Coarse microstructure

Fast nitridation, coarse microstructure, high a content... 

Accelerated nitridation, increased /1-content More homogenous reaction. High a-content, fine microstructure, high strength and KIC Coarse microstructure, low strength and KIC... 

The possibility to obtain a uniformly dispersed composite powder was shown for the a-Fe-Al203 system where metal particles with an average size of 55 nm were formed in an amorphous/nano alumina matrix.18 Other studies attempting to obtain dense bulk composites based on the sol-gel route using conventional pressure-assisted sintering ( 1400°C and an applied force of 10 MPa) resulted in a coarse microstructure.16 However, if reaching theoretical density is not a necessary requirement, a porous ceramic microstructure containing nanometer-sized metal particles can be used as a catalytic material.19 Certain combinations of composite materials demand... 

A remarkably large discrepancy between the hardness of plastically deformed single crystalline volumes and of polycrystalline microstructures with grains of the same size, indicates a significant contribution of grain-boundary deformation at the indentation site in polycrystalline alumina, even at room temperature and even for coarse microstructures. 

Since pressureless sintering allows the fabrication of complex shapes but results in coarse microstructures and some residual porosity, this process is only applicable... 

Burki and Braun (1988) asserted that the clinker structure from laboratory tests is principally determined by raw meal properties and to a lesser extent by the heating rate. Rapid heating was said to increase the alite formation rate, accelerated with a homogeneous raw meal made of a chalky, clayey limestone (cement rock). A coarse microstructure (large voids and large crystals) was produced from coarse meal made largely of monomineralic particles. No influence of the final size of the alite and belite was observed after variations in heating rates. 

The criteria for designing fibers for use in ceramic matrix composites (CMCs) are different from those for designing fibers for use in poiymer or metal matrix composites. The key properties are thermal stability and mechanical properties at high temperatures [43]. As a consequence, relatively coarse microstructures are obtained at elevated temperatures, corresponding to somewhat lower failure strengths (-2 GPa), but high thermal stability and creep resistance are preferable to ultrafine microstructures. 

Slow cooling underground Fast cooling on surface Coarse microstructure Fine microstructure... 

Ferrite Positive Increased ferrite content increases the N, Cr. and Mo contents of the -y-phase. Too high ferrite can enhance chromium carbide/nitride precipitation in a coarse microstructure. 

Figure 8.4. Diagram illustration of the R-curve [SAK 87] -case of an alumina of coarse microstructure [STE 92]...

The extremely high melting point and the low self-diffusion coefficient make these ceramics very difficult to sinter to full density temperatures above 2000°C and the application of pressure are necessary conditions. However these processing parameters lead to coarse microstructures, with mean grain size of the order of 20 pm and trapped porosity, all features which prevent the achievement of the full potential of the thermo-mechanical properties of UHTCs. 

Through the controlled and directed assembly of nanoscale molecular building blocks one should be able to alter and engineer materials with desired properties. For example, ceramics and metals produced through controlled consoUdation of their MBBs have been shown to possess properties substantially improved and different from materials with coarse microstructures. Such different and improved properties include greater hardness and higher yield strength in the case of metals and better ductility in the case of ceramic materials [4,5]. 

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