Pure Molybdenum Injection Molding Process

Molybdenum,which has high melting point,excellent thermal conductivity and low expansion coefficient,is widely used in power generation,computer circuitry,microelectronics,solid-state lighting and flat-panel displays.Further,this low toxicity enables molybdenum to play a significant part in the protection of human health and the environment. Molybdenum has high melting point and its ductile-to-brittle transition temperature(DBTT)can be at or below room temperature,making them difficult to manufacture by traditional methods.The research of MIM Mo, which is a relatively new manufacturing process and will produce small and intricate shape Mo parts,accord the requirement of modern Mo industry.In this work the processing for producing molybdenum parts by metal injection molding technique including milling,mixing,debinding and sintering,were investigated.The optimal deagglomeration of the applied powder was carried out in mill using a stainless steel ball and vial at speed of 258 r/min for 4 h,the weight ratio of the ball to the powder 5 to 1 and 0.5wt%SA as process control agent.By means of theological measurements of different feedstock formulations,it is prefer in injection molding that feedstock including 50% by volume of milled molybdenum powder,which flow behavior exponent n and flow activation energy E is 0.52 and 11.24 kJ/mol respectively.The optimal molding parameters for the feedstock are as following: temperature of molding 155℃,mould 45℃and injection pressure 104 MPa.The binder removal was successfully carried out by two different processes,thermal and a combination of solvent and thermal debinding. The ideal process of thermal debinding under H₂ atmosphere is as following:First,heating up to 160℃with rate of 2℃/min and holding 120 min. Second,taking 1℃/min to 250℃for holding 120min.Then up to 350℃with rate of 2℃/min and holding 60min.The last heating up to 500℃ takes place at 3℃/min.Finally,the specimen was prsintered at 900℃.The ideal solvent debinding process is as following:After immersed in a bath with n-heptane for 2 h at 50℃,68%binder was removed without defects.Then the following thermal debinding process is needed.First, heating up to 200℃with rate of 3℃/min and holding 60 min.Second, taking 2℃/min to 350℃for holding 60min.Then up to 500℃with rate of 3℃/min and holding 60min.Finally,the specimen was prsintered at 900℃.After thermal and solvent debinding,the specimens were without fractures.The time thermal debinding took was 13h,and in solvent debinding,the time was reduced to 10.7h.The content of carbon and oxygen were respectively less than 0.060% and 0.0042%after the parts were sintered under hydrogen atmosphere.The parts sintered at 1 850℃for 120 min exhibits a highest density of 9.70 g/cm³,meanwhile the tensile strength and hardness was 229 MPa and 193 HV10.