Alpha-to-gamma reverse phase transformation of molten removal in alumina ceramics laser processing. Issue 9 (15th June 2018)

• Record Type: Journal Article
• Authors: Luo, Yonghao; Wang, Xuyue; Wang, Chenglin; Hu, Yebing; Liu, Mucan
• Is Part Of: Ceramics international. Volume 44:Issue 9(2018)
• Page Start: 10412
• Page End: 10419
• Publication Date: 2018-06-15
• Subjects: α-to-γ phase transformation -- Pulsed laser cutting -- Alumina ceramics -- Molten removal -- Micro morphology -- XRD investigation; Ceramics -- Periodicals; Céramique industrielle -- Périodiques; Ceramics; Periodicals; Electronic journals; 666
• DOI: 10.1016/j.ceramint.2018.03.057
• Languages: English
• ISSNs: 0272-8842

Abstract

Abstract: Generally speaking, in the melting process of alumina ceramics, all the metastable transitional phase will be gradually transformed into the stable α phase with rising temperature due to an irreversible lattice reconstruction. However, under the action of pulsed laser cutting, the lattice structure of α-alumina needs to withstand the great stress from instantaneous high energy impact. Thus, a slip dislocation of 1/4 at. diameter is generated on the atomic plane of each second basal layer to produce γ-alumina. In this work, a ceramic plate comprised of α-alumina is taken as the object of study. The α-to-γ reverse phase transformation of the molten removal is verified by the observed microstructure from scanning electron microscope (SEM) and transmission electron microscope (TEM). Simultaneously, the X-ray diffraction (XRD) investigation shows that the basis of molten removal after laser cutting is still α-alumina. The micrographs of octahedral corners or hexagons are shown in different observation directions. There is no γ-alumina phase transformation product in the spherical granular removal at each vapor-to-melt ratio (rvmr ). In contrast, γ-alumina is detected in the adhering slag with a micro-morphology of cubic phase. The mass fraction is increased with the rising of vapor-to-melt ratio. At the same time, θ-alumina also exists in some spattering removal as intermediate product between α and γ phase. It is indicated that the generation of α-to-γ reverse phase transformation occurs mainly in the melting process of temperature rise, and the maintenance of phase transformation results mainly occurs during cooling process of condensation.