K. Pietrzak

The production and application of metal matrix composite materials

Abstract The production methods and properties of metal matrix composite materials reinforced with dispersion particles, platelets, non-continuous (short) and continuous (long) fibres are discussed in this paper. The most widely applied methods for the production of composite materials and composite parts are based on casting techniques such as the squeeze casting of porous ceramic preforms with liquid metal alloys and powder metallurgy methods. On account of the excellent physical, mechanical and development properties of composite materials, they are applied widely in aircraft technology and electronic engineering, and recently in passenger-car technology also.

Effect of rhenium addition on the strengthening of chromium–alumina composite materials

Abstract Chromium–alumina composites are well known for their good mechanical properties in comparison to pure ceramics or metals. These composites are characterized by high hardness and high mechanical strength. The aim of the present work was to improve the properties of chromium–alumina composites even more and expand the range of their possible applications by addition of rhenium. To achieve this goal, chromium–alumina composites containing 2 and 5 vol.% of rhenium were produced via powder metallurgy. The microstructural characterization of the processed material was performed using light microscopy, scanning and transmission electron microscopy as well as X-ray diffraction analysis. Measurement of selected properties such as Youngs modulus, bend strength and hardness revealed an advantageous influence of rhenium additions. The results are discussed in terms of the influence of rhenium volume content on the microstructure and on the physical and mechanical properties of the chromium–alumina composites. The solid solution is only partially formed. The properties strongly depend on the amount and distribution of both aluminium oxide and rhenium content.

The influence of hot pressing conditions on mechanical properties of nickel aluminide/alumina composite

The influence of hot pressing conditions on mechanical properties of nickel aluminide/alumina composite has been investigated in the present paper. In particular, effect of the process parameters, viz. compacting pressure, sintering temperature and sintering time on the evolution of density, elastic constants and tensile strength properties of the intermetallic-ceramic composite has been studied. Elastic constants, the Youngs modulus and Poissons ratio, have been evaluated using an ultrasonic testing method, and the tensile strength has been determined by a Brazilian-type splitting test. Microscopic observations of microstructure evolution complemented the experimental procedure. Experimental results have been confronted with theoretical models showing a good agreement between the data compared.

Effects of Carbon Allotropic Forms on Microstructure and Thermal Properties of Cu-C Composites Produced by SPS

Combination of extreme service conditions and complex thermomechanical loadings, e.g., in electronics or power industry, requires using advanced materials with unique properties. Dissipation of heat generated during the operation of high-power electronic elements is crucial from the point of view of their efficiency. Good cooling conditions can be guaranteed, for instance, with materials of very high thermal conductivity and low thermal expansion coefficient, and by designing the heat dissipation system in an accurate manner. Conventional materials such as silver, copper, or their alloys, often fail to meet such severe requirements. This paper discusses the results of investigations connected with Cu-C (multiwall carbon nanotubes (MWNTs), graphene nanopowder (GNP), or thermally reduced graphene oxide (RGO)) composites, produced using the spark plasma sintering technique. The obtained composites are characterized by uniform distribution of a carbon phase and high relative density. Compared with pure copper, developed materials are characterized by similar thermal conductivity and much lower values of thermal expansion coefficient. The most promising materials to use as heat dissipation elements seems to be copper-based composites reinforced by carbon nanotubes (CNTs) and GNP.

Bonding of alumina to steel using copper interlayer

The experiments carried out show that multilayer bonding by using thin and very plastic material interlayer is a good solution of the problem of making alumina - st Joints with large dimensions. Using of this type interlayer allows for relaxation of stresses generated during bonding cycle. It was concluded that copper material interlayer is suitable for this purpose. Direct bonding using active products of reduction reaction of CuO (Cu2O, O2) can be the adequate process of bonding joints with copper interlayer. Using this method, we can partly to fix the relation between the quality of the bond (homogenious microstructure at the whole bonding surface) and a protective atmosphere. This paper contains the conditions of alumina - steel joining process and results of strenght tests. Another part of this work are microstructure examinations, showing the homogenity of bonds. The elaborated method can be used for joining alumina to copper and copper to steel in one thermal cycle. Such bonded joints have high mechanical strenght and homogenous microstructure. Comparing to other joining methods this process does not need to use any special joining conditions (following bonding features - low bonding temperature ≈ 1340K, protective atmosphere of N2 containing below 40 ppm O2, bonding time ≈ 90 minutes).

The Influence of Al2O3 Powder Morphology on the Properties of Cu-Al2O3 Composites Designed for Functionally Graded Materials (FGM)

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 (αAl2O3 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.

SIMULATION OF POWDER SINTERING USING A DISCRETE ELEMENT MODEL

Abstract This paper presents numerical simulation of powder sintering. The numerical model introduced in this work employs the discrete element method which assumes that material can be modelled by a large assembly of discrete elements (particles) of spherical shape interacting among one another. Modelling of sintering requires introduction of the cohesive interaction among particles representing interparticle sintering forces. Numerical studies of sintering have been combined with experimental studies which provided data for calibration and validation of the model. In the laboratory tests evolution of microstructure and density during sintering have been studied. Comparison of numerical and experimental results shows a good performance of the numerical model developed

Microstructure and thermal properties of Cu-SiC composite materials depending on the sintering technique

The presented paper investigates the relationship between the microstructure and thermal properties of copper-silicon carbide composites obtained through hot pressing (HP) and spark plasma sintering (SPS) techniques. The microstructural analysis showed a better densification in the case of composites sintered in the SPS process. TEM investigations revealed the presence of silicon in the area of metallic matrix in the region close to metal-ceramic boundary. It is the product of silicon dissolving process in copper occurring at an elevated temperature. The Cu-SiC interface is significantly defected in composites obtained through the hot pressing method, which has a major influence on the thermal conductivity of materials.

Fabrication of an Alumina–Copper Composite Using a Ceramic Preform

In this work alumina preforms with an open porosity of 85 and 90% were produced by the replication method. The obtained preforms were used for the fabrication of Cu–Al2O3 composites. We analyzed the effect of applying pressure during a hot-pressing process on the microstructure and mechanical and thermal properties of the obtained materials. It was found that application of higher pressure (10 MPa) during sintering led to the destruction of the ceramic preforms. It facilitated filling of the remaining pores with copper, which resulted in a more homogeneous material with better mechanical and thermal properties.

Thermal Residual Stresses Generated during Processing of Cr-Al2O3 Composites and their Influence on Macroscopic Elastic Properties

This work is focused on the modeling of thermal stresses induced during the fabrication of the metal/ceramic composites. On example of Cr-Al2O3 composite processed by powder metallurgy, thermal stresses after fabrication are determined by FEM model for different contents of metal and ceramic phases. Numerical model of microcracking induced by thermal stresses is then proposed and applied to compute the overall elastic properties of the damaged composite. Comparison of the model predictions with the measured data for Youngs modulus is presented.