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Laser cladding, as an advanced surface modification technology, has the advantages of a high energy density, controlled dilution rate and good metallurgical bonding between the coating and the substrate. Its rapid heating and cooling properties help to form a dense and fine coating structure on the surface of the substrate, thus enhancing wear and corrosion resistance. In recent years, the in situ generation of carbide-reinforced iron-based composite coatings has gradually become a research hotspot because it combines the high hardness values of carbide with the high toughness values of iron-based alloys, which significantly improves the comprehensive performance of the coatings. This paper reviews the research progress of laser cladding in situ carbide-reinforced iron-based alloy coatings and explores the role of different types of in situ synthesized carbides (TiC, NbC, WC, etc.) in the coatings and their effects on their wear resistance and mechanical properties. The distribution of carbides in the coatings and their morphological characteristics are also discussed, and the effects of laser power, scanning speed and auxiliary treatments (ultrasonic vibration, induction heating, etc.) on the microstructure and properties of the coatings are analyzed. Finally, the problems and future directions of development in this field are envisioned.

As a novel type of metal material emerging in recent years, high-entropy alloy boasts properties such as a simplified microstructure, high strength, high hardness and wear resistance. High-entropy alloys can use laser cladding to produce coatings that exhibit excellent metallurgical bonding with the substrate, thereby significantly improvement of the wear resistance of the material surface. In this paper, the research progress on improving the high-temperature wear resistance of high entropy alloy coatings (LC-HEACs) was mainly analyzed based on the effect of some added alloying elements and the presence of hard ceramic phases. Building on this foundation, the study primarily examines the impact of adding elements such as aluminum, titanium, copper, silicon, and molybdenum, along with hard ceramic particles like TiC, WC, and NbC, on the phase structure of coatings, high-temperature mechanisms, and the synergistic interactions between these elements. Additionally, it explores the potential of promising lubricating particles and introduces an innovative, highly efficient additive manufacturing technology known as extreme high-speed laser metal deposition (EHLMD). Finally, this paper summarizes the main difficulties involved in increasing the high-temperature wear resistance of LC-HEACs and some problems worthy of attention in the future development.

The effect of the modification treatment on the refinement of primary carbides and wear resistance of 35% Cr-4.0% C hypereutectic high chromium cast iron (HHCCI) was investigated using the first-principles calculations, XRD, SEM, TEM, hardness tests, and wear tests. The addition of N elements to HHCCI refined the size of the M7C3 primary carbide from 13.25 ± 0.72 μm to 11.67 ± 0.33 μm under the effect of adsorption refinement. When the compound modification elements (N + Ti + V + RE-Mg) were added, the combination of adsorption refinement and heterogeneous nucleation refinement significantly reduced the carbide size to 5.35 ± 0.15 μm. The refinement of the M7C3 primary carbide can be attributed to two components: 1) the refinement of the heterogeneous nucleation of TiC and VC. 2) the combination of N, Ti, and V with the M7C3 preferred growth surface (0001) resulting in the refinement by adsorption and reduce the size of the primary carbide. The hypereutectic high chromium cast iron after the compound modification exhibited excellent wear resistance. Under dry sliding wear condition, Compared with the unmodified sample, the wear resistance increased by 75%. Under corrosive wear conditions, the wear resistance is increased by 98.1%.

The microstructure and mechanical properties of three kinds of low-carbon medium-manganese steels with different Si contents under an intercritical heat treatment process were studied. The results show that the microstructure of the test forged steel is mainly composed of ferrite and pearlite. After 900 °C complete austenitizing quenching + 720 °C intercritical quenching, the microstructure of the test steel is mainly composed of ferrite and martensite. With the increase in Si content, the microstructure becomes finer and more uniform. The microstructure of the test steel after 900 °C complete austenitizing quenching + 720 °C intercritical quenching + 680 °C intercritical tempering is dominated by ferrite and tempered martensite, with a small amount of retained austenite and cementite. As the Si content increases, the boundaries between ferrite and tempered martensite become more clear. The tensile strength and hardness of the test steel increase with the increase in Si content, while the elongation first increases and then decreases; the comprehensive performance of the test steel is the best when the Si content is 0.685 wt. %, with a tensile strength of 726 MPa, a yield ratio of only 0.65, the highest elongation of 30.5%, and the highest strong plastic product of 22,143 MPa.%.

In this paper, the finite element software ProCAST version 14.5 was used to simulate the temperature field, flow field and defect prediction in the filling and solidification process of hypereutectic high-chromium cast iron. The effects of pouring temperature, negative pressure and the amount of suspension agent added during the technological process were explored. The optimum process parameters were presented. It was found that the suspension agent has a certain hindrance to the filling process, but the filling process remains stable. In the solidification stage, 89.4% of the suspension agent melted, resulting in a relative supercooling degree of 50 °C, which had a certain chilling effect and improved the solidification rate.

In situ NbC-reinforced laser cladding Ni45 coatings have the advantages of high bond strengths, low dilution rates, small heat-affected zones and good wear resistance and have broad application prospects in the field of surface strengthening and repair of workpieces such as automotive molds and engine turbines. Previous studies have mostly used pure niobium powder for in situ synthesis to prepare Ni-based NbC coatings with a high production cost. In this paper, NbC was successfully synthesized in situ in Ni45 powder using inexpensive FeNb65 and Cr3C2. The prepared coating has a uniform microstructure and excellent wear resistance, and the reinforced phases are mainly NbC and Cr23C6. Coating 4# with 25 wt.% FeNb65 + Cr3C2 has the highest microhardness of 776.3HV0.2, about 1.45 times that of the Ni45 coating, and its wear resistance is 36.36 min/mg, about 60.6 times that of the Cr12MoV steel base material and about 23.76 times that of the Ni45 coating.

Ni-based composite coatings containing transition metal carbides exhibit high hardness, and the rapid heating and cooling characteristics of laser cladding lead to the formation of cracks in these coatings, significantly limiting their practical industrial applications. In this study, (Ti, V)C/Ni composite coatings were prepared at different preheating temperatures to investigate the effect of preheating on crack formation. The microstructure of the coatings was investigated by XRD, OM, and SEM, and the differences in wear resistance were studied by block-on-ring wear tests. The results show that with increasing preheating temperature, the residual stress in the coatings decreases significantly, the secondary dendrite arm spacing increases, and the number of cracks decreases. No crack defects were observed in the coating preheated at 700∘C, indicating that substrate preheating can effectively suppress crack formation during the laser cladding process. Compared with the coating prepared without preheating, the hardness and wear resistance of the coating prepared by preheating at 700∘C were reduced, which was still 5.6% higher than that of the substrate after quenching, and the wear resistance was 1.76 times higher than that of the substrate. [ABSTRACT FROM AUTHOR]

The effects of different quenching temperatures on the microstructure and properties of 3.3C-20.0Cr-1.0W-0.5B-2.0V-1.8Mo (wt.%) high-chromium cast iron were investigated using an optical microscope, scanning electron microscope, X-ray diffractometer, Rockwell hardness tester, microhardness tester, and wear testing machine. The results show that the microstructure of as-cast multivariate high chromium cast iron mainly consists of eutectic carbides (M7C3), austenite and martensite matrix. In the process of quenching temperature increasing from 950 °C to 1150 °C, the morphology of massive eutectic carbide (M7C3) did not change. Acicular eutectic carbide (M7C3) appeared to aggregate and grow, and was distributed in the form of blocks or rods. Secondary carbides (M23C6) were precipitated in the matrix. The matrix is transformed from austenite to martensite, with a small amount of residual austenite. The hardness and wear resistance firstly increased and then decreased. The hardness of the 1100 °C × 1 h + fog-cooled high-chromium cast iron reaches a peak of 67.0 HRC, and the abrasion resistance increases by 37.0% compared with that of the 950 °C × 1 h + fog-cooled specimen. [ABSTRACT FROM AUTHOR]

The microstructure, hardness, impact toughness and ring block wear properties of a novel bainitic steel were investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), laser confocal microscopy (LCM), X-ray diffraction (XRD), Rockwell hardness tester, impact tester and MM-200 wear tester (Jinan Sida Testing Technology Co., LTD, China). The above steel was austenitized at 900 °C, and was isothermally quenched at 250, 280, 310, 340, 370, 400 and 430 °C respectively. The results showed that the microstructure of the bainitic steel was mainly composed of bainitic ferrite (BF), retained austenite (RA), and martensite/austenite (M/A). A part of the RA underwent a phase transition and transformed into martensite during the wear process, resulting in the increase of the hardness. The wear morphology of bainitic steel was dominated by straight furrows. The wear mechanisms were mainly abrasive wear and oxidative wear. With the increase of the austempering temperature, the microstructure coarsened, the amount of the blocky RA content increased, the hardness of the high silicon bainitic steel increased slightly first and then decreased, the impact toughness improved significantly first and then reduced, and the wear resistance increased first and then decreased. Under the same test conditions, the high silicon bainitic steel after austempering at 340 °C had better combination of hardness and toughness, stable and low friction coefficient, and excellent wear resistance.

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 (1.35 J/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.

Nickel-based coatings obtained by laser melting are broadly applied for surface modification owing to their high bond strength and exceptional wear resistance. Nickel-based laser cladding coatings are also extensively employed in high temperature wear environments. In this paper, the research progress on improving the high temperature wear resistance of laser cladding nickel-based composite coatings was reviewed by introducing a hard ceramic phase, adding solid lubricants and rare earth elements. On this basis, the material system to enhance the high temperature wear resistance of coating was summarized from the perspectives of the type, addition amount, morphology and distribution law of the hard ceramic phase, etc. The synergistic effect of various lubricants on improving the high temperature wear resistance of coating was discussed, and the action mechanism of solid lubricants in the high temperature extreme environment was analyzed. Finally, this paper summarizes the main difficulties involved in increasing the high temperature wear resistance of nickel-based coatings and some problems worthy of attention in the future development.

Hypereutectic High Chromium Cast Iron (HHCCI) is a new type of corrosion-wear-resistant material developed from ordinary high chromium cast iron by increasing the chromium and carbon content and is often used in abrasive environments where wear and corrosion interact. The corrosion wear resistance of the HHCCI is related to the number, size, shape and distribution of carbides and the microstructure of the matrix. This paper reviews the research progress in improving the corrosion wear resistance of HHCCI from various aspects such as primary carbide refinement, heat treatment, deep cooling treatment and alloying, etc. Among the methods of refining primary carbides are modification, semi-solid treatment and current pulse treatment. In addition, we also analyze the potential of Cr, V, Nb, Mo, Mn, W, Ni, Cu, Si, N and other alloying elements to improve the corrosion wear resistance of HHCCI. The mechanism for improving the corrosion wear resistance of HHCCI is also explored in depth and research contents worthy of attention are proposed to further improve the corrosion wear resistance of HHCCI. In the future, the author believes that modification + alloying + heat treatment is the most potential application method to improve the corrosion wear resistance of HHCCI. The corrosion wear resistance of HHCCI can be further improved by refining the primary carbide (such as adding rare earth, Ti and other modified elements) + heat treatment (with cryogenic treatment) to improve the strength + alloying (such as adding low-cost, high-potential alloy elements such as N and Si) to improve the corrosion wear resistance of the matrix.

Based on cold metal transfer (CMT) welding, wire-arc additive manufacturing (WAAM) technology was adopted to manufacture 2Cr13 part. The spatial periodicity of the microstructural evolution and the anti-indentation properties was explored. The results show that the as-deposited part was featured by periodic martensite laths within the block-shaped ferrite matrix in the inner layers, followed by epitaxial ferrite grains containing ultra-fine acicular martensite in the top layer only. A slightly decreased Fe intensity was caused by local elemental segregation during the re-melting process; the homogeneity of Fe and Cr was attributed to similar cooling conditions in the top layer. The martensite size gradually coarsened from the fine grain zone to the coarse grain zone and the shape transformed correspondingly from irregularly short bar-like to orderly long rod-like due to the location-related thermal history. Elongated ferrite grains exhibited a slight fiber texture in the top layer and a random crystallographic orientation in the middle region. The anti-indentation properties evolved periodically due to the periodic microstructural characteristics. The obtained experimental results confirmed higher anti-indentation properties of the as-deposited part following comparison with the as-annealed base metal, while the elastic moduli of samples were not significantly different. Keywords: 2Cr13 thin-wall part, Wire-arc additive manufacturing, Cold metal transfer welding, Periodic structure, Anti-indentation properties

Pure Copper (Cu) is very difficult to prepare using selective laser melting (SLM) technology. This work successfully prepared the pure Cu with high relative density and high strength by the SLM technology using a surface oxidation treatment. The gas-atomized pure Cu powder was used as the feedstock in this work. Before the SLM process, the pure Cu powder was initially handled using the surface oxidation treatment to coat the powder with an extremely thin layer of Cu2O. The SLMed highly dense specimens contain α-Cu and nano-Cu2O phases. A relationship between the processing parameters (laser power (LP), scanning speed (SS), and hatch space (HS)) and density of Cu alloy in SLM was also investigated. The microstructure of SLMed Cu consists of fine grains with grain sizes ranging from 0.5 to ~30 μm. Tensile testing and detailed microstructural characterization were performed on specimens in the as-SLMed and pure copper state specimens. The mechanical property experiments showed that the specimens prepared by SLM technology containing nano-oxide phases had higher yield strength and tensile strength than that of other SLM-built pure copper. However, the elongation was remarkably decreased compared to other SLM-built pure copper, due to the fine grains and the nano-oxides.

Wire-arc additive manufacturing (WAAM) has been considered as one of the potential additive-manufacturing technologies to fabricate large components. However, its industrial application is still limited by the existence of stress and distortion. During the process of WAAM, the scanning pattern has an important influence on the temperature field, distortion and final quality of the part. Four kinds of deposition patterns, including sequence, symmetry, in–out and out–in, were designed to deposit H13 steel in this study. An in situ measurement system was set up to record the temperature history and the progress of accumulated distortion of the parts during deposition. An S value was proposed to evaluate the distortion of the substrate. It was shown that the distortion of the part deposited by sequence was significantly larger than those of other parts. The distortion deposited by the out–in pattern decreased by 68.6% compared with sequence. The inherent strain method and strain parameter were introduced to expose the mechanism of distortion reduction caused by pattern variation.

This work investigated the microstructure and mechanical property of high-boron multi-component alloy with Fe, B, C, Cr, Mo, Al, Si, V, Mn and different contents of Ti. The results indicate that the as-cast metallurgical microstructure of high-boron multi-component alloys consist of ferrite, pearlite and borocarbide. In an un-modified alloy, continuous reticular structure of borocarbide is observed. After titanium addition, the structure of borocarbide changes into a fine and isolated morphology. TiC is the existence form of titanium in the alloy, which acts as the heterogeneous nuclei for eutectic borocarbide. Moreover, impact toughness of the alloy is remarkably improved by titanium modification.

The study reported was intended to improve the leaching rate of boron-bearing tailings, using a method of sodium roasting that uses boron-bearing tailings as the raw material and Na2CO3 as the sodium agent. The effects of the roasting temperature and Na2CO3 amount on the leaching rate of boron-bearing tailings are mainly evaluated. The morphology and composition of the samples after sodium roasting are analysed by scanning electron microscopy and X-ray diffraction. The results show that sodium roasting can significantly improve the leaching rate of boron-bearing tailings. Under the optimal conditions where roasting temperature is 950°C, Na2CO3 amount is five times the theoretical amount and roasting time is 2 h, the leaching rate of boron-bearing tailings is up to 86.78%. Based on the analysis of the characterization results and the mechanism analysis of the sodium roasting process, the main reason for the increase of leaching rate is the reaction between Na2O produced by the decomposition of Na2CO3 and the boron in boron-bearing tailings resulting in soluble sodium borate. The results provide a scientific basis for the efficient comprehensive use of boron-bearing tailings.