Superlattice melting

Because the appearance of a superlattice is usually well characterized qualitatively in terms of an interaction parameter w which has nothing to do, in the usual treatments, with the melting of the parent solid solution, one does not expect to find a simple relationship between the critical temperature for disordering of the superlattice, and Ts, the solidus temperature of the corresponding solid... 

All Ni and Fe—Ni-based superalloys are alloyed with Al. This leads to a two-phase matrix consisting of the y-(Ni, Fe, Al) solid solution phase (fee, Al stmeture) and the intermetallic y -NisAl phase (LI2 stmeture), which has a superlattice structure relative to the fee stmeture of the y phase. The binary Al—Ni phase diagram in Fig. 3.1-128 shows clearly that the y phase is stable up to the melting range. The matrix phase y is solid solution strengthened by allo3dng additions of Cr, Mo, W, and... 

Fig. r.3-58 Effective Fe cNi3,Alj phase diagram after cooling from the melt at 10 K/h. Broken lines indicate superlattice phase boundaries the point-dash line the magnetic phase boundary in the Ni(Al,Fe) phase field, ai bcc 0 FesAl-type superlattice phase U2 (Fe,Ni)Al-type superlattice phase y fee yi- NisAl-type superlattice phase ... 

Within the PRISM approach, one can formally view a block copolymer as a special case of the multisite systems discussed in Section III.B. However, the block structure results in novel physical phenomena, not displayed by simple polymer melts, which is important both scientifically and from a materials engineering viewpoint. The most prominent feature is the ability of such a fluid to spontaneously self-assemble into microdomains of variable purity, spatial symmetry, and fV-dependent size. Ultimately a first-order microphase separation transition, or weak crystallization, into an ordered superlattice-type structure can occur where the characteristic domain size or lattice constant is typically 50-500 A. Such microscopic segregation represents a dramatic structural reorganization of the fluid and can be driven by changing temperature, increasing degree of polymerization, or increasing copolymer density in solution. 

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