Strength enhancement of Nicalon-reinforced lithium aluminosilicate containing a Ta(2)O(5) second phase

The purpose of this study was to follow up the preliminary results of a previous thesis which appeared to indicate that the addition of Ta{dollar}sb2{dollar}O{dollar}sb5{dollar} to the matrix of a Nicalon fiber reinforced lithium aluminosilicate glass ceramic composite increased the mechanical properties of the resulting composites. The strength increase was attributed to the presence of a TaC platelet phase in the matrix material. The TaC was thought to be a result of the reaction between the {dollar}rm Tasb2Osb5{dollar} additions and soluble CO from the hot press atmosphere used in the densification of the composites. These preliminary results (the strength increase and TaC formation) were a side experiment to a larger work and consequently were not rigorously investigated.; The present work showed that the CO did react with {dollar}rm Tasb2Osb5{dollar} to form TaC, but only as a surface coating. The surface coating reached a terminal thickness of 5-10 {dollar}mu{dollar}m after 1 h at 1400{dollar}spcirc{dollar}C. There was no evidence of soluble CO reacting to form TaC in the matrix. What was previously thought to be TaC platelets appears to be a two phase eutectic structure of {dollar}beta{dollar}-spodumene and {dollar}rm Tasb2Osb5{dollar}. When the {dollar}rm Tasb2Osb5{dollar} content was increased to 15%, {dollar}rm Tasb2Osb5{dollar} crystals were formed in addition to the eutectic structure. The formation of the eutectic structure could be suppressed in samples containing less than 3.5% {dollar}rm Tasb2Osb5{dollar} by cooling at 10{dollar}spcirc{dollar}C/min. Cooling rates of 1{dollar}spcirc{dollar}C/min promoted the two phase structure.; The interfacial shear strength and flexural strength did not appreciably increase with {dollar}rm Tasb2Osb5{dollar} additions. Increasing the hot pressing time did increase the interfacial shear strength, but resulted in lower flexural strengths and less graceful failure modes. There was great variation in the flexural strength of the composites which increased with increasing {dollar}rm Tasb2Osb5{dollar} content. With the very limited sample size of the preliminary study the large variation may have suggested a trend which did not statistically exist.