Effects of Solid Solution Strengthening Elements Mo, Re, Ru, and W on Transition Temperatures in Nickel-Based Superalloys with High γ′-Volume Fraction: Comparison of Experiment and CALPHAD Calculations

Abstract

We prepared 41 different superalloy compositions by an arc melting, casting, and heat treatment process. Alloy solid solution strengthening elements were added in graded amounts, and we measured the solidus, liquidus, and c¢-solvus temperatures of the samples by DSC. The c¢-phase fraction increased as the W, Mo, and Re contents were increased, and W showed the most pronounced effect. Ru decreased the c¢-phase fraction. Melting temperatures (i.e., solidus and liquidus) were increased by addition of Re, W, and Ru (the effect increased in that order). Addition of Mo decreased the melting temperature. W was effective as a strengthening element because it acted as a solid solution strengthener and increased the fraction of fine c¢-precipitates, thus improving precipitation strengthening. Experimentally determined values were compared with calculated values based on the CALPHAD software tools Thermo-Calc (databases: TTNI8 and TCNI6) and MatCalc (database ME-NI). The ME-NI database, which was specially adapted to the present investigation, showed good agreement. TTNI8 also showed good results. The TCNI6 database is suitable for computational design of complex nickel-based superalloys. However, a large deviation remained between the experiment results and calculations based on this database. It also erroneously predicted c¢-phase separations and failed to describe the Ru-effect on transition temperatures.

Improving the Effectiveness of the Solid-Solution-Strengthening Elements Mo, Re, Ru and W in Single-Crystalline Nickel-Based Superalloys

“…An exemplary DSC curve of the alloy ERBO/19 can be seen in Figure 1. For further information on the analysis technique and the accuracy of this method, the reader is referred to Ritter et al [23].…”

“…An exemplary DSC curve of the alloy ERBO/19 can be seen in Figure 1. For further information on the analysis technique and the accuracy of this method, the reader is referred to Ritter et al [23]. For electron-probe micro-analysis (EPMA), the γ′-precipitates were coarsened to a size of several micrometers by a special heat treatment, initially developed by Heckl et al [24].…”

Influence of Excess Volumes Induced by Re and W on Dislocation Motion and Creep in Ni-Base Single Crystal Superalloys: A 3D Discrete Dislocation Dynamics Study

“…Assuming an edge dislocation segment with a length of 1 nm, the back stresses for its glide and climb due to the presence of a Re or W atom was calculated using the DFT excess volumes and Equations (4)- (6). Neglecting any influence along the dislocation line direction, the back stresses decreased with increasing distance between the atom and the dislocation core, as shown in Figure 3.…”

“…Both the γ/γ microstructure and dislocation motion inside are influenced by these elements. An increasing content of Re and W increases the volume fraction of cuboidal γ phase, and Re decreases the γ particle size, while W has no effect on the size of γ [5,6]. During creep, Re decelerates the coarsening and rafting of γ precipitates [7,8], as well as Re and W retard the dislocation motion through solid solution strengthening mechanisms [9,10].…”

Room temperature tensile deformation behavior of a Ni-based superalloy with high W content

“…However, the application of the nickel-based superalloys containing Re and Ru is limited, mainly due to the prices of these two elements being much more expensive than the others. The element W, by contrast, has a lower price and could well improve the high temperature properties of the alloy [8,9] , which is thought to be an ideal alloying element to some extent to replace Re and Ru [10] . W mainly distributes in γ matrix Abstract: K416B Ni-based superalloy with high W content has good high temperature properties and low cost, which has a great development potential.…”