Precipitate-matrix interface

In order to elucidate whether such a precipitate can trap positrons, the positron affinities A+ for the host material and the precipitate were calculated [154], The A+ values were found to be relatively high and the positron lifetimes very short for perfect MC carbides. This fact confirms that perfect MC (M s Cr, V, Ti, Mn, Fe, Zr, Nb) carbides are very dense materials that cannot trap positrons when embedded in the Fe matrix. In general, from a PAS point of view, radiation damage can be interpreted as a combination of radiation-induced point defects, dislocations and small vacancy clusters [129,130] that occur mainly in the region of the precipitate-matrix interface. 

A.D. Brailsford, L.K. Mansur, The effect of precipitate-matrix interface sinks on the growth of voids in the matrix, J. Nucl. Mater. 103 104 (1981) 1403—1408. 

Above the threshold, deformation occurs as a consequence of direct particle interaction. Several mechanisms of interaction have been suggested solution-precipitation flow of fluid between particles and cavity formation at the particle matrix interface. These theories of creep suggest several rules to improve creep behavior (1) increase the viscosity of the matrix phase in multiphase materials (2) decrease the volume fraction of the intergranular phase (3) increase the grain size (4) use fiber or whisker reinforcement when possible. As the creep rupture life is inversely proportional to creep rate, lifetime can be improved by improving creep resistance. 

Detailed microstructural investigation [12] revealed enhanced precipitation of Nd-rich phases at the SiC/matrix interfaces in the QE 22 -SiC composite after T6 heat treatment and during creep (Fig. 9). Such precipitation can detrimentally affect the creep behavior in a similar way as to fiber-reinforced composites. Further, Moll et al. [11] have proposed that poor creep resistance of the QE 22-SiC composite may be explained by taking into account interfacial sliding as an additional creep mechanism... 

Figure 9. TEM micrograph showing enhanced precipitation of Nd-rich phases at the SiC/matrix interfaces in the QE 22 - SiC after T6 heat treatment and creep at 423 K.

Phase segregation — A second phase precipitates or segregates at the fiber-matrix interface to promote debonding. 

Mica particles were cast in various aluminum alloys [87, 88]. In 3.5 wt % NaCl solutions, the presence of mica particles depressed pitting potentials by approximately 20-30 mV, in comparison to the monolithic matrix Eilloys, suggesting that the presence of mica particles may slightly weaken the passive aluminum film. Corrosion behavior was also affected by the precipitation of secondary phases. In some cases, precipitates were preferentially attacked. Pits around and away from mica particles, interfacial corrosion of the mica-matrix interface, and exfoliation of mica particles were also observed. 

The extraction of precipitates for further examination is also possible by the same techniques. Conditions would have to be chosen to give matrix or interface attack. 

The most important of the extrinsic factors that affect the hardnesses of the transition metals are covalent chemical bonds scattered throughout their microstructures. These bonds are found between solute atoms and solvent atoms in alloys. Also, they lie within precipitates both internally and at precipitate interfaces with the matrix metal. In steel, for example, there are both carbon solutes and carbide precipitates. These effects are ubiquitous, but there... 

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