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

Abstract

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 °C—2 h. In the milled powders, the crystallite size of the ZrO₂ matrix was reduced from 130 to 40 Å, 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 °C—2 h. In comparison, the conventional powder-mixture achieved high densification only after sintering at 1600 °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 °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 °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.