SPRAY FORMING

Spray forming is a relatively new manufacturing process for near net shape preforms in a wide variety of alloys. Spray formed materials have a characteristic equiaxed microstructure with small grain sizes, low levels of solute partitioning, and inhibited coarsening of secondary phases. After consolidation to full density, spray formed materials have consistently shown properties superior to conventionally cast materials, and comparable to powder metallurgy equivalents. The reduction of processing steps for spray forming in comparison with powder metallurgy and conventional cast/forge routes offers potential economic advantages. However, serious economic barriers to the widespread commercialisation of spray forming remain. These include the high cost of inert gases for atomization, significant losses from overspray, bounce-off and machining, poor process reproducibility and problems of implementing robust on-line control for metallurgical quality. Extensive model experiments with process monitoring and numerical simulation have been used to understand the underlying process physics and the development of preform shape and microstructure in an effort to enable full process control and so reduce losses. However, despite considerable progress, the cost of spray forming has not yet reduced significantly to compete broadly with existing technologies. © 1995.