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Abstract: High-entropy alloys have been found to have novel microstructures and unique properties. The main method of manufacturing is vacuum arc remelting. As in situ cladding laser cladding has capability of achieving a controllable dilution ratio, fabricating highentropy alloy by laser cladding is of great significance and potential for extensive use. In this study, a novel AlxFeCoNiCuCr high-entropy alloy system was manufactured as the thin layer of the substrate by laser cladding; also high temperature hardness, abrasion performance, corrosion nature of the AlxFeCoNiCuCr high-entropy alloy were tested under the different ratio of aluminum. This study shows higher aluminum clad exhibit higher hardness, better abrasion resistance and corrosion resistance. [Copyright &y& Elsevier]

Abstract: WC/Ni coating was formed by laser cladding of a W/C/Ni powder blend. The formed WC crystals have rectangular or quadrangle cross-section shapes with size of 2–30μm. Step, twist and cross growth morphologies of WC formation were observed. The coating contains WC, CW3, WNi, FeW3C, Fe6W6C, W3O, W, C, and (Fe,Ni) phases. [Copyright &y& Elsevier]

Abstract: To reduce the mixed fuel induced excessive wear of the cast iron engine cylinder liners, research on laser alloying of NiCr alloy with powder feeding was performed to locally change both the composition and the microstructure of the liner. The research indicated that laser alloying of 75Ni25Cr on grey cast iron liner demonstrates sound alloying layers free of cracks and porosities. The microstructure of the alloyed layer is composed of pre-eutectic austenite and ledeburite. The alloying element Ni is mainly located in the austenite, while Cr is mainly in cementite. The average hardness is HV0.2500. The corrosion resistance of the alloyed layers in diluted H2SO4 solution and NaOH solution is dramatically improved compared to the grey cast iron. The relative wear resistance of the laser-alloyed 75Ni25Cr layer is 4.34 times of that of the grey cast iron. The improvements on the corrosion and wear resistance of the cast iron are attributed to the composition and microstructure change by laser alloying of 75Ni25Cr. Laser alloying can be a good solution to improve wear and corrosion resistance of the grey iron liners in mixed fuel environment. [Copyright &y& Elsevier]

Abstract: In order to improve the wear resistance of an aluminum alloy, an in situ synthesized TiB2 particulate-reinforced metal matrix composite coating was formed on a 2024 aluminum alloy by laser cladding with a powder mixture of Fe-coated boron, Ti and Al was successfully achieved using a 3-kW CW CO2 laser. The chemical composition, microstructure and phase structure of the composite clad coating were analyzed by energy dispersive X-ray spectroscopy (EDX), SEM, TEM and XRD. The nanohardness and the elastic modulus of the phases of the coating have been examined. The dry sliding wear behaviour of the coating was investigated using a pin-on-ring machine under four loads, namely 8.9, 17.8, 26.7, and 35.6N. It has been found that the wear characteristics of cladding were completely dependent on the content and morphology of the TiB2 particulate and intermetallic in the microstructure and the applied load. At the lowest load (8.9N), with increasing content of TiB2 particulate and intermetallic, the wear weight loss of the laser cladding was decreased. At higher loads (17.8, 26.7, and 35.5N), the 2024 Al alloy exhibited superior wear resistance to the particle-reinforced metal matrix composite cladding. [Copyright &y& Elsevier]

The high temperature wear behavior of Ni–W–Co/SiC composite brush plated coatings deposited on a hot work die steel has been investigated using a plate-on-ring test rig. The microstructure and wear characteristics of coating have been analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that typical microstructure of Ni–W–Co/SiC composite coating consists of Ni-based solid solution and SiC particles. The TEM observation of Ni–W–Co/SiC composite coating has revealed the fine SiC particles of nano-size in the brush plated coatings and the matrix of Ni–W–Co plated coating is composed of a mixed crystalline and amorphous structure. The worn surface morphology of the plated coating is observed by SEM and laser profile analysis. In the temperature range 400–600 °C, wear rate and average friction coefficient of the Ni–W–Co/SiC brush plated composite coatings are lower than that of the 3Cr2W8V (ASTM H21) hot work die steel. Abrasive and adhesive wears are the major wear mechanisms of brush plated composite coating at high temperature. [Copyright &y& Elsevier]

The microstructural evolution in high power CO2 laser cladding of steel with Stellite 6+WC powder mixture was investigated, among which the WC vol.% was, respectively, 0, 9, 18, 27, 36, 45, 54, 72 and 100% by dual powder feeding Stellite 6 and WC powders with different feeding rates. Two significantly different solidification characteristics were found in the microstructural evolution in laser clads of Stellite 6+WC. The first one was characterized by the dendrites and interdendritic eutectics from 0 to 36% WC, in which the added WC was completely melted into the melt pool and the re-solidified structure contained α-Co,σ-CoCr and various carbides such as M7C3. The second one was characterized by various faceted dendrites in block, flower, butterfly, star shapes and the matrix from 45 to 100% WC, in which most of the WC was melted, the microstructure contained re-solidified WC, Co and various Co–W–C/Fe–W–C complex carbides. Maximum 26 and 64 wt.% W were, respectively, dissolved into the matrix and the faceted dendrites. When laser cladding WC powder with severe dilution from the substrate, a microstructure with different composition appeared within the faceted dendrites with interior approximately 90 wt.% of W and exterior approximately 70 wt.% of W. Such a structure was probably the frozen result of the peritectic reaction during laser cladding rapid solidification. [Copyright &y& Elsevier]

[Display omitted] • Reducing particle size intensifies heat transfer, sintering, and densification. • High-density MgO particles of 0–6 mm in primary sizes can be produced at 1300–1600 °C for less than 10 min. • The MgO grain growth is controllable by optimizing sintering temperature and time. • Processing small particles is effective in reducing energy consumption and carbon emission. Magnesia densification is essential for Mg-based refractories and materials to attain better thermal performance and longer service life. Few industrial-scale processes can produce magnesia with the required bulk density of above 3.40 g/cm3 (or relative density of over 95 %) from natural magnesites. The inability to achieve the desired densification is related to the low heat transfer between gas and solids inherent in large-sized greenbodies typically sintered in industrial shaft kilns. This study proposes sintering particles of 0–6 mm in primary sizes corresponding to those employed in most refractory end-products of sintered magnesia. Microstructures of the sintered particles are analyzed, and the underlying sintering mechanisms are discussed. The sintering of small particles can achieve over 95 % of densification at 1300–1600 °C for less than 10 min. This study provides an alternative approach to producing high-density magnesia with the potential for substantial reductions in energy consumption and carbon emissions. [ABSTRACT FROM AUTHOR]

Abstract: Fe-based composite coatings reinforced by in situ synthesized particles have been produced by laser melting a precursor powder mixture of Fe-based alloy powder, Ti, Zr and C. The microstructure of the coating is typically hypo-eutectic, which consists of martensite, residual austenite, ledeburite and dispersed in situ carbide particles. The experimental results show that laser melting a precursor containing both Zr and Ti is favorable to form particles in the maximum volume fraction compared with those containing either of them. The particles are investigated to be multiple carbides. [Copyright &y& Elsevier]

Various weight ratios of TiC particulate nickel-based composite coatings were produced on carbon steel substrates by laser cladding. The experimental results showed that the coating was uniform, continuous and free of cracks when a CaF2 flux was used. Excellent bonding between the coating and the medium carbon steel substrate was ensured by the strong metallurgical interface. The microstructures of the coating were mainly composed of γ-Ni dendrites, M23C6, a small amount of CrB, and dispersed TiC particles. The morphologies of TiC particles changed from the globular, cluster to flower-like shape. The volume fraction of TiC particles and the microhardness gradually increased from the bottom to the top of the coating, and the volume fraction of TiC particles increased with increasing of volume fraction of Ti and C. The maximum microhardness of the coatings with 10, 15 and 20 wt.% (Ti+C) in the preplaced alloy powder was approximately HV0.2750, HV0.2850 and HV0.2920, respectively, which was much larger than that of the steel substrate, HV0.2240. [Copyright &y& Elsevier]

In order to improve resistance to high temperature and wear resistance of pure aluminum, laser-cladding experiments were conducted on a 3 kW continuous wave CO2 laser to produce in situ synthesized molybdenum silicide (MoSi2)/SiC composite coatings on pure aluminum. The laser consolidified microstructure and phase evolution were investigated using scanning electron micrograph and X-ray diffraction (XRD). The in situ formation of MoSi2/SiC was carried out by adding a mixture of Mo, Si and C precursor powder layer followed by melting the layer and substrate under a laser beam. The experimental results showed that these compounds, MoSi2 and SiC, can be formed from three distinct powders of Mo, Si and C on Al alloy, and, provided that supplied energy is sufficient to start the reaction between the initial products, a good metallurgical bond between coating and the substrate can be achieved. The microstructures of the coating were composed of MoSi2, Mo5Si3 and SiC phases. The microhardness of coating was about 12 times that of the aluminum substrate, the maximum value reached HV0.2 1200. [Copyright &y& Elsevier]

A series of laser surface remelting experiments of Al-1.1, 3.2 and 5.6 wt% Mn alloys has been conducted using a 5 kW CW CO[sub 2] laser, and the microstructures of samples have also been investigated. The experimental results show that no apparent eutectic growth appears in the whole growth rate range for Al-3.2 wt% Mn alloy under laser rapid solidification condition, and the microstructure grows in the form of α(Al) cell/dendrite. With the increase of growth rate, the microstructures of Al-5.6wt% Mn alloy change from Al[sub 6]Mn dendrite to α(Al) + Al[sub 6]Mn eutectic, α(Al) cellular/dendrite and segregation-free solid solution. The critical rates of Al-1.1, 3.2 and 5.6 wt% Mn alloys to attain absolute stability are 44.1, 134.6 and 230.1 mm/s respectively, and a reasonable agreement has been found between the experimental results and those calculated according to Mullins-Sekerka's theory. [ABSTRACT FROM AUTHOR]

Detailed experiments were carried out to investigate the effects of crystallography on the microstructure evolution during the solidification of the laser molten pool with a DD2 single crystal specimen using a 5 kW CO2 laser. The experimental results showed that crystallographic effects can influence dendrite growth by favoring growth along a preferred crystallographic direction, and crystallographic effects are greater than that of heat flux during dendrite growth. On the same crystal face, the microstructures in the molten pool are very different when laser beam scanning along different crystal orientation. The same conclusions can be obtained by laser beam scanning along a fixed direction on different crystallographic surface. A growth velocity analysis was carried out during laser surface remelting processing based on a minimum velocity or minimum undercooling criterion and the relationships between dendrite growth velocities in the three <100> directions, moving velocities of the solid/liquid interface and laser scanning velocities for the different crystallographic orientations were also set up. According to this analysis, the reconstructed and predicted molten pools concurred with the experimental results very well. [ABSTRACT FROM AUTHOR]

One methodology of binderless joint by swelling of dowels with very low moisture content to obtain pre-stress for fast-growing timber was proposed in this paper. The results showed that performance of binderless joint after 48 h conditioning was close to traditional glued-joint, that is 31.5 N·m for ultimate bending moment capacity and 1743.4 N for maximum withdrawing force of two-pin joint. Clear densification of intersection between dowels and poplar beams was observed from micro-structure analysis. The theoretical model to predict the maximum withdrawal force of pre-stressed joint was setup, which is in coincidence with test results. [ABSTRACT FROM AUTHOR]

Abstract: Hydrophobic Cu surfaces with tunable regular microstructure and random nanostructures were fabricated by nanosecond pulsed laser texturing and chemical etching. The regular micro-scale roughness can be tuned from 5μm to 30μm Rz by nanosecond laser texturing while the ligament width and spacing of the random nano porosity about 10–50nm can be realized by selective chemical etching. Wettability tests demonstrate that the Cu surface with this micro/nanostructural hierarchy, analogous to that of lotus leaves found in nature, is superhydrophobic with a water contact angle around 153°. The random nanostructure by selective etching plays an important role for hydrophobicity in addition to the regular microstructure by nanosecond laser texturing. [Copyright &y& Elsevier]

Abstract: The aluminum matrix composite (AMC) coating reinforced with TiB was prepared utilizing in situ synthesized technique by laser cladding. Microstructural characterization and dry sliding wear behavior of in situ TiB/Al metal matrix composite were studied by SEM, XRD, TEM and Pin-on-disc friction and wear tester. The phase structure of the composite coating consists of α-Al, TiB, Al3Ti and Al3Fe. It has been found that the shape of in situ synthesized TiB is mainly taken on micro-magnitude lump and nano-magnitude whisker. Owing to B27 structure of TiB, the TiB has an anisotropy axis of growth, which results in the TiB strip and whisker preferring grown along [010] direction. It is worth to notice that the novel microstructure inside of TiB is particle and strip Al5Fe2 phase and definite crystallographic relationship between the Al5Fe2 phase and TiB has been determined by selected area diffraction pattern. The wear tests results show that the composite coatings can only improve wear resistance at the lower applied load (below 26.7N), but at higher applied load (26.7–35.6N) the wear resistance behavior of the coating is worsened due to the fracture and pullout of reinforcement phase. [Copyright &y& Elsevier]