| The melting point, boiling point, and density of tungsten are the highest of all metals, and it is a kind of refractory metal, the hardness, elasticity modulus and compression modulus are also very high, but the vapor pressure is quite low. In addition, with the excellent high temperature mechanical properties and creep resistance, good electric conduction, heat conductivity and electron emission property, tungsten is used widely in many fields, such as military, aviation, industry and so on. Recently, the demands of tungsten is growing rapidly in many countries, but the global reserves is relatively few. Now tungsten alloy is widely used in remedy, communication and aerospace fields, as the material of electrical contact, electronic packaging and heat sink. With many excellent properties in heat, electronic, mechanics and optic, tungsten and its alloys have broad application prospects in many areas. It is of great significance to improve the processing technology of pure tungsten and its alloys for promoting the development of national defense, aerospace technology and economic development.Tungsten is a body-centered cubic metal crystal, with characteristics of high ductile to brittle transition temperature, sensitive to fracture and easy to brittle fracture. The microstructure and stress-strain variety cause the ductile to brittle transition temperature varying, and then influence the working plasticity. In the deformation process of tungsten, the microstructure is arranged along a certain deformation direction in fiber streamline, which will make the ductile to brittle transition temperature decrease, and with the increase of the deformation degree, the formation of the fibrous microstructure is smaller, and the ductile to brittle transition temperature is also decreased, that is, the working plasticity of tungsten increase with the deformation degree increase. Tension stress in the forming process can easily lead to the generation and expansion of the brittle fracture in pure tungsten, reduce the working plasticity. Shear stress can cause plastic deformation at the crack tip, make tension stress relaxed and can inhibit the crack generating and expanding, therefore the shear stress can improve the working plasticity of tungsten. The stress status is quite different in various plastic deformation technological processes of the metal material, such as in the rolling process the material is subject to uniaxial compression stress and biaxial tension stress, and in the swaging process the material is subject to triaxial compressive stress, thus the working plasticity of tungsten is different in rolling and swaging process. For different plastic work conditions of pure tungsten and its alloys, providing guidance on production practice is quite necessary to analyze the flow characteristic and deformation behavior, study the influence of technological parameters on microstructure evolution and forming process, and optimize the technological parameters.By carrying out isothermal compression experiment of pure tungsten, the flow stress-strain data of plastic deformation is acquired, and the constitutive model formula parameters are obtained by data fitting. Take the constitutive model as the numerical simulation material data, the plastic deformation behavior of tungsten in rolling and swaging is analyzed. The influence of process parameters such as roller convexities on rolled 93 W alloy plate head rupture is studied, the variation and distribution of stress triaxiality during the rolling process of 93W plate are analyzed, the cause of the head rupture of the plate during the rolling process and the variation of the stress state of the cracking point are discussed; the material deformation behavior of pure tungsten (>99%) plate rolling, rod rolling, bar swaging and wire drawing process are investigated, and the plasticity working characteristic of pure tungsten with different process parameters is analyzed. Combined with metallographic and SEM tests, influence of rolling reduction, roller rotational speed, blooming temperature and friction coefficient on rolling load and stress-strain distribution in deformation zone of pure tungsten plate rolling process, and the crack phenomenon of the rolling tungsten plate are analyzed. The influence of technological parameters on material flow and stress-strain distribution of deformation zone is studied, the microstructure evolution is analyzed. By carrying out the rolled tungsten rod annealling experiment, the influence of annealling temperature and soaking time on recrystallization texture size and distribution is investigated. The influence of die angle on drawing force, drawing compression force and deformation is studied. The main contents in this paper are as follows:(1) The isothermal and constant strain rate axial compression experiment for powder sintered pure tungsten is carried out by using GLEEBLE 3800 thermo mechanical simulator, the deformation temperatures range from 1250? to 1550? and strain rates range from 0.001 s-1 to 1s-1. The thermal deformation behavior of pure tungsten at elevated temperature is studied, the relation of flow stress with temperature, strain rate and strain is obtained based on 6 different constitutive models. By comparing the correlation coefficients and average absolute relative errors of the 6 models, the Arrhenius model with strain compensation, the modified Johnson-Cook model, the modified Zerrili-Armstrong model and the KHL model which can accurately describe flow stress, deformation temperature and strain rate at elevated temperature are derived. The hot processing map of pure tungsten is established based on power dissipation and instability criterion, combined with the microstructure evolution, the stability deformation temperature and strain rate range for pure tungsten are analyzed, basic data for plastic processing is provided.(2) The deformation behaviors of pure tungsten and 93 W alloy are investigated respectively, the variety and distribution law of stress triaxiality with different roller convexities on the rolling plate head are analyzed, the influence of reduction, blooming temperature, roller rotational speed and friction coefficient on spread, length and stress-strain distribution of rolled pure tungsten and its alloys are investigated, the variation of material flow and rolling load in the multi passes rolling process are studied, the crack generation cause of pure tungsten and its alloys plate are discussed combined with the metallographic and SEM tests.(3) The double directional rolling, three directional Y type rolling, three directional round type rolling and four directional rolling numerical simulation models are established. The varying law of spread, length, and effective stress and strain on the axial section of the rolled rod with reduction, and the influence of different rolling type on rolling load and stress-strain distribution of rolled tungsten rod are analyzed comparatively. The three directional Y type multi passes rolling model of pure tungsten rod is established, the varying law of rolling load and stress-strain are investigated. The annealling experiment of the rolled tungsten rod is carried out, the influence of annealling temperature and holding time on the size and distribution of recrystallization microstructure is investigated.(4) The different diameter sizes tungsten bar swaging simulation models are established, the stress-strain variation and material flow law in the tungsten bar swaging process are investigated, the influence of processing parameters such as conical feeding angle and wrap angle on tungsten bar swaging process is investigated, the influence of technological parameters on crack generating in the tungsten bar swaging process is analyzed, the voids in the powder sintering crushing and grain structure evolution in the swaging stroke are analyzed.(5) The numerical simulation model of tungsten wire drawing is established, the distribution law of the stress-strain in the deformation zone is investigated, and the influence of model angle and friction coefficient on axial drawing force and diameter compression force is studied. |
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