Study On The Preparation,microstructure And Properties Of Al₂O3 Doped W Alloy

Tungsten and tungsten alloys possess excellent properties,such as high melting point（the highest of all metals）,high heat shock resistance and low thermal expansion coefficient,thus exhibit good performances in all kinds of high temperature structural applications.Nowadays nanostructures of ultra fine grained（UFG）tungsten material fabricated by tungsten workers shows higher performances,including low brittleness and high toughness.In addition,compared with traditional materials,UFG tungsten alloy has better high temperature performance and low temperature ductility.People pursue higher performance of tungsten alloy while at the same time the preparation becomes a new challenge.This article takes the Al（NO₃）₃ · 9H₂ O and CO（NH₂）₂,AMT and HNO₃ as raw materials,in the process of powder preparation,three kinds of preparation technology（sol-gel,azeotropic distillation and hydrothermal synthesis）were adopted,followed by calcinations,reduction to prepare Al₂O₃ doped W alloy precursor powder.And then SEM,HRTEM and XRD methods were taken to characterize the phases,morphologies and microstructures of composite powders.The results show that compared with the pure tungsten,the powder fabricated by the three methods show better morphologies,the particle size is reduced to nano-scale.The existence of Al₂O₃ hindered the deposition of W atoms,which have played an important role in refining grain size.Three kinds of powder through the same conditions of calcination（550℃,4 h,along with the furnace cooling）,have produced monoclinic WO3 and hexagonal WO₃,then turn into WO₂ and WO_3-x in the same condition（600℃,2h）of reduction.Although sol-gel method produced the powder with the smallest particle size,but there was no aluminized phase distribution,and sol-gel process is complex,uncontrollable,however,hydrothermal products possess moderate particle size,uniform dispersion,on the other hand,the process of hydrothermal is easy to control,that become the reasons of further researching.Based on the experiments,the hydrothermal synthesis was optimized and every preparation step of the precursor powder was carried on the detailed research,the phase changes and morphologies were also discussed.And speculated that crystal growth according to the results of the experiment results,established the relevant model analysis.At the same time,this paper studies the effects of reactant concentration of nitric acid on the W-Al₂O₃ alloy precursor powder,and according to the experimental results speculate growth process,and establish related model to analysis.In the study of Al₂O₃ doped tungsten alloy densification,the CIP-hydrogen and SPS processes were taken respectively to sinter the precursor powders,the results showed that: After CIP-hydrogen sintering,1wt% Al₂O₃ doped W alloy sintered at 2300℃ showed the highest relative density,2wt% Al₂O₃ doped W alloy sintered at 2250℃ showed the highest hardness,1wt% Al₂O₃ doped W alloy sintered at 2250℃ showed the highest compressive strength;After SPS process,2wt% Al₂O₃ doped W alloy sintered at 1800℃ showed the highest relative density and the highest hardness,1wt% Al₂O₃ doped W alloy sintered at 1800 ℃ showed the highest compressive strength.The surface of simples after SPS sintering is smooth,the second phase is distributed uniformly,and there is no segregation phenomenon,the shape variables are smaller,the toughness is higher.On the other hand,owing to the higher speed,less energy consumption and more effective,SPS sintering shows more advantages.The innovation points of this article are as follows: Liquid-liquid doping method in-situ authigenic Al₂O₃ nanoparticles reinforced tungsten alloy,which is different from the traditional mechanical mixing methods,it makes the Al₂O₃ and W precursor powders in water solvent completely amalgamation in the form of ions or molecules,so that the composite powder are spherical,tiny and possess good dispersibility,uniform particle size,After sintering the grain of composite powder is fine and homogeneous,the tungsten matrix and Al₂O₃ particles were metallurgy combined completely.