Eutectic Ceramic

Powder Metallurgy and Metal Ceramics, Vol. 48, Nos. 1-2, 2009

REFRACTORY AND CERAMIC MATERIALS
DIRECTIONALLY SOLIDIFIED EUTECTICS IN THE Al2O3–ZrO2–Ln(Y)2O3 SYSTEMS (Review)
S. M. Lakiza1
UDC 546-31:621:831:641:654-669 The current status of research on high-temperature composite oxide ceramics in the Al2O3–ZrO2– Ln2O3 systems (Ln are lanthanides, Y) is reviewed. It is emphasized that theiruse as structural materials at high temperatures (up to 1650°C) is promising. Conditions for growing binary and ternary eutectic composites and their properties are described. Weak and strong aspects of these materials are pointed out. The role of phase diagrams in developing high-temperature in situ composites is shown. Keywords: directional solidification, in situ composites, ceramics, zirconia,alumina, lanthanide oxides, phase diagrams.

INTRODUCTION
A new area of materials science ⎯ directional solidification of eutectic alloys ⎯ has developed and become increasingly recognized worldwide for the last 30 years. Directionally solidified eutectics (DSEs) represent composite materials with a fine submicron microstructure, whose properties depend on the solidification conditions. Theycombine thermodynamic stability and favorable properties of composite materials (in situ composites) and have some advantages. Owing to the progress in this area, high-temperature structural materials, aerospace engineering materials, new functional materials, etc., have been developed [1]. Modern nickel superalloys are basic materials for the hot area of gas turbine engines, but their meltingtemperature is somewhat lower than 1400°C and strength is abruptly reduced at about 1000°C. The service temperature of the metal blades of gas turbine engines has been somewhat increased owing to various improvements such as directional solidification, forced internal cooling, and deposition of thermal-protection coatings. This temperature increased by 1 deg per year on average, its further increasebeing limited by the reduced strength of the materials in the hot area. The increase in combustion temperature is known to improve engine and combustion efficiencies and to decrease environmental contamination. One-percent increase in the engine efficiency would save energy resources worth about 1000 billion dollars on a global scale [2]. Therefore, great research efforts are made to developstructural materials that would retain their properties in long-term operation in oxidizing media at superhigh temperatures.

Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, Kiev, Ukraine; e-mail: dep25@materials.kiev.ua; sergij-lakiza@ukr.net. Translated from Poroshkovaya Metallurgiya, Vol. 48, No. 1–2 (465), pp. 57–77, 2009. Original article submitted December17, 2007. 1068-1302/09/0102-0042 ©2009 Springer Science+Business Media, Inc.

1Frantsevich

42

Ultra high temperature regime Boron fibers

1000

SiC fibers Al2O3−GAP DSE Si3N4 SiC Al2O3−YAG DSE

Strength, MPa

100
Bulk graphite MgO

Aerospace materials (Space Shuttle) ZrO2 C/C W

BeO 500 1000 1500 2000 o Temperature, C

2500

Fig. 1. Temperature dependence of the strengthof new structural ceramics, refractory metals, and other high-temperature materials [3] Since the early 1990s, scientists have been trying to find materials capable of operating in oxidizing media at temperatures above 1650°C. These materials are needed to make turbine blades. The results are presented in Fig. 1 showing the temperature dependence of the strength of new structural ceramics,tungsten, and other well-known materials. Materials that retain their properties at superhigh temperatures (Fig. 1) meet the performance requirements for modern high-temperature gas turbine engines. Currently, there are no structural materials, besides directionally solidified oxide eutectics, that could be used in oxidizing media above 1650°C and would retain adequate strength under these conditions....