The Phase Equilibria Of The Co-Mo-Zn Ternary System

As an economical and effective anti-corrosion technology for steel materials,hot dip galvanizing has been widely used in various fields of national economic and social development.However,in the process environment of the galvanizing industry,the severe corrosion and wear of the molten zinc solution leads to a short service period of galvanizing equipment,and the frequent replacement of that makes a low galvanizing efficiency and a waste of resources.Therefore,it is necessary to find liquid zinc corrosion resistant materials which are suitable for galvanizing industrial equipment.So far,among the various hot dip galvanizing industrial materials,cobalt-based superalloys are favored for their relatively good corrosion and wear resistance.It has been found that cobalt-based alloys can react with zinc to form intermetallic compounds,which are involved in the corrosion and wear process of galvanizing equipment.Molybdenum is beneficial to improve the hardness,wear and corrosion resistance of cobalt-based alloys.Phase diagrams are one of the most basic guiding tools for the material developments and researches.The study of Co-Mo-Zn ternary phase diagram is helpful to understand the influence of molybdenum on the reaction between cobalt and zinc,and also provides the theoretical basis and data reference for the design and development of wear-resistant and corrosion-resistant materials.However,no related reports on the phase relationship of Co-Mo-Zn ternary systems have been found so far.The isothermal sections of the Co-Mo-Zn ternary system at 450 and 600°C have were experimentally determined in the present work by combining equilibrate alloy and diffusion couple methods using scanning electron microscopy coupled with energy-dispersive spectrometry?SEM-EDS?and X-ray diffractometry?XRD?.It is experimentally determined that there are nine three-phase regions in the isothermal section of Co–Mo–Zn ternary system at 450°C,namely:L+?₂+MoZn₂₂,MoZn₇+MoZn₂₂+?Mo?,?₁+?Mo?+MoZn₂₂,?₁+?₂+MoZn₂₂,?₁+?Mo?+?,?+?Mo?+?,?+?+?1,?1+?+?,and?+?-Co+?1.And four two-phase equilibrium regions,i.e.L+MoZn₂₂,MoZn₂₂+?Mo?,?+?Mo?,and?+?,were experimentally confirmed in the Co-Mo-Zn ternary system at 450°C.Experimental results indicate that Mo is almost insolubility in the Co-Zn intermetallic compounds?₁ and?₂,and the solubility in the Co-Zn intermetallic compounds?₁ and?are also limited,not more than 0.9 and0.5 at.%,respectively.Moreover,the maximum solubility of Zn in the?phase and?phase were determined to be 2.7 and 0.6 at.%,respectively.The maximum solubility of Co in MoZn₇ and MoZn₂₂ are 0.5 and 4.7 at.%,respectively.Six three-phase equilibrium regions were experimentally determined in the isothermal section of Co-Mo-Zn ternary system at 600°C,namely:L+?1+?Mo?,?1+?+?Mo?,?+?Mo?+?,?+?+?₁,?+?₁+?,and?+?-Co+?₁.In addition,three two-phase equilibrium regions,i.e.?+?Mo?,?+?,and?₁+?,exist in the isothermal section at 600°C.The maximum solubility of Mo in?₁,?and?₁ is less than l at.%,not more than 0.9,0.4and 0.5 at.%,respectively.Furthermore,the maximum solubility of Zn in the?phase and?phase are 2.1 and 1.5 at.%,respectively.No ternary compound is found in the two isothermal sections of the Co-Mo-Zn system at 450 and 600°C.