Microstructure And Properties Of Selective Laser Melting （AlCoCrFeNi）_1-x/（CoCrNi）_x Composites

Corrosion and wear are the main factors affecting the service life of key mechanical parts.Therefore,it is of great significance to study new wear-resistant and corrosion-resistant materials.As emerging materials,high-entropy alloys（HEA）and medium-entropy alloys（MEA）have become research hotspots of wear-resistant and corrosion-resistant materials,which is possessed of special microstructure and excellent propertie.In this paper,（AlCoCrFeNi）_1-x/（Co Cr Ni）_x composite samples（x=0,10,20,30,50,80,90,100wt.%）were prepared by SLM technology.The effect of different contents of Co Cr Ni MEA on the microstructure,hardness,wear resistance and corrosion resistance of（AlCoCrFeNi）_1-x/（Co Cr Ni）_x composites were studied by means of X-ray diffraction,scanning electron microscopy,energy spectrum analysis,electron backscatter diffraction,hardness tester,friction and wear tester,electrochemical workstation and X-ray photoelectron spectroscopy.The effect of different annealing temperatures（600°C,800°C,1000°C）on the microstructure,hardness,wear resistance and corrosion resistance of（AlCoCrFeNi）_80wt.%/（Co Cr Ni）_20wt.%were further analyzed.The main results are as follows:（1）AlCoCrFeNi HEA（x=0wt.%）is composed of BCC phase and a small amount of B2phase.Adding 10wt.%and 20wt.%Co Cr Ni MEA,the phase composition of the composite does not change.When 30wt.%Co Cr Ni MEA is added,the FCC phase begin to form.With the further addition of Co Cr Ni MEA,the FCC phase increases.When 80wt.%Co Cr Ni MEA is added,the composite consists of a single FCC phase.With the increase of Co Cr Ni MEA content,the grain size of the composite decreases first and then increases.When the content of Co Cr Ni MEA is 20wt.%,the grain size of the material is the smallest,which is closely related to the precipitation of hardσphase nanoparticles to inhibit grain boundary movement.（2）With the increase of Co Cr Ni content,the hardness of the composites increases first and then decreases.When the content of Co Cr Ni MEA is 20wt.%,the hardness is the highest,which is 12.9%higher than that of AlCoCrFeNi HEA.The increase of hardness is the result of the combination of fine grain strengthening,Orowan strengthening and mismatch strengthening produced by the precipitation of nanoparticles.With the increase of Co Cr Ni MEA,the surface roughness of the composite decreases first and then increases,the wear weight loss decreases first and then increases,and the wear resistance increases first and then decreases.When the content of Co Cr Ni MEA is 20wt.%,the wear resistance is the best.The change of wear resistance is due to the change of the hardness of the composite and the chemical composition in the oxide layer,which leads to the increase and then decrease of its ability to resist damage,and the surface roughness decreases first and then increases.（3）Compared with AlCoCrFeNi HEA,the corrosion resistance of the composites is significantly improved after adding Co Cr Ni MEA.With the addition of Co Cr Ni MEA,the phase composition of the composites changed,the B2 phase（easily corroded phase）decreases or even disappears,and the FCC phase gradually increases.The surface oxide film is optimized,the loose and porous Al₂O₃ is reduced,the dense and stable Cr₂O₃ is gradually increased,the corrosion resistance is continuously improved,and the corrosion resistance of Co Cr Ni MEA（x=100wt.%）is the best.（4）After annealing at 600°C,the phase composition of the composites does not change,and the grains is more uniform and fine than before annealing.After annealing at 800°C and1000°C,the FCC phase appears and the grains are coarser.The higher the annealing temperature,the heavier the FCC and the larger the grain size.With the increase of annealing temperature,the hardness and wear resistance of the composites increase first and then decrease.Due to the fine grain strengthening effect,the hardness of the sample annealed at 600°C is the highest and the wear resistance is the best.Due to the fine grain strengthening effect,the hardness and wear resistance of the sample annealed at 600°C were the highest.Compared with the sample before annealing,the hardness increased by 26.9%and the wear weight loss decreased by 32%.Annealing treatment promoted the enrichment of Cr₂O₃ in the passivation film and improved the corrosion resistance of the composites.The corrosion resistance of the samples annealed at 1000°C is the best.