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Reactive sintering in Fe-Co system

2002; Maney Publishing; Volume: 45; Issue: 4 Linguagem: Inglês

10.1179/003258902225007087

1743-2901

David Weston, C. C. Degnan, J. V. Wood,

Injection Molding Process and Properties

Low porosity powder metallurgy compacts have been manufactured from treated elemental iron and cobalt powders sintered at 1150°C under an H2(g) atmosphere. Their microstructures consist of an interconnected mixed oxide network which encapsulates both the iron and cobalt phases. The production technique employed is an innovative process termed reacto-thermitic sintering (RTS), which leads to near full density and near net shape parts utilising conventional uniaxial compaction and mesh belt furnace practices. The RTS technique relies on microscale exothermic reaction between small quantities of added elemental Al and oxides present on the surface of the bulk powder, together with the bulk powder itself. This results in the production of a transient liquid phase which freezes rapidly and consolidates the compact without slumping. In order to generate an interconnected mixed oxide network, experiments were designed such that the Al powder reacts with the cobalt and the surface of the iron powder which is artificially doped with Fe and Cr oxides.Differential thermal analysis (DTA) and energy balance calculations revealed that the Al and the oxide coating reaction does not proceed directly. Instead the main contribution to the exothermic process is the reaction between Al and Co/Fe. The system does not exhibit true RTS behaviour and the interconnected network of mixed Al, Cr, and Fe oxides is created by subsequent reaction of Co-Al and Fe-Al intermetallics with the artificial Fe-Cr oxide coating on the Fe. The microstructure obtained exhibits negligible porosity with the metallic particles on the whole fully encapsulated by the oxide.