Research On Chromium Alloy Powder And Injection Molding Technology

In this paper,the preparation of cobalt chromium molybdenum alloy powder by water and gas combined atomization and the injection molding technology of cobalt chromium molybdenum alloy powder were studied,the microstructure and properties of the cobalt-chromium-molybdenum alloy sintered parts were studied and analyzed.The preparation of cobalt chromium molybdenum metal powder by water and gas combined atomization process was studied,the important parameters of the metal smelting process were clarified.The relationship between atomization pressure and the morphology,particle size distribution and oxygen content of cobalt,chromium and molybdenum powder was analyzed,and the oxygen content of water-gas atomization was compared with that of conventional water atomization.In order to improve the relative density and mechanical properties of the sintering compaction,the process parameters of the MIM process of the cobalt chromium molybdenum alloy were optimized,and the sintering curves at different maximum sintering temperatures were studied.The microstructure of the alloys with different maximum sintering temperatures was observed by optical metallography microscope and scanning electron microscope.The microstructure of the two alloys was analyzed by XRD test.Tensile tests were carried out on cobalt-chromium molybdenum sintered parts and fracture analysis was carried out on the tensile samples after fracture.The median diameter D50(cumulative particle size distribution of 50%)and D90(cumulative particle size distribution of 90%)of the prepared Co-Cr-Mo powder decreased significantly with the increase of atomization water pressure,and the yield of powder less than 25?m increased from 62.9%to 72.3%after the optimization of water-gas atomization.When the atomizing water pressure is between 90?110 MPa,with the increase of atomization water pressure,the oxygen content of the powder decreased gradually,and the oxygen content decreased from 0.39%to 0.27%.When the atomizing water pressure is 90MPa,the vibration density of powder has reached more than 5.23 g/cm³.When the atomizing water pressure increases,the vibration density decreases slightly.For the same particle size powder,the better the sphericity,the higher the powder density.The vibrational density of the powders in this experiment is 4.8 g/cm³,much higher than the traditional level of water atomized powders which is 3.7?4.0 g/cm³.The cobalt chromium molybdenum powder prepared by this process is nearly spherical and the powder is fine,which is better than the powder prepared by water atomization process,and conforms to the standard of injection molding process.In the injection molding process,the loading amount of metal powder in the feed is 62%,so as to ensure the shrinkage rate of the feed.In this experiment,plastic based binder,binder composition includes polyoxymethylene(POM),paraffin wax(PW),polypropylene(PP),polyethylene(PE),stearic acid(SA),which POM accounted for about 80%of the overall proportion of the binder.When the ratio of POM in the binder is 85%,it is difficult to remove POM completely,and the yield of sintered sample decreases 3%.The degreasing process takes the degreasing process of acid and heat.In the sintering process,negative pressure degreasing is performed at 0?600?,vacuum sintering at 600?1050?,and partial pressure sintering at 1050?1340?,in the partial pressure sintering process,divided into 1340?,1360?,1380?three highest sintering temperature,the maximum sintering density is 8.10g/cm³ at 1380?.At the three highest sintering temperatures,the magnetic permeability of Co-Cr-Mo alloy is 1.0 H/m,belonging to the non-magnetic state.The microstructure and mechanical properties of Co-Cr-Mo alloys with different maximum sintering temperatures were analyzed.When the maximum sintering temperature was 1380?,it was found that with the increase of the maximum sintering temperature,the carbon content exceeded the standard,and the eutectic structure of carbides with low melting point was produced,and the melting state appeared.Phase analysis of intercrystalline and intracrystalline carbides was carried out,and the carbides were M₂₃C₆and M₆C containing Cr or Mo.It is found that the chromium content in intercrystalline and intracrystalline carbides is 61.41%and 64.84%,respectively.The matrix structure is FCC phase,and the cobalt content is 60.88%.When the maximum sintering temperature increases from 1340?to 1380?,the densification degree of the alloy surface increases gradually.The sintering density increases from 7.88 g/cm³ to 8.10 g/cm³,and the hardness increases from 265 HV to 295 HV.At the three highest sintering temperatures,the magnetic permeability of Co-Cr-Mo alloy is 1.0H/m,belonging to the non-magnetic state.At the maximum sintering temperature of 1340?,the tensile strength and yield strength of Co-Cr-Mo alloy are 748 MPa and 361 MPa respectively.Both of them are close to the strength level of casting alloy,which indicates that the sintering curve with the highest sintering temperature of 1340?is the optimal process parameter in the injection molding process.