Developments in superalloy castability and new applications for advanced superalloys

Abstract

Increasing emphasis is being paid to optimising castability of cast superalloys to absolutely minimise defects which impact casting yield and alloy performance and to improve structural weldability of weld repairable alloys. The objective is to maximise casting yield and quality and minimise any rectification costs. To accomplish these aims the controls on deleterious elements such as [N], [O], S, P and Si at the ppm level, including accurate measurement, are critical. Conversely, the addition of highly reactive elements, La and Y at the ppm level, in conjunction with very low (1 ppm or less) sulphur content has dramatically improved bare oxidation resistance (for unshrouded blade tip life) and thermal barrier coating (TBC) adherence and life including prime reliant applications. This technology has been applied to the following new or improved cast superalloys: CM 939 Weldable®, CMSX-486® and CMSX-4® (SLS) [La+Y] (Cannon-Muskegon Corporation). In this paper, the role (both positive and negative) and control of critical elements at the ppm level as it applies to many advanced superalloys will be examined and discussed.

Development of wrought precipitation strengthened IN939 superalloy

“…At present, this alloy is used as a cast alloy in manufacturing gas turbine blades/vanes and other structural parts such as burner nozzles and turbine casings. 4 It is one of the best alloys among the hot corrosion and oxidation resistant alloys having desirable mechanical properties. Although considerable investigations have been carried out on the microstructure and mechanical properties of this alloy in the as cast and heat treated condition, [4][5][6][7] there are no published data dealing with the microstructure and mechanical properties of this alloy in wrought form.…”

“…4 It is one of the best alloys among the hot corrosion and oxidation resistant alloys having desirable mechanical properties. Although considerable investigations have been carried out on the microstructure and mechanical properties of this alloy in the as cast and heat treated condition, [4][5][6][7] there are no published data dealing with the microstructure and mechanical properties of this alloy in wrought form. Therefore, IN939 might not have been used in wrought form so far.…”

Solubility of Nitrogen in Liquid Ni, Ni–Nb, Ni–Cr–Nb, Ni–Fe–Nb, and Ni–Cr–Fe–Nb Systems

“…3,4) Therefore, residual concentration of this element must be perfectly controlled. 5) The achievement of extremely low nitrogen levels requires the knowledge of thermodynamic data for nitrogen solubility in liquid pure nickel and nickel-based alloys. Its importance is not only for fundamental researches but also for industrial and economic reasons.…”

Nitrogen Solubility in Liquid Ni-V, Ni-Ta, Ni-Cr-V, and Ni-Cr-Ta Alloys

“…Nitrogen has consistently emerged as one of typical gaseous impurity elements in nickel-based super-alloys that generally imparts negative influences on mechanical properties of these alloys [1][2][3][4]. In particular, small amounts of nitrogen can be very deleterious [5]. For instance, the dissolved nitrogen can segregate with the decrease of the nitrogen solubility during the solidification, subsequently, nitride inclusions and nitrogen bubbles may be produced, which are harmful to the creep and fatigue properties.…”