Bimodal grain distribution

FIGURE 16.30 Schematic of grain size distribution at various times for normal and abnormal grain growth. For abnormal grain growth a bimodal size distribution is produced from initially a monomodal size distribution. 

In essence, the population balance should be able to predict the conditions where a bimodal grain size distribution is initiated. Rearranging the population balance for the derivative of the population with respect to size, Rg, gives... 

Fig. 19. Microstructure of Y203 and MgO-doped Al20, showing bimodal grain size distribution as a result of the liquid phase present during sintering.

Schneider et al. (1986b) note that path A, involving the Fe particles, is faster than path B that consumes the Fe2B particles. Consequently, the grains that have their origin in Fe particles have the possibility to grow more than the others and one can expect the < grains to have a bimodal size distribution. 

Figure 10. Microstructure of sol/gel derived sintered alumina grits (a) platelet shaped microstructure ( Cubitron , manufactured by MMM, USA), (b) bimodal grain size distribution after seeding with transitional alumina nuclei, (c) anisotropic grain growth (Ce doping) [16].

Figure 23. (a) SEM micrograph of a polished and plasma-etched section of sintered SiC, EKasic D , note bimodal grain size distribution, (b) SEM micrograph of EKasic D sliding face after about 4000 h of successful service as a mechanical seal face (SiC/carbon pair, lubricated with water, maximum pressure 50 bar), (c) Schematic of the operational condition of a relief structured sliding surface in the lubricated state and after breakdown of the lubricant film. 

Work we have been doing indicates a factor of 1.27 (equals 4/tc), as used by other workers, and also indicates that this factor applies not only to uniform grain sizes, but to skewed and bimodal grain diameter distributions. It also shows a method for getting the actual grain size distribution from the intercept distribution, as attempted in section V of Professor White s paper. 

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