A low-cost second generation single crystal (SC) superalloy, designated DD6, has been developed for aeroengine turbine blade applications. DD6 contains 2 wt. % rhenium, which is about 2/3 of that of the second generation single crystal superalloys such as PWA1484, CMSX-4 and Rene N5. The alloy system employs the relatively high additive refractory element (tungsten molybdenum, tantalum, rhenium and niobium) content of about 19.5 wt. %. A cost reduction of about 25% is expected for this alloy.DD6 alloy has an approximate 40 "C improvement of creep strength relative to the fast generation single crystal superalloys such as DD3, a Chinese first generation single crystal alloy whose creep rupture properties are comparable with PWA1480 alloy. The tensile properties and creep rupture properties of the alloy are comparable to those of the second generation single crystal alloys such as SC180, Rene NS, CMSX-4 and PWA1484. Most notably, the alloy provides superior oxidation resistance and good hot corrosion resistance. The advantage shown in the creep rupture properties over DD3 also generally hold for fatigue properties.DD6 also has good microskucture stability, heat treatment characteristics and environmental properties.Casting trials have been conducted on DD6 involving a great number of bars and some complex shaped hollow turbine blades. These trials demonstrated that DD6 possesses excellent single crystal castability. Table 1 presents the compositions of first, second and third generation single crystal alloys, including DD6 and DD3. A main distinction of the chemical compositions of the fast, second and third generation single crystal superalloys is rhenium-free, 3 wt. % Re and 6 wt. % Re, respectively -. I1 *II The effects of Re on the mechanical properties of single crystal superalloys are very significanf especially in improving the creep rupture life. However, Re is a rare element and the price of Re is very expensive. The aeroengine manufacturers all consider Re as a strategic element. Therefore, the development of low-Re second generation single crystal alloy is important. The goals of the present research were as follows: 1) develop a low cost second generation single crystal alloy, using low Re; 2) maintain the mechanical properties of the alloy at levels equivalent to those of the second generation single crystal alloys, such as SC180, Rene N5, CMSX-4 and PWA1484; 3) design a alloy combining high strengths with good environmental properties, microstructural stability, heat treatment characteristics and castability.A low-cost second gene&ion Single crystal alloy, designated DD6, has been developed by Beijing Institute of Aeronautical Materials for aeroengine blade applications. Based on the study of single crystal superalloys for many years, with the help of the computer aided design of alloy compositions, the contents of tungsten, molybdenum, tantalum, rhenium and alumimun were judiciously balanced with the predominating rhenium requirement. A large number of trials were carried out, and the composition f...

Interfaces have long been known to be the key to many mechanical and electric properties [1]. To nickel base superalloys which have perfect creep and fatigue properties and have been widely used as materials of turbine blades [2], interfaces determine the strengthening capacities in high temperature. By means of high resolution scanning transmission electron microscopy (HRSTEM) and 3D atom probe (3DAP) tomography, Srinivasan et al. [3] proposed a new point that in nickel base superalloys there exist two different interfacial widths across the γ/γ´ interface, one corresponding to an order-disorder transition, and the other to the composition transition. We argue about this conclusion in this comment.Srinivasan et al. showed an averaged intensity profile and intensity ratio of a filtered high angle annular dark field (HAADF) image of HRSTEM. However, their original image (the non-filtered image) shown as Fig. 1(b) in reference [3] does not show high quality so that there is too much difference between the non-filtered image and the filtered image as shown in Fig.

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The tensile properties of a low-cost first generation single crystal superalloy DD16 have been investigated. The results show that values of the tensile strength and yield strength of DD16 alloy were similar at typical temperatures; from room temperature to 760, the yield strength of DD16 alloy increases; However, above 760, the yield strength of DD16 alloy decreases remarkably, and the maximum of the yield strength was 1145.5MPa at 760. From room temperature to 760, the fracture mode was cleavage fracture; But above 760, the fracture characteristics changed from cleavage to dimple.

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