Unveiling the influence of dendrite characteristics on the slip/twinning activity and the strain hardening capacity of Mg-Sn-Li-Zn cast alloys

This work explores the correlation between the characteristics of the cast structure(dendrite growth pattern,dendrite morphology and macro-texture)and strain hardening capacity during high temperature deformation of Mg-5Sn-0.3Li-0 and 3Zn multi-component alloys.The three dimensional(3D)morphology of the dendrite structure demonstrates the transition of the growth directions from<1123>,<1120>and<1122>to<1123>and<1120>due to the addition of Zn.The simultaneous effects of growing tendency and the decrement of dendrite coarsening rate at the solidification interval lead to dendrite morphology transition from the globular-like to the hyper-branch structure.This morphology transition results in the variation of the solidification macro-texture,which has effectively influenced the dominant deformation mechanisms(slip/twin activity).The higher activity of the slip systems increases the tendency of the dendrite arms for bending along the deformation direction and fragmentation.Apart from this,the dendrite holding hyper-branch structure with an average thickness below 20μm are more favorable for fragmentation.The dendrite fragmentation leads to considerable softening fractions,and as an effective strain compensation mechanism increases the workability of dendritic structure.

A 3-D morphological approach on spatial form and cultural identity of ethnic mountain settlements:Case from Guizhou,China

Ethnic mountain settlements are living heritage of varied vernacular cultures.The preservation of both the built form and the intangible socio-cultural associations with them are global concern in process of urbanization,and in the notion of sustainable development.However,there is a lack of multi-dimensional and cross-cultural quantitative research in settlement morphology,making it difficult to guide practice effectively.Therefore,this study focuses on exploring an automatic or semi-automatic quantification and classification method for the morphological identity of ethnic mountain settlements.We introduce and combine 3-D morphological indicators with existing 2-D indicators to build and test three different sets of indication systems for semi-automatic classification for the settlements’ethnic attribute basing on spatial morphology.Taking the Miao,Dong,and Tunpu(Han)ethnic settlements in Guizhou province,southwest China as research samples,we applied factor analysis and hierarchical clustering methods to compare the classification accuracy under the three systems using data from topographic map,field investigation map,satellite imageries,and ethnography or local chronicle.The results showed that,the 3-D indication system has succeeded in semi-automatic quantification and classification of settlement morphology and ethnic identity by greatly increasing the classification accuracy to 96.30%,which is a huge improvement compared with the basic 2-D indication system(42.59%)and the advanced 2-D indication system(61.11%).The settlement samples are further divided into two sub-types with significant morphological differences in each major ethnic category under the 3-D indication system.We then discussed the potential improvement and future large-scale application of this method with the help of machine learning and other smart techniques.We hope to provide a comprehensive quantitative perspective and a more scientific reference for the future preservation and sustainable development of the massive and diverse vernacular heritages across the world.

The 3-dimensional morphology of dendrite during equiaxed solidification of an Al-5 wt.% Cu alloy

In a sample quenched during equiaxed solidification of an Al-5 wt.% Cu alloy, the multi-scales 3-dimensional morphology of equiaxed dendrite was observed. The slim primary stem and secondary branches constitute the frame of dendrite, and rows of dense tertiary branches further divide the 3-dimensional space. In the divided space, the quartic branches grow further. The dendritic branches,which are perpendicular to each other, can change their growth directions and coalesce into a whole. In the tertiary branches and quartic branches, the formation of double branch structures is induced by competitive growth. The branch that wins in the competitive growth will produce a cabbage-like structure by wrapping the failed branches. In addition, the side branch can also wrap the original parent branch to produce cabbage-like structures. Depending on the historical growth direction, the dendritic arms can form vein-like and spicate structures, and the shapes of single dendritic arm may be the cylinder, plate and trapezoid platform. According to the compositions and etching morphology, the single dendritic arm in the final solidification structures should coalesce from a fine porous structure. The porous structures at different length-scales are principally induced by the preferential growth. Based on 3-dimensional morphology of equiaxed dendrite, a new research object for the investigation of microsegregation was suggested.

3-D Seismic Identification and Characterization of Ancient Channel Morphology

It is easy to identify ancient fluvial morphologic types by the outcrop,log and core data.However,the horizontal distribution and geometry of the channels can only be identified and predicted by relying on the 3-D seismic data.The 3-D seismic horizon slices,especially,can play an important role in the sandstone prediction of meandering rivers,distributary channels and low-sinuosity channels.Every microfacies unit,including main channels,such as sinuous or branching channels,levee,crevasse channels,ligule crevasse splay and floodplain etc.can be identified.Braided channel sandstones are planar tabular lateral-connected sandbodies and the distribution of thick main channel belts can only be identified from 3-D seismic data.As the braided sandstones are ubiquitous,their occurrence and distribution do not need to be predicted.Generally,the coal velocity is so low that it can create a strong amplitude reflection in coal strata.It consequently conceals the amplitude respondence to anastomosing channel sandstone which could be identified from 3-D seismic inversion data sometimes.Case studies of mud-rich low-sinuosity rivers identified with 3-D seismic data indicate that the scales and width-to-thickness ratio of such sandbodies are small,laterally unconnected,and generally occurred on distant or further parts of an alluvial fan under dry climate conditions.Sometimes extraction of seismic attributes of every reflection event along horizons is expected to maximize expression of the spatial evolutions of ancient channels.

Intergrowth mechanism and morphology prediction of faceted Al_(3)Ni formed during solidification by a spatial geometric model

The interplay and intergrowth characteristic of faceted intermetallic compounds(IMCs)during solidification was originally investigated through the rod-like Al3 Ni crystals in the liquid Al/solid Ni interconnection by using synchrotron radiography,and the diversified 3-D morphologies were reconstructed by synchrotron tomography.A spatial geometric model was established to effectively predict the diversified growth patterns of two spatial crystals.For the two overlapping Al3 Ni crystals,the impeded crystal growth was divided into three different stages,decided by the hindrance form the other crystal.Further,the groove formed on the crystal surface is directly related to the solute redistribution under the critical condition of boundary layer thickness larger than two crystals distance.The closer distance and smaller crystal size indicate the deeper and larger groove,and the morphology changes from hemispheroid to hemi-ellipsoid with the increased opposite and interacted faces.

三维枝晶生长数值模拟及实验验证(英文)

建立了用于模拟立方晶系合金三维枝晶生长的改进元胞自动机模型。该模型将枝晶尖端生长速率、界面曲率和界面能各向异性的二维方程扩展到三维直角坐标系,从而能够描述三维枝晶生长形貌演化。应用本模型模拟在确定温度梯度和抽拉速度条件下三维柱状晶生长过程的一次臂间距调整机制和不同择优取向柱状晶之间的竞争生长。使用NH4Cl?H2O透明合金进行凝固实验,模拟结果和实验结果吻合较好。