Features of Transformation in Soli 上游充通大警 SHANGHAI JIAO TONG UNIVERSITY 1.Interphase interfaces in solids -Coherent Coherent interface:two crystals match _perfectly at the interface place so that the two lattices are continuous across the interface Disregarding chemical species,the interfacial plane has the same atomic configuration in both phases,and two crystals are oriented relative to each other in a special way. When the distance between the atoms in the interface is not identical> straining one or both of the two lattices>coherency strain a (b) Fig.3.32 Strain-free coherent interfaces.(a)Each crystal has a different chemical composition but the same erystal structure.(b)The two phases have different lattices. Fig.3.34 A coherent interface with slight mismatch leads to coherency strains in the adjoining lattices. K.Chen 22
K. Chen 1. Interphase interfaces in solids - Coherent Coherent interface: two crystals match perfectly at the interface place so that the two lattices are continuous across the interface Disregarding chemical species, the interfacial plane has the same atomic configuration in both phases, and two crystals are oriented relative to each other in a special way. When the distance between the atoms in the interface is not identical straining one or both of the two lattices coherency strain Features of Transformation in Solid 22
Features of Transformation in Sol 上游充通大警 SHANGHAI JIAO TONG UNIVERSITY 1.Interphase interfaces in solids-Coherent 国 At the interface,each atom is partly bonded to wrong neighbors across the interface increase the energy of the interfacial atoms(interfacial energy increase due to a chemical contribution) Elastic strain energy due to lattice distortions y(coherent)=Ych +Yst AI JIAO TONG UNIVE K.Chen 23
K. Chen Features of Transformation in Solid 23
Features of Transformation in Soli 上游充通大警 SHANGHAI JIAO TONG UNIVERSITY 1.Interphase interfaces in solids -Semicoherent The coherency strains raise the total energy of the system For sufficiently large atomic misfit or interfacial area>energetically more favourable to replace the coherent interface with a semicoherent interface Semicoherent interfaces:the disregistry (or,misfit)is periodically taken up by misfit dislocations. Misfit btw.two lattices (6): d邱-da 6= da Spacing(D): D 6 b For smallδ：D 8 Fig.3.35 A semicoherent interface.The misfit parallel to the interface is accommo- dated by a series of edge dislocations b (da dB)/2 K.Chen 24
K. Chen 1. Interphase interfaces in solids - Semicoherent The coherency strains raise the total energy of the system For sufficiently large atomic misfit or interfacial area energetically more favourable to replace the coherent interface with a semicoherent interface Semicoherent interfaces: the disregistry (or, misfit) is periodically taken up by misfit dislocations. Features of Transformation in Solid 24 Misfit btw. two lattices (δ): Spacing (D): For small δ :