The Pilot Study Of CoCrMo And Stellite 6 Alloys By Combustion Synthesis

Cobalt-base alloys have excellent high temperature properties,outstanding heat workability,corrosion and thermal fatigue resistance,especially good high resistance to abrasion in heat condition.Co-base alloys have seen extensively used in high requirements of wear and corrosion resistance environments mainly due to their excellent properties,such as aviation,astronavigation,nuclear energy,dynamic force, medicine and so on.Co-base alloys have high melting points,so they require high temperature and long time for heat during melting.How to seek a method which has low cost,low energy consumption and shortening period of processing is our object.In this paper,the CoCrMo and Stellite 6 alloys are synthesized by combustion. The main raw materials are CO₃O₄ and Al powder,adding some alloy elements,such as Cr,Mo and W.During the process of study CoCrMo alloys,the main discussion is microstructure,solidification process and the effects of processing parameter including the material styles of crucible,atmosphere,the way of ignition and cooling speed on the experiments.Stellite 6 alloy is prepared based on the study of CoCrMo alloys and its microstructure is compared with the counterpart of as-cast state HS111. It has been shown that CoCrMo and Stellite 6 alloys can be successful synthesized by combustion synthesis,and the residue of Al₂O₃ can be separated from alloy.At the same time,the change trend of chemical composition of alloy can also be controlled. The content of Cr is lower than the expectation;and the content of Al is higher,which is existed in the form of Al₂O₃.The main phases of CoCrMo alloy areε-Co solid solution of close-packed hexagonal(hcp)andγ-Co solid solution of face-centered cubic(fcc),and the amount ofε-Co phase is reach to 88%,which outclass the counterpart synthesized by conventional melting.Microstructure of alloys is cast dendritic morphology and interdendritic segregation existed;moreover,Co is rich in pine-tree crystal and Mo is rich in interdendritic and Cr is distributing uniformly.It is found that the material of crucible,atmosphere and the way of ignition have not obvious effected on the experiment,but cooling speed affect the microstructure.It is showed that the amount ofεphase is higher with furnace-cooling than that with air-cooling.In the same way, the pure Co alloy is prepared by combustion synthesis without adding alloy elements that its main phase isε-Co solid solution,and the diffraction peak is moved to high angle compared with CoCrMo alloy.Besides,the grain of pure Co is coarsening,and twin existed.The main phases of Stellite 6 alloys synthesized by combustion synthesis method areγ-Co solid solution and carbide of Cr.The microstructure of as-cast HS111 and the Stellite 6 are same,all of them are constituted by Co-rich matrix and lots of carbides. By using the combined techniques of XRD,SEM and EPMA,the majority of carbides are carbide of Cr,and the appearance of islands shape are eutectic of M₂₃C₆ and M₆C; letter shape is MC.Because of special processing,the size of carbide in Stellite 6 is four times bigger than that in HS111.Altogether,the way prepared Co-base alloys by combustion synthesis has many merits,such as economy cost,low energy consumption,shortening period of processing and so on.Although a little of residue of Al₂O₃ can't be separated from alloy,it can be improve the purity during second melting because of density difference. So instead of first melting,the way of combustion synthesis is advisable in some degree.