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The two glass-ceramics studied here derive from the complex system (MgO,ZnO,Li2O)-Al2O3-SiO2 and are obtained by controlled devitrification of the same parent glass. Although they have the same chemical composition, one is a “β-quartz” (or “β-eucryptite”) type while the other one is a “β-spodumene” glass-ceramic. A detailed microstructural analysis of these materials has been performed at different scales by several complementary characterization methods (SEM, TEM, DTA, XRD and FTIR). This extensive study has shown the great microstructure difference (grain distribution, grain size, nature of vitreous and crystalline phases) between these two glass-ceramics obtained from the same parent glass. [ABSTRACT FROM AUTHOR]

Abstract: Cobalt base superalloy hardfacings have been deposited by manual arc welding. Such deposits of total thickness 15 to 17 mm are realised in four successive layers on a steel substrate. The aim of this study is to analyse the role of the welding energy on hardfacings microstructural variations. Microstructure of these hardfacings is formed of a mixture of eutectic precipitates between primary dendrites of a cobalt-rich fcc phase. The high resulting dilution with the substrate induced by such manual arc welding process generates a chemical gradient in the deposit thickness able to involve various carbides volume fraction: the eutectic precipitates volume fraction varies in the reverse order of dilution with no significant difference versus welding energy. On the other hand, the fact of producing hardfacing in successive layers causes a secondary precipitation. In other terms, this kind of deposit involving high temperatures for a sufficient long time makes the dendritic Cr and Co-rich zones precipitate. Thus, fine cuboids particles of Cr23C6 carbides are formed in the dendrites. In accordance with higher welding energy used, the higher temperatures reached generate the Cr23C6 carbides size increasing. [Copyright &y& Elsevier]