF, and (D) tungsten carbide coating by HVOF. The flat/ball tribological pairs investigated were A/B (TRIM 8), B/B (TRIM 5), C/B, and D/B. The coefficient of friction (COF), surface wear, and wear mechanisms were comparatively evaluated. The results showed that the newly proposed surfaces (C and D) are promising alternatives to reduce material consumption and improve the performance of valves in operation according to the application requirements.

Microstructure and performance of NiCrBSi coatings prepared by modulated arc currents using powder plasma transferred arc welding technology

This study examines the impact of varying plasma arc currents 70 A, 80 A, 90 A, and 100 A on NiCrBSi coatings applied to 15HM steel substrates using powder plasma transferred arc welding (PPTAW). Finite element analysis identifies two thermal cycle zones: the coating middle and coating/substrate transition. Microstructural analysis reveals dendritic structures in all samples, primarily rich in Cr. At the transition zone, various solidification modes are observed, accompanied by a coarse-grained heat-affected zone and minor macrosegregation. Energy-dispersive X-ray spectroscopy (EDS) confirms metallurgical bonding, while electron backscatter diffraction (EBSD) and X-ray diffraction indicate grain refinement as current decreases, with γ-Ni, Cr23C6, and Cr3C2 strengthening phases. PTA current of 70 A emerged as the optimal fabrication current within the tested range of currents, producing coatings exhibiting superior properties over the others. The results show improved corrosion resistance and tribological properties as current drops from 100 A to 70 A. Notably, corrosion current density decreases from 23.6 µA/cm2 to 12.8 µA/cm2, and average microhardness increases from 488 HV to 832 HV, reducing wear rate from 2.9 × 10−2 m3/m to 1.8 × 10−2 m3/m.

The Effect of Niobium on <i>In Situ</i> Synthesis of Titanium Carbide in Composite Hardfacings

Niobium (Nb) and titanium (Ti) react with carbon to form high-melting-point and high-hardness MC-type carbides. This study explores the in-situ synthesis of mixed NbC-TiC carbides during plasma transferred arc welding of a steel-based hardfacing. Feedstock powders consisted of stainless steel AISI 316L, TiO2, and graphite with and without 5 wt.% Nb addition. Feedstock powders were ball milled for 72 hours, then mixed with paraffine and pre-placed on the S235 steel. The cladding current was 125 A, and the plasma torch travel velocity was 1 mm/s and 0.7 mm/s. The effect of Nb on TiC generation was examined using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS). Vickers hardness was also measured at the surface of hardfacings. Results show that previously formed NbC grains acted as nucleation sites for TiC precipitation. Increased torch velocity has resulted in improving distribution and decreasing agglomeration of carbon phases. Hardness tests showed that Nb and Ti increased the hardness resistance of the substrate steel.

Effect of mating material on wear behaviour of Ni-based hardface coating

The selection of tribopairs, including mating materials, plays a crucial role in controlling material loss under rubbing conditions. In a fast breeder nuclear reactor, almost all moving components have been provided with a hardfaced coating at the mating surfaces for their longer life. Though, in most cases, the hardfaced surfaces come into contact with the components having the same coating; in some instances, they are allowed to rub against other materials. In the present investigations, an effort was made to study the wear behaviour of a Ni-based hardfaced coating made on 316LN stainless steel under similar and dissimilar mating conditions. Prior to wear tests, a defect-free hardface coating of Ni-based hardfacing alloy was made on 316LN stainless steel using plasma transferred arc welding process and subsequently characterized for its microstructure and hardness. Wear tests under dry sliding conditions were carried out at ambient temperature. The specific wear rate for dissimilar mating conditions was found to be one order of magnitude higher than the same rate obtained from similar mating conditions. Moreover, adhesive wear was the dominant wear mechanism in both mating conditions. It is clear from the study that similar material combinations should be given preference in the design of tribopairs instead of dissimilar material combinations to avoid significantly higher material losses for materials with lower hardness. The reported results will provide insight for carefully designing the tribopairs for critical applications.

Experimental Comparison of Laser Cladding and Powder Plasma Transferred Arc Welding Methods for Depositing Wear-Resistant NiSiB + 60% WC Composite on a Structural-Steel Substrate.

A Ni-based powder composed of NiSiB + 60% WC was deposited onto a structural-steel substrate using two methods: laser cladding (LC) and plasma powder transferred arc welding (PPTAW). The resulting surface layers were analyzed and compared. Both methods resulted in the precipitation of secondary WC phases in the solidified matrix, but the PPTAW clad exhibited a dendritic microstructure. The microhardness of the clads prepared by both methods was similar, but the PPTAW clad showed higher resistance to abrasive wear compared to the LC clad. The thickness of the transition zone (TZ) was thin for both methods, with a coarse-grain heat-affected zone (CGHAZ) and peninsula-like macrosegregations observed in clads from both methods. The PPTAW clad showed a unique cellular-dendritic growth solidification (CDGS) and a type-II boundary at the TZ attributed to its thermal cycles. While both methods resulted in metallurgical bonding of the clad to the substrate, the LC method exhibited a lower dilution coefficient. The LC method also resulted in a larger HAZ with higher hardness compared to the HAZ of the PPTAW clad. The findings of this study indicate that both methods are promising for antiwear applications due to their wear-resistant properties and metallurgical bonding to the substrate. The PPTAW clad may be particularly useful in applications that require higher resistance to abrasive wear, while the LC method may be advantageous in applications that require lower dilution and larger HAZ.

Design and performance of nitrogen-alloyed iron-based coating for enhancing galling resistance by plasma transferred arc welding

Iron-based alloys have been widely used as high-temperature galling resistant coatings. In this study, we designed and prepared a galling-resistant coating using plasma transferred arc welding with cored wires of varying nitrogen content. Our approach was based on the concept that nitrogen alloying can lead to the formation of hard precipitates and promote strain-induced phase transformations. The coating was primarily composed of austenite, and as the nitrogen content increased, the grain size decreased and the amount of nitride precipitation increased. The threshold galling stress of this cobalt-free coating was found to reach 80% of that of a laser-clad Stellite 21 coating at 300 °C. Following the galling test, the hardness of the worn area increased and a phase transformation from austenite to martensite occurred beneath the worn surface. The improvement in galling resistance under dry heavy load sliding conditions can be attributed to the synergistic effect resulting from multiple strengthening mechanisms, including fine-grain strengthening, second phase strengthening and phase transformation strengthening.

PTA-Welded Coatings with Saturation Magnetization above 1.3 T Using FeCrBSi Powders with Chemical Composition Similar to AISI 430 Ferrite Stainless Steel

Fe-Cr-based soft magnetic alloy (SMA) monolayer coatings with high saturation magnetization (Ms) above 1.3 T were deposited onto AISI 1010 substrate by co-axial powder feeding plasma transferred arc (PTA) welding, using FeCrBSi self-fluxing powders Fe313, which have a similar chemical composition to AISI 430 ferritic stainless steel (FSS). The effect of welding parameters on the phase assemblage, microstructure, hardness and magnetic performance of the coatings was investigated. The results show that the coating’s maximum width and the welding surplus height increased with the rise in welding heat input and powder distribution density, respectively. The coating’s Ms increased sharply, but its coercivity (Hc) decreased with the growth in the substrate dilution ratio. The coating’s Hc increased whereas its Ms decreased with the increment in welding heat input. The as-welded coating C3 with optimum magnetic performance had a dendrites–eutectics composite structure, where the columnar or equiaxed sorbitic pearlite dendritic cores surrounded by network-like eutectics α(Fe,Cr) + (Fe1−xCrx)2B were the main contents. Moreover, (Fe,Cr)7C3 and CrB had also been detected, and they were mainly distributed in the interdendritic regions. The body-centered cubic (b.c.c.) α(Fe,Cr) multi-element solid solution contributes to a high Ms of 1.61 T, and the borides (Fe1−xCrx)2B and CrB as well as (Fe,Cr)7C3 and other carbides cause a high Hc of 58.6 Oe and hardness HV0.3 of 4.90 ± 0.06 GPa, much higher than that of AISI 430 FSS (HV < 1.8 GPa). The current work verifies the feasibility of fabricating Ni- and Co-free FeCrBSi SMA coatings with high Ms and high hardness via PTA welding, and since the feedstock powders have chemical composition similar to AISI 430 FSS, the work may bring about novel applications for AISI 430 FSS in particular cases where the considerable wear-resistant performance as well as superior soft magnetic and anti-corrosive properties are required.

Tribological investigation of contact pairs applied in metallic gate valve seals for onshore application

Valves are equipment used in fluid management in industrial processes. Among the components of a valve, the set considered most critical for its operation and performance is the obturator sealing system, whose function is to make the fluid tight. This paper aims to analyze the tribological performance of two pairs in contact used in gate valves for onshore applications in oil installations. The specimens were manufactured using martensitic stainless steel with 13Cr as base material, varying the surface hardening processes under the following conditions: (A) heat treated and (B) Stellite 6 deposited by Plasma Transferred Arc Welding (PTAW). Pin-on-disc tests (PoD) were executed to compare the tribological performance of A/B and B/B configurations. In disc A versus pin B, the predominant wear mechanism was adhesion, resulting in a material pullout. For disc B versus pin B, the wear mechanism started with adhesion, followed by transfer film formation, generating elongated abrasive marks in the direction of movement on the surfaces of the pin and disc. With the results obtained, it was found that pair B/B showed less wear and friction. Based on these results, it is possible to indicate the use of the B/B pair for applications in valves that commonly require more activations and lower efforts for equipment actuation.

Alloy modification for additive manufactured Ni alloy components—part I: effect on microstructure and hardness of Invar alloy

Alloy 36 (1.3912), also known as “Invar,” is an alloy with 36% nickel. The alloy has a remarkably low thermal expansion coefficient in certain temperature ranges. This peculiarity is called the invar effect, which was discovered in 1896 by the Swiss physicist Charles Édouard Guillaume Sahoo and Medicherla Mater today Proc 43:2242-2244, (2021). Therefore, it is used in applications in which dimensional stability is critical, such as molding tools for composite materials in aerospace, automotive applications, or liquified natural gas (LNG) cargo tanks. Moreover, increasingly complex structures and the optimization of resource efficiency also require additive manufacturing steps for the production or repair of components Frazier J Mater Eng Perform 23:1917-1928, (2014); Treutler and Westling, (2021). Additively manufactured components have a heterogeneous microstructure and anisotropic mechanical properties Guévenoux et al. (2020). In addition, the manufactured components require subsequent machining surface finishing, like finish milling, to achieve their final contour. Nickel iron alloys are difficult to machine Zheng et al. Adv Mater Res 988:296–299, (2014). Additionally, inhomogeneous microstructure may lead to unstable cutting forces and conditions. In part I of this investigation, the initial alloy 36 is modified with the elements Ti, Zr, and Hf up to a maximum of 0.33 wt.-%. The influence of the modification elements on the microstructure as well as on the hardness of the AM components is examined. Furthermore, one modification is applied to metal arc welding process and investigated. Part II focuses on the effect of the alloy modifications on machinability as well as on the surface integrity of plasma-transferred-arc-welded (PTA) and finish milled invar components.

Comparison between the spherical and angular type WC particles reinforced in Nickel-based matrix deposited using Plasma Transferred Arc Welding process

This research work aims to compare two different WC types (Spherical and angular) particles reinforced in a Nickel-based matrix to be produced by Plasma Transferred Arc Welding (PTAW) process on stainless steel (SS 304) substrate. The angular WC particles were recycled and crushed to obtain the desired size to have it reinforced in the Ni-Cr matrix. The weight percentages of reinforcement (WC) and matrix (Ni-Cr) have been kept at 30% and 70% respectively. The PTAW process parameters were optimized considering the flowability of angular particles and dilution. The produced coatings were characterised for microstructure (Scanning Electron Microscope), phase analysis (X-Ray Diffraction) and hardness (Vickers Hardness Tester). The spherical WC particles reinforced coatings have produced higher local hardness in the WC region and the angular type coatings exhibited higher matrix hardness due to higher dissolution.

Fe–Co-based crystalline soft magnetic coatings with ultra-high saturation magnetization above 1.9T via co-axial powder feeding plasma-transferred arc welding

Fe–Co-based crystalline soft magnetic coatings with ultra-high saturation magnetization above 1.9T via co-axial powder feeding plasma-transferred arc welding

Influence of tungsten carbide raw materials to microstructure and wear performance on PTA hard-facing materials with its micro-mechanism analysis

The wear performance of the plasma transferred arc (PTA) welding hard-facing materials manufactured reinforced by cast WC/W2C and coarse grain WC with different shapes are investigated. Coarse grain WC-Ni coating shows the best wear resistance in a high applied load condition, with spherical reinforced particles give higher wear performance than angular shape. WC, W2C, γ-Ni, M23C6, and M7C3 (M = Cr, Fe, W, and Ni) are detected in PTA coatings. The spherical cast and angular cast WC/W2C particles contain a higher volume of W2C, which is easier to be dissolved during the PTA welding process, resulting in lower retained reinforced particle volume and more precipitates concentration. In the PTA coating, the cast WC/W2C particles have a higher hardness, whereas the matrix has a relatively low hardness. The wear performance of PTA coating is more affected by the hardness rather than the coefficient of friction (COF). At a load of 5 N applied on the Si3N4 ball, the contact area between reinforced particles and counterparts, resulting in wear resistance is controlled by the hardness of the reinforced particles. When the load increases to 10 N, the hardness of the matrix controls wear performance. The precipitates formed between the carbides and matrix smooth the interface and strengthen the bonding, which prevents the cast WC/W2C from being pulled out from the matrix during the wear test.

Effect of Welding Current on Wear Behavior of PTA-Welded Cu35Ni25Co25Cr15 HEA Coating

High-entropy alloys (HEAs) have received increasing attention because of their excellent properties. To improve the surface hardness and wear resistance of pure Cu, a Cu35Ni25Co25Cr15 HEA coating was, for the first time, deposited on a pure Cu substrate by plasma transfer arc (PTA) welding. The welding current varied from 130 to 160 A. The microstructures and mechanical properties of the coating were investigated. The Cu35Ni25Co25Cr15 HEA coating comprised face-cubic-centered A1 (Cu-rich) and γ′ (NiCoCr-rich) phases. The coating had an apparent structural gradient with coarse grains at the interface with the Cu substrate. The bottom, middle, and top zones of the coating exhibited a fine smooth cellular structure, fine-needle structure, and long dendrites, respectively. As the welding current was increased, the dilution ratio of the coating and interfacial bonding strength gradually increased, whereas the hardness of the coating increased and then decreased. Under a welding current of 150 A, no gaps or pores appeared in the interface, and the coating exhibited good metallurgical bonding with the Cu substrate. The wear mechanisms of the Cu35Ni25Co25Cr15 HEA coating at different temperatures were also determined. Compared with pure Cu, the Cu35Ni25Co25Cr15 HEA coating exhibited excellent wear resistance, especially at high temperatures. This study paves a new way for coating on pure Cu and enhances the wear resistance of Cu components.

Comparison between heat treatment and SPS treatment on CoCrFeMnNi/WC coatings

ABSTRACT In this study, spark plasma sintering (SPS) was used for the thermoelectric composite treatment of CrMnFeCoNi/WC plasma transfer arc welding (PTA) coating to explore the difference compared with common heat treatment (HT). X-ray diffraction (XRD) was used to detect the phase composition, and a combination of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) was used to characterize the microstructure. The performance of nano-indentation was tested. The results show that the coating after PTA has a large dislocation density due to internal stress, while HT and SPS treatment significantly reduce the internal stress and dislocation density of the coating. Nano-indentation test shows that the hardness of the coating after PTA is 4.24 GPa, and after HT, the hardness decreases to 4.05 GPa. However, the coating after SPS treatment has significant precipitation-strengthening effect due to the wide existence of the precipitated phase, and the hardness rises to 4.78 GPa.

Hardfacing of mild steel with wear-resistant Ni-based powders containing tungsten carbide particles using powder plasma transferred arc welding technology

Abstract This study explores the use of powder plasma transferred arc welding (PPTAW) as a surface layer deposition technology to form hardfaced coatings to improve upon the wear resistance of mild steel. Hardfaced layers were prepared using the PPTAW process with two different wear-resistant powders: PG 6503 (NiSiB + 60% WC) and PE 8214 (NiCrSiB + 45% WC). By varying the PPTAW process parameters of plasma gas flow rate (PGFR) and plasma arc current, hardfaced layers were prepared. Microscopic examinations, penetration tests, hardness tests, and abrasive wear resistance tests were carried out on the prepared samples. Hardfacings prepared with PG 6503 had a hardness of 46.3–48.3 HRC, while those prepared with PE 8214 had a hardness of 52.7–58.3 HRC. The microhardness of the matrix material was in the range of 573.3–893.0 HV, while that of the carbides was in the range of 2128.7–2436.3 HV. The abrasive wear resistance of the mild steel was improved after deposition of hardfaced layers by up to 5.7 times that of abrasion-resistant heat-treated steel, Hardox 400, having a nominal hardness of approximately 400 HV. The hardness and wear resistance were increased upon addition of Cr as an alloying element. Increasing the PGFR increased the hardness and wear resistance of the hardfacings, as well as increasing the number of surface cracks. Increasing the plasma transferred arc (PTA) current resulted in hardfacings with fewer cracks but lowered the wear resistance.

Influence of WC grain size on the microstructure and wear property enhancement of 18Ni300 coatings

18Ni300-based cladding layers with micro/nano WC additives were fabricated via plasma transferred arc welding (PTA) technology. This work investigates the influence of WC grain size on microstructure evolution and wear performance. The comparative investigation of the microstructure results indicates that the nano-WC particle-reinforced 18Ni300 coating sample shows more fine grains and nanoparticles. These nanoprecipitates are Ni3Mo and WC, which are uniformly distributed in the martensite matrix. The in-situ precipitation forms Ni3Mo precipitates in the maraging matrix, which is triggered by the intrinsic heat treatment effect of PTA. The hardness of the 5 wt% nano-WC/18Ni300 composite exhibits the highest value (395.8 ± 10.7HV0.3), which is 12.41 % higher than that of the original 18Ni300 coating (352.1 ± 12.1HV0.3). Meanwhile, the nano-WC-reinforced 18Ni300 coating shows the highest wear resistance, which is approximately 2.5 times higher than the original 18Ni300 cladding layer. It could be concluded that the refining and strengthening effects of nano-WC addition on the microstructure and wear resistance of the 18Ni300 coating were superior to those of micro-WC. Molecular dynamics simulation results indicate that melting begins at the surface of nano-WC and then proceeds to the solid core as the temperature rises from 300 K to the melting point. Meanwhile, the nano-WC particles have a more sensitive diffusion tendency with the matrix than the micro-WC particles. This diffusion of the surface atoms can generate solid bonding with the surrounding atoms in their matrix and promote the agglomeration and in situ precipitation of Ni3Mo, finally synergistically improving the wear resistance of the nano-WC-reinforced composite.