Investigation On Microstructure And Property Of Pure Tungsten By HPT

Refractory metals such as W, Mo are usually produced by powder metallurgy inindustry, which has introduced defect, impurity and a low ductility at roomtemperature. The brittleness, however, has greatly limited its application.Ultra-finegrain(UFG) tungsten has high plasticity,toughness and low ductile-brittle transitiontemperature(DBTT). It is a important way to solve the brittleness problem inconventional technology.Severe plastic deformation (SPD) is an effective way to produce bulk crystallinesolids with ultra-fine grain and nano-microstructure. High pressure torsion (HPT) isone of SPD with significant accumulated strain which leads to an effective refinementin grain.The present work is to obtain ultra-fined grain with nano-microstructure incommercial tungsten powder via HPT by Bridgman mould structure. Microstructure,microhardness, recrystallization temperature and ductile-brittle transition temperaturewas studied. Thus we analyze the improvement in W produced by HPT. The resultsreveals that:After HPT(440℃,4GPa,10turns and440℃,2GPa,5turns), the grain size oftungsten has been refined with an elongated shape. Microharndess near the center is850HV, while microhardness away from center is above1200HV. Indentation has nocrack nearby, which means a certain toughness. Sample of2GPa,5turns does not fullyrecrystallized under1450℃, however, sample of4GPa,10turns have got an fullyrecrystallization under800℃. Which means sample of2GPa,5turns has a betterthermostability.