Abstract
The cost of failures in gas turbine discs, both in human life and financial terms, is particularly high, and it has always been recognized that the component must be fully specified against the design requirement, and totally predictable in operation. This was originally achieved by making a reproducible forging consistent with the design strength assumptions and which approached the engineer's model of the material as ‘elastic, isotropic, and free from defects’. Today's improved understanding of materials behaviour in terms of the relationship between material property and microstructure, together with the designer's need for higher–strength materials, has led to an approach which now recognizes the role of both structure and ‘defects’ within the forging. This, and the need to improve the cyclic properties of components, is now imposing on the forger complex microstructural and quality requirements that can be met only by process control and by a move towards closer-to-size and more complex shape requirements. Future material needs are discussed in relation to controlling the discontinuity behaviour, together with the change in philosophy that this is bringing to the control of the manufacturing process.
MST/255
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