Effects Of Carbon And Oxygen Content On Magnetic Properties Of Fe-50%Ni Soft Magnetic Alloy Prepared By Metal Injection Molding

Due to its excellent magnetic properties in weak magnetic fields,permalloy have been widely used in industry,Fe-50%Ni soft magnetic alloys have the highest magnetic induction in permalloy.Metal injection molding is a new method to produce precision parts with complex shapes.The utilization rate of materials can be improved when metal injection molding is used to prepare samples.Fe-50%Ni soft magnetic alloys were prepared by metal injection molding with carbonyl iron powder,carbonyl nickel powder and iron oxide powder as raw materials.A large number of experiments were carried out by changing the sintering process and the amount of iron oxide added,combining with carbon and oxygen content test,metallographic microscopic analysis and dc soft magnetic property test,etc.,the influence of carbon and oxygen contents on soft magnetic properties of Fe-50%Ni soft magnetic alloys was systematically studied.Results are as follows:When there is more oxygen in Fe-50%Ni soft magnetic alloys,the change of carbon content has no obvious influence on soft magnetic properties of alloys,the main effect on soft magnetic properties of alloys is the oxygen content.When alloys are sintered at 1260℃～1340℃,the density of alloys and the saturation magnetic induction intensity increase with the sintering temperature increasing.At the same time,the grain size increases but the content of carbon and oxygen in alloys decrease.The oxygen element in alloys basically exists on the surface of alloys in the form of oxide.With the increase of sintering temperature,oxides on the surface of alloys are reduced by graphite and escapes as gases,and the content of oxygen in alloys decreases.When the oxygen content is between 0 and 1200 ppm,the coercivity of alloys decreased from 46.28 A /m to 24.53 A/m,and the permeability increased from 2408 to 5095 with the decrease of oxygen content.The density of alloys was greatly increased by heat isostatic pressure treatment.After the heat isostatic pressure treatment,the relative density of alloys ranges from 90% to 95%,and the saturation magnetic induction which is structurally-insensitive parameter and closely related to the density of alloys would increase accordingly,up to 1.416 T.However,the coercivity of alloys was increased and the permeability of alloys was decreased by heat isostatic pressure treatment.When there is more carbon in Fe-50%Ni soft magnetic alloys,the surface of the sample is fusible.When the carbon content of alloys exceeds 0.8 wt.%,the surface melting is very obvious at the sintering temperature of 1340℃,and magnetic properties cannot be measured.Alloy samples with high carbon content can be sintered normally within the sintering temperature range from 1260℃ to 1320℃.When there are amounts of carbon in alloys,as sintering temperature increase,the sintering temperature increasing faster than the gas escaping,pores tend to appear in alloys and alloys densities decrease.Proper addition of carbon to alloys can promote grain growth,reduce coercivity and increase permeability of alloys.The content of carbon and oxygen can be controlled by adding different amounts of iron oxide powder into the high carbon iron powder.At the same sintering temperature,the best soft magnetic properties can be obtained at the carbon and oxygen content of the alloy is lower than 1000 ppm.