Using in-situ microLaue diffraction to understand plasticity in MgO

The present study investigates the micromechanical modes of deformation in MgO prior to cracking at room temperature. A combination of time resolved white beam Laue diffraction technique and in-situ nano-indentation of large single crystal micropillars provides a unique method to study the operating mechanisms of deformation in this otherwise brittle oxide ceramic. Upon indenting an [100]-oriented MgO micropillar, rotation and streaking of Laue spots were observed. From the streaking of the Laue spots, differential slip on orthogonal {110} slip planes was inferred to take place in adjacent areas under the indent - this was consistent with the results from the transmission electron microscopy studies. Upon cyclic loading of the pillar, subsequent stretching and relaxation of peaks was hypothesised to happen due to pronounced mechanical hysteresis commonly observed in MgO. Also, time-resolved spatial mapping of the deformation gradients of the area under the indent were obtained from which the strain and rotation components were identified

Using coupled micropillar compression and micro-Laue diffraction to investigate deformation mechanisms in a complex metallic alloy Al13Co4

In this investigation, we have used in-situ micro-Laue diffraction combined with micropillar compression of focused ion beam milled Al13Co4 complex metallic alloy to study the evolution of deformation in Al13Co4. Streaking of the Laue spots showed that the onset of plastic flow occured at stresses as low as 0.8 GPa, although macroscopic yield only becomes apparent at 2 GPa. The measured misorientations, obtained from peak splitting, enabled the geometrically necessary dislocation density to be estimated as 1.1 x 1013 m-2

Pt accelerated coarsening of A15 precipitates in Cr-Si alloys

The effect of alloying Cr-rich Cr-Si alloys with Pt was investigated by a combination of complementary experimental methods and atomic scale modelling. The investigated Cr-Si and Cr-Si-Pt (Cr ⩾86 at.%) alloys developed a two-phase microstructure consisting of Cr solid solution (Crss) matrix and strengthened by A15 precipitates during annealing at 1200\ub0C. It was found that additions of 2 at.% Pt increase the coarsening rate by almost five times considering annealing times up to 522 h. Pt was found to change the precipitate matrix orientation relationship, despite its low influence on the Crss matrix/A15 precipitate misfit. Through this experimental and modelling approach new insight has been gained into mechanisms of enhanced coarsening by Pt addition. The increased coarsening is principally attributed to a change in interface composition and structure resulting in different thermodynamic stabilities: Pt-containing A15 phase was found to have a broader compositional range if both elements, Pt and Si, are present compared to only Si. Additionally, the Crss phase was found to have a higher solubility of Pt and Si over just Si. Both factors additionally facilitated Ostwald ripening

Data on a new beta titanium alloy system reinforced with superlattice intermetallic precipitates.

The data presented in this article are related to the research article entitled "a new beta titanium alloy system reinforced with superlattice intermetallic precipitates" (Knowles et al., 2018) [1]. This includes data from the as-cast alloy obtained using scanning electron microscopy (SEM) and x-ray diffraction (XRD) as well as SEM data in the solution heat treated condition. Transmission electron microscopy (TEM) selected area diffraction patterns (SADPs) are included from the alloy in the solution heat treated condition, as well as the aged condition that contained < 100 nm B2 TiFe precipitates [1], the latter of which was found to exhibit double diffraction owing to the precipitate and matrix channels being of a similar width to the foil thickness (Williams and Carter, 2009) [2]. Further details are provided on the macroscopic compression testing of small scale cylinders. Of the micropillar deformation experiment performed in [1], SEM micrographs of focused ion beam (FIB) prepared 2 µm micropillars are presented alongside those obtained at the end of the in-situ SEM deformation as well as videos of the in-situ deformation. Further, a table is included that lists the Schmidt factors of all the possible slip systems given the crystal orientations and loading axis of the deformed micropillars in the solution heat treated and aged conditions

Ultra-fine Grain Materials by Severe Plastic Deformation: Application to Steels

Severe plastic deformation techniques are known to produce grain sizes up to submicron level. This leads to conventional Hall-Petch strengthening of the as-processed materials. In addition, the microstructures of severe plastic deformation processed materials are characterized by relatively lower dislocation density compared to the conventionally processed materials subjected to the same amount of strain. These two aspects taken together lead to many important attributes. Some examples are ultra-high yield and fracture strengths, superplastic formability at lower temperatures and higher strain rates, superior wear resistance, improved high cycle fatigue life. Since these processes are associated with large amount of strain, depending on the strain path, characteristic crystallographic textures develop. In the present paper, a detailed account of underlying mechanisms during SPD has been discussed and processing-microstructure-texture-property relationship has been presented with reference to a few varieties of steels that have been investigated till date

Microstructural characterization of ultrafine-grain interstitial-free steel by X-ray diffraction line profile analysis

This paper highlights the microstructural features of commercially available interstitial free (IF) steel specimens deformed by equal channel angular pressing (ECAP) up to four passes following the route A. The microstructure of the samples was studied by different techniques of X-ray diffraction peak profile analysis as a function of strain (epsilon). It was found that the crystallite size is reduced substantially already at epsilon=2.3 and it does not change significantly during further deformation. At the same time, the dislocation density increases gradually up to epsilon=4.6. The dislocation densities estimated from X-ray diffraction study are found to correlate very well with the experimentally obtained yield strength of the samples

Microstructural characteristics and strengthening mechanisms in a polycrystalline Ni-based superalloy under deep cold rolling

Surface modification is an essential process route to improve the fatigue performance of aerospace components. Microstructural evolution in Ni-based superalloy Udimet720Li processed by deep cold rolling (DCR) was investigated experimentally using X-Ray diffraction, electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM). Deep cold rolling produces hardened surface due to a range of microstructural changes associated with grain refinement, low angle grain boundaries (LAGBs) formation, and pile-up of dislocations around precipitates and across twin boundaries. The defect structures within the deformed subsurface comprised of equiaxed and elongated dislocation cells at grain boundaries, mutual interactions of slip bands, slip bands- precipitate at grain boundaries and multi-variant modes of twinning. The plastic deformation is predominantly driven through slip and dislocation multiplication mechanism during DCR. Surface compressive residual stresses, FWHM, micro-hardness, the fraction of LAGBs and the depth of plastically strained region increased with DCR hydrostatic pressure. These fundamental understanding on process-microstructure-property could provide a deep insight into the fatigue crack initiation mechanism of surface modified Ni-based superalloys.Accepted versio

Characterization of carbide particle-reinforced 316L stainless steel fabricated by selective laser melting

In this study, we have fabricated a TiC particle strengthened 316L stainless steel metal matrix composite using selective laser melting and characterized the microstructure with a particular focus on the TiC carbides in terms of their crystallography and orientation relationship with the austenitic matrix. Two families of TiC carbides are found to form in the SLM fabricated microstructure – firstly, the carbides that form along the high angle grain boundaries and secondly, those that form in the grain interior. The latter is primarily nano-crystalline TiC that are believed to precipitate out from the melt pool following a cube-on-cube orientation relationship with the f.c.c. austenitic matrix. Under this crystal registry, due to the differences in lattice parameters, a lattice mismatch between two phases occurs. The formation of TiC carbides and their morphology and distribution have been explained on the basis of melting of the powder bed under laser beam and strong melt pool dynamics during SLM process. Finally, the contribution of coherent nano-sized TiC precipitates on the overall strength of SLMed 316L-TiC metal matrix composite has been discussed wherein the TiC precipitates were found to contribute to ~50% of the strength increment in comparison to SLMed pure 316L