Study On High-temperature Oxidation Resistance Of MoNbTiV_yCr_x Refractory High-entropy Alloys

High-entropy alloys are a type of multi-principal element alloy discovered in recent times,possessing excellent heat resistance,impact resistance,and corrosion resistance,allowing them to withstand harsh operating environments.Refractory high-entropy alloys are made from refractory metal elements,having a high melting point,and displaying outstanding high-temperature stability and oxidation resistance.These alloys have extensive application prospects in the aerospace field,where they can be used to manufacture engine turbine blades,combustion chambers,and gas turbine blades,among other high-temperature components,in order to improve the engine’s high-temperature performance and extend its service life.When used in high-temperature environments,alloy materials can oxidize,reducing their service life.In this study,MoNbTiVCrx(x=0.2,0.4,0.6,0.8,1.0)and MoNbTiV_y Cr(y=0,0.2,0.4,0.6,0.8)series refractory high-entropy alloys were prepared using Mo,Nb,Ti,V,and Cr,five elements,and a non-consumable vacuum arc melting furnace.The oxidation resistance of the two sets of alloys at 800°C was investigated.Ultra-deep-field microscopes,X-ray diffractometers,field-emission scanning electron microscopes,energy spectrometers,and thermogravimetric analyzers were employed to study the effects of Cr and V element content on the phase composition,microstructure,element distribution,and oxidation resistance of MoNbTiVCrx and MoNbTiV_y Cr alloys.The main conclusions are as follows:It was found that the change in Cr content had no effect on the as-cast phase structure of MoNbTiVCrx alloys,all of which exhibited a single body-centered cubic structure.After oxidation at 800°C for 100 hours,the weight gains of MoNbTiVCr0.2 and MoNbTiVCr alloys were 59.2 mg/cm~2 and 8.8 mg/cm~2,respectively,while the height differences of the surface oxides were 55.96μm and 20.16μm,respectively.Increasing the Cr content in MoNbTiVCrx alloys reduced the weight gain due to oxidation,and the oxide layer surface became smoother.Investigating the growth of oxide layers in MoNbTiVCrx alloys,it was found that an increase in Cr content promoted the formation of Cr VNbO6 and Ti4Cr3Nb3O2 within the oxide layer,weakened the outward diffusion of Nb,and gradually eliminated the loose oxides Nb9VO25 and V2Nb6O19 from the outer oxide layer.This resulted in the MoNbTiVCr alloy oxide layer composed of dense TiO2,Ti4Cr3Nb3O2,and Cr VNbO6 oxides,which reduced the thickness of the oxide layer and improved the alloy’s oxidation resistance.Research revealed that all five MoNbTiV_y Cr as-cast alloys had a single body-centered cubic structure.At 800°C,the weight gains of MoNbTiV0.8Cr and MoNbTiCr alloys after 100hours of oxidation were 3.36 mg/cm~2 and 0.5 mg/cm~2,respectively,while the height differences of the surface oxides were 24.8μm and 3.37μm,respectively.As the V content in MoNbTiV_y Cr alloys decreased,the weight gain due to oxidation decreased,and the oxide layer surface became smoother.Investigating the growth of oxide layers in MoNbTiV_y Cr alloys,it was found that a decrease in V content promoted the formation of dense TiO2 and Ti4Cr3Nb3O2 oxides in the oxidation layer,improving the high-temperature oxidation resistance of MoNbTiV_y Cr series refractory high-entropy alloys.As the V content decreased,the amounts of V2Nb6O19,Cr VNbO6,and V2O5 in the MoNbTiV_y Cr alloy oxide layer also decreased.The MoNbTiCr alloy oxide layer,which did not contain V,consisted of dense TiO2 and Ti4Cr3Nb3O2,with a thickness of only 16μm,significantly improving the oxidation resistance of MoNbTiV_yCr alloys.