The Effect of Nb/Ti Ratio on Hardness in High-Strength Ni-Based Superalloys

Abstract

Abstract:The age-hardening behaviour and microstructure development of high strength Ni-based superalloys ABD-D2, D4, and D6 with varying Nb/Ti ratios have been studied. The studied alloys have large volume fractions and multimodal size distributions of the γ precipitates, making them sensitive to cooling conditions following solution heat treatment. Differential scanning calorimetry was conducted with a thermal cycle that replicated a processing heat treatment. The hardness of these alloys was subsequently evaluated by nanoindentation. The Nb/Ti ratio was not observed to influence the size and distribution of primary and secondary γ precipitates; however, the difference in those of tertiary γ and precipitate morphology were observed. The nanoindentation hardness for all alloys reduces once they have been solution-heat-treated. The alloys exhibited specific peak hardness. The alloy with the greatest Nb content was found to have the best increase in hardness among the alloys studied due to its large tertiary γ precipitate.

Characterization of Phase Chemistry and Partitioning in a Family of High-Strength Nickel-Based Superalloys

“…Most of the ABD alloys express this c¢ volume fraction as a mixture of small tertiary precipitates in addition to a bimodal distribution of secondaries, which is backed up by research on the same ABD-series alloys carried out by Hisazawa et al [35] In the as-received state, the alloys were reported to have a very small fraction of primary c¢ due to the super-solvus heat treatment regime, plus secondaries in the~200nm size range and tertiaries < 50 nm, which almost perfectly matches the SEM observations and size distributions shown in Figures 1 and 2. The only discrepancy involves the high-Nb ABD-6 alloy, which was observed in this study to have a unimodal size distribution with little differentiation between secondary and tertiary precipitates.…”

On the Effect of Nb on the Microstructure and Properties of Next Generation Polycrystalline Powder Metallurgy Ni-Based Superalloys

“…In addition, while both alloys were found to behave similarly following P-SHT2, the tertiary c¢ distributions were markedly different following P-SHT1, with Alloy B exhibiting a finer tertiary c¢ distribution, consistent with reports in the literature. [21] The effect of Nb on the material microstructure following P-SHT1 can also be used to understand the tensile behavior of the alloys. The superior tensile properties exhibited by Alloy B are believed to be directly correlated to the Nb content, due to both its effect on increasing the c¢ APB energy as well as in increasing the c¢ fraction and producing a refinement in the tertiary c¢ distribution.…”

“…[18,19] In addition, alloys with elevated concentrations of Nb have been shown to exhibit finer secondary and tertiary c¢ distributions, further increasing the strength of the material. [20,21] Nb has also been reported to be a potent solid solution strengthening element when present in sufficient concentrations in the c matrix. [22,23] However, high Nb concentrations have been linked to the precipitation of the d and g phases, both of which are generally considered deleterious to alloy properties.…”

Ni- and Co-Based Superalloys and their Coatings

“…The present Special Issue is composed of seven articles related to alloy development [1], mechanical behavior during forging of polycrystalline alloy [2], a coating deposition process [3], microstructure in an additively manufactured Ni-based superalloy [4], mechanical behavior during close-to-service conditions of cast alloys [5,6] and repair of a cast alloy [7].…”

“…In more detail, the effect of the Niobium/Titanium ratio on age hardening behavior has been investigated by Hisazawa et al [1] using different alloys whose compositions have been selected through an "Alloy-by-Design" approach formerly developed in Roger Reed's group. Microstructural stability and the size distribution evolution of precipitates as a function of the aging time at 1123 K have more specifically been investigated.…”