High-temperature strength

9 Log-log plot of tensile creep strain rate against applied stress for alumina and an alumina-17vol%SiC nanocomposite tested in tension at 1200°C. 

Superplastic ceramics have several obvious potential advantages for commercial application. These include net size and shape forming and the possibility of forming complex components from initially flat sheets. Whilst the practical problems of forming at temperatures in excess of 1200°C obviously 

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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. 

Refractories. Calcined alumina is used in the bond matrix to improve the refractoriness, high temperature strength/creep resistance, and abrasion/corrosion resistance of refractories (1,2,4,7). The normal, coarse (2 to 5 )J.m median) crystalline, nominally 100% a-Al202, calcined aluminas ground to 95% —325 mesh mesh are used to extend the particle size distribution of refractory mixes, for alumina enrichment, and for reaction with... 

High temperature strength of refractory materials is determined on rectangular prisms 25 x 25 x 150 mm cut from the product being tested. The specimens are placed ia a furnace, heated to a desired temperature, and the modulus of mpture is determined. A detailed description is given ia ASTM C583. 

Forsterite Refractories. Refractories made from forsterite, Mg2Si04, resist alkah attack and have good volume stabiUty, high temperature strength, and fak resistance to basic slags. Uses include nonferrous metal furnace roofs and glass-tank refractories not in contact with the melt, ie, checkers, ports, and uptakes. 

Soda-lime glass Borosilicate glass 70 SiOj, 10 CaO, 15 Na O 80 SiOj, 15 BjOj, 5 NajO Windows, bottles, etc. easily formed and shaped. Pyrex cooking and chemical glassware high-temperature strength, low coefficient of expansion, good thermal shock resistance. 

Fig. 19.5. Liquid phase sintering a small amount of additive forms a liquid which accelerates sintering and gives fully dense products but with some loss of high-temperature strength.

The addition of cathodically active elements to pure lead was the main objective of investigations to improve its corrosion resistance to H2SO4 [42,44]. Best known is copper-lead with 0.04 to 0.08% Cu. By adding combinations of alloying elements, it was possible to produce lead alloys that not only had much better corrosion resistance, but also had greater high-temperature strength. Lead alloy with 0.1% Sn, 0.1% Cu and 0.1% Pd is an example [45]. 

Nickel alloys have two main properties good resistance to corrosion and high-temperature strength. There are alloys for medium-and low-temperature applications and for high-temperature conditions in which creep resistance is of main importance [24]. 

Alloys with thoria (Th02> are used for TIG (Tungsten Inert Gas) welding electrodes and in electronic applications where its increased electron emission properties and high temperature strength prove advantageous. 

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