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Laser-cladding experiments have been performed with STELLITE 6 powder on mild steel substrates, using a 1.5 kW linearly polarized continuous wave CO 2 laser as a heat source. The clad height, the mass efficiency, the dimensions of the melt pool, as well as the global absorptivity, were measured as functions of the powder feed rate and the scanning speed. A quantitative analytical model of the process is proposed, based on the overall mass and energy balance. It allows the calculation of the mass efficiency and of the global absorptivity, taking into account the incorporation of the powder into the melt pool as well as the energy absorbed by the powder jet and the substrate. It successfully explains the experimental results and demonstrates the role played by the melt pool inclination with respect to the substrate. A processing diagram is given to find rapidly the optimal laser treatment conditions and the desired clad height. It is discussed with respect to the other limiting conditions of the process, the geometrical maximum powder efficiency, the porosity, the dilution, and the maximum power of the laser installation.

Thermodynamic modelling shows that while TiC is a stable phase in Al ± Ti ± C grain re®ners, it should decompose on addition of the re®ners to typical Al alloys. The present work assesses the impact of melt composition on TiC stability and on grain re®ner performance, which has been tested at various addition levels in Al and Al ± Mg alloys. In melts with compositions that stabilise TiC, there is effective grain re®nement with little fading of performance on holding the re®ner in the melt. In melts with compositions in which TiC is not stable, grain re®nement is impaired even at short holding times, and becomes markedly worse at longer holding times. It is concluded that in typical cases progressive decomposition of TiC does occur, and that this can have a signi®cant effect on grain re®nement by inoculation with Al ± Ti ± C master alloys.MST/4663