Evaluation of metallic alloys microstructure by correlative microscopy, backscattered electrons diffraction and digital image processing

Abstract

The correlative microscopy is defined as the evaluation of the same sample field by different microscopy techniques. In this project, the correlative microscopy experiments will provide the superposition of information from a light microscope and a scanning electron microscope, integrated with X-ray microanalysis and electron backscatter diffraction systems. It will define a kind of microstructural pattern, permitting the analyst to preview the chemical elements or crystallographic orientation distributions in a metallic alloy just from low cost light microscopy images, then reducing the quality control costs and accelerating quality inspection or materials research procedures.Furthermore, this proposal aims to develop methodologies based on digital image processing for quantitative analysis of hardening level for an aluminum alloy, based on the morphological and crystallographic texturing degrees, to evaluate the influence of local energy storage on precipitates formation. Also, the precipitates size and distribution effects on hardening mechanisms will be studied. The main goal is the proposal of a new parameter to estimate the crystallographic texturing degree from the morphological texture measured with a light microscope, based on measurements from processing and analysis of digital images, to reduce the costs for thermomechanical treatment processes optimization. The proposed methodology includes: thermomechanical treatments for AA-7475 aluminum alloy based on experimental design; microstructural analysis by correlative microscopy including light microscopy (LM), scanning electron microscopy (SEM), microanalysis by X-ray energy dispersive spectrometry (EDS) and atomic force microscopy(AFM); crystallographic analysis by electron backscatter diffraction (EBSD); mechanical testing; development of digital image processing routines; and statistical data analysis.Other metallic alloys will also be studied by correlative light-electron microscopy, EDS, EBSD and AFM: the 300-M and 15-5PH steels, and the Ti-6Al-4V titanium alloy. The major innovation in this proposal consists on the development of a digital image processing and analysis method to reduce the costs for EBSD crystallographic analysis by using light microscope images, just based on correlative microscopy.It is also proposed the development and free offering of NIH ImageJ macro programs for quantitative microstructural analysis, providing large access for materials researchers to image analysis tools for measurements of particle and grain sizes and morphology, steel inclusions and phases volumes and distribution.In this way, it is necessary to provide an infrastructure for advanced preparation of metallographic samples and to add imaging and analysis resources for the motorized light microscope of our laboratory, the LAIMat (Materials Imaging Lab). The LAIMat is a microscopy and digital image processing facility, offering free services in materials imaging as a multidisciplinary and multiuser environment. Its equipment are new and updated, including one scanning electron microscope, one atomic force microscope, one motorized light microscope, one confocal-interferometer microscope for topographic measurements and a system for correlative light-electron microscopy.So, the LAIMat offers an interesting and large counterpart for this project development, exceeding many times the required budget in this proposal. It was built with later financial resources from FAPESP, UNESP, CNPq and CAPES. It means that this new investment will preserve the invested public fund by enlarging the LAIMat's capabilities and support capacity, which is interesting due to the exclusive characteristics of this Laboratory in the São Paulo State. Finally, there is no other laboratory of microscopy and sample preparation with those equipment in the region of Vale do Paraíba. (AU)