Critical grain size

The prefactor introduced in Eqs. (3) and (8) remains the open parameter within the above scaling analysis. A theoretical determination of from experiment from the upper critical grain size where coercivity no longer follows a D6 law and tends to reach its maximum (cf. Fig. 4). This yields type alloys and is consistent with rough theoretical estimates [28]. 

This mechanism is similar to the mechanism of drastic hardness increasing in nanocrystalline composite materials, which was proposed for multi-component system by S. Veprek [8], In general it is possible to assume that for multi-component system after achievement of some critical grain sizes and at a correct choice of components transition to nanocrystalline or to an amorphous state should be accompanied not only prevention downturn of the hardness and yield point, but also considerably increase them in contrast to one-component system. 

To estimate the critical grain size above which spontaneous microcracking would occur, the various energy terms have to be considered. For the sake of simplicity, the grains are assumed to be cubes with grain size d in which case the total energy of the system is " ... 

Derive an expression for the critical grain size below which Coble creep dominates and above which Nabarro Herring creep dominates (at constant temperature). 

Park HH, Kwon OJ, Yoon DN (1986) The critical grain-size for liquid flow into pores during liquid-phase sintering. Metall Trans A-Phys Metall Mater Sci 17 1915-1919... 

Table 28.1 Comparison of the measured and predicted strongest critical grain sizes for IHPR transition with / = 0.5, 0.668 and m = 1 otherwise as indicated...

Another approach for the flow stress of an A-B aUoy suggests that the strongest grain size represents the emergence of GB diffusion that causes the HPR breakdown. For the A-B aUoy, the critical grain size is given by [21] ... 

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