The tensile properties of the intermetallic compound TiAl have been determined at several temperatures in the range 25 to 1000°C. Additional variables studied were the influence of strain rate and the effect of exposure to oxidizing conditions prior to testing. The modes of deformation under the various testing conditions were studied in the electron microscope, the modes of fracture were studied in the scanning electron microscope, and these data were correlated with the mechanical properties. The results indicate that the ductilebrittle transition behavior of TiAl at about 700°C is controlled by the trailing a/6 [112] partial dislocation components of the a [011] superdislocations overcoming their pinning barriers. It was also shown that prior exposure to oxidizing conditions does not markedly influence the mechanical properties of TiA1.

GE Aircraft Engine's interest in Alloy 718 dates to the early 1960's. New jet engines were under development for the Supersonic Transport (SST) and the Air Force's C-5A, the first of the wide-body airplanes. These new engines required a stronger, more temperature-capable alloy than A286, without the fabrication limitations of Rene 41. Alloy 718 subsequently became the most widely used superalloy for aerospace applications. It is the alloy most used at GE Aircraft Engines (GEAE) with application in critical rotating parts, airfoils, supporting structures and pressure vessels.

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High temperature structural materials, such as nickel-based superalloys, have contributed immensely to societal benefit. These materials provide the backbone for many applications within key industries that include chemical and metallurgical processing, oil and gas extraction and refining, energy generation, and aerospace propulsion. Within this broad application space, the best known challenges tackled by these materials have arisen from the demand for large, efficient land-based power turbines and light-weight, highly durable aeronautical jet engines. So impressive has the success of these materials been that some have described the last half of the 20 th century as the Superalloy Age. Many challenges, technical and otherwise, were overcome to achieve successful applications. This paper highlights some of the key developments in nickel superalloy technology, principally from the perspective of aeronautical applications. In the past, it was not unusual for development programs to stretch out 10 to 20 years as the materials technology was developed, followed by the development of engineering practice, and lengthy production scaleup. And many developments fell by the wayside. Today, there continue to be many demands for improved high temperature materials. New classes of materials, such as intermetallics and ceramic materials, are challenging superalloys for key applications, given the conventional wisdom that superalloys are reaching their natural entitlement level. Therefore, multiple driving forces are converging that motivate improvements in the superalloy development process. This paper concludes with a description of a new development paradigm that emphasizes creativity, development speed, and customer value that can provide superalloys that meet new needs. IntroductionThe modern world has made great use of high strength structural materials to design facilities and equipment that we cannot live without. Structural materials are the backbone of any mechanical system since they must support the loads and endure the degradation modes of the operating environment. The critical roles played by materials that reliably serve under difficult conditions is impressive. For example, electric generating plants, oil refineries, chemical processing plants, industrial furnaces, and aircraft engines all depend on nickel-based superalloys. Our industrial age could hardly exist without the capabilities enabled by these materials. But the public is generally not aware of these materials since they are specialized and oftentimes are not directly observed.The aviation industry, with its current fleet of airplanes powered by fast, fuel efficient, quiet engines, would not be possible without superalloys. Jet engines are particularly challenging for structural materials since the operating environment is hot, loads are high to minimize weight, stiffness is crucial to maintain clearances throughout the operating envelope, critical structural components are buried deep within the engine and not easily accessible for inspe...

Superalloys have contributed markedly to societal benefit. It is difficult to imagine the modern world without superalloys. These materials provide the backbone for many applications within key industries that include chemical and metallurgical processing, oil and gas extraction and refining, energy generation, and aerospace propulsion. Within this broad application space, arguably the highest visibility challenges tackled by these materials have arisen from the demand for large, efficient land-based power turbines and lightweight, highly durable aeronautical jet engines. So impressive has been the success of these materials that the last half of the 20 th century has been known as the Superalloy Age. While superalloys have met many technical challenges, the overarching consideration is that no use of these materials occurs unless value to the customer is demonstrated. This paper discusses the emerging paradigm within the aviation industry that applies customer requirements to drive materials development and implementation on an accelerated timeline. This new paradigm is first of all spurring on competition to materials from other technologies, and secondly opening the door to other material classes to compete with superalloys for key applications. The superalloy community has the opportunity to respond with innovative alloys and processing improvements. In the ideal case, this competition will result in the development of the best ideas, such that the end customer, whether a civilian or military aeronautical system operator, receives optimal value. This new development paradigm is leading to overall faster application of advanced materials.

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