Papers by Keyword: Re₂O₃

Abstract: Commercial α−Si3N4, Al2O3 and a mixed yttrium and rare earth oxides, RE2O3, were used as starting-powders. Powder batches were milled using different Al2O3/RE2O3 contents, as additive. Hot-pressing was done at 1750oC-30 min-20MPa in N2 atmosphere. Specimens neat to 6x3x3mm3 were polished and characterized by XRD and SEM. Specimens were submitted to creep tests, under compressive stresses between 100 and 350 MPa at temperatures ranging from 1250 to 1300oC in air. Higher additive amounts resulted in larger grains of higher aspect ratios and in a decreased anisotropy in the hot-pressed ceramics. The compressive creep behavior depends on the intergranular phase content. While higher amounts of additives resulted in higher creep rates, • ε , and higher stress exponents, n, the activation energy Qss, has been inferior for samples with lower additive contents. Grain sliding has been identified to be the predominant mechanism responsible for creep deformation of these ceramics.

Abstract: In the present work, titanium matrix composites reinforced with TiB, TiC, and Re2O3 (Nd2O3 or Y2O3) were fabricated via common casting and hot-forging technology utilizing the chemical reaction between Ti, B4C (or C), rare earth (Re) and B2O3 through homogeneously melting in a non-consumable vacuum arc remelting furnace. In this work, Nd and Y were chosen as rare earth (Re) added in the in situ reaction. The thermodynamics of in situ synthesis reactions was studied. The results of X-ray diffraction (XRD) proved that no other phases appeared except for TiB, TiC and Re2O3. The microstructures of the composites were examined by optical microscopy (OM). The results showed that there were mainly three kinds of reinforcements: TiB whiskers, TiC particles and Re2O3 particles. The reinforcements were fine and were homogeneously distributed in the matrix. The interfaces of TiB-Ti and Y2O3-Ti have been examined by high-resolution transmission electron microscopy (HREM).Transmission electron microscopy (TEM) and selected area diffraction (SAD) were used to analyze the orientation relationships of TiB-Ti, Nd2O3-Ti, and Y2O3-Ti. The mechanical properties at room temperature improved with the addition of TiB whiskers and TiC particles although some reduction in ductility was observed. The (TiB+TiC)/Ti6242 composite with TiB:TiC=1:1 shows higher tensile strength and ductility.