Influences of ruthenium and crystallographic orientation on creep behavior of aluminized nickel-base single crystal superalloys F.H. Latief a,n , K. Kakehi a , H. An-Chou Yeh b , H. Murakami c a Department of Mechanical Engineering, Tokyo Metropolitan University, 1-1 Minami-osawa, Hachioji-shi, Tokyo 192-0397, Japan b Department of Materials Science and Engineering, National TsingHua University,101, Section 2, Kuang-Fu Road, Hsinchu 30013, Taiwan c Hybrid Materials Center, National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan article info Article history: Received 9 July 2013 Received in revised form 28 October 2013 Accepted 30 October 2013 Available online 13 November 2013 Keywords: Ruthenium Ni-base superalloy Creep Crystallographic orientation Aluminide coating abstract The influences of ruthenium and surface orientation on creep behavior of aluminized Ni-base single crystal superalloys were investigated by comparing two different types of NKH superalloys. The aluminized coated specimens were then subjected to creep rupture tests at a temperature of 900 1C and a stress of 392 MPa. The coating treatment resulted in a significant decrease in creep rupture lives for both superalloys. The diffusion zones between the coating and substrate led to changes in micro- structure, which diminished the creep behavior of the aluminized superalloys. Because of the interdiffusion of Ru, Al and Ni, the solubility of some of the refractory elements, such as W, Re. Mo, Co and Cr decreased in the diffusion zone; the precipitation of topologically close-packed (TCP) phases was thus inevitable. In the present study, the addition of Ru increased the degree of Re and Cr supersaturation in the γ matrix. Consequently, the addition of Ru indirectly promoted the precipitation of TCP phases in aluminized Ni-base single crystal superalloys. Furthermore, the growth of TCP precipitates was greatly influenced by the specific surface orientations of the Ni-base single crystal superalloys. In conclusion, the {110} specimens showed shorter creep rupture life than the {100} specimens, this was due to the difference in the crystallographic geometry of {111}〈101〉 slip system and TCP precipitates between the two side-surface orientations of the specimens. & 2013 Elsevier B.V. All rights reserved. 1. Introduction Aluminide coatings have been applied to Ni-base single crystal superalloys used for turbine components in order to protect them from oxidation and corrosion during their service lives. Details of these coatings have been reported [1–5]. Problems have arisen with these coated superalloys, leading to the loss of the coating. These problems include the precipitation of topologically close- packed (TCP) phases, the formation of Secondary Reaction Zones (SRZs) and the ‘rumpling’ of the coating caused by thermal cycling. Such problems degrade the properties of coated Ni-based super- alloys, and are potentially life-limiting to turbine blades. In particular, TCP phase precipitation and SRZ formation are regarded as serious problems in both coated and uncoated Ni-base super- alloys. As is well known, topologically close-packed (TCP) phase is a collective designation for several intermetallic compounds rich in the elements W, Mo, Re and Cr precipitated in Ni-base single crystal superalloys [6]. TCP phases form during service at elevated temperatures in such superalloys with high concentrations of these elements added to promote strength the loss of these elements from the matrix impairs the mechanical properties of the blade. Precipitation of the TCP phases [7–9] deteriorates the ductility and creep resistance of Ni-base superalloys. However, the damage mechanisms by aluminide coatings are not yet well understood. In the present study, we investigated the influence of crystallographic orientation on creep behavior of aluminized Ni-base single crystal superalloys, one Ru-free and the other Ru-containing. 2. Experimental materials and procedures Fully heat-treated (solution and aging) Ni-base single crystal superalloys NKH-304 and NKH-510 were used as substrate materi- als in this study. The details of chemical composition and heat treatment route for each superalloy are given in Table 1. NKH-304 is the base alloy, and NKH-510 is a 3 mass% Ru-addition alloy, where 3% Ru is substituted for Ni. The creep specimens with {100} and {110} side-surfaces (Fig. 1) were prepared by electric discharge machining (EDM), and had cross-section areas of 2.8 mm  2.8 mm and gauge length of 19.6 mm. The specimens were mechanically polished with emery paper prior to the aluminizing process. Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/msea Materials Science & Engineering A 0921-5093/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.msea.2013.10.092 n Corresponding author. Tel./fax: þ81 42 6772709. E-mail address: fahamsyah78@gmail.com (F.H. Latief). Materials Science & Engineering A 592 (2014) 143–152