INFILTRATION OF MOLTEN AL-7WT.%SI INTO TIC BEDS WITH THE AID OF A K-AL-F BASED FLUX

Abstract

Trials to infiltrate TiC beds with and without flux were conducted with an Al-7wt.%Si alloy. The metal infiltrant is simply placed on top of the ceramic bed and the two are heated to 680, 820 and 1100°C in an Ar atmosphere or in atmospheric air and held at temperature for 1 hour. TiC powder was mixed with the K-Al-F flux in different ratios. Infiltrated specimens were microstructurally characterised using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD). It was found that TiC beds could not be infiltrated, with and without flux, across the interval of temperatures studied in air, only partial infiltration was seen with a high flux ratio. Conversely, when the flux was present in Ar, successful infiltration occurred at temperatures as low as 680°C and the single TiC bed was only infiltrated at elevated temperature. The K-Al-F flux, which is similar to cryolite and has high solubility for Al2O3, is thought to dissolve the oxide skin and prevent further oxidation of the melt enabling thus infiltration to occur as low as 680°C. The microstructural characterization revealed different levels of reaction depending on infiltrating temperature, the reaction products being Al4C3 and complex Ti-Al-Si intermetallics.