Al2O3/ZrO2/Y3Al5O12 Composites: A High-Temperature Mechanical Characterization

Abstract

An Al2O3/5 vol%·ZrO2/5 vol%·Y3Al5O12 (YAG) tri-phase composite was manufactured by surface modification of an alumina powder with inorganic precursors of the second phases. The bulk materials were produced by die-pressing and pressureless sintering at 1500 °C, obtaining fully dense, homogenous samples, with ultra-fine ZrO2 and YAG grains dispersed in a sub-micronic alumina matrix. The high temperature mechanical properties were investigated by four-point bending tests up to 1500 °C, and the grain size stability was assessed by observing the microstructural evolution of the samples heat treated up to 1700 °C. Dynamic indentation measures were performed on as-sintered and heat-treated Al2O3/ZrO2/YAG samples in order to evaluate the micro-hardness and elastic modulus as a function of re-heating temperature. The high temperature bending tests highlighted a transition from brittle to plastic behavior comprised between 1350 and 1400 °C and a considerable flexural strength reduction at temperatures higher than 1400 °C; moreover, the microstructural investigations carried out on the re-heated samples showed a very limited grain growth up to 1650 °C.

Bottom‐up vs reactive sintering of Al2O3–YAG–YSZ composites via one or three‐phase nanoparticles (NPs). Bottom‐up processing wins this time

“…produced (23/26/51) vol% composites at 95% TD after sintering 1 h at 1500°C with AGSs of 550 nm for Al 2 O 3 , 560 nm for YAG, and 460 nm for YSZ, slightly higher than the grain sizes reported here. Kim and Kriven produced (33/33/33 vol%) composites with grain sizes 1‐7 μm after 1 h of sintering at 1550°C‐1750°C.…”

“…Cubic‐yttria stabilized ZrO 2 is the primary phase visible by XRD, along with hexagonal YAlO 3 and δ*‐Al 2 O 3 . Hexagonal YAlO 3 is a common intermediate phase in the synthesis of YAG, and δ*‐Al 2 O 3 is the most common phase in LF‐FSP produced Al 2 O 3 NPs (R. M. Laine, N. J. Taylor & S. Stangeland‐Molo unpublished work) . The phases indicated by XRD match the corresponding powder diffraction files for equilibrium crystal structures.…”

“…A few examples of powder processed Al 2 O 3 –YAG–YSZ or AYZ composites have been reported. Palmero et al . synthesized AYZ composites from YCl 3 and ZrCl 4 decomposition on nanosized transition Al 2 O 3 NPs of 90 Al 2 O 3 –5 YAG‐5 vol% YSZ, 60 Al 2 O 3 –20 YAG‐20 vol% YSZ, and 34 Al 2 O 3 ‐33 YAG‐33 vol% YSZ.…”

Fabrication and creep properties of eutectic-composition Al2O3/YAG/YSZ sintered composites

“…Precisely on this last material, fabricated by surface modification of the alumina powder with inorganic precursors of the second phases, Palmero et al [23] have reported the only study addressing the high-temperature mechanical behavior of AYZ sintered ceramics; by means of four-point bending tests from room temperature up to 1500 °C, the authors found an enhanced deformability at temperatures above 1400 °C (though the maximum strain was limited to 4% due to restrictions of the experimental setup). The aim of the present study is therefore twofold: first, to fabricate and characterize the crystalline phases and microstructure of three-phase AYZ composites with the eutectic composition produced by a conventional ceramic processing route; and second, to investigate their creep response at high temperatures by constant crosshead speed and constant load tests in correlation with microstructural observations, in order to assess the microscopic mechanisms involved in the plastic deformation.…”

Fabricating a Novel Intragranular Microstructure for Al2O3/GdAlO3 Ceramic Composites

“…Generally, the fracture mode of Al 2 O 3 grains is intergranular fracture [20,21]. It reveals that the intragranular structure tended to induce the transgranular fracture of Al 2 O 3 grains in Figure 5d.…”