Ali Khosravani

High throughput exploration of process-property linkages in Al-6061 using instrumented spherical microindentation and microstructurally graded samples

Recent spherical nanoindentation protocols have proven robust at capturing the local elastic-plastic response of polycrystalline metal samples at length scales much smaller than the grain size. In this work, we extend these protocols to length scales that include multiple grains to recover microindentation stress-strain curves. These new protocols are first established in this paper and then demonstrated for Al-6061 by comparing the measured indentation stress-strain curves with the corresponding measurements from uniaxial tension tests. More specifically, the scaling factors between the uniaxial yield strength and the indentation yield strength was determined to be about 1.9, which is significantly lower than the value of 2.8 used commonly in literature. The reasons for this difference are discussed. Second, the benefits of these new protocols in facilitating high throughput exploration of process-property relationships are demonstrated through a simple case study.

The effect of length scale on the determination of geometrically necessary dislocations via EBSD continuum dislocation microscopy

Electron backscatter diffraction (EBSD) dislocation microscopy is an important, emerging field in metals characterization. Currently, calculation of geometrically necessary dislocation (GND) density is problematic because it has been shown to depend on the step size of the EBSD scan used to investigate the sample. This paper models the change in calculated GND density as a function of step size statistically. The model provides selection criteria for EBSD step size as well as an estimate of the total dislocation content. Evaluation of a heterogeneously deformed tantalum specimen is used to asses the method.

Tensile and Microindentation Stress-Strain Curves of Al-6061

Recent spherical microindentation stress-strain protocols were developed and validated on Al-6061 (DOI: 10.1186/s40192-016-0054-3). The scaling factor between the uniaxial yield strength and the indentation yield strength was determined to be about 1.9. The microindentation stress-strain protocols were then applied to a microstructurally graded sample in an effort to extract high throughput process-property relationships. The tensile and microindentation force-displacement and stress-strain data are presented in this data set.

Dislocation Activity in AZ31B Magnesium Deformed at Moderately Elevated Temperatures via EBSD

Activation of type slip in wrought magnesium has typically been associated with forming temperatures of 200°C or higher, while contraction twinning has been observed to be more prevalent at lower temperatures. A recent investigation showed that when AZ31B sheets with strong basal texture were formed in biaxial or plane strain tension at room temperature, contraction twins were observed in banded structures. These banded structures disappeared at moderate forming temperatures of 75°C and 125°C. The hypothesis is that type slip was sufficiently activated at the moderate forming temperatures that thinning of the sheet was accommodated less by twinning and more by slip. This paper uses mesoscale electron backscatter diffraction continuum dislocation microscopy in an SEM to determine type geometrically necessary dislocation density. Preliminary results suggest that the relative amount of geometrically necessary dislocations is unrelated to the onset of twinning.