Evaluation of porosity in spray deposited A2 tool steel

The objective of the present study is to provide a numerical model to serve as a guide in the determination of optimum processing parameters for the s pray forming Of tool steels Pdl;Porosity is predicted using a heuristic mod el that incorporates the effect of the relative magnitudes of the fluid flo w characteristic time and the solidification characteristic time on the por osity formation process. Two regimes the "fast flow" regime and the "fast s olidification" regime, are identified a priori Expressions for porosity as a function of the particle size distribution, the average solid fraction of the incident spray and the solidification contraction are derived based on these assumptions The average solidification of the incident spray is esti mated from the droplet size distribution and the solid fraction of a single droplet of a given sire, The latter is determined by calculating tbe dropl et dynamics and thermal history. The effects of process parameters (melt su per-heat, atomization pressure, deposition distance and melt mass flow rate ) on the level of porosity are investigated By determining the conditions c orresponding to a minimum in predicted porosity, optimum processing paramet ers can be assessed As a result processing maps are provided as a reference for achieving spray formed tool steels with minimum porosity.