Reactive sintering of stainless steel

Pressed and sintered 316L type stainless steel compacts have been produced using an innovative process termed reactothermitic sintering (RTS). This technique has the ability to produce full density, near net shape parts using conventional compaction and mesh belt furnace practices. It utilises chemical reactions at the surface of the stainless steel powders in which the energy balance is matched to provide transient liquid films that can be frozen at high cooling rates to consolidate the material without slumping. Small quantities of elemental aluminium and nickel powders are added before compaction that react, during sintering, both with themselves and with oxide layers present on the bulk stainless steel powder surfaces. In addition to the naturally occurring oxides present on the surface of stainless steel powders, artificial oxide layers, deposited by sol-gel and direct thermal oxidation, have been used to aid investigations into the nature of the reactions involved. The RTS technique leads to the generation of novel microstructures in the systems described that are characterised by negligible interconnected porosity. The present paper details the experimental programme undertaken to ascertain and substantiate these phenomena together with a model of how porosity is eliminated in this system.