Evaluation of strain caused by coherent precipitates in an Al alloy using TEM techniques

• Published in: Materials characterization Vol. 73; no. Complete; pp. 61 - 67
• Main Authors: Hernández-Rivera, J.L., Rivera, J.J. Cruz, Garay-Reyes, C.G., Azpeitia, M. Ramos, Zúñiga-Alonso, I., Martínez-Sánchez, R.
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01.11.2012; Elsevier
• Subjects: Age hardening; ALUMINIUM ALLOYS; Aluminum alloys; Aluminum base alloys; Coherence; Computer programs; Cross-disciplinary physics: materials science; rheology; Crystal defects; DEFORMATION; DISLOCATIONS; Electron microscopy; Exact sciences and technology; Guinier Preston zone; HOLOGRAPHY; KINETICS; MATERIALS SCIENCE; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; PRECIPITATION; Solidification; SPATIAL RESOLUTION; Strain; TRANSMISSION ELECTRON MICROSCOPY; Electron microscopy; Aluminum alloys; Age hardening; Precipitation; Aluminium base alloys; Transmission electron microscopy; Coherent precipitate
• ISSN: 1044-5803; 1873-4189
• DOI: 10.1016/j.matchar.2012.07.017

Elastic strains, caused by GP zones in an aged Al alloy, were determined quantitatively using two techniques: Dark Field In-line Holography (DFH) and High Resolution Transmission Electron Microscopy-Geometric Phase Analysis (HRTEM-GPA). The results obtained by both techniques showed that the elastic strain was not uniform along the precipitate–matrix interface. In some areas, it was found that strain had negligible value and this was attributed to the loss of coherence between the lattices. It is suggested that a possible explanation for this fact could be a variation in the “vacancies pump mechanism” kinetics. To obtain a better interpretation of the experimental deformation maps, a reference GP precipitate–matrix structure was built using QSTEM software. The main advantages of DFH over HRTEM-GPA were a bigger field of view and low electron dose requirements without spatial resolution loss. Another difference found was that crystalline defects such as dislocations were evidenced by HRTEM-GPA in contrast to the result obtained by DFH. However, strain measurements were affected by mask size effect in the former. ► Strain around GP precipitates was not uniform and was in a more relaxed state. ► Strain values determined by HRTEM had more artifacts compared with holography ones. ► Strain distribution was attributed to differences in the release of vacancies. ► Holography showed important advantages over HRTEM regarding field of view mainly.