A SEM-X-Ray assisted experimental approach for the determination of mechanical and thermal load – induced damage in MMCs

Victor Kytopoulos,Alexandros Altzoumailis,John Venetis,Emilios Sideridis,Chrysoula Riga

doi:10.3221/igf-esis.50.35

Victor Kytopoulos, Alexandros Altzoumailis + Show 3 more

Open Access

https://doi.org/10.3221/igf-esis.50.35

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Abstract

An experimental technique is presented to evaluate mechanical and thermal load-induced microstructural damage, based on the Electron Probe Micro-Analysis (EPMA) principle, by which certain analytical potentialities of Scanning Electron Microscopy (SEM) are used. The aim of the study is to apply this technique in the case of metal matrix composites (MMCs). Based on earlier findings it is shown that by this technique the damage-controlled microstructural integrity distribution ahead of an edge-notch under tension is determined with sufficient reliability. To demonstrate this fact two MMCs were tested. Dog-bone specimens with an edge notch were subjected to slow tension up to their ultimate stress, the loading process was terminated and the EPMA technique was applied. The procedure was also applied after sudden cooling of the specimens by immersion in liquid hydrogen. It is shown that the MMC with larger differences between the elastic and plastic constants of the inclusion and the matrix exhibit increased proneness to mechanical and thermal load-induced damage. The findings obtained are discussed on the basis of the dominating combined influence of macro-microscopic mechanical and thermo-elastic stress concentration processes on the matrix-particle interfacial fracture strength.

Highlights

M odern materials such as aluminum-alloy-based Metal Matrix Composites are the new candidates for a variety of engineering applications
I n Figs.2(a,b) the data obtained from the measurements of micro-damage controlled micro-structural integrity distribution ahead of the notch root for a 2124 metal matrix composites (MMCs)- and a 8090 MMC-specimen, respectively are presented
The experiments conducted showed that, within the experimental scatter of the proposed semi-quantitative approach and under the same experimental conditions, the MMC with higher ductility of the matrix exhibits a higher proneness to mechanical load - induced damage compared to the MMC material with lower ductility

Summary

Introduction

M odern materials such as aluminum-alloy-based Metal Matrix Composites are the new candidates for a variety of engineering applications. In tribological applications [2, 4] due to high level of localization of the micro-cracks or crack-like micro effects mainly at the surface, the ability of a correct recording and estimation of surface damage becomes a challenging task Such recording of damage would make it possible to retain the components in service until replacement is indicated by the damage level approaching a critical value. It would be of importance to establish certain complementary experimental techniques for surface damage evaluation and characterization at microscopic level Such a technique, called Scanning Electron Microscopy-aided Electron Probe Microanalysis (SEM-EPMA), was used for this purpose in the present study. The proper application of this technique on a tensile loaded edge-cracked (notched) specimen was found to allow the evaluation, in a semi quantitative way, of the continuous distribution of mechanical and thermal load-induced micro-damage and the description of the microstructural integrity changes, ahead of the notch root

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