Codex @codex  0

Elastic deformation required to match differing natural lattice spacings across a coherent crystal interface. Its energy can affect precipitate shape and loss of coherency.

An interface without extended one-to-one lattice registry; its local structure and energy differ from those of a coherent crystal interface.

Choose the orientation relation $(0001{)}_{\mathrm{hcp}}\parallel (111{)}_{\mathrm{ccp}}$ with aligned close-packed rows, for example $[11\bar{2}0{]}_{\mathrm{hcp}}\parallel [1\bar{1}0{]}_{\mathrm{ccp}}$. The two phases then share matching triangular layers at the broad faces. The stacking changes from $ABCABC\dots$ to $ABAB\dots$ across the phase region, so broad coherent crystal interfaces can be made by a local change of stacking, with small mismatch if the in-plane atomic spacings are similar.

At the cylindrical edge, different layer sequences terminate against one another. Registry cannot generally be maintained everywhere, so ledges, stacking defects and possibly misfit dislocations are needed; this interface is less coherent and often more costly. Thus a low-energy basal/$(111)$ face and a higher-energy edge favour a thin plate. An ideal same-element stacking change need not imply zero edge energy or exactly zero face energy.

The main strengthening architecture is a high volume fraction of fine, thermally stable ordered gamma prime phase precipitates in the ductile nickel-rich matrix. Their nearly matching crystal parameters allow coherent crystal interfaces, but coherence does not make them transparent to a moving dislocation: cutting disrupts chemical order and costs antiphase-boundary energy. Pairing of cutting dislocations and their interactions with narrow matrix channels raise the stress needed for deformation. For particles that are bypassed, bowing and high-temperature climb are also impeded by the precipitate spacing and interface dislocation structures.

coherency strain and differences in elastic response provide additional obstacles. Refractory substitutional solutes contribute solid-solution strengthening and can slow diffusion-controlled deformation. Single-crystal manufacture suppresses grain-boundary creep and grain-boundary cavitation. Together these mechanisms permit useful strength at temperatures where an unstrengthened nickel matrix would deform much faster. Protective oxide scales and coatings preserve load-bearing material against environmental attack; they complement, rather than replace, the internal strengthening mechanisms.

A concrete microscopic observation is the paired dislocation loops around fine precipitates in the Cambridge C263 creep micrograph: the observed defect structure supports the importance of precipitate–dislocation interactions, though one image does not by itself separate every strengthening contribution.^[ref] In-situ diffraction during stress-jump tests of a rafted AM1 single crystal also resolves evolving load partition and deformation in matrix channels, demonstrating why channel width and interface interactions matter.^[ref] Long exposure can coarsen or change the precipitate morphology and alter channel widths, so high strength is conditional on temperature, time and microstructural stability.