The Influence of Al2O3 Powder Morphology on the Properties of Cu-Al2O3 Composites Designed for Functionally Graded Materials (FGM)
Journal of Materials Engineering and Performance
The Influence of Al O Powder Morphology 2 3 on the Properties of Cu-Al O Composites Designed 2 3 for Functionally Graded Materials (FGM)
Agata Strojny-Ne˛ dza 0
Katarzyna Pietrzak 0
Witold We˛ glewski 0
0 Agata Strojny-Ne ̨dza and Katarzyna Pietrzak, Institute of Electronic Materials Technology , 133 Wolczynska str., 01-919 Warsaw , Poland; and Witold Weglewski, Institute of Fundamental Technological Research , 5B Pawinski str., 02-106 Warsaw , Poland. Contact
In order to meet the requirements of an increased efficiency applying to modern devices and in more general terms science and technology, it is necessary to develop new materials. Combining various types of materials (such as metals and ceramics) and developing composite materials seem to be suitable solutions. One of the most interesting materials includes Cu-Al2O3 composite and gradient materials (FGMs). Due to their potential properties, copper-alumina composites could be used in aerospace industry as rocket thrusters and components in aircraft engines. The main challenge posed by copper matrix composites reinforced by aluminum oxide particles is obtaining the uniform structure with no residual porosity (existing within the area of the ceramic phase). In the present paper, Cu-Al2O3 composites (also in a gradient form) with 1, 3, and 5 vol.% of aluminum oxide were fabricated by the hot pressing and spark plasma sintering methods. Two forms of aluminum oxide (aAl2O3 powder and electrocorundum) were used as a reinforcement. Microstructural investigations revealed that near fully dense materials with low porosity and a clear interface between the metal matrix and ceramics were obtained in the case of the SPS method. In this paper, the properties (mechanical, thermal, and tribological) of composite materials were also collected and compared. Technological tests were preceded by finite element method analyses of thermal stresses generated in the gradient structure, and additionally, the role of porosity in the formation process of composite properties was modeled. Based on the said modeling, technological conditions for obtaining FGMs were proposed.
functionally gradient materials; hot pressing; metal matrix composites; microstructure; spark plasma sintering; thermal conductivity
1. Introduction
Rapid progress in technology requires new materials with
special properties. Composite materials are an answer to the
constantly increasing demand for materials with improved
structural and operating parameters, and enable required
properties and features to be shaped deliberately to a degree
unavailable for traditional types of monolithic materials. Metal
matrix composites (MMCs) and functionally graded materials
(FGMs) were developed to reach better parameters, especially
high-temperature resistance to wear and corrosion, mechanical
strength, thermal and electric conductivity, and magnetic
properties. In particular, FGMs make suitable candidates for
materials whose properties vary depending on the distance from
the material surface (Ref 1). The idea of functionally graded
materials was intensively developed in early 1984 in Japan,
where it was proposed to increase adhesion and minimize the
thermal stress in metal-ceramic composites developed for
reusable rocket engines (Ref 2). At present, graded materials
are widely used in power, aircraft, aerospace, electronics,
automotive, and chemical industries (Ref 3).
Copper is characterized by high electrical and thermal
conductivity, which makes copper a great prospective
component of metal matrix composite materials. However, poor
adhesion to widely used reinforcements, chemical reactions at
interfaces, and quick oxidization of Cu can create serious
problems with the formation of the strong bonds at the interface
between composite components (Ref 4, 5). Copper matrix
composites with different ceramic reinforcements (AlN, SiC, C,
Al2O3) are extensively used in aerospace industry in products
that are subjected to severe thermal and mechanical loadings
such as rocket thrusters and components in aircraft engines (Ref
6, 7). A thruster is a drive unit of stabilizing motors used in
rockets. It constitutes an element of an outlet in combustion
engines, entered by gases from the combustion chamber. This
particular part is exposed to the unfavorable impact of external
factors such as high temperature, abrasive wear, and corrosion,
hence being a frequently replaced element of the engine. The
most common defects include layer degradation or numerous
cracks resulting from a chemical reaction with exhaust gases
(Ref 8). At present, a material used for thrusters is copper alloy,
showing low resistance to wear. The application of a gradient
material composed of Cu-Al2O3 composite layers with a slight
addition of aluminum oxide is expected to enhance tribological
properties, at the same time preserving good thermal properties.
The selection process of the composition of the gra (...truncated)