Creep resistant materials

Mechanisms of creep, and creep-resistant materials 189, Climb... 

Current creep-resistant materials are successful because they satisfy these criteria. 

These requirements severely limit our choice of creep-resistant materials. For example, ceramics, with their high softening temperatures and low densities, are ruled out for aero-engines because they are far too brittle (they are under evaluation for use in land-based turbines, where the risks and consequences of sudden failure are less severe - see below). Cermets offer no great advantage because their metallic matrices soften at much too low a temperature. The materials which best fill present needs are the nickel-based super-alloys. 

Explain what is meant by creep in materials. What are the characteristics of a creep-resistant material ... 

The anode is stabilized by using mixed powders of Ni-Cr, Ni-Al, or refractory oxides and sintered at 900-1100°C under a reducing atmosphere to provide a creep resistant anode structure. The function of the additives is to reduce the loss of porosity during sintering and develop creep resistant materials. The creep is referred to as the shrinkage in thickness and change in shape. The sintering resistance is increased by the additives, which are usually metals or oxides of metals. 

Steel fibrous RubCon is a creep-resistant material the coefficient of creep at compressive load kCT 0.75. 

Avoiding access of humidity to the contact region between the materials, e.g. as shown in Figure 7.12b. A sealer of a polysulphide-based, creep-resistant material may for instance be used [7.11]. 

Kotliar et al. [74-76] have explored the use of carpet face yam and textiles as a fibrous filler for a composite or laminate. Because of the fine diameter of the fibers involved, a low-viscosity prepolymer in a water base was used to ensure complete coverage of the fibers. Adhesives were selected to result in a high-modulus and creep-resistant material with good weathering characteristics. 

The complex crystal structure of mullite provides creep resistance materials if a sintered microstructure can be obtained without the help of an excess of silica. 3M produced a dense mullite-a-alumina fibre, called Nextel 720 (Wilson et al., 1995), by using an aqueous sol, composed of intimately mixed silica and alumina precursors, with iron compounds used as the seeds for a-alumina. The fibre shown in Figs, 16 and 17 is composed of a continuum of mullite mosaic grains of about 0.5 p-m with wavy contours, with no silicate intergranular phase (Deleglise et al., 2001). 

Summing up the accepted rules for producing creep-resistant materials, the approach should be such that (i) high-melting materials are preferential ... 

Veronski A, Hejwowsld T (1991) Creep-resisting materials. Thermal fatigue of Metals. CRC Press, p 81-93... 

Similar to time-independent plastic deformation, creep deformation in metals is dominated by dislocation movement, especially at higher stresses. Mechanisms that impede dislocation movement are thus also important in producing creep>-resistant materials. However, these mechanisms have to be temperature resistant. 

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