Size Effects in Ti micro-cantilevers

The effect of sample size on strength has been recieving considerable attention. The majority of the work has concerned compression testing of micro- and nano-scale pillars, and has examined fcc metals.

Here we use cantilevers with widths ranging from 1 to 10 microns cut in the hexagonal metal Ti. The cantilevers were cut within a selected grain of a large grained polycrystal and oriented so that a type slip on the prismatic planes is activated. The cantilevers were tested by bending them in a nanoindenter.

Comparison of the measured load-diplacement curves with crystal plasticity finite element simulations allows us to determine the critical resolved shear stress (CRSS).

The CRSS increases dramatically as the cantilever width is reduced toward 1 micron. The variation fits well to an inverse reltionship to the cantilever width plus a constant term representing the macroscopic behaviour. This can be explained by the effects of backstresses generated as dislocations generated near the surface of the beam move toward its interior and pile-up at the neutral axis.

load displacement
CRSS vs size

Contact: Jicheng Gong and Angus Wilkinson

Micro-cantilever testing of a prismatic slip in commercially pure Ti
JC Gong, AJ Wilkinson
Philosophical Magazine, (2011), vol. 91, 1137-1149

A microcantilever investigation of size effect, solid-solution strengthening and second-phase strengthening for <a> prism slip in alpha-Ti
J Gong and, AJ Wilkinson
Acta Materialia, (2011), vol. 59, 5970-5981