MC-type Carbides Research Articles

The effect of quenching/double quenching and tempering heat treatment cycles on the microstructure, impact energy and hardness of AISI H13 tool steel

ABSTRACT In this study, microstructure modifications of AISI H13 steel were studied with different heat treatments such as conventional quenching, quenching + tempering/double tempering and double quenching + tempering/double tempering. Carbide volume ratio analyses were performed. The XRD analysis was used to determine the type of carbide, the average crystallite size, and the dislocation density in the samples. Charpy impact tests were performed. The hardness values of the samples were measured with the Rockwell C scale. The presence of MC, M23C6, and M7C3 type carbides was determined in the microstructures. Heat treatment cycles caused a high dislocation density in martensite laths. The dislocation density of martensite laths decreased with double quenching. The tempering process caused the formation of fine carbide particles in the microstructure. In addition, tempering processes gave rise to an increase in the volume ratio of M23C6-type strip carbides. The length/width ratio of the strip-type carbides increased with the effect of double tempering. As a result of the applied heat treatments, the impact energies of the samples decreased. The tempering process caused a secondary hardening of the samples. While the double quenching process increased the impact energy value by approximately 2%, it caused a decrease in hardness by 24%.

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.

Influence of heat treatment on the microstructure and creep response of additively manufactured cobalt superalloy Mar M509

ABSTRACT This work explores the influence of various post-build heat treatment procedures on the microstructural characteristics and creep response of laser powder bed fusion (L-PBF) Mar M509 superalloy. Besides MC-type carbides formed primarily during the L-PBF process, the obtained results indicate the influence of heat treatment on the nucleation of M6C and M7C3 carbides due to elemental segregation. Short-term creep-rupture tests have been conducted at 900°C/110MPa on eight specimens, each subjected to a specifically individual heat treatment procedure. Rupture times are found to be sensitive to the heat treatment applied and vary from ~178 to ~641 hours. Detailed microscopic characterisation of ruptured specimens highlights the synergistic influence of oxidation and M7C3/M6C precipitate-free zone formation on macroscopic intergranular failure facilitated by grain boundary sliding along favourably oriented small grains. Besides notable grain growth, the presence of a serrated grain boundary structure with relatively less MC-type carbide coarsening is found to offer the best creep resistance among the eight L-PBF specimens. Further improvement of the elevated temperature performance of the alloy is seen to require a focus on the L-PBF process conditions to optimise the morphology of MC carbides, as they form.

Effect of Mo addition on the microstructure and high-specific tensile strength of Fe–Mn–Al–Ni–C ferrous medium-entropy alloy

Molybdenum (Mo) is known to play various roles in ferrous materials, including promoting lattice distortion and forming different types of precipitates. In this study, Mo was added to the Fe–Mn–Al–Ni–C lightweight medium-entropy alloy system, and its effects on microstructure and tensile properties were investigated in comparison to the Mo-free counterpart. The addition of Mo retarded the kinetics of recrystallization and led to the precipitation of M6C-type carbides. In terms of tensile properties, the addition of Mo improved the strength of the alloy by enhancing solid solution strengthening and precipitation strengthening. In particular, the Mo-added alloy, annealed at 800 °C for 7.5 min, exhibited a yield strength of 1274 MPa and an ultimate tensile strength of 1550 MPa. This corresponds to a specific ultimate tensile strength of approximately 218 MPa g−1 cm3, along with a uniform elongation of ∼8.5 %. The Mo content in the solid solution and the presence of Mo-rich M6C-type carbides also contributed to high back stress hardening, which enhanced the alloy's ability for strain hardening and resulted in reasonable uniform elongation.

Effects of deep cryogenic treatment on the microstructure evolution, mechanical and thermal fatigue properties of H13 hot work die steel

The service life of hot work die steel is significantly influenced by its microstructure and thermal fatigue properties. This paper explores the impact of deep cryogenic treatment (DCT) on H13 hot work die steel's microstructural evolution and mechanical as well as thermal fatigue properties. The results demonstrate that a portion of unstable retained austenite transforms into martensite during deep cryogenic treatment and numerous finely dispersed carbides precipitate from the matrix, thereby enhancing hardness. Analysis of the average crack length and distribution of thermal fatigue test samples reveals that the average crack length and crack density of DCT-treated samples are lower than those of non-DCT-treated samples. Thermal fatigue cracks in the specimens primarily originated from trigeminal grain boundaries and the carbides are found at the crack tips. DCT facilitates the precipitation of fine and dispersed carbides, imparting a robust pinning effect on boundary migration and thereby impeding the initiation and propagation of thermal fatigue cracks. Furthermore, deep cryogenic treatment results in a reduction in the number of M23C6 type carbides with large particles and an increase in smaller M6C type carbides during the thermal fatigue test. This indicates a positive influence on the carbide distribution and further contributes to the improved thermal fatigue resistance of the hot work die steel.

Study Of the Effect of Titanium Additions on The Mechanical and Corrosion Properties of AISI 316 Powder Metallurgical Steel

Context: Powder metallurgy uses metallic and/or non-metallic powders that, through mixing, compacting, and sintering operations, allow obtaining large series of products. In austenitic stainless steels, Cr23C6-type carbides can precipitate at temperatures between 450 and 950 °C. When this occurs, the steel is susceptible to being attacked at its grain boundaries by a phenomenon called sensitization. Titanium is added as a ‘stabilizer’ because it has a greater affinity with carbon for the formation of species at a temperature of approximately 900 ºC, and, during cooling, it consumes the carbon forming MC-type carbides, inhibiting the precipitation of Cr23C6. Method: The composition and morphology of the powders were characterized, leading to the formulation of an alloy matrix consisting of a mixture of AISI 316 steel powders of two different particle-size distributions in a proportion that produced the highest density and the lowest porosity in the sintered material. Titanium was added at two levels (0,4 and 1,0 wt%), and sintering was carried out with nitrogen. The corrosion rate was determined by potentiodynamic polarization. Vickers hardness and pin-on-disk wear tests were performed. The stages were complemented with a microstructural analysis. Results: The addition of 0,4 wt% of titanium decreased the steel’s rate of corrosion, albeit in the absence of passivation. The microstructure consists of austenite, ferrite, and TiC precipitates. The addition of 1,0 wt%Ti showed an increase in the corrosion rate, with a microstructure containing austenite, ferrite, TiC carbides, and the Laves ɳ-Fe2Ti phase. Conclusions: The results were compared against thermodynamic simulations in the Thermo-Calc software, which were consistent with the microstructural analysis, showing the phenomena of stabilization as well as the precipitation of intermetallic phases and highlighting the importance of establishing strict controls in the formulation of powder metallurgical alloys due to the transformations that can take place due to the effect of the thermal cycles of the process.

Metallographic Evaluation of Increased Susceptibility to Intermediate Embrittlement of Engine Valve Forgings Made of NCF 3015 High Nickel and Chromium Steel.

This paper focused on determining the increased tendency of cracking after the die forging process of high nickel and chromium steel. The increase in carbon content in austenitic nickel-chromium steel promoted the tendency of valve forgings to forging intergranular crack on the valve head. Attention was paid to issues related to the chemical composition of the material to be considered when hot forming nickel-chromium steel components. Optical and scanning electron microscopies were used to examine the microstructure and fracture features of the samples removed from a fractured valve head. The embrittlement was due to microcavity formation at grain boundaries. Creep theory at grain boundaries was used to explain crack formation. The tensile behavior was interpreted from the evolution of the microstructure during deformation and referred to intermediate brittleness to explain the effect of carbon. It was found that the increased carbon content of the nickel-chromium steel and the strong undercooling observed at the edges of the valve head are factors that promote a reduction in grain boundary cohesion and enhance intermediate temperature embrittlement. Finally, it was found that the formation of a heterogeneous structure manifested by the presence of grain boundary M23C6-type carbides in the austenitic matrix was most likely related to the occurring brittleness.

Room- and elevated-temperature mechanical property of selective laser melting-fabricated Hastelloy X with different heat treatments

Superalloy alloy Hastelloy X was fabricated by selective laser melting (SLM), and heat treatments have been designed to optimize microstructures for better mechanical property at high temperature. Specimens of as-printed, aging treatment (AT), solution treatment (ST), and wrought conditions are of interests to this study, and their grains, dislocations, grain boundaries, precipitates, twins and defects have been characterized. Compared to the wrought specimens, the as-printed specimens showed sub-micron cellular microstructure, while M23C6-type carbides and Fe2Mo phases were found after AT condition with partial recrystallization. The ST treatment introduced a large number of high angle grain boundaries (HAGBs) and a high twin boundary ratio due to recrystallization. With this, their post-mortem microstructures at both room temperature (RT) and elevated temperature (ET) of 850 °C were easily correlated to the mechanical performance. AT yielded the highest ultimate tensile strength (UTS) of ∼1067 MPa, while ST gave the highest ductility of ∼51% at RT. At ET, the as-printed, AT, and ST SLM specimens showed improved UTS over the wrought counterparts, all with a reduced ductility. With these observations, a comprehensive heat treatment roadmap has been proposed to summarize their microstructure-property relationship, which rigorously included the traditional ST + AT heat treatment and proved SLM-fabricated Hastelloy X's incompatibility. This research not only deepens our understanding of its mechanical behavior after possible heat treatments, but also semi-quantitatively guides its feasible processing even for high-temperature applications.

Solidification microstructure characteristics and their formation mechanism of K447A nickel-based superalloy for dual-performance blisk

In this paper, the effects of cooling rate after casting and stirring process on γ’ phase, γ / γ’ eutectic phase, MC type carbide morphology and grain structure of K447A alloy turbine blisk were studied systematically. The quantitative relationships between cooling rate, stirring process and γ’ phase, γ / γ’ eutectic phase, MC type carbide and grain size were described in detail. The results show that with the increase of cooling rate, the distribution region of γ / γ ‘eutectic phase from the center of blisk to blade decreases gradually and MC type carbide changes from skeleton to block due to the shorter formation time of eutectic and carbide in the later stage of solidification. Besides, with the decrease of cooling rate, the size of γ’ phase increases under the influence of interfacial strain energy and elastic strain energy, and the morphology of γ’ phase gradually evolves from cuboid to concave cuboid, octet and dendritic. At the same time, due to the synergistic effect of cooling rate and stirring process, the blade part is columnar grain and the central part of the blisk is equiaxed grains. In this paper, the evolution mechanism of γ ‘phase, γ / γ’ eutectic phase, MC type carbide and grain size with cooling rate and stirring process was proposed. The research results would play a key supporting role in precise control during solidification for microstructures and properties of dual-performance superalloy blisk.

Effect of precipitation on the mechanical behavior of vanadium micro-alloyed HSLA steel investigated by microstructural evolution and strength modeling

In the current work, the relationship between the microstructural evolution and strengthening mechanisms in a vanadium micro-alloyed high strength low alloy (HSLA) martensitic steel has been systematically investigated by multi-scale characterizations and modeling. Two heat treatment routes, i.e., solution quenching plus tempering (SQT) and solution quenching plus isothermal annealing (QIA) are applied to produce a martensitic matrix combined with considerable nano-scale MC-type carbides (M = V, Mo, Cr) in the experimental steels. Theoretic calculations of the strengthening contributions are conducted based on quantitative characterizations of microstructural parameters, the overall modeling results agree quite well with the experimental results for estimating yield strength of the specimens. Precipitation and dislocation strengthening are found to be the main factors causing strength evolution with different isothermal holding time (IHT) at 600 °C. In both SQT and QIA specimens, the prolonged IHT contributes to an increased particle size and volume fraction of MC precipitates but a decreased dislocation density, and the most excellent mechanical properties are achieved with IHT of 2 h. The precipitation strengthening of SQT specimens is higher than that of QIA specimens because of its finer particle size and higher volume fraction of the MC precipitates, resulting in the higher yield strength of the SQT specimens than that of the QIA specimens. This can be explained by the hierarchy lath martensite that is highly dislocated with numerous interfaces, providing considerable nucleation points and high-speed atomic diffusion paths for precipitation, leading to the significantly refined MC particle size in the SQT specimens. Moreover, the MC precipitates exhibit no significantly coarsening during isothermal holding at 600 °C, which is a result of the presence of Mo/Cr atoms in MC precipitates that yields precipitate size stabilization due to its higher chemical potentials than that of V, thus maintaining a stable precipitation strengthening after IHT exceeding 2 h.

Microstructure-property gradients in the GH4099 superalloy fabricated by directed energy deposition and its response to heat treatment

In this study, GH4099 superalloys were produced by directed energy deposition (DED) and then heat treated. The microstructural distribution characteristics of the top, middle, and bottom regions along the deposition direction of the samples have been investigated by various microscopic techniques. The results showed that in the as-DEDed state, the microhardness was observed to be lower in the top and bottom regions, but higher in the middle region. The corresponding microstructure was the MC-type carbides precipitating in the bottom and top regions, while the middle region was replaced by M23C6-type carbides. The middle region also had higher dislocation density and recrystallization fraction than the other regions based on electron backscatter diffraction analysis. After heat treatment, only M23C6-type carbides were observed along the grain boundaries, and fine γ' precipitates approximately 30 nm in diameter were dispersed within the γ matrix. In addition, the recrystallized grains were observed at stress concentration locations attributed to high misorientation. The data acquired revealed that modeling the microstructure evolution in the top, middle, and bottom regions can serve as a theoretical guide for achieving a uniform distribution of mechanical properties.

Processing of Niobium-Alloyed High-Carbon Tool Steel via Additive Manufacturing and Modern Powder Metallurgy.

Niobium is recently considered one of the potential alloying elements for tool steels due to the formation of hard and stable carbides of MC type. Its use is limited by the fact that these carbides tend to coarsen during conventional melting metallurgy processing. This work explores the potential of additive manufacturing for processing Nb-alloyed tool steel with a high content of carbon. Directed energy deposition was used as the processing method. It was found that this method allowed us to obtain a microstructure very similar to that obtained after the use of consolidation via spark plasma sintering when subsequent heat treatment by soft annealing, austenitizing, oil quenching and triple tempering for secondary hardness was applied. Moreover, the soft annealing process could be skipped without affecting the structure and properties when machining would not be required. The hardness of the steel was even higher after additive manufacturing was used (approx. 800-830 HV 30) than after spark plasma sintering (approx. 720-750 HV 30). The wear resistance of the materials processed by both routes was almost comparable, reaching 5-7 × 10-6 mm3N-1m-1 depending on the heat treatment.

Investigation on microstructure and mechanical properties of electron-beam-welded joint of reduced activation ferritic/martensitic steel fabricated by selective laser melting

The microstructure and mechanical properties of the complex low-activation ferritic–martensitic components of the China Fusion Engineering Test Reactor (CFETR) were examined in this study. The quenching–tempering treatment of CLF-1 steel formed by selective laser melting (SLM) (referred to as the QTed material) was carried out to analyze the effects of heat treatment on the microstructural and mechanical properties. Meanwhile, the microstructural and mechanical characteristics of CLF-1 steel electron beam welding (EBW) joints after quenching–tempering (referred to as the EBWed material) were investigated. Compared with the untreated sample (referred to as the SLMed material, with an ultimate tensile strength (UTS) = 979.8 ± 12.7 MPa and elongation (EL) = 3.7% ± 0.4%), the quenching–tempering treatment improved the EL of CLF-1 steel effectively (QTed material, 22.3% ± 0.1%), while it decreased the UTS correspondingly (505.6 ± 11.8 MPa), which mainly was due to the change in the grain size and structure during the heat treatment. The special microstructural distribution characteristics of the CLF-1 fabricated via SLM determined that the fracture mechanism was transgranular ductile/intergranular brittle mixed fracture. After electron beam welding of the QTed material, the tensile properties of the joint (UTS = 710.6 ± 21.4 MPa, EL = 9.7% ± 0.1%) were between those of the SLMed and QTed materials. The fracture appeared in the heat-affected zone (HAZ), proving that the strength of the weld was higher than that of the base metal. The microstructure of the weld was almost completely composed of coarse lath martensite, and the accumulation of dislocation clusters, precipitated M23C6-type carbides, and precipitated MX-type carbides contributed to the improvement of the yield strength (YS). The HAZ could be divided into three regions based on the different heating temperatures, and every region had different grain structures composed of mainly martensite and ferrite. The contributions of four strengthening mechanisms to the YS of CLF-1 steel were analyzed quantitatively, which lays a foundation for further improving the performance of CLF-1 steel and improving its application feasibility on the first wall of a fusion reactor.

Microstructural Characterization and Prior Particle Boundary (PPB) of PM Nickel-Based Superalloys by Spark Plasma Sintering (SPS).

This research investigates the microstructure and defects of powder metallurgy (PM) nickel-based superalloys prepared by spark plasma sintering (SPS). The densification, microstructural evolution, and precipitate phase evolution processes of FGH96 superalloy after powder heat treatment (PHT) and sintering via SPS are specifically analyzed. Experimental results demonstrate that SPS technology, when applied to sinter at the sub-solidus temperature of the γ' phase, effectively mitigates the formation of a prior particle boundary (PPB). Based on experimental and computational findings, it has been determined that the presence of elemental segregation and Al2O3 oxides on the surface of pre-alloyed powders leads to the preferential precipitation of MC-type carbides and Al2O3 and ZrO2 oxides in the sintering necks during the hot consolidation process, resulting in the formation of PPB. This study contributes to the understanding of microstructural modifications achieved through SPS technology, providing crucial information for optimizing sintering conditions and reducing the widespread occurrence of PPB, ultimately enhancing the material performance of PM nickel-based superalloys.

Reassessment of the Matrix Composition of Co-Re-Cr-Based Alloys for Particle Strengthening in High-Temperature Applications and Investigation of Suitable MC-Carbides.

This study reassesses the optimum matrix composition of Co-Re-Cr-based alloys for strengthening by MC-type carbides. It is found that the composition of Co-15Re-5Cr is ideally suited for this purpose as it allows the solution of the carbide-forming elements such as Ta, Ti, Hf, and C within a matrix consisting entirely of fcc-phase (typically at 1450 °C), having a high solubility for these elements, while precipitation heat treatment (typically at 900-1100 °C) occurs in a hcp-Co matrix, displaying a much lower solubility. In the case of the monocarbides TiC and HfC, this was investigated and achieved for the first time in Co-Re-based alloys. TaC and TiC emerged as suitable particles in Co-Re-Cr alloys for creep applications due to a large population of nano-sized particle precipitation, which is not the case for the mainly coarse HfC. Both Co-15Re-5Cr-xTa-xC and Co-15Re-5Cr-xTi-xC exhibit a formerly unknown maximum solubility close to x = 1.8 at.%. Therefore, further research on the particle-strengthening effect and the governing creep mechanisms of carbide-strengthened Co-Re-Cr alloys should focus on alloys with the following compositions: Co-15Re-5Cr-1.8Ta-1.8C and Co-15Re-5Cr-1.8Ti-1.8C.

Effect of cerium on the primary carbides and inclusions in electroslag remelted M35 high speed steel

To restrain the formation of primary carbides in M35 high speed steel, the present work investigated the effect of cerium on the microstructure, primary carbides and inclusions in electroslag remelted M35 high speed steel based on experimental characterizations and thermodynamic calculations. The primary carbides in M35 high speed steel are M2C-type carbides with orthorhombic crystal structure and MC-type carbides with FCC crystal structure. M2C-type carbides are the dominant carbides, whose precipitation is prior to the MC-type carbides. With adding cerium content to 0.0230wt%, the evolutionary process of inclusions is: MgO∙Al2O3→Ce2O3, CeAlO3 and Ce2O2S→Ce2O3, Ce2O2S and Ce2O3 core surrounded by Ce–As–P layer. Adding cerium content from 0 to 0.0230wt% causes the secondary dendrite arm spacing to decrease from 36.8 μm to 29.4 μm, as the heterogeneous nucleation of Ce2O3, Ce2O2S and CeAlO3 inclusions, as well as the effect of dissolved cerium including the increase in the constitutional undercooling and the drag on the migration of liquid–solid interface. Ce2O3, Ce2O2S and CeAlO3 are the less effective heterogeneous nucleation cores for M2C-type and MC-type primary carbides precipitation than MgO∙Al2O3 inclusions, which is conducive to the decrease in the area fraction of primary carbides with adding 0.0067wt% cerium. Further increasing cerium content to 0.0230wt%, the formation of Ce–As–P inclusions surrounding Ce2O3 promotes the precipitation of M2C-type primary carbides, causing the increase in the area fraction of primary carbides.

Microstructure evolution and high temperature wear resistance of in-situ synthesized carbides reinforced NiCoFeCrSiMo high entropy alloy coatings fabricated by laser cladding

In this work, we reported a novel strengthening strategy of NiCoFeCrSiMo high entropy alloy by high density in-situ synthesized carbides. The external WC particles were introduced into the laser molten pool and basically dissolved which facilitate the in-situ reactions of carbides. The microstructure of composite coatings consists of high-density carbides which formed dendrites, while the FCC based solid solution matrix of high entropy alloy filled the inter-dendritic zone. The original added WC particles were almost dissolved in the laser pool and M6C type carbides or M2C carbides were in-situ synthesized. The composite coating was strengthened by dislocation pinning and plugging effects. Notably, the average microhardness of the composite coating can reach as high as 947 HV, while the friction coefficient of high entropy alloy coatings with 50 % WC addition could be as lower as 0.2 at 600 °C. The wear surface morphology analysis shows that the wear mechanism of M6C/FCC composite coating was adhesive wear and abrasive wear. The results in this work may provide some new thoughts for the design of ceramic particles reinforced HEA composite coatings.

Effect of microwave hybrid heat treatment on the microstructure and hardness of 3D printed Inconel 718 superalloy

ABSTRACT This study explores the potential of a microwave hybrid heating (MHH) technique as an efficient post-heat treatment route for an Inconel 718 (IN718) superalloy processed by laser powder bed fusion (LPBF). The LPBF-IN718 alloy is post-heat-treated using an industrial microwave (MW) oven and a conventional heat treatment route to eliminate the segregates and Laves phase. The MW treatment generates a relatively higher back diffusion rate of the segregated elements releasing more Nb into the γ-matrix compared to the conventional treatment. This results in lower fraction of intergranular δ-phase in the MW-processed microstructure (≈ 0.2%) relative to conventionally processed microstructure (≈ 0.81%). However, more precipitation of the MC-type carbides is observed in the matrix after the MW-treatment, indicating the supersaturation of the γ-matrix in the back-diffused elements. Both the MW and conventional treatments affect the hardness similarly owing to the combined effect of the precipitation hardening and the substructure strengthening. Compared to conventional heating, the MW processing time, to heat the sample to the set temperature, is reduced by a factor of 2, and the consumed energy is decreased by 80%. As a result, an MW-treatment can be considered as a cost-effective alternative to a conventional post-heat treatment for LPBF-IN718 components.

Fabrication and abrasive wear property of high chromium cast iron with high vanadium and high nitrogen content (HCCI-VN)

High chromium cast irons (HCCIs) have excellent wear resistance because of high hardness chromium carbides (M7C3). However, the hardness of M7C3 is relatively low compared with MC-type carbides, such as VC, NbC and TiC. To improve wear resistance of HCCI, a new HCCI, named HCCI-VN, was fabricated by replacing wt.5.0% chromium with 5.0 wt% vanadium and adding 0.1 wt% nitrogen in traditional HCCI with 20 wt% Cr, and the abrasive wear properties of HCCI-VN were researched under different abrasive size and load conditions. Results show that the microstructure of HCCI-VN was characterized by many V(C, N) carbides besides chromium and molybdenum carbides (M7C3, M23C6, M2C), which were distributed in the matrix composed of martensite and austenite. The new HCCI-VN has excellent wear resistance. The relative wear resistance HCCI-VN is 2.2–9.1 times that of HCCI with 23 wt% Cr under different abrasive size and wear load. Among them, the reduction of abrasive size or the increase of wear load will bring better wear resistance. The excellent wear resistance of HCCI-VN is attributed to high hardness V(C, N), which cooperates with multi-scale and multi-type chromium and molybdenum carbides to resist abrasive scratch efficiently.

Tribological properties of laser cladding nickel-based WC reinforced Ag self-lubricating coating on RuT450 surface

Through laser cladding, an Inconel 718-WC reinforced Ag self-lubricating coating was designed on the surface of the vermicular cast iron (RuT450) to enhance its wear resistance. The results indicated that the Inconel 718-WC-Ag wear-resistant self-lubricating coating with no cracks and no pores was manufactured by laser power of 700 W and 1000 W. The hardness of 1000 W coating was 386HV0.5, which was somewhat greater than the hardness of 700 W coating (363HV0.5). The wear rate of 1000 W coating at room temperature and 300 °C was 0.59 and 0.68 times that of 700 W coating. At room temperature, the wear rate of 700 W coating and 1000 W coating was 0.43 and 0.25 times that of the substrate RuT450. The two coatings outperformed the substrate in terms of wear resistance due mostly to the interaction between Ag and M23C6, MC, and M2C type carbides. The 700 W coating's main wear mechanisms were severe fatigue wear, abrasive wear, and minimal oxidation wear. Minor fatigue wear, abrasive wear, and oxidation wear made up the majority of the wear mechanism of 1000 W coating. At 300 °C, the wear rates for the 700 W and 1000 W coatings was 0.24 and 0.16 times that of the substrate RuT450. The remarkable wear resistance of the two coatings was mostly due to the interaction of Ag with NiO, Ag2O, and Ni2O3 type oxides. The plastic deformation of the wear surface of both coatings was relatively light compared to the substrate RuT450, and only small grooves and furrows on the surfaces of the two coatings were visible.