Infiltration of Reaction-Bonded Silicon Nitride with Equilibrium Y-Si-O-N Melt

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65413/1/j.1151-2916.1994.tb07020.x.pd

Mechanical properties and thermal expansion behaviour in leucite containing materials

The effect of a change in sodium content and thermal history on a leucite composition material produced by a coprecipitation process was studied. Five materials with formulae of (K( 1− x ),Na x ) 2 O-Al 2 O 3 -4SiO 2 ( x = 0.0, 0.2, 0.4, 0.6, 0.8) were investigated for differences in phases, thermal expansion, and strength. Strengths of up to 175 MPa were obtained for a leucite composition material ( x = 0.0). Sodium was effective in lowering the thermal expansion coefficients of these materials. Leucite was linked to higher flexural strengths, but was present only in those specimens which were sintered at 1200 °C. Leucite was not present in those specimens sintered at 1100 °C or lower. Porosity was present in all specimens sintered at 1000 °C or higher.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44726/1/10853_2004_Article_BF00356582.pd

Phase stability of zirconia solid solutions.

Using three analytical methods, X-ray diffraction, EDX composition analysis, and thermal expansion, a zirconia rich part of ZrO$\\sb2$-Sc$\\sb2$O$\\sb3$ phase diagram was re-examined. The result shows the tetragonal solubility is similar to that in Stricker's phase diagram and cubic phase boundary is close to that in Thornber's or in Spiridonov's phase diagram. A diffusionless phase transformation from cubic (c) to tetragonal (t$\\sp\\prime$) was found in this system when a sample with a high temperature cubic phase was quenched through a cubic plus tetragonal region to room temperature. This observation has been used to explain the discrepancies among the previously reported ZrO$\\sb2$-Sc$\\sb2$O$\\sb3$ phase diagrams. Through careful sample preparation and composition selection, a cubic plus tetragonal (t$\\sp\\prime$) coexistence microstructure was found in the ZrO$\\sb2$-Sc$\\sb2$O$\\sb3$ system. From a TEM micrograph observation, the habit plane of the t$\\sp\\prime$ phase in a cubic matrix was found and analyzed as \\{1 0 1\\} planes. This was the first time the coexistence of t$\\sp\\prime$ and cubic matrix was observed in a zirconia containing system. Because of the shear stress-assisted transformation at room temperature and the existence of a habit plane, the c to t$\\sp\\prime$ transformation was identified as a martensitic type. The formation of t$\\sp\\prime$ phases was found in the ZrO$\\sb2$-M$\\sb2$O$\\sb3$, and ZrO$\\sb2$-MO systems, where M$\\sp{+3}$ = Y, Yb, In, and Sc and M$\\sp{+2}$ = Ca and Mg. The as-quenched t$\\sp\\prime$ phase with large tetragonality (c/a ratio) was likely to transform to monoclinic after grinding of the sample. Different tetragonal (t) precipitate morphologies in the ZrO$\\sb2$-Yb$\\sb2$O$\\sb3$, ZrO$\\sb2$-Sc$\\sb2$O$\\sb3$, and ZrO$\\sb2$-In$\\sb2$O$\\sb3$ systems were observed. The tetragonal precipitate habit planes in these three systems were analyzed as \\{1 0 1\\}. Tetragonal precipitates were suggested to grow by a strain-induced coarsening mechanism. After a prolonged aging treatment, the tetragonal precipitates in the ZrO$\\sb2$-Sc$\\sb2$O$\\sb3$, and ZrO$\\sb2$-In$\\sb2$O$\\sb3$ systems were able to transform to monoclinic after thermal cooling; but those in the ZrO$\\sb2$-Yb$\\sb2$O$\\sb3$ system could not. Using data from ZrO$\\sb2$-Y$\\sb2$O$\\sb3$, ZrO$\\sb2$-MgO, ZrO$\\sb2$-Y$\\sb2$O$\\sb3$-MgO, and the above three systems, two theoretical models (Khachaturyan's single domain theory and the phenomenological crystallographic theory) have been found successful in predicting the tetragonal precipitate habit planes. The anisotropic thermal expansion properties of the tetragonal phases were found in the ZrO$\\sb2$-Sc$\\sb2$O$\\sb3$, ZrO$\\sb2$-In$\\sb2$O$\\sb3$, ZrO$\\sb2$-Yb$\\sb2$O$\\sb3$, and ZrO$\\sb2$-YTaO$\\sb4$ systems. Tetragonal phases with large anisotropic thermal properties show high transformation tendencies from tetragonal to monoclinic. In the t$\\sp\\prime$ phase, the tetragonality increases and then decreases as the temperature increases. The cubic and t$\\sp\\prime$ phases have a very small misfit at high temperature. As a result, c to t$\\sp\\prime$ is classified as a special type of martensitic transformation.Ph.D.Materials scienceUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/162526/1/9014014.pd