Mechanical properties of biocompatible Y-TZP/Al2O3 composites obtained from mechanically alloyed powders

In this study, an alumina-toughened zirconia composite (ATZ) was developed from mechanical alloyed nano-scale powder mixtures using low-sintering temperatures. A powder mixture, composed of 80 wt.% Y-TZP, ZrO2 (3 mol.% Y2O3), and 20 wt.% Al2O3, was prepared by mechanical alloying (MA) in a planetary ball mill under argon atmosphere, with milling times of up to 60 h, using a rotary speed of 200 rpm and a ball-to-powder weight ratio of 10:1. The mixtures were compacted at 100 MPa and sintered at 1400 degrees C-2 h. In the milled powders, the crystallite size of the ZrO2 matrix was reduced from 130 to 40 angstrom, when increasing the milling time from 1 to 60 h. After sintering, the samples were characterized by its phase composition, microstructure, relative density, fracture toughness and biaxial flexural strength. Fully dense samples were obtained after sintering the powder-mixture milled for 60 h at 1400 degrees C-2 h. In comparison, the conventional powder-mixture achieved high densification only after sintering at 1600 degrees C-2 h. Sintered samples prepared with mechanical alloyed powder mixtures presented a fracture toughness (K-IC) of 8.2 +/- 0.3 MPa m(1/2) and a bending strength of 880 +/- 45 MPa, significantly higher compared to samples prepared from the conventional processed powder mixture sintered at 1600 degrees C-2 h, presenting a K-IC of 6.7 +/- 0.5 MPam(1/2) and a bending strength of 697 +/- 85 MPa. The improved mechanical strength of the composites prepared from mechanical alloyed powders is attributed to the increased sinterability of these powders, allowing full densification at 1400 degrees C, and also resulting in a reduction in the tetragonal ZrO2 grain size. Thus, a larger population of these grains is formed in the microstructure, increasing fracture toughness and strength by the tetragonal to monoclinic phase transformation toughening mechanism.