Volume 55, Issue 10

A wide range of methods and procedures exists to characterize microstructures and to quantify phases. This work presents a comparison between light microscopic examinations as a function of different etching methods and electron backscatter diffraction analyses. The procedures used in this context were etching with V2A solution, Kalling I and Beraha II etchants. The objective was to quantify the austenite phase in Q&P heat treated X46Cr13. The Q&P heat treatment allows to achieve high mechanical strengths (for X46Cr13 approx. R p0.2 = 1750 MPa) alongside high elongations at break (A = 14 %). This can be attributed to a combination martensite tempering and the TRIP effect. The required specific ratio of martensite and austenite can be established by the heat treatment. In order to define the heat treatment's optimal parameters, the mechanical characteristic values need to be determined and comprehensive phase fraction determinations must be performed. Beraha II provided particularly promising results. Compared with EBSD, matching phase fractions of austenite could be determined with deviations of the absolute values between one and three percent. This method offers a possible alternative to, or supplements the microstructural characterization and assessment of the material development for a high sample throughput and at reduced cost and effort.

Metallographic methods which are typically comprising chemical etching processes are applied to reveal grain boundaries in sections of metallic materials. In the case of an optically anisotropic material, grain boundaries can also be detected suing polarized light microscopy (PLM). To this end, the identification of grain boundaries, an automated image processing procedure, based on PLM, was developed. In this context, two different α Ti-based alloys were examined: a cast, non-porous rod material and a material obtained by powder metallurgy which, owing to its high porosity, places specific demands on the image processing system. The present work outlines the underlying metallographic and computer-based methods.

In an intermetallic γ-TiAl alloy possessing the nominal composition of Ti-43Al-4Nb-1.5Mo-0.5C-0.1B (in at. %), the precipitation behavior of the hexagonal Ti 2 AlC phase was studied using complementary metallographic methods. By the addition of C, the alloy can be solid solution strengthened and precipitation hardened. However, during an annealing process, coarse H carbides are formed in the β single-phase field which is practically insoluble for carbon. These coarse carbides are under the scope of this investigation. After determining the area of existence of the phase fields by means of differential scanning calorimetry, the occurrence and the morphology of the H-carbides were analyzed by applying specific heat treatments in the area of the α + β → β phase transformation. By the use of a laser scanning confocal microscope, the formation of the carbides was tracked in-situ as well as their growth kinetics determined. The mutual orientations of the microstructural constituents were determined in an scanning electron microscope by means of electron backscatter diffraction. Therefore, the specimen was not subjected to an additional surface treatment. Thus, the orientation relationship between the α 2 -Ti 3 Al phase and the H carbides could be verified and their formation within a C containing intermetallic TiAl-alloy could be illuminated.

In this work, two commercial indexable inserts with different coatings were examined with regard to their damage and wear characteristics after tool life testing on two different types of gray cast iron. The surface and chemical analysis by means of Scanning Electron Microscopy (SEM) and/or Energy Dispersive X-ray Spectroscopy (EDS) revealed a removal of the respective protective layer on the wear surface in varying degrees. In addition to that, crack structures were identified that take various forms as a function of the coating. The integrated Focused Ion Beam technology (FIB) also allowed to examine the identified cracks with regard to their propagation in the depth of the respective component. The cracks extend deep into the WC-Co base material and mainly propagate through the ductile Co phase.