Some conclusions on the 2nd international symposium on high-temperature corrosion, Les Embiez, May 22–26, 1989

Abstract

It would be too ambitious to give an overview of all the ideas and results presented by authors of 145 oral communications and posters. Instead, I will attempt to answer the question, What are the main trends in high-temperature corrosion studies pursued by the many experts in the world? The answer will be useful for developing new research toward the goal of improving the performance of materials in hot gaseous environments. A division of these 145 oral communications and posters into the ll topics of this 2nd International Symposium on High-temperature Corrosion of Advanced Materials and Coatings shows the present research emphasis (see Table 1). In addition to the papers shown in Table l, two plenary lectures were presented concerning topics 1 and 5. The majority of papers were presented for topics l, 2 and 4. The next most prevalent topics were 3 and 5-7. In sharp contrast, topics 8 and above all 9 attracted a minimum of authors. Similarly, topic l0 was poorly represented despite the effort of the Advisory Scientific Committee to enlarge the field of hot gaseous corrosion for different systems producing energy, such as thermal and nuclear plants. In fact, most of the papers treated problems of the aerospace industry. A round table or a panel discussion at future conferences may promote a useful discussion among different experts in the chemical, nuclear and metallurgical industries. The first plenary lecture of G. H. Meier presented a review of the recent advances in fundamental research on high-temperature corrosion. The transition from internal to external oxidation of binary alloys and the effects of transient oxidation and third-element additions was considered. The author showed that the classic concept for calculating the critical solute content to form an external oxide scale must be modified for alloys in which the thermodynamic stability of the lowest oxide of the matrix element approaches that of the solute oxide and/or the oxygen diffusivity in the alloy is very small. Recent developments in the understanding of the hightemperature corrosion of alumina-forming alloys were also reviewed. The second plenary lecture of R. Mevrel was a critical and prospective review of high-temperature corrosion-resistant coatings. Four main aspects were developed. The first analyzed the degradation mechanisms of protective metallic coatings at high temperatures. The understanding of this degradation requires more fundamental studies on the growth mechanism of oxide scales and on the role of minor addition elements such as palladium and platinum. The second problem concerns the mechanical properties of coated systems which determine the adhesion of a coating on the substrate. The third point concerns the present trend to use ceramic coatings in turbine engines. For about 15 years these ceramic coatings were successfully used on sheet metal combustor components. However, two problems must be solved to exploit these ceramic coatings on turbine blades; their reliability and their hightemperature corrosion resistance in isothermal, and above all, thermal cycling conditions. The fourth part of Dr. Mevrel's paper compared alternative techniques for depositing MCrAIY coatings; electrolytic codeposition, and electrophoresis, which would permit a more economical deposition of MCrAIY coatings. In addition to both of these principal lectures which emphasized the need to pursue certain fundamental research efforts, I would like to emphasize three other fields of fundamental interest. The first is the continued study of the beneficial