Microstructural evaluation of monolithic and continuous fibre reinforced Al-12wt.%Si produced by low pressure plasma spraying

The spray/wind process is a concurrent fibre winding and plasma spraying te chnique and may be used for the manufacture of continuous fibre reinforced composites in a single spraying operation. The microstructure of low pressu re plasma sprayed (LPPS) Al-12wt.%Si coatings and spray/wind Al-12Si compos ites reinforced with continuous fibres has been investigated. The LPPS mono lithic Al-12Si deposit sprayed in a single-pass was characterised by splat- quenched microstructure and Si solubility extension in alpha-Al, whereas mu lti-pass spraying of thicker deposits promoted precipitation and growth of Si particles because of a corresponding increase of substrate-deposit tempe rature during LPPS. Four-layer Al-12Si composites reinforced with stainless steel wire and Sigma 1140 + SIC fibre have been successfully manufactured by the spray/wind process. Both composites exhibited low porosity and well- controlled fibre spacing. Surface roughness of the sprayed Al-12Si matrix w as the key factor in controlling composite porosity and fibre distribution. During subsequent vacuum hot pressing (VHP) consolidation, there were mini mal fibre movement and no fibre breakage. Limited fibre/matrix interfacial reactions occurred because the relatively low spray/wind porosity of spray/ wind composite reduced thermal exposure during VHP consolidation. However, some surface damage of the Sigma 1140 + SiC fibres occurred during both spr ay/wind and subsequent VHP consolidation. (C) 1999 Elsevier Science S.A. Al l rights reserved.