The mechanical properties of precipitation-hardened dilute mixtures of KCl in NaCl were studied. Two peaks in the flow stress occur. The suggested sequence of events is growth of coherent KCl-rich platelets, loss of coherence, growth of incoherent KCl-rich platelets, and finally recrystallization. The fracture stress is maximum for a long aging time considerably beyond the second hardness peak where the presence of rather coarse precipitates interferes with the cleavage process and increases the energy to propagate a fracture. This is an important principle for increasing the fracture strength of ceramics.
Thin films containing cubic phase boron nitride have been synthesized using an ion beam extracted from a borazine (B3H3H6) plasma.We report on x-ray diffractometry, hardness tests, and Auger analysis of the deposited films. The x-ray diffractometer peak corresponding to cubic phase boron nitride was detected while peaks corresponding to hexagonal phase were usually absent. Consistent with the presence of cubic phase indicated by the x-ray analysis, the indentation hardness of boron nitride-coated substrates was higher than the same uncoated substrates. Auger compositional profiles indicated a film stoichiometry corresponding to boron nitride and suggested that the deposition method produced an intermixing layer between the boron nitride film and the substrate.
The crystallographic aspects of silicon/corundum epitaxy were investigated. Epitaxial deposition was carried out on corundum substrates of two orientations, and the observed crystallographic relationships were shown to be determined by three-dimensional matching between the silicon structure and the sublattice of possible cation sites in corundum.
Single-crystal silicon layers were deposited onto (0001) and (8̄629) corundum substrates. For growth on (0001) corundum, (111) silicon is parallel to the interface with [1̄10] silicon parallel to [2̄110] corundum. For growth on (8̄629) corundum, the silicon plane parallel to the interface is irrational, but the epitaxial relationship closely approximates to the following: (001) silicon parallel to (0001) corundum with [1̄10] silicon parallel to [2̄110] corundum.
These two epitaxial relationships are the only ones which permit three noncoplanar symmetry axes of the silicon to coincide with three such axes of the cation site sublattice of the corundum. They insure compatible surface symmetries and similar surface densities on an arbitrary deposit/substrate interface. In general, the silicon atom density on the interface does not exceed the cation site density. When it does so, however, the rational crystallographic relationship is modified slightly in order to lower the density of silicon atoms below that of the possible cation sites.
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