| The bipolar plate is one of the key assemblies of the proton exchange membrane fuel cell.Stainless steels are considered as one of the promising candidates because they permit properties such as high strength,ease of machining and shaping into thin sheets,low gas permeability and low cost.Nevertheless,interfacial contact resistance and corrosion resistance are two major drawbacks that prevent stainless steel from commercial application as bipolar plate material.The high entropy alloy is a new type of alloy system developed in the last few years,which shows great potential in the aspect of corrosion resistance.Based on the simple microstructure,excellent corrosion resistance performance and controllable property of the high entropy alloy and its film,combining with the good conductivity of transition metal nitride,CrNbTiVZr high entropy alloy in this paper was prepared by vacuum arc melting.With the alloy being the sputtering target,a high-entropy alloy film and its nitride film were prepared on the surface of 304SS by magnetron sputtering.The structural evolution,microstructure,chemical composition,corrosion resistant and conducting behavior in the simulated PEMFC environment of the alloy and the film were investigated.The influence of the microstructure and composition of the alloy and the film on the corrosion-resistant conductivity could be analyzed.The research results are as follows:?1?The as-cast and annealed CrNbTiVZr high entropy alloys were BCC phase+Laves phase structure,in which the Laves phase accounted for 60%of the volume fraction of the annealed alloy.Ti,Nb elements enriched and Cr element lacked in the BCC phase;Cr element enriched and Ti element lacked in the Laves phase.The homogenization annealing leaded to the further separation of the two phases and the composition of the Laves phase in the annealed alloy basically satisfied?Cr,Nb,V?2?Ti,Zr?.The results of electrochemical measurement showed that both as-cast and annealed alloys exhibited good corrosion resistance in the simulated PEMFC cathode environment.The corrosion current density reduced by an order of magnitude compared with 304SS,and the corrosion resistance of both as-cast and annealed alloys were comparable to that of 304SS in anode environment.?2?The CrNbTiVZr high entropy alloy films prepared at different power and substrate temperature were all composed of amorphous phase and dispersed Laves phase.After adding nitrogen for deposition,the film structure gradually changed to crystal with the nitrogen flow ratio increased.While the nitrogen flow ratio was 20%,the film showed obvious FCC structure and the peak intensity of Laves phase decreased greatly,which the crystalline morphology of the film was typical columnar structure.The content of all the elements were nearly constant in the alloy film prepared under different sputtering power and substrate temperature,and after adding nitrogen the content of each metal element reduced and the nitrogen content was gradually increscent.?3?The electrochemical tests in the simulated PEMFC environment indicated that the alloy film prepared at 240W and 300?substrate temperature possessed good corrosion resistance.The nitride film prepared at 20%nitrogen flow ratio had the best corrosion resistance and conductivity.The corrosion current densities in the cathode and anode environment were 1.50?A/cm2 and 4.78×10-5A/cm2,respectively,being one order of magnitude lower than 304SS substrate.The corrosion of the film was dominated by pitting.?4?The contact resistance measurement before and after potentiostatic polarization showed that the contact resistance of all the alloy films were higher than that of 304SS substrate.The contact resistance of nitride film deposited with nitrogen decreased significantly.The contact resistance of nitride film prepared under 20%nitrogen flow ratio were 29.8m??cm2 and 22.5m??cm2 after cathodic and anodic potentiostatic polarization,respectively,reducing nearly 1/3 and 1/4 compared with 304SS substrate?97.1m??cm2 and 86.7m??cm2?. |
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