Creep mechanism and microstructure evolution in silicon nitride ceramics

Abstract

Tensile creep processes in a commercial grade of silicon nitride, SN 88, are reviewed with the focus on cavitation and microstructure changes. Experimental measurements showed that cavitation at multigrain junctions is the rate controlling creep mechanism. The cavitation creep model of Luecke and Wiederhorn was extended to explain non-power law behaviour and strong creep asymmetry. Secondary phase composition changes after prolonged creep tests resulted in the formation of Ybdisilicate phase at the expense of Yb-oxynitride due to oxidation. Such secondary phase changes affect residual glass composition, which has crucial effect on the processes involved in cavitation and resulting creep behaviour.

Microstructure and Creep Behavior of a Si3N4–SiC Micronanocomposite

“…Extensive investigation of cavitation creep has been conducted by Wiederhorn and his coworkers 14,15 . According to their study, cavities nucleate and grow primarily in the interstitial pockets located at multigrain junctions.…”

“…Extensive investigation of cavitation creep has been conducted by Wiederhorn and his coworkers. 14,15 According to their study, cavities nucleate and grow primarily in the interstitial pockets located at multigrain junctions. As these cavities grow, the silicate phase flows through the network of triple junctions of Si 3 N 4 grains to other pockets.…”

“…Apparently, creep of silicon nitride has to be explained in terms of a series of mechanisms that occur simultaneously. According to their suggestion, the main creep mechanism taking place during compression creep is grain-boundary sliding accommodated by solution precipitation, 15,16 whereas tensile creep is considerably influenced by cavitation. 17,18 Potential utilization of silicon nitride-based ceramics for hightemperature applications focuses primarily on the study and understanding of high-temperature mechanical properties.…”

“…Apparently, creep of silicon nitride has to be explained in terms of a series of mechanisms that occur simultaneously. According to their suggestion, the main creep mechanism taking place during compression creep is grain‐boundary sliding accommodated by solution precipitation, 15,16 whereas tensile creep is considerably influenced by cavitation 17,18 …”