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.
Highlights
As underlined by the recent scientific literature, there is an increasing interest towards new structural materials, able to maintain both stability and mechanical properties at high temperature.Within the group of high-temperature ceramics, the nitrides and the oxides are by far the most important ones from a technological and industrial point of view [1]
Besides a slightly better crystallized cubic-ZrO2 phase, a small peak at 34.4 2θ can be detected, imputable to the crystallization of the perovskite YAlO3 phase (ICDD No 70-1677). This secondary phase disappeared by increasing the calcination temperature: the YAG phase started to crystallize at 1300 °C [20], and after calcination at 1500 °C/3 h, the powder was purely composed by the α-Al2O3, c-ZrO2 and
The results show an overall fine microstructure, made by a sub-micronic alumina matrix and ultra-fine YAG and Al2O3/5 vol% ZrO2/5 vol% YAG (AZY) as-sintered
Summary
As underlined by the recent scientific literature, there is an increasing interest towards new structural materials, able to maintain both stability and mechanical properties at high temperature.Within the group of high-temperature ceramics, the nitrides and the oxides are by far the most important ones from a technological and industrial point of view [1]. Ceramic oxides can be used in harsh environments, withstanding extremely severe operating conditions, such as high temperatures, oxidant and corrosive atmospheres [2]. This characteristic can enlarge their use in aeronautic and aerospace applications, such as for aircraft jet engines and high-efficiency power-generation gas turbines [3]. Composites, due to their good mechanical properties, high thermal stability and good chemical resistance [4] Both single-crystal and polycrystalline YAG present excellent creep resistance, due to the large lattice parameter and, large Burgers vector of the dislocations [5,6]
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