Particulate-reinforced alloys

Sohd rocket propellants represent a very special case of a particulate composite ia which inorganic propellant particles, about 75% by volume, are bound ia an organic matrix such as polyurethane. An essential requirement is that the composite be uniform to promote a steady burning reaction (1). Further examples of particulate composites are those with metal matrices and iaclude cermets, which consist of ceramic particles ia a metal matrix, and dispersion hardened alloys, ia which the particles may be metal oxides or intermetallic compounds with smaller diameters and lower volume fractions than those ia cermets (1). The general nature of particulate reinforcement is such that the resulting composite material is macroscopicaHy isotropic. 

A typical tensile creep curve for a particulate reinforced ceramic matrix composite, siliconized silicon carbide (Si/SiC),28 is shown in Fig. 4.1. In comparison to the behavior of metals and metallic alloys, tertiary creep is suppressed in this material. There is only a slight upward curvature of the creep curve prior to failure. In many other ceramic matrix composites, tertiary... 

Thus, the aim of the present paper is not to review the bulk of the results published to date relating to the creep response of various magnesium-based composites. Instead of such an approach this paper provides a comprehensive report on the extensive experimental results obtained by authors in an investigation of the high temperature creep behavior of the two magnesium alloys, AZ 91 and QE 22, and their discontinuous composites. The objective of the present research is a further attempt to clarify the direct and indirect strengthening effects of short-fiber and particulate reinforcements in creep of magnesium-matrix composites. 

The metalworking nature of the process leads to the plunge and rehll FSSW methods, with properties comparable to riveted and resistance spot-welded joints. The use of FSP to locally modify the microstructure of arc welds and castings has shown to increase strength, improve fatigue life, and remove defects. Using FSP to stir particulate materials into the surface has shown increased wear resistance and creates particulate-reinforced surface layers. Friction stir reaction processing can be used to create new materials and alloy combinations on part surfaces. 

DMO composites with particulate reinforcements of alumina and silicon carbide were found to possess moduli of 302 and 324 GPa, respectively [92]. In the former case, the total alumina content, including the reinforcement, was 81% while in the latter, the SiC volume fraction was 46% and the matrix alumina 37%. The alloy content and porosity were in the vicinity of 15 and 2 vol-%, respectively. A similar value of 313 GPa was reported for a SiC reinforced DMO composite whose composition was not disclosed [93],... 

A different approach to the synthesis of dense hard materials is reported by Degnan and Wood [91]. They describe a process in which Fe-(W,Ti)C cermet powders, produced by the SHS method, are used as additives to molten iron for the production of a particulate-reinforced material with improved wear properties. The presence of the additive provided an enhancement of wetting between the metal matrix and the added particles. The product was a fairly uniform material which showed a considerably improved wear resistance over iron-based alloys. Sharivker et al. [92] followed a somewhat similar route by using SHS-produced TiC or Tio 97Moo.o3C as additives to produce metal-based hard materials. 

Preform infiltration This process usually involves the infiltration of a preform of fibers or particulate reinforcement with a liquid metal. Depending on the wetting characteristics and the type of alloy, either pressureless or pressure-assisted infiltration can be used. 

Spray deposition The spray deposition process, which was developed by Osprey Ltd during the late 1970s for producing monolithic alloys [365], has been adapted by several manufacturers to produce particulate-reinforced MMC billets with a residual porosity of 5% [366]. The porosity is eliminated by a secondary processing, such as extrusion or rolling. A spray gun is used to produce an atomized stream of aluminum alloy, into which heated SiC particles are injected. An optimum particle size is... 

Other applications of P/M processing include mechanical alloying and the production of particulate-reinforced titanium composities such as CermeTi . These and other developments are reviewed in a recent article by Froes and Suryanarayana... 

Ding, H., G. A. Hawthorn, and L. H. Hihara, Inhibitive effect of seawater on the corrosion of particulate-reinforced aluminum-matrix composites and monolithic aluminum alloy. Journal of the Electrochemical Society, 156, 2009, C352. 

T Imai, G L esperance, BD Hong, Y Tozawa. High strain rate superplasticity of T1B2 particulate reinforced aluminium alloy composite. J Mater Sci Lett 14 373, 1995. 

Corrosion Proporlios. Marine corrosion of silicon carbide/aluminum composites is much less severe than that observed on graphite/aluminum MMCs. Discontinuous silicon carbide/aluminum MMCs, however, are susceptible to localized corrosion. Mild-to-moderate pitting has been reported on SiC whisker- and particulate-reinforced composites containiirg 6061 and 5000 series aluminum matrices exposed for a maximum of 42 months in splash/spray and marine atmospheric environments. The d ree of corrosion present on the composites is slightly accelerated compared to that on unreinforced alutrtittum alloys. 

Adhesion promoters include the substances that create close physical and/or chemical bonds between two substrates [108]. The substrates to be cormected are fibrous reinforcing or particulate fillers on the one hand and plastics or metals on the other. The adhesion promoters always form bridges between the interfaces of the two components. For example, adhesion promoter resins based on styrene/butadiene alloys serve as adhesive layers for laminating panels and coextrusion of foils made of styrene polymers with polyolefins, PC, PMMA, and PA [30]. 

Even this definition needs to be classified [7, 8]. To some researchers it is still too broad because it includes many materials that are not usually thought of as composites such as concrete, copolymers and blends, reinforced plastics, and carbon-black-filled rubber. On the other hand, some of the more recent composites are excluded from the category of composites if this definition is strictly applied. For example, many particulate-type composites such as dispersion-hardened alloys and cermets have composite structures that are microscopic rather than macroscopic [2,8]. In some cases, the composite structures are nano-scopic, with the physical constraint of several nanometers as the minimum size of the components [9-16]. The terms... 

Description and General Properties. Metal matrix composites (MMCs) consist of a metal or an alloy matrix with a reinforcement material (e.g., particulates, monofilaments, or whiskers). The matrix alloy, the reinforcement material, the volume and shape of the reinforcement, the location of the reinforcement, and the fabrication method can all be varied to achieve required properties. Most of the metal-matrix composites are made of an aluminum matrix. But aluminum-matrix composites must not be considered as a single material but as a family of materials whose stiffness, strength, density, and thermal and electrical properties can be tailored. Moreover a growing number of applications require improved matrix properties and therefore, metal matrices of magnesium, titanium, superalloys, copper, or even iron are now available commercially. Compared to bulk metals and their alloys, MMCs offer a number of advantages such as ... 

Uniform corrosion of MMC matrices can be expected in environments that attack the matrix metal uniformly. In continuous-fiber MMCs, however, fibers will be left in relief as the matrix corrodes, whereas, in particulate MMCs, reinforcement particles fall free as they are undercut. Uniform corrosion rates of MMCs may be greater than that of the monolithic matrix alloys, due to galvanic action between the matrix and reinforcement constituents. 

Polymer alloys may be considered as independent composite materials because they have many common features similar to filled systems such as two-phase structure and interphase layer. Considering the reinforcement of pol5Tner alloys, one should have in mind a very complicated structure of the matrix, consisting conventionally of three phases. The distribution of particulate filler in such a system will be dependent both on the structure of various regions and on their composition, determining the affinity of the matrix to the filler surface. In its turn, as shown below, the filler may influence the formation of the alloy structure, which is especially important when reinforcing with fibrous fillers. 

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