Single crystal growth of oxides using additive laser material deposition

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Laser material deposition (LMD) involves the feeding of a powder onto a substrate which is completely melted by laser radiation. Bulk volumes can be built up through layer-by-layer deposition. Single crystal growth by LMD is performed in a furnace which is accessible form the top. The furnace allows the temperature management regarding heating and cooling rates and setting of small temperature gradients in melt and crystal. Compared to conventional single crystal growth methods LMD avoids contamination of the melt from the heat source (gas flame in Verneuil method) or from the crucible (Czochralski method). Laser based growth of bulk single crystals has not been developed so far.The main goal of the project is the fundamental understanding of single crystal growth of oxides by additive laser material deposition using sapphire as demonstrator material. To achieve this goal knowledge has to be gained in the correlation between process parameters one side and growth performance and properties of the crystals on the other side as well as in processing technology. The following sub-goals should be achieved:Modeling of the growth process using FEM simulation of space and time resolved temperature fields. Based on these fields temperature gradients in the liquid and solid state can be studied. Beam intensity distribution and laser power will be adapted to create optimum conditions for single crystal growth of sapphire.Influence of the process parameters on the growth and properties of the crystal. The main parameters are laser power, intensity distribution, heating and cooling rates, powder feeding, properties of the powder and the substrate, furnace temperature and rotation of the crystal. Adaptation of processing and system engineering to achieve optimum growth conditions. This involves the development of a beam homogenizer for CO2 laser radiation for a maximum power of 3 kW. Furthermore the powder feeding has to be adapted to achieve a homogeneous distribution of the powder on the substrate.Additive laser material deposition as a flexible method for the growth of single crystals opens many opportunities for future applications, e.g. the free form manufacturing of different geometries (cylinder, cube, disc) by beam shaping or scanning or the manufacturing of gradient crystals by variation of powder composition during layer wise build-up.