Study On Microstructure And Properties Of Y₂O₃ Stabilized ZrO₂ Doped Tungsten-base Alloy

Tungsten is widely used in national defense,medical,aerospace and other fields.It can be used in the production of cemented carbide,casting mould,armor piercing bullet,electrolytic contact and electrode.ZrO₂ is a kind of material with very stable properties,its chemical stability,it also has high hardness,high melting point,excellent thermal properties,mechanical properties,electrical properties and high wear resistance,corrosion resistance.it has been widely used in many fields of machinery industry,electronic industry,aviation industry etc..Based on the excellent properties of ZrO₂ and W,it can improve the mechanical properties of tungsten alloy at room temperature and high temperature,a new type of ZrO₂ doped tungsten alloy has been developed.In this experiment,liquid-liquid doping methods is adopted,respectively by hydrothermal method and azeotropic distillation method of ZrO₂ doped tungsten alloy powder was synthesized by the conventional powder metallurgy method,and through pressing,sintering,swaging process preparation of tungsten alloy.In this paper,the preparation process of ZrO₂ doped tungsten based alloy was studied,and the phase composition,particle morphology and microstructure and properties of the alloy were studied.The amount of ZrO₂ and pH has a important effect on the morphology and particle size of precursor powders in the hydrothermal process.When pH=0.5,the particles are the smallest.The agglomeration of precursor powder is easy to occur when the doping amount of ZrO₂ increases.The mixed powder is m-W and m-ZrO₂.The composite powders are mainly composed of c-W and m-Zr O2.With the increase of ZrO₂ doping amount,the particle size of tungsten alloy powder decreases gradually.ZrO₂ doped tungsten powder with fine particle size and uniform distribution can be prepared by azeotropic distillation method.The morphology of powders prepared by hydrothermal method and azeotropic distillation method is the same,and the particle size is small.Azeotropic distillation method is easy to prepare a large number of quantitative,so this method was used to prepare the powder for subsequent sintering processThe sintered tungsten alloy matrix obtained by vertical sintering.The matrix is tungsten and the doping phase is ZrO₂.The ZrO₂ particles are dispersed in the matrix and the particle size is about 1?m.Changing the crystalline of m-ZrO₂ to c-ZrO₂ in the sintering process,after cooling to room temperature,it still keeps cubic phase,It showed that the addition of Y₂O₃ can be stabilize the ZrO₂ crystal at room temperature.The grain size of sintered tungsten alloy is about 25?m,and the grain size of the sintered tungsten alloy is refined by swaging,and the grain size is about 15.0?m,and the grain is grown after annealing at high temperature,and its size is more than 40?m⁸0?m.The grain size of the tungsten alloy decreases with the increase of the doping amount of ZrO₂.Because the ZrO₂ particles distributed at the grain boundaries of the matrix can inhibit the outward diffusion of grains,and it play a role in grain refinement.With the increase of ZrO₂ mass fraction,the absolute density of tungsten alloy decreases.The rotary forging process can improve the defects in the sintered state and increase the relative density.With the increase of the doping amount of ZrO₂,the hardness of tungsten alloy is also increasing.The defects can be improved and the grain size can be refined,so the hardness is increased.After high temperature annealing,recrystallization occurs,it caused the growth of the grains,so the hardness is reduced.The compressive strength of tungsten alloy increases with the increase of the doping amount of ZrO₂.After high temperature annealing,the compressive strength decreased because of grain growth.The fracture of ZrO₂ doped tungsten alloy at room temperature was observed by SEM.The ZrO₂ particles distributed at grain boundaries hinder the intergranular fracture and increase the yield strength.With the increase of temperature,the compressive strength of Zr O2 doped tungsten alloy bar and pure tungsten bar decreases with the increase of temperature.The compressive strength of Zr O2 doped tungsten alloy is higher than that of pure tungsten rod at 1000? ¹200?,and the compressive strength of pure tungsten is higher than that of ZrO₂ doped tungsten alloy when the temperature is higher than 1200 ?.This is due to the weakening of the interfacial bonding ability between the tungsten matrix and Zr O2 particles,which results in the decrease of the overall compression performance.When at the same temperature,the compression strain rate is different,when the strain rate is 1/s,the true stress is obviously higher than the true stress under strain rate of 0.01/s and 0.005/s.The higher strain rate,the greater the compressive strength,the lower the plastic deformation ability of the material.