Gas Pressure Infiltration Research Articles

Effect of Metal Matrix Alloying on Mechanical Strength of Diamond Particle-Reinforced Aluminum Composites

Diamond particle-reinforced Al matrix (Al/diamond) composites were produced by a gas pressure infiltration method, where 0.5-4.0 wt.% Ti was added to Al matrix. An interfacial TiC layer of about 2 μm thickness was formed between Al and diamond at 4.0 wt.% Ti addition. The mechanical properties of the Al/diamond composites were enhanced by both the formation of interfacial layer and the strengthening of the matrix. The mechanical strength increased with increasing alloying Ti content, and a tensile strength of 153 MPa was obtained at 4.0 wt.% Ti addition. The tensile flow stress of the composites was found to be in broad agreement with the prediction of the Mori-Tanaka model. The effect of interfacial layer on mechanical properties provides guideline for the production of mechanically reliable Al/diamond composites.

On Porosity Formation in Metal Matrix Composites Made with Dual-Scale Fiber Reinforcements Using Pressure Infiltration Process

This is the first such study on porosity formation phenomena observed in dual-scale fiber preforms during the synthesis of metal matrix composites (MMCs) using the gas pressure infiltration process. In this paper, different mechanisms of porosity formation during pressure infiltration of Al-Si alloys into Nextel™ 3D-woven ceramic fabric reinforcements (a dual-porosity or dual-scale porous medium) are studied. The effect of processing conditions on porosity content of the ceramic fabric infiltrated by the alloys through the gas PIP (PIP stands for “Pressure Infiltration Process” in which liquid metal is injected under pressure into a mold packed with reinforcing fibers.) is investigated. Relative density (RD), defined as the ratio of the actual MMC density and the density obtained at ideal 100 pct saturation of the preform, was used to quantify the overall porosity. Increasing the infiltration temperature led to an increase in RD due to reduced viscosity of liquid metal and enhanced wettability leading to improved feedability of the liquid metal. Similarly, increasing the infiltration pressure led to enhanced penetration of fiber tows and resulted in higher RD and reduced porosity. For the first time, the modified Capillary number (Ca*), which is found to predict formation of porosity in polymer matrix composites quite well, is employed to study porosity in MMCs made using PIP. It is observed that in the high Ca* regime which is common in PIP, the overall porosity shows a strong downward trend with increasing Ca*. In addition, the effect of matrix shrinkage on porosity content of the samples is studied through using a zero-shrinkage Al-Si alloy as the matrix; usage of this alloy as the matrix led to a reduction in porosity content.

Design of composites for thermal management: Aluminum reinforced with diamond-containing bimodal particle mixtures

A new design route is proposed in order to fabricate aluminum matrix diamond-containing composite materials with optimized values of thermal conductivity (TC) for thermal management applications. The proper size ratio and proportions of particulate diamond–diamond and diamond–SiC bimodal mixtures are selected based on calculations with predictive schemes, which combine two main issues: (i) the volume fraction of the packed particulate mixtures, and (ii) the influence of different types of particulates (with intrinsically different metal/reinforcement interfacial thermal conductances) on the overall thermal conductivity of the composite material. The calculated results are validated by comparison with measurements on composites fabricated by gas pressure infiltration of aluminum into preforms of selected compositions of particle mixtures. Despite the relatively low quality (low price) of the diamond particles used in this work, outstanding values of TC are encountered: a maximum of 770W/mK for Al/diamond–diamond and values up to 690W/mK for Al/diamond–SiC.

Manufacturing with Application of Gpi Method and Selected Properties of Al Matrix Composites Reinforced Unidirectionally and Three-Directionally with Carbon Fibres/ Wytwarzanie Metodą Infiltracji Gazowej I Wybrane Własności Kompozytów Na Osnowie Aluminium, Umocnionych Jedno I Trójkierunkowo Włóknami Węglowymi

Abstract The discussion of the possibility of application of the GPI (gas pressure infiltration) process to the manufacturing of composites based on selected aluminium alloys reinforced with carbon fibres coated with nickel protective layer, as well as the determination of selected properties of materials obtained using this technique, is presented in the article. The composites reinforced unidirectionally (UD) were produced, the suitable volume fraction of fibres was determined and the proper forming parameters were established. Basing on the obtained results, with application of the same components, the composites reinforced three-directionally (3D) were subjected to infiltration. The preforms were designed and prepared using plaiting and joining methods. The GPI process parameters were verified for the assumed fibre arrangement. Thermal expansion of matrix alloys and composites obtained with application of most favourable parameters was determined and the influence of fibre arrangement and chemical composition of the matrix on the obtained results was analysed. The comparative abrasion tests with application of different velocities were performed for the selected alloy and the composite reinforced unidirectionally. In order to evaluate the changes taking place in the matrix during infiltration, the analysis of chemical composition of composites was performed for materials reinforced unidirectionally, as an example. The correctness of distribution of fibres in the composite matrix was also evaluated by means of microstructure observation as well as non-destructive testing with application of computed tomography technique. The results obtained during the investigations provide information concerning suitability and limitations of the GPI method to the manufacturing of light structural parts from the proposed components.

Aluminium AA6061 Matrix Composite Reinforced with Spherical Alumina Particles Produced by Infiltration: Perspective on Aerospace Applications

Metal matrix composites, based on AA6061 reinforced with 60 vol% Al2O3 spherical particles, were produced by gas pressure infiltration and characterized for hardness, impulse excitation modulus, tensile properties (at room temperature and at 250°C), and machining. It was experimentally demonstrated that the novel alumina powder used in the present work does not react with the liquid Mg-containing matrix during the infiltration process. The AA6061 matrix therefore retains its ability to be strengthened by precipitation heat treatment. The latter behaviour combined with the spherical particle shape confers the studied material higher strength and better machinability in comparison with similar composites produced using standard angular alumina particles. The overall features are promising for applications in the aerospace industry, where light and strong materials are required.

Optimisation of high thermal conductivity Al/diamond composites produced by gas pressure infiltration by controlling infiltration temperature and pressure

In this study, Al/diamond composites were fabricated by the gas pressure infiltration method. The infiltration temperature and pressure were varied to study their influence on the interfacial microstructures and thermal conductivities of composites. The results show that the infiltration temperature and pressure dramatically affect the reaction between the Al matrix and the diamond particles. The appropriate conditions activate the reaction on the {111} faces of diamond which possesses a higher chemical stability than the {100} faces. The course of the reaction can lead to the structural and chemical modification of the interface, which strongly affects the thermal conductivity of the final composites. Using our optimised parameters of 800 degrees C and 0.8 MPa, a superior thermal conductivity above 760 W m(-1) K-1 was obtained. Controlling the fabrication parameters to optimise the reaction on the {100} and {111} faces can result in a superior Al/diamond material with greater thermal conductivity.

Microstructure and Thermal Expansion of Hybrid - Copper Alloy Composites Reinforced with both Tungsten and Carbon Fibres

Tungsten as refractory material and high thermal conductive carbon fibres are promising candidates for production of copper matrix composites for high temperature applications. Three types of rod-like samples were prepared by gas pressure infiltration of different carbon/tungsten fibre preforms with copper and/or copper alloy (Cu-0.5Cr) respectively. The fibres are aligned parallel to rod axis and were combined with the tungsten wire cloth. The microstructure of prepared hybrid composites was examined. The samples were thermally cycled 3 times up to 550 °C at a relatively high heating/cooling rate (10 K/min) to touch real condition in applications where high heat is formed during short time. The thermal expansion behaviour in radial direction was also analysed. Results show that a combination of both types of reinforcements in rod-shapes samples insures good protection against composite disintegration during high temperature thermal loading.

Laser-weldable Sip–SiCp/Al hybrid composites with bilayer structure for electronic packaging

Laser-weldable Sip–SiCp/Al hybrid composites with high volume fraction (60%–65%) of SiC reinforcement were fabricated by compression moulding and vacuum gas pressure infiltration technology. Microscopic observation displayed that the Sip–SiCp/Al hybrid composites with bilayer structure were compact without gas pores and the intergradation between Sip/Al layer and SiCp/Al layer was homogeneous and continuous. Further investigation revealed that the Sip–SiCp/Al hybrid composites possessed low density (2.96 g/cm3), high gas tightness (1.0 mPa·cm3)/s), excellent thermal management function as a result of high thermal conductivity (194 W/(m·K) and low coefficient of thermal expansion (7.0×10−6 K−1). Additionally, Sip–SiCp/Al hybrid composites had outstanding laser welding adaptability, which is significantly important for electronic packaging applications. The gas tightness of components after laser welding (48 mPa·cm3)/s) can well match the requirement of advanced electronic packaging. Several kinds of these precision components passed tests and were put into production.

Manufacturing and Characterization of Interpenetrating SiC Lightweight Composites

The current work deals with the gas pressure infiltration of SiC - preforms of selected porosities with an aluminum alloy in order to manufacture an interpenetrating composite with higher ductility in comparison to SiC bulk material and a higher temperature and creep resistance in comparison to aluminum bulk materials. The quality of the manufactured composite is analyzed metallographically which attests a good infiltration of the composite. The residual porosity is also determined and can be attributed to the closed porosity and insufficient infiltration of open porosity. It can be shown that the infiltration of the preform leads to an increase in compressive strength with reasonable ductility in comparison to the unreinforced matrix material.

Thermophysical properties of SiC/Al composites with three dimensional interpenetrating network structure

Silicon carbide (SiC) reinforced aluminum composites with three dimensional interpenetrating network structure (3D-SiC/Al) were fabricated by the gas pressure infiltration method, and their thermophysical properties were investigated. The results show that the geometry of SiC reinforcement has a significant impact on the thermophysical properties of the composites. Continuous SiC reinforced aluminum composites (3D-SiC/Al) have higher thermal conductivities and lower coefficients of thermal expansion (CETs) than those of particulate SiC reinforced aluminum composites (SiCp /Al) with the same SiC volume fraction. The co-continuous structures of both the SiC reinforcement and the Al matrix in 3D-SiC/Al can be the reason behind this phenomena. As a result, when SiC volume fraction values were the same, 3D-SiC/Al composites will be more suitable for electronic packaging applications comparing with SiCp/Al composite.

Interfacial reactions and bending strength of SiC/A356/FeNi50 composite fabricated by gas pressure infiltration

The SiC/A356/FeNi50 composite was fabricated by gas pressure infiltration. The interfacial region of the SiC/A356/FeNi50 composite consisted of FeNi50 reaction layer, Al reaction layer and Al alloy matrix. The main intermetallic compounds were (Fe,Ni)4(Al,Si)13 and (Fe,Ni)2(Al,Si)5 at the Al reaction layer and FeNi50 reaction layer, respectively. The bending behavior versus different infiltration temperatures and holding times was also investigated. The bending strength at 670 °C was the highest and close to the bending strength of Al alloy (223 MPa), and 46% of SiC/A356. The brittle intermetallic compounds existing at the interface induced the decreasing of the bending strength. The pores were reduced by adequate heating time due to the homogeneous temperature of preform, which was beneficial to improve the bending strength of the composite.

MICROSTRUCTURE AND THERMAL CONDUCTIVITY OF Cu-Cr ALLOYS AND COMPOSITE REINFORCED WITH SHORT HIGH MODULUS CARBON FIBRES

Cu-0.2Cr/Granoc composite was prepared by gas pressure infiltration of molten metal alloy into fibre preform in laboratory autoclave. Rod like carbon fibre preform was manufactured from Granoc ® XN-100 high modulus short C fibres with the length of 1 mm via their disintegration and subsequent sedimentation in polyvinylalcohol solution. The fibres were randomly oriented in planes parallel to the x,y directions (in-plane); z-direction is perpendicular to this plane. Thermal diffusivity was measured by means of the flash method and thermal conductivity (TC) was calculated using values of density and specific heat of composite. All measurements were performed at room temperature on disc shaped composite samples with the diameter of 10 mm and the thickness of 5 mm. The TC of composite exhibits anisotropy. TC in z-direction as high as 259.0 Wm -1 K -1 and in-plane as high as 292.0 Wm -1 K -1 were determined. The influence of Cr addition on the TC of four copper alloys (Cu-0.1Cr, Cu-0.2Cr, Cu-0.5Cr and Cu-1Cr) was also determined.

Silicon dissolution and interfacial characteristics in Si/Al composites fabricated by gas pressure infiltration

The silicon dissolution and interfacial characteristics of Si/Al composites were investigated by microstructure analysis and thermodynamic calculation. A new method of gas pressure infiltration was proposed to fabricate the Si/Al composites with near-net shape. The interfacial characteristics were examined using SEM, TEM, EDS and X-ray Diffraction, especially, silicon particles with reaction products were extracted through the electrochemical etching. The results show that some Si particles have been dissolved and a lot of crusts filled with Al matrix are left. The SiO2 layer in Si/Al composites has three functions: to enhance the interfacial strength by interfacial reactions between Si particles and Al matrix, to serve as barriers to prevent the Si particles from being dissolved by molten Al alloy, and to join Si particles to form Si preform. However, the barriers will not perform these functions when they are damaged. The SiO2 barriers are consumed by molten Al alloy, and the major phase in the interfacial reaction products between the SiO2 barriers and the molten Al is Al2O3, while MgAl2O4 is the minor phase. Furthermore, the reaction of an equation “4Al (L) + 3SiO2 (S) = 2Al2O3 (S) + 3Si (S)”is the dominant interfacial reaction in the Si/Al composites, which is different from the dominant reaction in SiC/Al composites.

Optimizing thermal conductivity in gas-pressure infiltrated aluminum/diamond composites by precise processing control

The effects of processing conditions on the thermal conductivity (TC) of aluminum/diamond composites fabricated by means of gas-pressure infiltration, have been evaluated using a device that allows a highly precise control of infiltration temperature and contact time between the liquid metal and diamond. Both variables have strong effects on the TC of final materials, through chemical and morphological modifications of the interface. Thus, maximizing heat conduction requires a proper choice of those two variables. TC’s up to 670W/mK have been obtained.

Fabrication of Continuous Nickel-Coated Carbon Fiber Reinforced Aluminum Matrix Composites Using Low Gas Pressure Infiltration Method

Based on the principle of vacuum counter-pressure casting, a low gas pressure infiltration technology was developed to fabricate the Ni-coated carbon fiber reinforced A357 alloy composites. The soundness and microstructure of the as-cast composites were investigated. The results show the relative density increases with the increase of melt temperature, while it firstly increases and then declines as the fiber temperature and infiltration pressure increased. The enhancement of melt and fiber temperature can eliminate the incomplete infiltration defects and improve the uniformity of fiber distribution. The insufficient infiltration pressure leads to some micro-pores in the matrix alloy. However, the over high fiber temperature and infiltration pressure may result in the separation of nickel coating and the fiber aggregation respectively, both of which are responsible for the partial un-infiltrated or insufficient filling defects. The appropriate infiltration parameters identified in this study could provide a reference for inhibition of the hazard interfacial reactions by optimizing the low gas pressure infiltration process.

Enhanced thermal conductivity in diamond/aluminum composites: Comparison between the methods of adding Ti into Al matrix and coating Ti onto diamond surface

The enhancement of thermal conductivity (TC) in diamond/A356 aluminum alloy composites was investigated by comparing the Ti coating on diamond surface with the Ti content in Al matrix. Diamond/A356 aluminum alloy composites with Ti coating on diamond surface (Ti–diamond/aluminum) and Ti added into matrix (diamond/aluminum-Ti) were fabricated by gas pressure infiltration. The microstructure, TC and interfacial thermal conductance (ITC) of these two types of composites were compared. Unlike the homogeneous interfacial bonding for the Ti–diamond/aluminum composite, it exhibits a transition from weak to strong interface bonding as the content of Ti in the Al alloy increases. The method of coating appears more effective than the method of adding active metal into the matrix on enhancing the diamond/aluminum interface thermal conductance with the help of calculation by differential effective medium (DEM) and acoustic mismatch model (AMM).

Fabrication of Ceramic-Metal Composites with Percolation of Phases Using GPI

Al2O3/AlSi12CuMgNi composites were fabricated using gas-pressure infiltration (T=700°C, p=4 MPa) of an aluminium alloy into alumina performs. Volume fraction of the ceramic phase was up to 30%, while the pore sizes of the ceramic preforms varied from 300 to 1000 µm. Ceramic preforms were formed by method of copying the cellular structure of the polymer matrix. The results of the X-ray tomography proved very good infiltration of the pores by the aluminium alloy. Residual porosity is approximately 1 vol%. Image analysis has been used to evaluate the specific surface fraction of the interphase boundaries (Sv). The presented results of the studies show the effect of the surface fraction of the interphase boundaries of ceramic-metal on the composite compressive strength, hardness and Young’s modulus. The composites microstructure was studied using scanning electron microscopy (SEM). SEM investigations proved that the pores are almost fully filled by the aluminium alloy. The obtained microstructure with percolation of ceramic and metal phases gives the composites high mechanical properties together with the ability to absorb the strain energy. Compression tests for the obtained composites were carried out and Young’s modulus was measured by the application of the DIC (Digital Image Correlation) method. Moreover, Brinell hardness tests were performed. Gas-pressure infiltration (GPI) allowed to fabricate composites with high compressive strength and stiffness.

Microstructure and properties of Al/Si/SiC composites for electronic packaging

The Al/Si/SiC composites with medium volume fraction for electronic packaging were fabricated by gas pressure infiltration. On the premise of keeping the machinability of the composites, the silicon carbide particles, which have the similar size with silicon particles (average 13 μm), were added to replace silicon particles of same volume fraction, and microstructure and properties of the composites were investigated. The results show that reinforcing particles are distributed uniformly and no apparent pores are observed in the composites. It is also observed that higher thermal conductivity (TC) and flexural strength will be obtained with the addition of SiC particles. Meanwhile, coefficient of thermal expansion (CTE) changes smaller than TC. Models for predicting thermal properties were also discussed. Equivalent effective conductivity (EEC) was proposed to make H-J model suitable for hybrid particles and multimodal particle size distribution.

Manufacture studies and impact behaviour of light metal matrix composites reinforced by steel wires

Magnesium alloys play an important role in the development of light metal matrix composites. Magnesium based metal matrix composites reinforced by particles and fibres (especially carbon fibres) are successfully applied in various fields of automotive and aircraft industry. Equally high potential in large-batch production regarding to relatively low price and high strength is expected from MMC with wires made of iron-based alloys. However, their application is hampered by the absence of intermetallic phase between iron and magnesium and low solubility of iron in magnesium.This paper makes a contribution to the investigation of the effect of steel wires surface preparation and of optimised production methods to improve the quality and type of adhesion with selected industrial magnesium alloys. The Fe/Mg-MMC specimens with steel wires reinforcement were manufactured by the help of advanced gas pressure infiltration method (GPI) in a graphite mould at Institute of Lightweight Engineering and Polymer Technology (ILK) of TU Dresden. For the examination of the obtained composites the computer tomography (CT), SEM microscopy with EDX, strength tests and fracture surface inspection has been used.

Al2O3 particle rounding in molten copper and Cu8wt%Al

We investigate processing-microstructure relationships in the production of Al2O3 particle reinforced copper composites by solidification processing. We show that during production of the composites by gas-pressure infiltration of packed Al2O3 particle preforms with liquid Cu or with liquid Cu8wt%Al at either 1,150 or 1,300 °C, capillarity-driven transport of alumina can cause rounding of the Al2O3 particles. We use quantitative metallography to show that the extent of particle rounding increases markedly with temperature and with the initial aluminum concentration in the melt. An analysis of the thermodynamics and kinetics governing the transport of alumina in contact with molten copper, considering both interfacial and volume diffusion, leads to propose two mechanisms for the rounding effect, namely (i) variations in the equilibrium concentration of oxygen in the melt as affected by the initial aluminum concentration, or (ii) segregation of aluminum to the interface with the ceramic.