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Defect formation and control of tungsten-based alloy forward extrusion bars during solvent debinding process

LIU Wen-sheng,CAI Qing-shan,MA Yun-zhu(State Key Laboratory for Powder Metallurgy,Central South University,Changsha 410083,China)  
Power Extrusion Molding(PEM) is one of the most effective way to fabricate tungsten heavy alloy rod with large aspect ratio.The debinding process affects the defect control of sample and the improvemnet of mechanical properties of alloy.In this paper,the formation and control of defects in forward extrusion rods(Φ12 mm and Φ15 mm) during solvent debinding process were discussed.Constant temperature controlling device was used to control solvent debinding rate,the surface and the microstructure of extrusion rods were observed by digital camera and Scanning Electron Microscope(SEM),respectively.The results showed that there was big residual stress in tungsten-based alloy extrusion rods,which was the major factor leading to the cracking of green rods extruded during solvent debinding process.The residual stress of the green rods could be relieved by an annealing process(at 40 ℃ annealing temperature),and it could effectively avoid the cracks.Under annealing at 40 ℃ and solvent debinding at 30 ℃ for 12 h,the rods structures were uniform with no defects,and the debinding efficiency levels of Φ12 mm and Φ15 mm could reach 40% and 30% respectively.
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