Microstructure and Properties of AlCoCrFeNiTi High-Entropy Alloy Coatings Prepared by Laser Cladding

21-4N(5Cr21Mn9Ni4N)is extensively employed in the production of engine valves,operating under severe conditions.Apart from withstanding high-temperature gas corrosion,it must also endure the impact of cylinder explosion pressure.The predominant failure mode of 21-4N valves is abrasive wear.Surface coatings serve as an effective approach to prevent such failures.In this investigation,Laser cladding technology was utilized to fabricate AlCoCrFeNiTi high entropy alloy coatings onto the surfaces of 21-4N valves.According to the findings,the cladding zone has a normal dendritic microstructure,a good substrate-to-cladding layer interaction,and no obvious flaws.In terms of hardness,the cladding demonstrates an average hardness of 620 HV.The hardness has increased by 140%compared to the substrate.The average hardness of the cladding remains at approximately 520 HV even at elevated temperatures.Regarding frictional wear performance,between 400℃and 800℃,the cladding layer exhibits an average friction coefficient of 0.4,with the primary wear mechanisms being abrasive wear,adhesive wear,and a minor degree of plastic deformation.

Ligand effect in surface atomic sites of group VI B transition metals on ultrathin Pt nanowires for enhanced oxygen reduction

Increasing the utilization efficiency of platinum is critical for advancing proton exchange-membrane fuel cells(PEMFCs).Despite extensive research on catalysts for the cathodic oxygen reduction reaction(ORR),developing highly active and durable Pt-based catalysts that can suppress surface dealloying in corrosive acid conditions remains challenging.Herein,we report a facile synthesis of bimetallic ultrathin PtM(M=Mo,W,and Cr)nanowires(NWs)composed of group VI B transition metal atomic sites anchored on the surface.These NWs possess uniform sizes and well-controlled atomic arrangements.Compared to PtW and PtCr catalysts,the PtMo0.05 NWs exhibit the highest half-wave potential of 0.935 V and a mass activity of 1.43 A·mgPt^(−1).Remarkably,they demonstrate a remarkable 23.8-fold enhancement in mass activity compared to commercial Pt/C for ORR,surpassing previously reported Pt-based catalysts.Additionally,the PtMo NWs cathode in membrane electrode assembly tests achieves a remarkable peak power density of 1.443 W·cm^(−2)(H_(2)-O_(2)conditions at 80℃),which is 1.09 times that of commercial Pt/C.The ligand effect in the bimetallic surface not only facilitates strong coupling between Mo(4d)and Pt(5d)atomic orbitals to hinder atom leaching but also modulates the d-states of active site,significantly optimizing the adsorption of key oxygen(*O and*OH)species and accelerating the rate-determining step in ORR pathways.

In-situ study for the elastic structure evolutions of threedimensional Ir-O framework during the oxygen evolution reaction in acid

Understanding the dynamic structural and chemical evolutions at the catalyst-electrolyte interfaces is crucial for the development of active and stable electrocatalysts.In this work,β-Li_(2)IrO_(3)is employed as a model catalyst for the oxygen evolution reaction(OER).Its elastic three-dimensional Ir-O framework enables us to investigate the Li^(+)cation dissolution-induced structure evolutions and the formation mechanism of amorphous IrO_(x)species.Electrochemical measurements by rotating ring disk electrode(RRDE)reveal that up to 60%of the measured OER current can be ascribed to catalyst degradation.A series of in-situ X-ray diffraction spectroscopy(XRD),X-ray absorption spectroscopy(XAS),and Raman spectroscopy are conducted.Structure vibration is observed with oxidation states of Ir being reduced abnormally during OER at high potentials.It’s hypothesized that the reversible proton intercalations are responsible for the Ir turn-over mechanism.Results of this work demonstrate a stable and elastic iridate structure and reveal the initial catalyst degradation behaviors during OER in acid media.