Study On Microstructure And Properties Of AlCoCrFeNiZrTiV High-entropy Alloys And Preparation Of Coating

The unique design concept of high-entropy alloy endows it with marvellous comprehensive mechanical properties,special physical and chemical properties.High-entropy alloys have broad application prospects in the field of structural and functional materials.However,the traditional casting method for preparing bulk high-entropy alloys are too expensive,which limits its application in engineering.It is one of the effective ways to break through the limitation of high-entropy alloys industrial application to prepare high-entropy alloy coatings by laser cladding technology.45#steel and H13 steel are the common steel materials in the industry.In practical application,they often fail due to the surface defects.In order to improve they surface properties and service life,AlCoCrFeNiZrTiV high-entropy alloys were studied in this paper.The effects of alloying elements and cooling rate on the microstructures and hardness of the alloys were studied by arc melting and suction casting using copper mold.A high hardness eutectic high-entropy alloy composition was designed.The single-pass,single-layer and multi-layer laser cladding experiments were carried out on the 45#steel and H13 steel substrates with the eutectic alloy powder as the cladding material.The microstructures and mechanical properties of the high-entropy alloy cladding layer were studied.The research results show that:Two phases,BCC solid solution and Laves phase,are identified in the AlCoCrFeNiZrTiV system high-entropy alloy ingots.The volume fraction of eutectic microstructure increases,the volume fraction of primary Laves phase decreases,and the hardness value decreases gradually by increasing A1 or V content.Laves phase is mainly enriched in Zr element,and BCC phase is mainly enriched in V elements.Based on the EDS results of the eutectic structures in this alloy system.The eutectic high-entropy alloy,Al1.5CoCrFeNiZr0.7TiV1.5 ingot,which with fine fully lamellar microstructure was successfully prepared.Its microhardness can reach 702 HV0.05.AlCoCrFeNiZrTiV high-entropy alloy occurred pitting corrosion in BCC phase firstly and then Laves phase is dissolved in the corrosion of aqua regia.The phase formation criteria,?Hf.are suitable for this alloy system.The microstructures are refined and the hardness increases in the condition of rapid solidification,but the brittleness increase for the alloys,which have more primary Laves phase.The microstructure of Al1.5CoCrFeNiZr0.7TiV1.5 high-entropy alloy cladding layer are eutectic and equiaxed dendrite composed of Laves phase and BCC phase under optimized conditions.The bonding zone are cell crystal and columnar dendrite growing perpendicular to the interface.The cladding layers form a good metallurgical bond with the substrates.The average hardness of the cladding layer on 45#steel is about 3.8 times that of the substrate;the average hardness of the cladding layer on H13 steel is about 1.9 times that of the substrate.The mass loss of H13 steel substrate and 45#steel substrate is 5 times and 7 times that of the high-entropy alloy coating in the same time,respectively.The high-entropy alloy coatings significantly improve the surface properties of 45#steel substrate and H13 steel substrate.The combination of fine-grain strengthening,solid solution strengthening,boundary strengthening and second-phase strengthening are the main reasons for high hardness and high wear resistance of Al1.5CoCrFeNiZr0.7TiV 1.5 high-entropy alloy cladding layer.