Design of Solutionizing Heat Treatments for an Experimental Single Crystal Superalloys

Abstract

The heat treatment response between 1170°C and 1320°C of an experimental single crystal Ni base superalloy is presented. The temperature range for solutionizing the alloy is determined by combinations of holding time and temperature. The effects of long isothermal holding within and beyond this solutioning temperature range are studied. Heat treatment steps below the γ′-solvus temperature stabilize the eutectic phase, while steps above the solvus temperature improve the homogenization and reduce eutectic phase fraction. However, prolonged holding above the solvus temperature indicates up-hill diffusion at the eutectic region leading to incipient melting. A new solutioning heat treatment approach with continuous heating between solvus and solidus is proposed

Microstructure and creep behavior of DMS4-type nickel based superalloy single crystals with orientations near 〈001〉 and 〈011〉

“…3 suggests: (i) segregation of alloying elements with higher atomic number, such as W and Re at DC, and depletion of these elements at IDR (PC > 1); (ii) enrichment of both Al and Ta at IDR and their depletion in other locations (PC < 1); and (iii) non-partitioning of Co and Cr to any of the three above-mentioned locations during solidification (PC ≈ 1). These observations are in reasonable agreement with the results reported earlier for similar types of single crystal Ni-based superalloys [27,28].…”

Processing, Microstructures and Mechanical Properties of a Ni-Based Single Crystal Superalloy

“…That is, dendrite formation is more likely to happen with refractory elements, and so is the solute segregation. Consequently, additional processing steps and heat treatments in solid solution treatments are required to improve the compositional and microstructural homogeneity and thus the resulting better mechanical properties of these alloys [14][15][16]. During the solution treatment, the alloy is heated above γ solvus so as to dissolve the intermetallic γ phases, eliminate interdendritic microstructures, and make the entire alloy have a uniform elemental distribution [15][16][17][18][19].…”

“…Consequently, additional processing steps and heat treatments in solid solution treatments are required to improve the compositional and microstructural homogeneity and thus the resulting better mechanical properties of these alloys [14][15][16]. During the solution treatment, the alloy is heated above γ solvus so as to dissolve the intermetallic γ phases, eliminate interdendritic microstructures, and make the entire alloy have a uniform elemental distribution [15][16][17][18][19]. During subsequent aging treatment, the γ re-precipitates to obtain the typical microstructures of the superalloy, in which a cuboidal γ strengthening phase with desirable size (normally 300 to 500 nm) is embedded homogeneously in the γ matrix [20].…”