Influence of Etchants on Quantitative/Qualitative Evaluations of the γ′ Precipitates in a Nickel-Base Superalloy

Abstract

To evaluate the microstructural characteristics of nickel-base superalloys, the size, number density, volume fraction, and morphology of the c 0 precipitates are frequently analyzed. For accurate microstructural analysis, a proper etching treatment should be applied evenly over the sample. Lack of care in choosing either the etchant or the etching technique can result in significant errors, not only in qualitative observations but also in quantitative analysis of the c 0 precipitates. This research examined the effects of etching technique as well as etchant type on the microstructural characterization of the c 0 precipitates in IN738LC nickel-base superalloy. The heat-treated samples with the same morphology of the c 0 precipitates were independently etched either in matrix phase (c) or in c 0 precipitate etchants. After quantitative analysis by scanning electron microscopy, the results were compared with electrolytically extracted c 0 precipitates for the same samples. The results show clearly that for qualitative and morphological observations of the c 0 precipitates, the matrix phase c etchants are desirable, while for quantitative analysis, the c 0 etchants can provide appropriate results.

Methodology for Revealing the Phases and Microstructural Constituents of the CMSX-4 Nickel-Based Superalloy Implicating Their Computer-Aided Detection for Image Analysis

“…The presented examples of a proposal of the γ' phase precipitates segmentation ( Figure 3) are a good illustration of the ability to enhance features, as well as extract information from the digital image of the microstructure; • Image segmentation performed by hand in the case of γ' phase precipitates would be timeand work-consuming, making its quantitative characterization very expensive. That is why the search for semi-automated or automated and simultaneously precise segmentation of the γ' phase precipitates is so important; • There is a similarity between the attitudes expressed by a quantitative determination of γ' phase using etchants dissolving the γ' phase in this study ( Figure 3) and those described in the works [15,16].…”

“…It is rather unusual to find literature data describing the role of the sampling strategy or the sample preparation and etching for the metallographic analysis of Ni-based superalloys. Among those few, there are works [15,16] suggesting that the etching time and the etchant type are two major factors which can remarkably affect not only the morphological observations of the precipitates but also the accuracy of the quantitative analysis. This study seems to be one of the not numerous works which outline the critical role of etching in the revealing of phases and microstructural constituents on the basis of one selected Ni-based superalloy CMSX-4.…”

Microstructural Stability and Properties of New Nickel‐Base Superalloys with Varying Aluminium: Niobium Ratio

“…[ 56 ] The fine scale of the precipitates meant that the precipitate size distribution and volume fraction were difficult to obtain experimentally (using etching techniques) without introducing significant stereological errors. [ 57,58 ] As a consequence of this, the precipitate volume fractions were estimated using Thermo‐Calc based on the observed phases (γ, γ′, and γ″ if present). The burgers vector b was assumed to be of the conventional type, and the shear modulus G equal to that of a similar polycrystalline nickel‐base superalloy, in this case 718Plus (64 GPa at 700 °C).…”

Investigation of the Effect of Short Exposure in the Temperature Range of 750–950 °C on the Ductility of Haynes® 282® by Advanced Microstructural Characterization

“…Etchants that remove γ from the matrix have been found to produce more accurate volume fraction estimates when comparing different methods on IN738LC [19]. They also found some variation in the average precipitate size when comparing different etchants.…”