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Unquestionably there is a tremendous amount of effort being expended currently on the newer metals. What has brought this about? Examination of the subjects covered in the ASTM Symposium on Newer Metals, presented in this book, gives an answer: needs for materials with properties superior to those of existing materials for new applications in aircraft, nuclear energy, and communications. These new applications did not come about as a result of the new materials that were available. Rather, the materials were developed in response to the new applications because conventional materials could not serve adequately. Recent aircraft and missile applications are tremendously demanding of materials. The advent of the turbojet engine was only a forerunner. The gas turbine inlet temperatures rose steadily as the design speed of the aircraft increased, first from 1500 to 1650 F, which caused a burst of development leading to improved nickel- and cobalt-base superalloys. Further requirements to develop speeds of Mach 3 increased turbine inlet temperatures to 2000 to 2200 F, if the weight penalty involved in a cooled engine was to be avoided. Nickel-base alloys could be improved to serve at 1800 F, but the ultimate ceiling for the nickel base appeared to have been reached. The refractory metals—molybdenum, columbium, or chromium—would have to be used in this application. It appears as though the strength problems in molybdenum and columbium alloys for turbojet applications can be met adequately, but the coating problem remains a hurdle which so far has not been overcome, although considerable progress has been made. In chromium, lack of ductility remains an unsolved problem. Airframe materials for jet aircraft shifted from aluminum to titanium and steel when the speeds approached Mach 3. In compressors, titanium and steel also were required as temperatures increased from 600 to 800, and currently to 1000 F for Mach 3 engines.
Jaffee, R. I.
ChiefChairman of Symposium, Battelle Memorial Inst., Columbus, Ohio