Research On Microstructure And Properties Evolution In Pure Molybdenum Rolled Sheets

Molybdenum has high melting point,high strength,and high modulus of elasticity is widely used in military components such as molybdenum electrodes,nuclear components,missiles and aircraft,and is used in emerging applications such as LCD displays,sensors,semiconductors,luminescent materials,and microelectronics.During the rolling process of pure molybdenum sheet,the plastic flow inside the metal has a great influence on the microstructure.In this paper,the influence of rolling reduction on the microstructure and properties of rolled sheets was analyzed.The microstructure evolution of rolled sheet under 95 % rolling reduction was studied.Firstly,a reasonable powder metallurgy preparation process and unidirectional rolling process were designed.Pure molybdenum sintered billets and cold rolled molybdenum sheets with 70%,80%,90% and 95% rolling reduction were successfully prepared.The following conclusions were obtained: The cold rolled molybdenum plate shows that the processing fibrous structure is more obvious with the increase of rolling reduction.As the amount of deformation of the rolling reduction increases from 70 % to95%,the porosity decreases significantly,the grain distortion is severe,the fibrous structure is more uniform and fine,the dislocation density is high,Vickers hardness increased by 36.7 %,from 238.78 HV to 326.35 HV,and the room temperature tensile strength is increased by 25.9%,from 816.528 MPa to 1028.095 MPa,the elongation decreased from 18.33% to 2.5%,indicating that the cold rolling deformation is the most obvious for the improvement of mechanical properties.Fracture morphology of 70%and 80% rolled molybdenum plate has tearing ridge and dimple characteristics,the fracture is uneven,showing obvious tough-brittle fracture characteristics;Fracture morphology of 90% and 95% rolled molybdenum plate are flush and bright,showing obvious brittle fracture characteristics.From 70% to 80% rolling reduction,the rolling direction is rotated from <111> direction to <211>,and 80%,90%,95% rolled molybdenum sheets are formed to be entangled in <111> and <211>,the texture between the <100> and <210> directions and the rolling direction are segregated in the texture between the <210> and <110> directions.Secondly,during the processing of the sintered billet to 95% reduction of the molybdenum sheet,the grains become finer and the anisotropy becomes obvious,and the Vickers hardness increases accordingly.Fracture morphology of 47% and 95%rolled sheet are smooth dissociated brittle fractures with brittle fracture.Since the work hardening coefficient of the 95% rolled molybdenum sheet is 0.02439,and the work hardening is serious,the plastic deformation fluidity is poor,and cracks are generated.The texture intensity of {011}<100> increases as the 47% rolling reduction increases to95%.In the 95% rolled molybdenum plate,the maximum intensity of the {011}<100>plate texture is 13;while the <111> oriented grains also rotate toward the <110>orientation,and are rotated into <100> and <110> oriented grains in the 95% rolled molybdenum plate.Compared with the 47% rolled sheet,the percentage of the large angle grain boundary is significantly reduced,the dislocation density is increased,the subgrain boundary is the most,the proportion of the small angle grain boundary is increased,and the average orientation difference is decreased in 95% rolled molybdenum sheet.