Misfit Distribution Research Articles

Directional coarsening behavior of primary γ′ phase in Ni3Al-based superalloy during aging heat treatment

Polycrystalline Ni3Al-based superalloy with up to 70% γ′ phase owns excellent strength at around 1100 °C. It has been successfully used as a substitute for turbine blade crown, which is one of the aircraft components working in the severest environment (i.e., sometimes nearly overheating). However, few studies concentrate on the coarsening resistance and phase thermal stability in this newly designed polycrystalline superalloy at the working temperature, hence, directional coarsening behavior of primary γ′(γI′) has remained restricted. This paper investigated directional coarsening behavior of γI′ during aging treatment (1100 °C) after overheating at 1270 °C with furnace cooling (SFA), air cooling (SAA) and water cooling (SWA) respectively. It clearly showed that γI′ grew into lamellar and gradually became irregular during the directional coarsening process. Moreover, its morphological combination mode was illustrated. Since parallel short lamellar γI′ connected each other, long lamellar formed. When perpendicular long lamellar γI′ connected each other, it became L-type or T-type, i.e., precursor of irregular γI′. The kinetics of directional coarsening regime of γI′ was in line with the matrix-diffusion-controlled (MDC) theory according to the evaluation of γI′ size. This was caused by higher migration of γI′ interfaces than the diffusion of solute elements. It was also confirmed that driving force of directional coarsening mainly depended on the competition of elemental diffusion, lattice misfit distribution and γ channel distance.

The Climatic Temporal Feature Space: Continuous and Discrete

Climatic zones, representing seasonal variations in temperature (T) and precipitation (P), are generally mapped geographically using discrete classifications with distinct boundaries. However, it is well known that global T and P vary continuously in space and time with steep gradients occurring infrequently. The objective of this analysis is to use complementary forms of dimensionality reduction to quantify the spatiotemporal dimensionality of the climate system and to produce a continuous representation of global climate based on the temporal feature space of historical T and P alone. We characterize the continuous global feature space using principal components (PCs) to identify a parsimonious set of temporal endmember T and P patterns bounding the feature space of all observed T and P patterns. These endmember T and P patterns provide the basis for a linear temporal mixture model that can represent decadal T and P patterns of any geographic location as fractions of the endmember T and P patterns. Inverting this linear mixture model for each geographic T+P time series gives an estimate of the fractional contribution of each endmember to the observed time series. The resulting temporal endmember fraction maps provide a continuous representation of the Euclidean proximity of T and P observations at every geographic location to each of the temporal endmember climates bounding the space. The spatiotemporal dimensionality implied by the variance partition of T + P time series for 67,420 land-based observations suggests that the T + P temporal feature space is effectively 3D, accounting for 92% of total variance. From the topology of the feature space, we identify 4 bounding temporal endmembers upon which to base the linear temporal mixture model. Inversion of the model for each normalized observed time series yields endmember fraction estimates and a model misfit distribution with 99% of misfit < 0.21. For comparison, we also render temporal feature spaces from ensembles of 2D manifolds within the T + P space derived from suites of t-distributed Stochastic Neighbor Embeddings (t-SNE) to identify discontinuities in the feature space. Comparison of spatial PC(t-SNE) across hyperparameter settings reveals consistent structure and little hyperparameter sensitivity to temporal feature spaces rendered by t-SNE. Combining the physically interpretable continuous global structure resolved by the PC feature space with the finer scale manifold structure resolved by the t-SNE feature space provides a continuous alternative to discrete classifications of climate that cannot represent the continuous character of its temporal feature space.

Microstructure Evolution of Primary γ′ Phase in Ni3Al-Based Superalloy

In this work, water cooling, air cooling (AC) and furnace cooling (FC) were applied to investigate the effect of cooling rate on microstructure evolution of primary γ′ in a newly designed Ni3Al-based alloy. The results showed that nucleation rate of primary γ′ increased with increasing cooling rate. In addition, higher cooling rate shortened growth period of primary γ′, which made its morphology close to the initial precipitated γ′. For AC and FC specimens, due to the lower cooling rate, primary γ′ possessed longer growth period and its morphology was mainly due to the evolution of lattice misfit between γ and primary γ′. Meanwhile, growth of primary γ′ depended on lattice misfit distribution between its corner and edge area. Moreover, primary γ′ morphologies of sphere, cube and concave cube with tip corners were illustrated by considering interaction between elemental diffusion and elastic strain energy.

Manufacturing of Metal Frameworks for Full-Arch Dental Restoration on Implants: A Comparison between Milling and a Novel Hybrid Technology.

To determine the trueness and precision of frameworks manufactured with a selective laser melting/milling hybrid technique (SLM/m) and conventional milling by comparing the implant-platform/framework interface with those of the original computer-aided design (CAD). Using a virtual 6-implant-supported full-arch framework CAD drawing, 27 titanium replicas were manufactured by 3 independent manufacturing centers (n = 9/center) using a hybrid SLM/m technology (labs 1 and 2) or the conventional milling technique (lab 3). Using an opto-mechanical coordinate measuring machine, the frameworks' misfit distribution and patterns were analyzed, and the position error between paired platform positions within each framework was evaluated to calculate the misfit tendency for each group. A multilevel analysis using a mixed-effects model was conducted (α = 0.05). The trueness was evaluated as the dimensional difference from the original, while the precision as the dimensional difference from a repeated scan. The 3 dimensional misfits differed significantly among the 3 groups, with the milled group exhibiting the least accurate outcome (p = 0.005). The mean 3D positioning errors ranged from 8 to 16 µm and from 9 to 22 µm for the SLM/m technique (labs 1 and 2, respectively), and from 20 to 35 µm for conventional milling (lab 3). Regarding the misfit distribution pattern, the misfit increased with the distance between paired platform positions in all groups. All groups had 3D misfits well within the error limits reported in the literature. The 3D misfits of new hybrid (SLM/milling) and conventional (milling) procedures differed significantly among them, with the milling technique the less accurate and precise. The largest errors in all groups were found between the most distant implants, resulting in a correlation between the framework span and the inaccuracies.

Elastic fields of 2D and 3D misfit particles in an infinite medium

In micromechanics, accurate quantification of the elastic field (stress, strain, and displacement) caused by the presence of an inclusion in an infinite body is desired for both the particle and matrix materials. Ideally, the solution should be applicable to any particle geometry or shape and for any distribution of misfit along the interface (i.e. misfit profile). This work presents a dislocation-based numerical method, that is an extension to earlier work in this journal [Lerma, J.D., Khraishi, T., Shen, Y.L., Wirth, B.D., 2003. The elastic fields of misfit cylindrical particles: a dislocation-based numerical approach. Mech. Res. Commun. 30, 325–334], for determining the elastic fields of volume misfit particles with arbitrary misfit distribution or particle shape.

Consistency regions in non-linear inversion

SUMMARY A disadvantage of fully non-linear methods of inversion, through exploitation of the properties of model space, is the absence of a well-developed framework for error assessment. To rectify this problem an auxiliary weighting function for ensemble properties is introduced that can be used with suitable thresholds to define consistency regions of suitable models. This approach requires neither a detailed knowledge of the misfit distribution nor an underlying probabilistic model. The use of a polyhedral representation of such consistency regions is illustrated with an example from non-linear seismic event location, showing the effect of different choices for the misfit measure. The auxiliary weight function can be used directly with the composite misfit measure used to drive the exploration of model space in the non-linear inversion. Such composite measures usually combine a data misfit and regularization term. However, considerable benefit can be obtained by storing the data misfit and associated model characteristics for each investigated model, as well as the composite measure. The properties of the model ensemble can then be used retrospectively to define preferred models by the intersection of a consistency region in data misfit with zones constrained by desirable model properties.