Study On Corrosion Resistance Of High Entropy With High Melting Point In Molten Salt

High-entropy alloy MoNbZrTiHf was prepared by vacuum arc melting,The static corrosion rate of high entropy alloy in cryolite molten salt was mensurated by salt immersed method.The microstructure,morphology,composition and thus corrosion behavior of MoNiZrTiHf high-entropy alloys in cryolite molten salt at 960℃ was studied by scanning electron microscopy(SEM)coupled with electron diffraction spectrometry(EDS)and X-ray diffractometry(XRD).The effect of molecular ratio of molten salt,corrosion time and corrosion temperature on the corrosion resistance of MoNbZrTiHf high entropy alloy were disscussed.The results show that:MoNbZrTiHf high entropy alloy is of single-phase structure,the structure and composition of matrix alloy maintain after corrosion,the composition of corrosion layer and corrosion products structure vary from molecular ratio of molten salt,corrosion time and corrosion temperature.MoNbZrTiHf high-entropy alloy shows the best corrosion resistance in the cryolite melt salt with a molecular ratio of 1.8 and the worst corrosion resistance in the cryolite melt salt with a molecular ratio of 2.2.Under the same conditions of temperature and time,the corrosion of the alloy in the molten salt with molecular ratio of 1.8 with the lowest corrosion rate,the smallest thickness of the corrosion layer,and the least cracks and eroding holes in the corrision layer.F and O elements exist in the entire corrosion layer of MoNbZrTilHf high entropy alloy,O element mainly exists in the corrosion surface layer and the interface layer,and the F element exists in the base layer.The corrosion mechanism of MoNbZrTilHf high entropy alloy in cryolite molten salt is the common effect of fluorination and oxidation,fluorinion penetration into the alloy internal,which lead to the diffusion accelerates of O,Al,Na and subsequent crack.At the same temperature,the change rule of corrosion weight loss rate of MoNbZrTiHf high-entropy alloy in the molten salt with molecular ratio of 1.5 and 1.8 is basically the same,with increasing corrosion time,alloy corrosion weight loss rate increased and then reduced,The amount of generated corrosion products generated in 5-10 hours is lager than the amount of exfliated corrosion products.And the corrosion weight loss rate of the alloy in the molten salt with the molecular ratio of 2.2 increases gradually with the corrosion time,and the exfliated corrosion product of the alloy in the corrosion process is always larger than the generated amount.With the prolonging of corrosion time,the content of oxides in the corrosion products decreased gradually,and the metal compounds appeared and then disappeared,and the metal oxyfluoride gradually increased.The corrosion resistance of MoNbZrTiHf high entropy alloy decreases with the increase of corrosion temperature,and the corrosion products in the molten salt of alloy are the same at different temperatures.With the increase of corrosion temperature,the corrosion rate of the alloy increases,and the cracks and eroding holes formed inside the alloy get more and the thickness of the corrosion layer becomes thicker.In cryolite molten salt,Intergranular phase in the MoNbZrTiCr high entropy alloy show high corrosion rate,and corrosion rate of grain is relatively slow.Corrosive ions diffuse along the grain boundary through theinterface of alloy.MoNbZrTiCr high entropy alloy showed the best corrosion resistance in molten salt with the molecular ratio of 1.8,and the corrosion layer of the alloy was obviously layered.