Microstructural and mechanical study of AL2O3/Er3Al5O12 eutectic rods grown by the laser floating zone method

Eutectic rods of Al2O3–Er3Al5O12 were grown by directional solidification using the laser-heated floating zone method at rates in the range 25–1500 mm/h. Their microstructure and mechanical properties (hardness, toughness and strength) were investigated as a function of the growth rate. A homogeneous and interpenetrated microstructure was found in most cases, and interphase spacing decreased with growth rate following the Hunt–Jackson law. Hardness increased slightly as the interphase spacing decreased while toughness was low and independent of the microstructure. The rods presented very high bending strength as a result of the homogeneous microstructure, and their strength increased rapidly as the interphase spacing decreased, reaching a maximum of 2.7 GPa for the rods grown at 750 mm/h. The bending strength remained constant up to 1300 K and decreased above this temperature. The relationship between the microstructure and the mechanical properties was established from the analysis of the microstructure and of the fracture mechanism

Fracture Toughness and Strength of Al2O3-Y3Al5O12 and Al2O3-Y3Al5O12-ZrO2 Directionally-Solidified Eutetic Oxides up to 1900K

Ceramics rods of binary (Al2O3–Y3Al5O12) and ternary (Al2O3–Y3Al5O12–ZrO2) eutectic ceramic oxides were grown in air and nitrogen using the laser-heated floating zone method. Both materials presented a fine and homogeneous microstructure, free from defects, with an average interlamellar spacing of 1.1 and 0.7 _mfor the binary and ternary eutectics, respectively. The strength and the toughness of the rods were measured from ambient temperature up to 1900K by three-point bending. For the fracture tests, a sharp notch was introduced in the rods using a femto second-pulsed laser. Samples grown in nitrogen presented higher strength than those grown in air. The mechanical properties of the Al2O3–YAG binary eutectic did not change with a temperature up to 1500–1600K and plastic deformation above this temperature led to a slight reduction in strength and an increase in toughness. In the case of the ternary eutectic, the toughening effect of the thermal residual stresses disappeared at high temperature and the toughness decreased by a factor of two at 1473 K. The behavior of the ternary eutectic above this temperature followed the trends of the binary one although the changes in strength and toughness were much larger because of the smaller domain size (which favored diffusion-assisted plastic flow) and the lower eutectic temperature

Microestructura y propiedades mecánicas de fibras cerámicas eutécticas Al2O3/Er3Al5O12/ZrO2 procesadas por fusión zonal por láser.

Se han estudiado las fibras eutécticas Al2O3-Er3Al5O12-ZrO2 procesadas por fusión zonal por láser a distintas velocidades. Con el aumento de la velocidad de procesado se ha observado un refinamiento de la microestructura así como un cambio en la morfología de la misma. Se ha determinado mediante piezoespectroscopía que la fase alúmina se encuentra a compresión como consecuencia de las tensiones residuales que aparecen en la solidificación tras el fundido. El módulo de la componente hidrostática de dichas tensiones residuales se reduce conforme lo hace el tamaño de las fases. Se ha estudiado la dureza, la tenacidad de fractura y la resistencia a la flexión. Las dos primeras magnitudes han resultado independientes del tamaño de las fases, mientras que la resistencia a la flexión aumenta conforme disminuye el tamaño de las mismas. Finalmente, también se ha estudiado la dependencia de la resistencia a la flexión con la temperatura, observándose un comportamiento superplástico a 1700 K para la fibra procesada a mayor velocida

Mechanical properties up to 1900 K of Al2O3/Er3Al5O12/ZrO2 eutectic ceramics grown by the laser floating zone method

Directionally solidified Al2O3–Er3Al5O12–ZrO2 eutectic rods were processed using the laser floating zone method at growth rates of 25, 350and 750 mm/h to obtain microstructures with different domain size. The mechanical properties were investigated as a function of the processing rate. The hardness, 15.6 GPa, and the fracture toughness, 4 MPa m1/2, obtained from Vickers indentation at room temperature were practically independent of the size of the eutectic phases. However, the flexural strength increased as the domain size decreased, reaching outstanding strength values close to 3 GPa in the samples grown at 750 mm/h. A high retention of the flexural strength was observed up to 1500 K in the materials processed at 25 and 350 mm/h, while superplastic behaviour was observed at 1700 K in the eutectic rods solidified at the highest rate of 750 mm/