Quantitative characterization of fracture surfaces of engineering materials with scanning electron microscopy

January 23, 2023

Seyedmahmoud Bayazid
Thesis. (January 2023). DOI: https://escholarship.mcgill.ca/concern/theses/rx913w10t


Quantitative microanalysis of rough surfaces is a big challenge in electron microscopy field. Although X-Ray microanalysis can be a useful tool for preliminary characterization, it is not quantitative because the geometry of rough surfaces introduces problems that are not present in the microanalysis of a bulk sample. The problem with the quantitative microanalysis of rough surfaces is that electrons can be scattered from all sides due to different slopes on the surface. Therefore, the geometry of rough surfaces impacts the generated, emitted, or measured x-ray intensities and thereby the quantitative analysis of the surface. The present Ph.D. study will focus on fabricating 3D reconstruction technique for fracture surfaces and producing a quantitative method to characterize the non-flat surfaces with electron microscopy. At first, a set of experiments, imaging, and modeling techniques were designed to get the 3D digital images of fracture surfaces. Using the backscattered signals, a 3D digital reconstruction was obtained. The effects of Scanning Electron Microscopy (SEM) parameters on the accuracy of the 3D reconstruction model which are taken via Backscattered Electron (BSE) images were studied. The results showed the best range of the working distance for our system is 9 to 10 mm. It was shown that by increasing the magnification to 1000X, the 3D digital reconstruction results improved. However, there was no significant improvement by increasing the magnification beyond 1000X. In addition, results demonstrated that the lower the accelerating voltage, the higher precision of the 3D reconstruction technique, as long as there are clean backscattered signals. Moreover, the behavior of the Peak to Background (P/B) as one of the quantitative candidate methods for characterization of rough surfaces was analyzed while the take-off angle, tilt angle, particle size, and beam energy were altered. It was observed that P/B highly depends on the beam energy, particle size, and the composition of the substrates. Results indicated that the P/B increases at high tilt angles. Results showed that by increasing the take-off angle, the P/B initially reduces and then reaches a plateau. Data showed that the P/B increases when the electron beam is moved from the center to the side of a particle. Additionally, the P/B is mover sensitive to the beam movement for the spherical particles than the cubical particles. In the next step, a geometrical correction factor (G) was introduced for the quantitative characterization of particles. Using the new ZAFG method (Z, atomic correction, A, absorption correction, F, florescence correction, and G, geometrical correction) makes it possible to quantify particles without using Monte Carlo simulation. Adding a geometrical factor to the convention ZAF method creates a very easy and simple way to quantify particles. Analyses showed that the G factor is a function of 𝐷 , (where D is the diameter of particles, and 𝑋𝑒 is the depth of emitted x- 𝑋𝑒 rays in a bulk sample with the same chemical composition). It was shown that when 𝑋𝑒 becomes greater than D, the G factor decomposes exponentially as the incident electron energy rises. Data showed that when 𝐷 > 1 for a particle, then G = 1. In this situation, the particle works almost as 𝑋𝑒 a bulk sample.It was shown that the G factor only dependson𝐷, neither the chemical composition 𝑋𝑒 nor the beam energy. Finally, in this work, preliminary results were presented using a real fracture surface. The existing Monte Carlo software (MC X-ray) was incorporated into the image processing software Dragonfly developed by Object Research Systems (ORS) Inc. The incorporation of the MC X-ray in Dragonfly allows users to do Monte Carlo simulation for any complicated geometry. An excellent agreement was observed between experimental data and Monte Carlo simulation.

How Our Software Was Used

Monte Carlo simulations were performed on the 3D fracture surfaces of a Monel alloy using Dragonfly’s MC X-Ray module.

Author Affiliation

(1) Mcgill University