Effects of W Alloying on the Lattice Distortion and Wear Behavior of Laser Cladding AlCoCrFeNiWx High-Entropy Alloy Coatings

Friction and wear properties of hot working die steel at above 800 °C are of particular interest for high temperature applications. Here, novel AlCoCrFeNiWx high-entropy alloy (HEA) coatings have been fabricated on the surface of hot working die steel by laser cladding. The effects of the as-prepared AlCoCrFeNiWx HEA coatings on the microstructure and high temperature friction and wear behavior of hot working die steel are investigated through scanning electron microscopy (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD), and X-ray absorption fine structure (XAFS). Having benefited from the formation of W-rich intermetallic compounds after the addition of W elements, the high temperature wear resistance of the coatings is obviously improved, and friction coefficient shows a large fluctuation. The microstructural characteristics of the AlCoCrFeNiWx HEA coatings after the high temperature wear resistance test shows a highly favorable impact on microstructure stability and wear resistance, due to its the strong lattice distortion effect of W element on BCC solid solutions and the second phase strengthening of the W-rich intermetallic compounds. These findings may provide a method to design the high temperature wear resistant coatings.

High-Temperature Oxidation Performance of 4Cr4Mo2NiMnSiV Hot Die Steel

A new type of hot working die steel was designed by using JMatPro, and high-temperature oxidation tests were carried out in the ambient atmosphere at 600 ℃ and 700 ℃. The heat treatment process and oxidation mechanism of the designed 4Cr4Mo2NiMnSiV steel were studied in detail. XRD, SEM and EDS were used to analyze the crystallographic phases, surface and cross-section morphologies of the oxide films. The results show that the main phases in the 4Cr4Mo2NiMnSiV steel were γ and α + δ. During the high-temperature oxidation, oxidation of the Fe outer layer and Cr inner layer occurred. After oxidation at 600℃, the surface oxidation layer comprised a monolayer with an uneven morphology. The surface oxide film had two layers after oxidation at 700℃. The outer oxide layer mainly contained Fe2O3 and Fe3O4, while the inner oxide layer mainly contained Cr2O3. The microstructure was relatively regular and had a significant effect on the protection of the metallic matrix. When oxidized, the 4Cr4Mo2NiMnSiV alloy steel easily formed protective layers, such as Cr2O3 and SiO2, so that the test steel had excellent oxidation resistance at high temperatures.

Effect of Laser Cladding Stellite 6-Cr3C2-WS2 Self-Lubricating Composite Coating on Wear Resistance and Microstructure of H13

In order to prevent the wear failure of the hot-working die, the composite coatings of Stellite 6-Cr3C2-WS2 was fabricated on H13 hot-working die steel by laser cladding. The composite coating was prepared through the in-situ generation technology, that can give H13 the ability of self-lubricating at the working temperature (about 200 °C). The effect of the various WS2 percentages on the properties of the coating was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), microhardness test, friction and wear test. In addition, the phase constitutions, microstructures and wear properties were also investigated systematically. The obtained hardness of the cladding coating is approximately 2.5 times higher than the substrate because of the constituents of γ-(Fe, Co)/Cr7C3 eutectic colony, (Cr, W)C carbide and dendritic crystals in the coating. Furthermore, the friction coefficient decreases to 70% of the substrate due to the CrS self-lubricating phase. The analyses results suggest that an 85% Stellite 6-10% Cr3C2-5% WS2 composite coating has excellent material properties.

Improving the Corrosion Resistance of Hot-Working Mold Steel against Al Alloy Melt by Coating

In order to reduce the adhesion tendency of aluminum melt on the die casting mold and extend the service life of the die, multi-arc ion plating technique was used to deposit Ti/TiN/CrN multi-layer coating on the surface of 8418 hot-working mold steel. Corrosion resistance of the steel and the Ti/TiN/CrN coating against Al alloy melt was studied. X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy were used to study the microstructure, phase constituent and phase composition of the materials. Uniform Ti/TiN/CrN coatings with good bonding interfaces and a total thickness of about 2 μm were obtained. Results showed that Ti/TiN/CrN coating can improve the corrosion resistance of the 8418 hot-working die steel significantly against the aluminum alloy melt.