A Low-Cost Second Generation Single Crystal Superalloy DD6

Abstract

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...

Fatigue Behavior in Monocrystalline Ni-Based Superalloys for Blade Applications

“…Early generation alloying of monocrystalline alloys was developed to improve creep resistance by adding slower diffusing elements, such as rhenium and ruthenium. Rhenium additions improve creep rupture life and oxidation resistance [7,8], while ruthenium decreases overall density compared to rhenium, stabilizes the microstructure, and increases oxidation resistance [8,9]. Additionally, creep resistance increases with a decreasing number of grain boundaries, and therefore the invention of the monocrystalline blade increased creep resistance.…”

Tensile behavior and deformation mechanism of secondary generation single crystal superalloy DD6 at 1070 C

“…The nominal chemical composition (weight fraction, %) of the DD6 alloy used in this work was : Cr 4.3，Co 9，Mo 2，W 8，Ta 7.5，Re 2，Nb 0.5，Al 5.6，Hf 0.1，C 0.006， Ni Bal. [7,8]. The single crystal bars of DD6 alloy were directionally solidified in a Bridgman furnace using seed technique.…”

“…The DD6 alloy was developed for the applications of turbine blade on aero-engine. Although the properties of the alloy are equivalent to those of other second generation single crystal superalloys, DD6 alloy is a low cost second generation single crystal superalloy with only 2 wt.% Re [7,8].…”

Microstructure evolution in a single crystal nickel-based superalloy joint by linear friction welding

“…In particular DD6 has been used in aero-engine and industrial gas turbine blades for its superior mechanical properties, high oxidation resistance, quality corrosion and creep resistance at high temperatures [1,[8][9][10].…”