Research On Preparation And Properties Of Novel High Density Tungsten Alloys Based On 93W-4.9Ni-2.1Fe

W-Ni-Fe alloys are typical biphasic composite consisting of BCC structure W phase and FCC structure bonding phase,which has been widely used in military and civil fields owing to its excellent physical and mechanical properties.At present,the preparation method of tungsten alloy is still liquid phase sintering after cold isostatic pressing or moulding.Besides sintering methods,alloy composition and post-treatment also have important effects on the properties of tungsten heavy alloys.In this study,novel tungsten heavy alloys were prepared based on 93W-4.9Ni-2.1Fe by adding nano-Al₂O₃/ZrO₂ ceramic phase and metal Co,then the alloys were subjected to deformation treatment or carburizing-cycle heat treatment.The effects of composition and post-treatment on the microstructure,composition distribution,mechanical and tribological properties of the tungsten heavy alloys were investigated.Tungsten heavy alloys reinforced by nano-Al₂O₃/ZrO₂ ceramic particles（ceramic phase content is 0 wt%³ wt%）were prepared by liquid phase sintering（holding at 1520℃for 90min）and solution quenching（holding at 1200℃for 60 min）.The relative density and tensile properties of tungsten alloys decrease with the increasing of ceramic phase content,relative density decreased from 99.1%to 98.2%,tensile strength and elongation decreased from 944MPa to 705 MPa,24.3%to 2.9%respectively,the fracture mode of tungsten alloys also change from transgranular cleavage fracture of W grain to W-W interfacial fracture.On the contrary,the compressive yield strength and hardness of the alloys increase with the increasing of nano-Al₂O₃/ZrO₂ phase content,the value of them increase from 743 MPa and 298 HV to 843 MPa and 350 HV（ceramics phase content is 3 wt%）respectively.The friction and wear experiments show that with the increasing of Al₂O₃/ZrO₂ phase content,the friction coefficient of tungsten alloys is basically maintained between 0.5 and 0.65,wear mechanism of tungsten heavy alloys change from adhesion wear and abrasive wear to abrasive wear.The wear amount decreased when the content of ceramic phase is more than 1wt%.93W-4.9Ni-2.1Fe alloys with different Co content（0 wt%¹.5 wt%）were prepared by liquid phase sintering（holding at 1480℃for 60 min）and post solution quenching.The relative density and tensile strength were improved with the increasing of Co content,when adding 1.5wt%Co,the tensile strength and elongation of the alloy reach the highest values,985 MPa and31%respectively.However,the compressive yield strength at room temperature and hardness of the alloys are insensitive to Co content.Deformation treatment was carried out for 93W-4.2Ni-1.8Fe-1Co alloy（deformation amount 0%³0%）,the tensile strength,compressive yield strength and hardness of the alloy increase with the increasing of deformation amount,the tensile strength,compressive yield strength and hardness reach 1403 MPa,1438 MPa,and 491HV respectively when deformation amount is 30%.However,the elongation of the tungsten heavy alloy drops sharply with the increasing of deformation amount.In order to get good surface hardness and core toughness,93W-3.85Ni-1.65Fe-1.5Co、92.07W-4.85Ni-2.08Fe-1（Al₂O₃/ZrO₂）and 93W-4.9Ni-2.1Fe alloys were studied by means of carburizing-cycle heat treatment.The results were as follows:after carburizing-cycle heat treatment,the total carburizing layer of the three tungsten alloys consists of the outermost WC layer and the sub-surface core-rim layer.The ternary carbides formed by 93W-4.9Ni-2.1Fe and92.07W-4.85Ni-2.08Fe-1（Al₂O₃/ZrO₂）alloy were Ni₂W₄C and Fe₆W₆C,while the ternary carbides formed by 93W-3.85Ni-1.65Fe-1.5Co were Ni₂W₄C and Co₂W₄C.With the increasing of cycle times（0²0）,the bending strength of the three tungsten alloys decreased continuously,the fracture mode of the carburized layer was dominated by carbides fracture and interface fracture between W particles and carbides,microhardness of the three tungsten alloys were significantly improved,maximum value is about 1050 HV.The better comprehensive mechanical properties were obtained when heat treatment was 5 times.