Highly Creep‐Resistant Silicon Nitride/Silicon Carbide Nano–Nano Composites

Abstract

A high creep resistance at specified temperature and compressive stress was obtained in this investigation in the silicon nitride/silicon carbide composite with a nano–nano structure (nanosized SiC and Si3N4 in dual‐phase mixture) by a novel synthesis method. Starting from an amorphous Si–C–N powder derived from pyrolysis of a liquid polymer precursor, nanocomposites with varied grain size were achieved. With yttria additive amount decreasing from 8 to 1 wt% and eventually to zero, the structure underwent a transition from micro‐nano (nano‐sized SiC included in sub‐micron Si3N4) to nano–nano type. Nanocrystalline silicon nitride/silicon carbide ceramic composite with 30–50 nm grain size was synthesized without using sintering additive.

Computer Aided Multi-scale Design of SiC-Si3N4 Nanoceramic Composites for High-Temperature Structural Applications

“…GBs which may ultimately resulted in very high strength SiC-Si 3 N 4 nanocomposites, [40]. Such mechanisms have been observed earlier for other SiC particle reinforced nanocomposites, [4] and [41].…”

“…To reduce computational time, results from Case C at iteration 7 are used as the starting design in this case, just before mean values of the deformation energy are used to construct the RSA. The table shows that the robust optimum microstructure is given by the design x * = [40,24,36,21,9,8,8]. Again, we notice how the robust optimum design is very similar to the conventional design (Case C), where variations in the objective function are not considered.…”

“…Table 5 shows the results of the sequential approximate optimization under uncertainty algorithm. It details the current design (x n ) and candidate design (x n *) per iteration, showing that the optimum microstructure is given by the design x * = [40,25,36,21,10,8,8]. It can be seen that most of the design variables moved to their upper bounds.…”

“…A slightly modified form (Eqn. (40)) was used in our analysis for less fitting errors and better convergence. …”

Mechanical Properties of Nanoscale Ceramics

“…Only a small amount of the glassy phase, which is dependent on the amount of oxygen and its distribution, may be observed. In the ceramic under consideration, the oxygen was not homogeneously distributed in the grain-boundary for 10 min, nano-nano structure, d sintered without additive at 1600°C for 30 min, nanonano structure [38]. With kind permission of John Wiley and Sons regions, some having more than others.…”