Dispersion-strengthened composites

Table 7. Nominal Compositions of Oxide Dispersion Strengthened Alloys, wt %...

Figure 5.81 Strength of dispersion-strengthened aluminnm compared with wronght aluminum. Reprinted, by permission, from M. Schwartz, Composite Materials Handbook, 2nd ed., p. 1.29. Copyright 1992 McGraw-Hill Book Co.

Figure 5.82 The strength of different dispersion-strengthened alloys relative to the pure metal strength as a function of relative temperature. Preparation techniques include sintered aluminum powder (SAP), internal oxidation, and salt decomposition. Reprinted, by permission, from A. Kelly, Composite Materials, p. 62. Copyright 1966 by American Elsevier, Inc.

The formula can also be used for dispersively strengthened metallic-nonmetallic composites, in which the host matrix is metal. 

J. S. Benjamin, C. B. Raymond, Nickel-Based Dispersion-Strengthened Alloys, in Mechanical Properties of Metallic Composites Ochiai, S., Ed. Marcel Dekker, 1993. 

Tantalum can be further strengthened by additions of Hf (solution-strengthening) or hafiiium nitrides, carbides, or oxides (precipitation/dispersion-strengthening). Typical alloy compositions of this type are Ta-8W-2Hf and Ta-10W-2.5Hf-0.01C. 

It should be noted that the elastic values of the composite are remarkably higher at all investigated temperatures than those of the conventional Ti-A16V4 or other advanced dispersion strengthened titanium alloys, such as IMI 834, respectively. 

To finalize this section, I would like to mention that some papers delve into the studies of radiation tolerance of laminated composites with the thickness of layers not increasing tens of nanometers. By varying the thickness of such materials, we can investigate the main mechanisms of influence produced by interphase boundaries on the behavior of radiation defects. The irradiation of multilayered structures with the ions of inert gases first of all with helium allows for the modeling of processes that may arise during the reactor-induced irradiation of oxide dispersion-strengthened steels and alloys. 

The particle-reinforced composites can be further classified into large-particle composites and dispersion-strengthened composites on the basis of particle size [23]. 

Particle reinforced composite systems can be either large particle or dispersion strengthened. If a composite is reinforced by large particles (larger than 0.1 [xm and equiaxed, which are harder and stiffer than the matrix), mechanical properties are dependent on volume fractions of both components and are enhanced by increase of particulate content. Concrete is a common large particle strengthened composite where both matrix and particulate phases are ceramic materials. 

Initially refractory metals were applied mainly in the pure state. Extensive developments mainly driven by US aerospace programs led to a wide variety of alloys now commercially available. The compositions of solid-solution, precipitation- and dispersion-strengthened alloys are given in Table 3.1-108. Tungsten heavy metals and refractory-metal-based composite materials are not included here. 

A composite material or simply a composite is a duplex and multifunctional material composed of at least two elements working together to produce a structural material with mechanical and physical properties that are greatly enhanced compared to the properties of the components taken separately. In practice, most composites consist of a bulk material called the matrix and a reinforcement material or filler, added primarily to increase the mechanical strength and stiffness of the matrix but also sometimes to modify its thermal conductivity and electrical resistivity. This reinforcement is usually made of fibers (e.g., monofilaments, whiskers) but can also be particulates (i.e., dispersion strengthened and particle reinforced) or even material having a more complex shape (e.g., mesh, ribbon, laminates, etc.). Composites are first classified according to their matrix phase into three major classes ... 

Sun, H. and Wheat, H. G., Corrosion Study of AI2O3 Dispersion Strengthened Cu Metal Matrix Composites in NaCl Solutions," Journal of Materials Science, Vol. 28, 1993, pp. 5435-5442. 

The boundary between dispersion-strengthened and grain-reinforced composites is based on the particle size and dimension level of the processes the grains control the crack propagation and not that of dislocations. 

In composites, different materials are combined to exploit favourable properties of each. That such combinations may be attractive was already shown in section 6.4.4 for particle strengthening of metals and in section 7.5 for dispersion-strengthened ceramics. 

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