Dispersion strengthening

Fig. 6. Properties of the ( ) oxide dispersion strengthening (ODS) materials MA-6000 and MA-754 and conventional (0) cast and (O) wrought superaHoys...

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

Table 8. Materials Properties of Oxide Dispersion Strengthened Superalloys ...

Dispersion-strengthened copper is made by dispersing a thoria or alumina phase through copper powder. The resulting P/M product retains its strength at elevated temperatures. It is used, for example, as the conductor or lead wine that supports the hot filament inside incandescent lamps. 

Mechanical alloying is another method of producing dispersion-strengthened metals. In this process, the powdered constituents of the ahoy are treated in an attrition mih. A finely distributed layer of the dispersed phase is distributed on particles of the base metal. Subsequent pressing and sintering strengthens the dispersion (25). 

Space technology has always demanded materials that can operate at temperatures between those of superaHoys and refractory metals and that have high temperature strength during operation and room temperature ductility for fabrication. The development of dispersion-strengthened and oxide alloy systems has solved part of this problem. 

The technique of rapid soHdification enables relatively large amounts of insoluble metallic elements to be finely dispersed within atomized powders. Upon freezing very small intermetaUic particles are formed, resulting, after further processing, in a high volume fraction of finely dispersed particles within the aluminum matrix and hence a dispersion strengthened aUoy. The intermetaUic phases, or possibly oxidic species, responsible for the dispersion strengthening are probably binary Al-Fe and ternary Al—Fe—Ce compounds. 

Extremely high softening resistance is available in alloy C15720 through dispersion strengthening by aluminum oxide. This alloy has been used successhiUy as a welding rod material and in other specific appHcations that can bear its cost. 

Aesthetic dental ceramics are essentially glass-matrix materials with varying volume fractions of crystalline fillers. Crystalline fillers are used in the glass matrix both for dispersion strengthening, usually at volume fractions of 40—70%, and for altering optical properties, usually at low volume fractions. Dental ceramics are generally manufactured from two distinct classes of materials, ie, beneficiated feldspathic minerals and glass—ceramics. 

Demonstrations (a) Atomix (to show grain boundaries), (b) Model of dispersion strengthening. Take piece of PMMA sheet == 2.5 mm thick and = 7 cm square. Glue four PMMA strips of section =7X7 mm on top of the sheet to form a tray = 7 mm deep. Cut six = 7-mm lengths of an = 6-mm-diameter PMMA rod. Glue the ends of these to... 

Dispersion-strengthened lead (DSL), obtained by a uniform dispersion of lead oxide through the lead particle matrix, has the traditional corrosion resistance of lead but much greater stiffness. DSL is fabrieated as pipe and other extruded items, but has a limited applieation for proeess plant construction because the welding technique does not provide adequate strengths in joints. 

Oxidative damage, role of ascorbic acid in preventing, 25 769 Oxidative degradation, 70 682 of gasoline, 72 399-400 Oxidative dehydrogenation, 23 342-343 Oxidative pyrolysis, 27 466 Oxidative stability, of olefin fibers, 77 229 Oxidative stability test, 72 400 Oxide crystal glass-ceramics, 72 641 Oxide-dispersion-strengthened alloys, 77 103-104... 

J.S. Beniamin, Dispersion strengthened superalloys by mechanical alloying Metall. Trans. 1 (1970) 2943-2951. 

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