| Abstract: |
This paper studies the influence of powder characteristics and powder mixing ratios on the cold sprayability of 316L/Fe mixed powders. Deposition efficiency (DE), porosity, microhardness and bond strength were measured and analysed. Porosity and microhardness correlated well with the coating flattening ratios (CFR), which in turn correlated with powder characteristics and mixing ratio. Bond strength also correlated with powder mixing ratio, but the DE values were more difficult to rationalise. Previous approaches to predict the DE of mixed powders were based on a simple rule of mixtures (DE=DE1×f1+DE2×f2, where fi is the corresponding weight fraction of the component). Since this proved ineffective, different particle-substrate impact scenarios during 316L/Fe mixed powders deposition were considered in this work. Individual particle impact tests, generated by very low feed rate spraying of powders on single component or mixed 316L/Fe substrates, were performed to simulate those impact scenarios. The bond ratio (BR), defined as the ratio of the number of bonded particles (deposits) to the total impinged particles (deposits+craters), was calculated for each impact scenario and a method was introduced to correlate BR with DE. The correlations, together with coating characterisations, reveal the various deposition mechanisms which could affect the DE.
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