Effect of some interface related phenomena on the mechanical behaviour of high temperature materials

High temperature materials range from ferritic steels to structural ceramics: some of them are in current use, but need upgrading, others are still in a research and development stage. For all these materials, improved reliability of mechanical properties, primarily creep, is an essential requirement. Moreover increased service temperature is particularly desiderable, with special reference to applications in heat engines. Mechanical properties are often impaired by subtle phenomena onan atomic scale such as grain boundary /GB) segregation, which needs highly sophisticated equipment to be investigated and is still poorly understood. When, in ana effort to increase their service temperature, and also erosion and hot corrosion resistance, metallic materials are protected by ceramic themal barrier coatings (TBC's) by means of modern technologies, such as plasma spraying, interfaces come again into play and bring out effects which are ofetn detrimental for overall mechanical behaviour of these new systems. Experimental evidences described in this overview pinpoints the importance of "alloy design" in the manufacturing of engineering materials. Minor constituents, through interface related phenomena, such as segregation and oxidation, greatly affect the mechanical behaviour of steels, superalloys and ceramic coatings. In particular creep embrittlement of 2.25 Cr-1 Mo steel and nickel base superalloy is determined by a newly disclosed selective segregation phenomenon of residual impurities to the internal walls of cavities and themla shock resistance enrichments of plasma sprayed ceramic coatings on superalloys is impaired by interface enrichments of easily oxidised elements.