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Stress-strain data for single crystals of MgO tested in compression with (110) and (11 1) loading axes are presented for temperatures ranging from 26' to 125OOC. Stress-strain data for polycrystalline MgO are also presented over the same temperature range. Single crystals with a (111) loading axis were found to deform plastically on the {loo) (110) slip systems at temperatures above 35OOC. The total strain at fracture for polycrystalline MgO at room temperature was about 0.6%; above 600'C it was about 2%. The general inability of the { 110) (110) slip systems of this structure to satisfy the Taylor requirement, i.e., the necessity of five independent slip systems, ease of cleavage, and slip nonuniformity, limits polycrystalline ductility at low temperatures. At higher temperatures, slip can occur on { 100) (110) slip systems, thus providing the additional slip ,systems necessary to satisfy Taylor's criterion ; also, stress-induced climb and high dislocation mobility inhibit cleavage fracture.

Stress-strain curves are presented for MgO single crystals, compressed with (100) and (111) stress axes, for temperatures from 1000' to 1600OC. The yield stress of (100) specimens decreases slightly in this temperature range. The strain-hardening rate passes through a maximum at about ll0O'C and decreases by a factor of about 8 at 1600°C. Above about llOO°C, the strain rate of (100) specimens is considerably less sensitive to changes in stress and the shape of t h e stress-strain curves changes. The yield stress of (1 11) specimens decreases rapidly with increasing temperature without a change of slope up to 1600'C. T h e ratio of the yield stresses for (111) and (100) specimens decreases continually from 1200' to 16OOOC. Various stress rates were used to obtain a measure of strain hardening at 13OO0C.Static recovery experiments were carried out at 1000' and 1400'C. At lO0O'C static pinning occurred during t h e unloaded period; at 1400°C orthorecovery occurred. Stress-strain curves were analyzed by a dynamic approach based on the length of moving dislocation line in the crystal and the average dislocation velocity.

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Laser-sustained plasma (LSP) and CCD imaging of reactant species were employed to investigate the role of near-surface plasma in CO2 laser nitriding of titanium in open atmosphere. Insights were gained regarding the role of plasma processes and the role of reactive nitriding species in the nitriding process. Studies of single nitrided trails have identified the following regimes, as a function of LSP off-focal distance and beam translation speed, characterized by (1) the formation of heavily oxidized surfaces, (2) the formation of titanium nitride (TiN) nanoparticulate, (3) nitride formation in the absence of a surface-struck or LSP and (4) the formation of near-stoichiometric, oxide-free TiN surfaces with a LSP. For the first time it will be shown that the LSP can access nitriding conditions beyond those achieved with surface-struck plasma (or in the absence of plasma) to produce uniform, near-stoichiometric, titanium nitride coatings.