The reaction of Lal-,Ca,Mn03 (x = 0, 0.1, 0.2) with ZrOz-8 mol% YzO3 (YSZ) has been investigated at temperatures ranging from 1300" to 1425°C in air. Substitution of Ca for La in LaMn03 depresses the reactivity with YSZ. A layer of La2Zrz07 is formed at the Lal-,Ca,MnO,/YSZ interface after an induction period, and its formation is accelerated when the Lal-,Ca,Mn03 phase is porous. The reaction proceeds by unidirectional diffusion of La, Mn, and/or Ca ions, mainly Mn ions, into YSZ. The diffusion coefficients of La and Mn ions in YSZ, which are estimated using a LaMn03/ single-crystal YSZ couple, are much lower than that of oxygen ion. From the experimental data, a reaction mechanism is proposed. [
This study measured the Vickers hardness of the sintered refractory carbides B 4 C, Mo 2 C, NbC, TiC, V 8 C 7 , W 2 C, WC, WC-SiC, and ZrC over a wide range of test forces between 0.49 and 196 N. The results showed an indentation size effect (ISE), with hardness values that increased with decreasing test force for the carbides. The test force dependence of the hardness was analyzed by the proportional specimen resistance (PSR) model. The value of the a 1 term that reflects the elastic resistance in the model was obtained for the carbides and compared with their measured elastic, shear, and bulk moduli. It was not clear what type of modulus related strongly to the a 1 term. There was a strict correlation between the hardness at an infinite test force and at a test force of 9.8 N. However, the hardness at a test force of 0.49 N a little poorly reflected the hardness at an infinite test force.
Tungsten hemicarbide W 2 C with no or small amounts of W or WC was prepared by reaction-sintering from W and WC powders using a resistance-heated hot-pressing technique called spark plasma sintering. The product phases, density, microstructure, elastic moduli, hardness, and fracture toughness of the sintered bodies were determined. The stable region of the W 2 C phase had a narrow carbon content below 1860 C. W 2 C had a Poisson's ratio of 0.286, and its Young's modulus at zero porosity was determined to be 444 GPa from the true density and bulk density dependence. These values suggest that W 2 C has elastic deformation behavior similar to that of W.
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