Mass Transport and Thermodynamics at the Interface in the High-Temperature Metal/Ceramics Composites

Metals/ceramics composites are the promising materials for structure application at high temperatures。Typical materials are superalloys with ceramic coatings，metallic particles dispersion ceramic matrix composites，and functionally gradual materials comprised of ceramics and metals.The interface between ceramics and metals has chemically and mechanically different feature from each bulk material.The objective of the present research is that the interface between ceramics and metals is generalized as a basis of the thermodynamics and transport phenomena to discuss the chemical stability of the interface。Two different topics are carried out to generalize the interfacial phenomena.One is the measurements of thermodynamic properties and diffusion coefficient of the complex oxides which are the products at the interface.Another is high temperature oxidation at the interface between oxide ceramics and metals.(1)Thermodynamic properties and diffusion coefficient of the complex oxidesPe…More rovskite type chromites(ABO I D23 I D2)are focused in the present work.They have important role at the interface between Cr I D22 I D 2 O I D 23 I D 2 scale and alloy to improve the scale adhesion.With respect to the thermodynamic properties，the standard Gibbs energy change of formation，ΔG°，on NdCrO I D23文件D2was determined by measuring the electroconductivities of the different two-phase samples，NdCrO I D23-D 2 with Cr I D 22-D 2 O I D 22 I D 2 and Nd I D 22 D 2 O I D 2 O I D 23 D 2.As compared with the reported ones of YCrO I D23 I D2 and LaCrO I D 23 ii D2，the value ofΔG°is consistent in the relationship betweenΔG°and ionic radius of A ion.Diffusion coefficients of A ions in LaCrO I D 23 D 2 and NdCrO I D 23 ii D 2 was determined by the solid state reaction technique.Discussed their diffusion coefficients with the reported value of Y ion in YCrO I D23 ii D2，the absolute values can be explained with the concentration of A site vacancy.The activation energy depends on the ionic radius of A ions.In order to compare with their chromites，diffusion coefficient of Ba ion in BaTiO ei D23锡D2is also measured by the same method。The values of BaTiO Ii D23 D2is very similar to their chromites.Diffusion coefficient of A ion in the perovskite oxides has little dependence of the valances of A and B ions.(2)High temperature oxidation at the interface between oxide ceramics and metalsOxidation of Ni covered by Y I D22 I D 2 O I D 23 D 2-stabilized ZrO I D 22 ii D 2(YSZ)is investigated in this work.The one dimensional model of the oxidation kinetics is established to assume that flux of O I D 12-I D 1 in YSZ is equal to one of Ni I D 12 I D 1 in the NiO scale.In order to verify the kinetic model，the oxidation rate and oxygen partial pressure at the interface were investigated on the close cell with YSZ thin plate including Ni in the inside.The experimental results are in agreement with the kinetic model.The life design of the interface of the ceramic coating on the metals and metal particle dispersion ceramics matrix composite can be enable as a basis of the kinetic model。Less：Less

Metals/ceramics composites are the promising materials for structure application at high temperatures. Typical materials are superalloys with ceramic coatings, metallic particles dispersion ceramic matrix composites, and functionally gradual materials comprised of ceramics and metals. The interface between ceramics and metals has chemically and mechanically different feature from each bulk material.The objective of the present research is that the interface between ceramics and metals is generalized as a basis of the thermodynamics and transport phenomena to discuss the chemical stability of the interface. Two different topics are carried out to generalize the interfacial phenomena. One is the measurements of thermodynamic properties and diffusion coefficient of the complex oxides which are the products at the interface. Another is high temperature oxidation at the interface between oxide ceramics and metals.(1) Thermodynamic properties and diffusion coefficient of the complex oxidesPe … More rovskite type chromites (ABOィイD23ィエD2) are focused in the present work. They have important role at the interface between CrィイD22ィエD2OィイD23ィエD2 scale and alloy to improve the scale adhesion. With respect to the thermodynamic properties, the standard Gibbs energy change of formation, ΔG°, on NdCrOィイD23ィエD2 was determined by measuring the electroconductivities of the different two-phase samples, NdCrOィイD23ィエD2 with CrィイD22ィエD2OィイD22ィエD2 and NdィイD22ィエD2OィイD23ィエD2. As compared with the reported ones of YCrOィイD23ィエD2 and LaCrOィイD23ィエD2, the value of ΔG°is consistent in the relationship between ΔG°and ionic radius of A ion.Diffusion coefficients of A ions in LaCrOィイD23ィエD2 and NdCrOィイD23ィエD2 was determined by the solid state reaction technique. Discussed their diffusion coefficients with the reported value of Y ion in YCrOィイD23ィエD2, the absolute values can be explained with the concentration of A site vacancy. The activation energy depends on the ionic radius of A ions.In order to compare with their chromites, diffusion coefficient of Ba ion in BaTiOィイD23ィエD2 is also measured by the same method. The values of BaTiOィイD23ィエD2 is very similar to their chromites. Diffusion coefficient of A ion in the perovskite oxides has little dependence of the valances of A and B ions.(2) High temperature oxidation at the interface between oxide ceramics and metalsOxidation of Ni covered by YィイD22ィエD2OィイD23ィエD2-stabilized ZrOィイD22ィエD2 (YSZ) is investigated in this work. The one dimensional model of the oxidation kinetics is established to assume that flux of OィイD12-ィエD1 in YSZ is equal to one of NiィイD12+ィエD1 in the NiO scale. In order to verify the kinetic model, the oxidation rate and oxygen partial pressure at the interface were investigated on the close cell with YSZ thin plate including Ni in the inside. The experimental results are in agreement with the kinetic model. The life design of the interface of the ceramic coating on the metals and metal particle dispersion ceramics matrix composite can be enable as a basis of the kinetic model. Less