Modelling the nucleation, growth and coarsening kinetics of γ″ (D022) precipitates in the Ni-base Alloy 625

Abstract

We report the use of diatom frustules as scaffolds for the growth of molybdenum disulfide nanosheets. The frustules were impregnated with a single source molecular precursor complex which is converted to MoS 2 by solventless thermolysis. Randomly oriented few-layer thick MoS 2 nanosheets are found to coat both the exterior surface and internal pores of the scaffold.Nature displays exquisite control of phase and morphology during biomineralisation and the resulting mineralised structures have been found to possess attractive functional properties, particularly in the area of photonics. [1][2][3][4] Consequently there is considerable scientific interest in replicating the intricate architectures found in nature, 5-9 as well as enhancing the intrinsic properties of biomineralised structures' by decoration with inorganic nanostructures. [10][11][12][13] Diatoms are marine-dwelling eukaryotic unicellular algae, 14 which produce biomineralised silica exoskeletons known as frustules. Diatom frustules comprise the majority of the biosilica found in oceans, 14 and bulk quantities of the fossilised shells are recovered by dredging. This material is known as diatomaceous-earth (DE). It is widely available and inexpensive and finds use in a number of products including toothpaste and as a laboratory filter aid (under the trade name Celite™). Additionally, the intricate hierarchical nanostructures found in diatom frustules have attracted considerable interest for nanotechnology applications. 15,16 Diatom frustules have the highest strength-to-weight ratio of all reported natural biomaterials, 17 their periodic nanoscale pores result in both high surface areas and unique photonic properties which enhance light uptake. 15, 18 In the living diatom this aids photosynthesis but the functional structures persist in the deceased organisms' biomineral shell. 15, 18, 19 Biosilica is an inert insulator which provides an ideal scaffold or template for functional materials. 13, 15,[20][21][22] By introducing semiconducting materials into the biomineralised architecture it is potentially possible to exploit the frustules' photonic properties for light harvesting or its large surface area for sensing and catalytic applications. 15, 19, 20 For example, diatom frustules coated with TiO 2 have been incorporated into dye sensitised solar cells, where the devices' enhanced performance was attributed to improved light scattering by the diatoms. 15 A surface sol-gel process has been used to coat diatom frustules with a ~50 nm thick layer of SnO 2 ; the resulting structures were used as NO gas detectors. 20 Bao et al. have reported the conversion of the insulating silica of diatom frustules to semiconducting silicon by magnesiothermic reduction, 23 after which the photocatalytic properties of the resulting structures was enhanced by subsequent deposition of CdS on the frustule's surface. 19 However, to-date, there have been no reports of the functionalization of biomineralised structure with twodimensional (2D) semiconductor materials.Mol...

Temperature-Dependent Misfit Stress in Gamma Double Prime Strengthened Ni-Base Superalloys

“…This relationship has been reported previously in literature. [19][20][21] The volume-averaged major and minor axes were determined to be 55.8 nm and 12.1 nm, respectively, and hence the overall volume-averaged aspect ratio was determined to be 0.22, which is consistent with the reported values. [20,21] C. Peak Deconvolution…”

Phase-field modeling of γ/γ″ microstructure formation in Ni-based superalloys with high γ″ volume fraction

“…This data is valid at 0 K, therefore, an estimate about temperature dependence has to be made. Due to the lack of experimental data, we propose to assume the same temperature dependence for all elastic constants considered, as it was already done by Moore et al [52]. In this work, we assume a linear temperature dependence of the elastic constants…”

Evaluation of classical precipitation descriptions for $$\gamma ^{\prime \prime } \,(\hbox {Ni}_{3}\hbox {Nb}{-}\hbox {D0}_{22})$$ γ ″ ( Ni 3 Nb - D0 22 ) in Ni-base superalloys

“…As the shape behaviour of c 00 precipitates is ultimately a consequence of precipitate-matrix strain anisotropy, which changes gradually with temperature [14,23] different isothermal ageings can exhibit different c 00 evolution behaviours. Furthermore, the mathematical descriptions developed by Cozar et al [5] and Ji et al [12] assume constant values for parameters such as the misfit strain for coherent precipitates in contrast to the measurements of Slama et al [23] in Table 2, which means that the step change can be more appropriately interpreted as the region where these assumptions completely break down.…”

“…6), is utilised. Specifically, following the hyperbolic relationship demonstrated for this parameter in Alloy 625 by the present authors elsewhere [14], the behaviour of aðL M Þ is defined according to a hyperbolic decay curve fitted to values of aðL M Þ measured by Devaux et al and others. The use of separate fits for each dataset is precluded because the small number of data points and/or their relative narrow range with respect to L M ðtÞ, despite the possible influences from temperature and composition differences.…”