Processing of a glass ceramic surface by selective focused beam laser treatment

Abstract

The context of the present work is a large research project aiming at manufacturing functionalised surfaces by selected laser treatment with a focused beam [1].More specifically, this paper aims at showing the possibility of obtaining a dense glass ceramic layer, with controlled microstructure, from a glass powder coating.In the present state of the research, laser scans are performed on glass powder compacts in order to investigate the operating conditions (power, speed and vectorisation) required to achieve the objective. The selected glass belongs to the Sr–Ti–Si–Al–K–O system, its crystalisation leads to a glass–ceramics containing piezoelectric Sr–fresnoïte crystals (Sr2TiSi2O8) Maury et al. (2011). The selective laser treatment is carried out by mean of a focused Nd–YVO4 laser beam. Characterisation of the thermal state of the surface during the treatment is performed thank to an IR camera. The surface microstructure is evaluated by X-ray diffraction and scanning electron microscopy.The results presented shows that Sr–fresnoïte glass ceramics layers can be processed by applying a two stage process: first the melting of a glass powder to form a dense amorphous layer; then the crystallisation of this layer. However, the microstructures resulting of a crystallisation step performed by mean of a one-scan laser treatment are heterogeneous. IR camera analysis highlights that this heterogeneity is due to thermal profile strongly depending on the position on the scanned surface. Moreover, the high energy scanning conditions required to promote crystallisation make that this later takes place on cooling after surface has been re-melted. Processing by a multi-scan mode (numerous successive rapid scans) seem more suitable. In that case, IR camera analysis shows a homogeneous thermal state of the surface. Additional investigations have to be performed in order to be able to master the relation between the thermal profile and the laser scan parameters.