= Solution
\b[Lower the operating <temperature> or <stress>, suppress <diffusion>, and remove or stabilize the paths that accommodate <material creep>.] Increasing the melting <temperature> can reduce $T/T_m$ at a specified operating <temperature>. Chemistry that reduces diffusivity or impedes <dislocation climb> can reduce the <material creep> rate; stable precipitates or dispersoids can resist glide and climb, provided they do not dissolve or coarsen rapidly in service.
Large grains reduce both Nabarro-Herring and <Coble creep>, according to their $d^{-2}$ and $d^{-3}$ dependencies. Directional <solidification> can reduce boundaries normal to the dominant tensile <stress>, while a single crystal removes grain-boundary transport and sliding from the ordinary polycrystal mechanism inventory. It does not remove bulk <diffusion> or <dislocation> <material creep>.
This is why room-temperature grain-refinement strengthening is not automatically a high-temperature <material creep> strategy: fine grains create more boundary transport paths. Any protective <microstructure> must remain stable at the service <temperature>, and the design must also avoid <stress> concentrations and unwanted thermal loading.
Back to article page
