PLASMA SPRAY JOINING OF AL-MATRIX PARTICULATE-REINFORCED COMPOSITES

Aluminum matrix composite joints have been produced on both aluminum a lloy and metal matrix composite (MMC) substrates using powders contain ing SIC and Al2O3 particulates. Most of the composite powders were pro duced by ball milling, but the most effective joints were produced usi ng Osprey composite powders. The results of preliminary joining experi ments indicate that the substrate should be preheated to 200 degrees C and a very wide bevel angle should be provided in order to obtain the highest strength joints. Silicon alloy additions to the matrix signif icantly improved strength but titanium additions had no effect. Heat t reatment after spraying significantly improved the bond strength and r estored precipitation hardening in the matrix. Significant amounts of Mg were lost from the deposit during spraying while some free silicon was produced by pyrolysis of the SIC powder; hence, further efforts mu st develop powder compositions that produce the optimum matrix composi tion in the sprayed deposit. Hot isostatic pressing of the samples to eliminate porosity had only a small effect on the final strength of th e joints. No significant amount of Al4C3 was detected in deposits whic h contained SiC.