Al_(0.2) CrFeNiCo and Al_(0.2) CrFeNiCu high entropy alloys were deposited with high velocity oxygen fuel(HVOF)on 316 L substrate.Later,a laser re-melting(LR)process was applied to enhancing the coating microstructure.LR process effects on dry sliding wear and oxidation behaviors were investigated.The mixture of powders with free elements led to the formation of inner oxides in HVOF coatings.The oxide and porosity were eliminated using LR.After LR,FCC was the dominant phase in both alloys,while BCC,sigma and Cr2 O3 phases were observed in Al_(0.2) CrFeNiCo alloy.The hardnesses of the Al_(0.2) CrFeNiCo and Al_(0.2) CrFeNiCu coatings after HVOF were HV 591 and HV 361,respectively.After LR,the hardnesses decreased to HV 259 and HV 270,respectively.Although HVOF coatings were most affected by increased load,they showed the highest wear resistance compared to other samples.The lowest wear resistance could be seen in the substrate.After the oxidation tests,HVOF coating layer was completely oxidized and also,the coating layer was delaminated from the substrate after 50 h oxidation due to its porous structure.LR coatings exhibited better oxidation performance.Al_(0.2) CrFeNiCo was dominantly composed of Cr2 O3,exhibiting a slower-growing tendency at the end of the oxidation tests,while Al_(0.2) CrFeNiCu was composed of spinel phases.
As-cast samples of the Al-3wt.%Ni-lwt.%Bi alloy resulting from the horizontal directional solidification process were subjected to the micro-abrasive wear test.The effects of the solidification thermal and microstructural parameters,such as the growth and cooling rates and the cellular and primary dendritic spacings(VL and TR;λ1 and λc;respectively),were evaluated in the wear resistance of the investigated alloy.The tribological parameters analyzed were the wear volume and rate(Vw and Rw).The solidification experiments and the wear tests were carried out by means of a water-cooled horizontal directional solidification device and a rotary-fixed ball wear machine,respectively.The results show lower Vw and Rw values correspond to finer microstructures and the Vw dependence on λ1 is characterized by an experimental mathematical equation.A better distribution of Bi soft droplets and Al3Ni hard intermetallic particles is observed within the finer interdendritic region and,in consequence,the better wear resistance is achieved in as-cast samples with dendritic morphology rather than cellular morphology.A transition of wear mechanism from adhesive to abrasive is observed.
