Temperature dependence of indentation size effect, dislocation pile‐ups, and lattice friction in (001) strontium titanate

Abstract

Nanoindentations with a Berkovich type indenter were performed on (001) strontium titanate (STO) single crystal at 25°C and 350°C, analyzing the influence of temperature on the indentation size effect (ISE) and dislocation structure around the residual impression. It is found that the STO exhibits an ISE, which is strongly reduced at 350°C compared to 25°C. The dislocation structure around the residual impression has been resolved using an etch-pit technique. At 25°C, the extension of the dislocation pile-ups were found to be shorter as compared to 350°C. This also correlates with the smaller size effects at 350°C. Peach-Koehler forces and the elastic-plastic indentation stress field were used to model the influence of the lattice frictional stress on the dislocation pile-ups. Based on an equilibrium position of the outermost dislocations, the average lattice frictional stresses were calculated to be 89 MPa and 46 MPa at 25°C and 350°C, respectively. K E Y W O R D Sdislocation etch-pits, elevated temperature, indentation size effect, strontium titanate

Bridging the Gap between Bulk Compression and Indentation Test on Room-Temperature Plasticity in Oxides: Case Study on SrTiO3

“…For comparison, the τ bulk CRSS is the stress for dislocation glide in bulk deformation and should be close to the lattice friction stress, τ f , at the yield of plastic deformation (incipient plasticity in bulk), where the effect of dislocation-dislocation hardening (in later stage with large strain) does not need to be regarded due to a very low dislocation density at this stage in single crystal [29]. In indentation, however, the friction stress τ f must not be correlated to the resolved maximum shear stress at pop-in (as it correlates mainly to dislocation nucleation, being either homogeneous or heterogeneous), but rather can be estimated from the dislocation pile-ups [9,40] as revealed by the etch pit patterns (Figure 3b). A nice correlation between τ bulk CRSS and τ indent f has been found in single crystal SrTiO 3 [29,40], which gives a value of about 60-90 MPa at room temperature.…”

“…In indentation, however, the friction stress τ f must not be correlated to the resolved maximum shear stress at pop-in (as it correlates mainly to dislocation nucleation, being either homogeneous or heterogeneous), but rather can be estimated from the dislocation pile-ups [9,40] as revealed by the etch pit patterns (Figure 3b). A nice correlation between τ bulk CRSS and τ indent f has been found in single crystal SrTiO 3 [29,40], which gives a value of about 60-90 MPa at room temperature. Consider τ bulk CRSS = τ bulk max = σ uniaxial 2 and the obtained yield stress from Figure 2, a good agreement is confirmed by our experiment as well.…”

Nanoindentation pop‐in in oxides at room temperature: Dislocation activation or crack formation?

“…for bi‐crystals of high quality. Third, dislocations can be introduced into samples by mechanical deformation, for example, via bulk compression at room temperature 28‐32 or high temperature, 13,15,33 by near surface mechanical treatment using nanoindentation at a small scale, 34‐40 micro‐scratching/machining, 41 and so on. While the first two approaches mainly involve processing and fabrication, the third approach relies on the dislocation mechanics of the target ceramic materials under mechanical loading.…”

Dislocation–grain boundary interactions: recent advances on the underlying mechanisms studied via nanoindentation testing

“…Over the last decade, substantial advances in the nanoindentation (also known as instrumented or depth-sensing indentation) systems and new test protocols have opened new directions to study the small-scale mechanical properties [63][64][65]. For example, fast time constant (10's of µs) and high data acquisition rates (close to MHz) [66] allow to capture various events (e.g., slip transmission across the GB [67][68][69][70], phase transformation [71,72], cracking [73][74][75][76], etc.) during nanoindentation in the form of strain bursts in the load-displacement curve.…”