A method is described for the creation of surfaces with cyclically reversible topographical form. Using spherical and cylindrical indenters applied to NiTi shape-memory alloys, an indentation-planarization technique is shown to result in a two-way shape memory effect that can drive flat-to-wavy surface transitions on changing temperature. First, it is shown that deep spherical indents, made in martensitic NiTi, exhibit pronounced two-way cyclic depth changes. After planarization, these two-way cyclic depth changes are converted to reversible surface protrusions, or "exdents." Both indent depth changes and cyclic exdent amplitudes can be related to the existence of a subsurface deformation zone in which indentation has resulted in plastic strains beyond that which can be accomplished by martensite detwinning reactions. Cylindrical indentation leads to two-way displacements that are about twice as large as that for the spherical case. This is shown to be due to the larger deformation zone under cylindrical indents, as measured by incremental grinding experiments.
|Number of pages||8|
|Journal||Journal of Materials Research|
|State||Published - Mar 2009|
Bibliographical noteFunding Information:
The authors gratefully acknowledge funding from the National Science Foundation under Grants CMS0336810 and CMS0510294 and from General Motors Corporation.
ASJC Scopus subject areas
- Materials Science (all)
- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering