Research On Mechanical Alloying And Strengthened Sintering Technologies Of Tungsten Heavy Alloy

Tungsten heavy alloy is widely used in top science fields,especially used as a very important kinetic penetrator in military,due to its combined physical and mechanical properties,such as high density,strength and hardness,good ductility and toughness,et al.Using nano-powder as the initial powder,the tungsten grain size can be greatly decreased,while strength,ductility and hardness can be greatly increased.Thus,it is an important orientation of preparation of a new tungsten heavy alloy with super high strength and ductility.In this paper,the nano-powders of tungsten and alloyed(Ni,Fe)solid solution are prepared by using mechanical milling,then 93W-4.9Ni-2.1Fe pressed compact was prepared by mixing two kind of powder by ratio,after sintered densification under constant pressure in hydrogen atmosphere,at last,with appropriate heat treating strengthening,completely densified 93W-4.9Ni-2.1Fe heavy alloy can be obtained with fine microstructure and good mechanical properties.In this paper,the evolution of particle morphology,microstructure and mechanical properties of tungsten and(Ni,Fe)powders have been firstly investigated during mechanical milling.The influence of milling technology parameter(such as speed of rotation,milling time,ratio of ball to powder)on structure property of tungsten and matrix is analyzed,as a result,a set of effective milling technology of tungsten and matrix is established,and tungsten of particle size about 500 nm and completely alloyed alloyed(Ni,Fe)solid solution with particle size about 14 nm are obtained.Based on the dynamic analysis of liquid-phase sintering densification,this paper revealed that the growth of sintering neck for tungsten particles depends on sintering temperature and sintering time,at the same time,associates with particles size.The particle of powder is fine and the growth of sintering neck is faster.As a result,the final property of sintering sample depends on the use of sintering technology parameter(such as temperature and holding time,et al),at the same time,associates with particles size.Comparative study of solid-liquid two step sintering process and the traditional sintering influence to the liquid phase sintering process on the properties of alloy organization,found that the liquid phase sintering by using nanocrystalline ultrafine particles of tungsten powder size(500 nm)of sample liquid phase sintering temperature is 1465℃ for 30 minutes of heat preservation,not only than the traditional sintering process(1530 liquid phase sintering)by 65℃ lower,but also greatly shortens the sintering time;Alloy of plastic about 25% higher than traditional powder sintering specimen,and strength is improved as well.And using nanocrystalline tungsten powder of solid-liquid two step sintering specimen,after sintering,W particle size only has an average of 10μm,including m or so,and traditional powder sintering samples W particle size is including 30μm),and were distributed homogeneously.Finally,vacuum heat treatment of tungsten heavy alloy alloys fabricated by the nanocrystalline tungsten powder and conventional liquid-phase sintering was investigated in order to eliminate hydrogen dissolved into binding phase.After vacuum heat treatment under the temperature of 1200℃ at vacuum condition for 2h,the sample were found no residual hydrogen in binder phase.Low content of C,O element have been found at the same time which greatly reduces the possibility of brittle phase precipitation and make the alloy phases boundary between tungsten and matrix to "purify".Meanwhile sample W particles distribution is homogeneous and W-W contiguity is relatively small.Thus,the comprehensive properties of 93W-4.9Ni-2.1Fe alloys were improved.