Study On Preparation And Properties Of Y₂O₃/CeO₂ Doped Molybdenum Alloy Plates

Molybdenum and molybdenum alloys have the properties of high melting point,high strength and high hardness.However,the high plastic-brittle transition temperature,low recrystallization temperature and poor wear resistance at high temperature of pure molybdenum make it difficult to meet the growing application demand.The mechanical properties of molybdenum can be improved by adding rare earth elements and their oxides because of their high melting point,and stable structure.In this paper,the mechanical properties of molybdenum are improved by Y₂O₃/CeO₂composite doping.In this paper,Mo-Y₂O₃/CeO₂ molybdenum plate is prepared by means of liquid-liquid doping,calcining,reduction,molding,sintering and rolling.Phase composition,particle morphology,morphology transformation at different preparation stages,and the microstructure and properties of Y₂O₃/CeO₂ doped molybdenum alloy plates are studied,and the effects of Y₂O₃/CeO₂ on microstructure and mechanical properties of molybdenum alloy are analyzed.The main conclusions are as follows:(1)The hydrothermal reaction environment has a great influence on the particle size of precursor powder Y₂O₃/CeO₂.The results show that Y₂O₃/CeO₂ powder can be prepared by these both methods.The second phase powder prepared by urea as a precipitant is spherical and has good dispersibility,but larger granularity.While,the second phase powder prepared by ammonia water as a precipitant has a small particle size,but has agglomeration.However,the agglomeration can be improved by ultrasonic dispersion of alcohol.(2)In the process of calcining and reduction,Y₂O₃/CeO₂ can effectively inhibit the growth of molybdenum particles.In the sintered molybdenum blank,the second phase Y₂O₃/CeO₂ particles are nearly spherical,with the size of submicron or nanometer.The larger Y₂O₃/CeO₂ particles tend to be distributed at the grain boundary,while the smaller Y₂O₃/CeO₂ particles tend to be distributed inside the molybdenum grain.Y₂O₃/CeO₂ particles can effectively prevent the grain boundary migration in the sintering process and refine the molybdenum grain.(3)The crystal plane spacing of(222)_Y2O3 in molybdenum alloy structure decreases by 1.4%,and the crystal cell constant correspondingly decreases by 1.4%,because Ce⁴⁺ions enter Y₂O₃ cell to replace Y³⁺ions.There is a coherent relationship between cerium oxide and molybdenum matrix in the phase,and the cerium oxide evenly distributed in molybdenum matrix can coordinate the deformation of molybdenum matrix,so as to improve the strength and toughness of molybdenum alloy.(4)With the increase of the addition amount of Y₂O₃/CeO₂,the hardness and tensile strength of rolled molybdenum plate increase significantly.The tensile strength of rolled Mo-0.8%Y₂O₃-0.12%CeO₂ molybdenum alloy plate reach 920MPa,about 22%higher than that of pure molybdenum plate,and the hardness was 327.3HV_2N,about 18%higher than that of pure molybdenum plate.After annealing at 1200?,the tensile strength is increased by 10%compared with that of pure molybdenum.The high temperature tensile strength of molybdenum plate can be significantly improved by adding Y₂O₃/CeO₂.The tensile strength of 0.8%Y₂O₃-0.12%CeO₂ molybdenum alloy plate is 41%higher than that of pure molybdenum at 1400?.(5)The tensile strength of molybdenum alloy prepared by mixed hydrothermal synthesis Y₂O₃/CeO₂ at room temperature increase by 18%and the elongation increase by 53%comparing with pure molybdenum.While the tensile strength and elongation of molybdenum alloys prepared by respectively hydrothermal synthesis increase by 21%and 81%,respectively.The high temperature tensile strength of molybdenum alloy plates prepared by the two methods is close to each other,but the high temperature elongation of molybdenum alloy prepared by respectively hydrothermal synthesis is higher.