The development of a new steam turbine generation for use in advanced coal fired power plants with prospective operating temperatures beyond 700 °C and a projected thermodynamic efficiency of about 55 % requires, amongst other innovations, the partial substitution of ferritic steels by wrought Ni‐base superalloys. Although Ni‐base alloys are already widely used in the aerospace industry, they are faced with demands regarding component size and operation temperature, which by far exceed current aero‐engine requirements. In this article, the potential of selected alloys for 700 °C steam turbine applications is discussed with respect to their manufacturability and mechanical performance. Hereby, the focus is on the steam turbine rotor, which probably is the most critical component. It is concluded that material solutions are available for operation conditions around 600 °C but not for temperatures of 700 °C and above. Based on these results, alloy development strategies are suggested in order to close this gap and two new alloys, DT 706 and DT 750, are introduced.
The plastic deformation behavior of the Mg wrought alloy AZ31 is investigated in tension–compression tests at room temperature. It strongly depends on the loading direction and is characterized by dislocation slip as well as by the formation of deformation twins. The latter is reversible in the case of a change of the deformation direction. Because of the pronounced crystallographic texture of the material investigated, a macroscopic deformation anisotropy exists with lower flow stresses in compression than in tension. Hysteresis loops with characteristic shapes are observed when the material is cyclically plastically deformed, depending on the tension–compression loading history.
Creep crack growth data of Inconel 706-MST between 600°C and 700°C are presented i n order to assess the materials suitability for ultra high temperature steam turbine applicat~ons. Hereby, "MST" stands for a heat treatment modification proposed earlier by the authors. It is demonstrated that the creep crack growth resistance can be raised to the level of more creep ductile materials such as Waspaloy and Inconel 617 and that the benefit relative to conventional heat treatment cycles is particularly pronounced at 700°C. The results are interpreted in terms of the precipitation sequence during thermal exposure. Siipcrallo! s 718. 625. 706 and Various Derimtivcs t;tlitc.d b~. t.:l. Loria T M S (Thc hlineruls. hletals & blatzrials Socirty). 2001
Oxide dispersion strengthened (ODS) and dual scale particle strengthened (DSPS) copper composites were successfully manufactured by a powder metallurgical processing route, containing Al2O3 particles with a mean diameter of 17 nm as dispersoids and, in the case of the DSPS material, 15% tungsten fibres about 3 mm long. Their mechanical behaviour was investigated at ambient and elevated temperatures. The ODS material displayed mechanical properties comparable to those of commercial GlidCop® alloys. Addition of tungsten fibres in case of the DSPS material increased the elevated temperature flow strength relative to the ODS counterpart by about 12 %. This result is rationalised by finite element calculations, taking fibre orientation, plastic deformation of the fibres as well as the role of the fibre coating into account.
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