Hardening dispersion

Zirconium oxide increases the refractive index of some optical glasses, and is used for dispersion hardening of platinum and mthenium. Very fine zirconium oxide has been used for polishing glass but ceria seems to be preferred. 

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. 

Copper. The physical properties of pure copper are given in Table 11. The mechanical properties of pure copper are essentially the same as those for ClOl and CllO. The coppers represent a series of alloys ranging from the commercially pure copper, ClOl, to the dispersion hardened alloy C157. The difference within this series is the specification of small additions of phosphoms, arsenic, cadmium, tellurium, sulfur, zirconium, as well as oxygen. To be classified as one of the coppers, the alloy must contain at least 99.3% copper. 

Additions of antimony, bismuth and tin to the lead appear to be detrimental. There is an indication that the addition of 0 - l<7o Ag is almost as effective as 1% and additions as low as 0-01% has been utilised in practice. Dispersion-hardened lead alloys have been unsatisfactory, showing pronounced spalling in the direction of extrusion. Pb-0-lTe-0-lAg has been also used with apparent success" . 

Dispersion devices, ozone, 17 801-802 Dispersion force, 12 4 Dispersion-free solvent extraction, 10 766 Dispersion hardening, 13 501, 502, 527 of refractory metal alloys, 13 528 Dispersion polymerization, 24 156-157 of acrylamide polymers, 1 323 of methacrylic ester polymers, 16 289 Dispersion processing of FEP polymer, 18 314... 

Ultrasonic Atomization 30-50 USWA >100 Medium size distribution Solder materials, Welding electrodes, Ag-, Cu-base alloys, Dispersion-hardened allovs USWA 107 0.02-0.8 Low Spherical high quality particles, Low cost, Small unit, High EE Low volume productivity... 

One important class of particulate composites is dispersion-hardened alloys. These composites consist of a hard particle constituent in a softer metal matrix. The particle constituent seldom exceeds 3% by volume, and the particles are very small, below micrometer sizes. The characteristics of the particles largely control the property of the alloy, and a spacing of 0.2-0.3 tim between particles usually helps optimize properties. As particle size increases, less material is required to achieve the desired interparticle spacing. Refractory oxide particles are often used, although intermetallics such as AlFes also find use. Dispersion-hardened composites are formed in several ways, including surface oxidation of ultrafine metal powders, resulting in trapped metal oxide particles within the metal matrix. Metals of commercial interest for dispersion-hardened alloys include aluminum, nickel, and tungsten. 

A cermet is a particulate composite similar to a dispersion-hardened alloy, but consists of larger ceramic grains (cer-) held in a metal matrix (-met) (see Figure 1.78). The refractory particulates can be from the oxide category, such as alumina (AI2O3),... 

Figure 1.78 Comparison of (a) cermet and (b) dispersion-hardened alloy. Reprinted, by permission, from M. Schwartz, Composite Materials Handbook, 2nd ed., p. 1.32. Copyright 1992 by McGraw-Hill.

Loss of internal surface of highly porous coatings by slow sintering can sometimes be prevented to a certain extent by stabilizing the porous structure by so-called internal or external dispersion hardening, that is, by interdispersion of a second electrocatalytically inactive, oxidic highly dispersed... 

Niobium in Tool Steels. In the matrix method of tool-steel development, the composition of the heat-treated matrix determines the steel s initial composition. Carbide volume-fraction requirements then are calculated, based upon historical data, and the carbon content is adjusted accordingly. This approach has been used to design new steels in which niobium is substituted for all or part of the vanadium present as carbides in the heat-treated material. Niobium provides dispersion hardening and grain refinement, and forms carbides that are as hard as vanadium, tungsten, and molybdenum carbides. 

Dispersion hardening or strengthening of a material means an increased resistance to deformation. The movement of dislocations in the metal facilitates metal deformation. Incorporated particles block the dislocation movement and thus strengthen the metal.4,11 12,21 Grain refinement of the metal due to the codeposition of particles has also been thought to contribute to the hardening effect, but this is not supported by experimental evidence. For several composites it was found that the grain structure of the metal matrix was not altered by the codeposition of particles. 

Other successful combinations have been reported to include molybdenum disulphide in dispersion-hardened silver, 15% molybdenum disulphide with 80% silver and 5% nickel, and 50% molybdenum disulphide, 33.3% silver and 16.7% nickel. Tanaka and Kimura " studied the effect of electric current on the wear of the last of those compacts. They found that the amount of wear increased progressively with increasing amperage, but that the increase represented a change in the size of wear particles rather than an increase in the number of particles. 

Key words high-strength aluminum alloys, dispersion hardening, quasicrystals, eutectic alloys, mechanical properties... 

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