Phase Equilibrium Of The Co-Mo-Cr-Si Quaternary System And Corrosion Resistance In Liquid Al Bath

Co-based alloys with corrosion resistance,abrasion resistance and good creep resistance at high temperature and high hardness and other advantages are widely used,Tribaloy alloy?Co Mo Cr Si alloy?is a kind of typical Co-based alloys designed by Deloro Stellite Holding Inc..The typical microstructure is the hard Laves phase+solid solution.The Laves phase ensures the strength and hardness,and the cobalt matrix to ensure its toughness.Due to the good mechanical properties at high temperature,the alloy is widely used in wear and corrosion resistance coating materials.In order to develop a new Co-based alloys and further study on the properties of Co-based alloys,it is necessary to study the phase relation in the Co-Mo-Cr-Si quaternary system and corrosion resistance in liquid Al bath.The phase relation of the Co-Mo-Si ternary system at 1000oC was determined based on the experimental results of equilibrated alloy,using SEM-EDS and XRD.The 1000oC isothermal section of the Co-Mo-Cr-Si quaternary system with Co fixed at 70 at.%was investigated experimentally coupled with the phase-disappeared approach.The experimental results show that three three-phase regions exist in the cobalt-rich corner of the 1000?isothermal section of the Co-Mo-Si ternary system,all of the cobalt-rich phases can be equilibrated with Co Mo Si phase.In the isothermal section of the Co-Mo-Cr-Si quaternary system with Co fixed at 70 at.%at 1000oC,there is a wide?Co?+Co₃Mo₂Si phase field,The experimental results show that there are 12 phases regions in the system,containing one four-phase region consisting of?Co?+Co₃Mo+Co₇Mo₆+Co₃Mo₂Si;five three-phase regions,namely?Co?+Co₃Mo+Co₇Mo₆?Co₃Mo+Co₇Mo₆+Co₃Mo₂Si??Co?+Co₃Mo+Co₃Mo₂Si??Co?+Co₇Mo₆+Co₃Mo₂Si??Co?+?Co₂Si+Co₃Mo₂Si;five two-phase regions,namely?Co?+?Co₂Si??Co?+Co₃Mo₂Si?Co₃Mo+Co₃Mo₂Si?Co₃Mo+Co₇Mo₆??Co?+Co₇Mo₆;and one one-phase regions,namely?Co?.The maximum solubility of Cr in?Co?,?Co₂Si,Co₃Mo,Co₇Mo₆ and Co₃Mo₂Si phase is 25.5 at.%,3.8 at.%,1.5 at.%,9.9 at.%and 16.7 at.%,respectively,and that of Si in?Co?,Co₃Mo and Co₇Mo₆ phase is 17.8 at.%,0.3 at.%and 2.6 at.%,respectively.Combined with the Co-Mo-Cr-Si quaternary system phase relationship,the effects of different elements on the microstructure and corrosion resistance in liquid Al bath at 700oC of Co-Mo-Cr-Si alloys were investigated.The results show that the content of Si is ranging from 0.6-2.4 wt.%,the crystal structure of?Co?is FCC;of Si is ranging from 2.8-5.6 wt.%,respectively,the crystal structure of?Co?is HCP.The content of Mo and Si affects the microstructure of alloy,the content of Mo and Si increases,and the ratio of Laves phase increases.Co Mo4Cr23.8Si0.6 alloy has the best corrosion resistance,the corrosion products are mainly?Co,Mo,Cr?₂Al₅ and?Cr,Mo?₇Al₄₅,The corrosion resistance of Co Mo28.5Cr16.7Six alloy increases with the increase of Si content,the corrosion products are mainly?Co,Mo,Cr?₂Al₉ and?Cr,Mo?₇Al₄₅.When the content of Mo element is high,the main chemical compound is?Mo,Cr?Al₅;when the content of Cr element is high,the main chemical compound is?Cr,Mo?₇Al₄₅.