Exploring the Ti-5553 phase transformations utilizing in-situ high-temperature laser-scanning confocal microscopy

• Published in: Materials characterization Vol. 159; p. 110013
• Main Authors: Campo, Kaio Niitsu, Fanton, Leonardo, de Mello, Mariana Gerardi, Moon, Suk-Chun, Dippenaar, Rian, Caram, Rubens
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01-01-2020
• Subjects: HT-LSCM; In-situ; Microstructure; Phase transformation; Ti-5553 alloy; Titanium; Titanium; Phase transformation; In-situ; Microstructure; HT-LSCM; Ti-5553 alloy
• ISSN: 1044-5803; 1873-4189
• DOI: 10.1016/j.matchar.2019.110013

Recently, the β metastable Ti-5553 alloy has attracted significant interest owing to the possibility of achieving excellent mechanical properties. In this study, for the first time, the Ti-5553 phase transformations were investigated using high-temperature laser-scanning confocal microscopy (HT-LSCM). During the continuous heating of an aged sample, the α phase dissolution was not clearly visible owing to the remaining grooves of former grain and interphase boundaries. However, the continuous cooling experiments (from the β field) showed that the α phase precipitation started preferentially at grain boundaries. With the increase in cooling rate, the α precipitates became more refined and the supercooling necessary to promote allotriomorphic precipitation increased. At a cooling rate of 100 °C min−1, no α phase was observed in the analyzed field of view. A higher oxygen content was suggested to contribute to the microstructural differences between the free surface and bulk. The volume fraction of the α phase was lower than that obtained on the original surface at cooling rates of 5, 25, and 50 °C min−1, while only minor differences were observed at cooling rates of 100 and 250 °C min−1. The α phase precipitation was analyzed in detail. The HT-LSCM technique can be a useful method for the analyses of solid-state phase transformations in Ti alloys.
•First in-situ phase transformation study of Ti-5553 alloy by confocal microscopy•The high oxygen affinity of Ti demands a highly controlled atmosphere.•Thermal etching grooves persist after phase dissolution, hindering the analysis.•Slower cooling rates favor the precipitation of allotriomorphic α phase.•The allotriomorphic and intragranular α precipitates become more refined as the cooling rate increases.