Papers by Keyword: Dislocation

Abstract: The effect of grain size on the initiation behavior of exfoliation corrosion in cold-rolled Mg-14mass%Li-3mass%Al alloy was examined. Exfoliation corrosion initiated after 30 minutes in the coarse-grained structure (279μm), whereas it was delayed to 60 minutes in the fine-grained structure (75μm) and further to 75 minutes in the ultrafine-grained structure (39μm). This delay is attributed to the suppression of shear band formation and localization during cold rolling with decreasing grain size, which enhances the uniformity of surface reactions in the corrosive environment and promotes faster and denser formation of the protective film at the early stage. Accordingly, the improved condition of the initial corrosion film is considered the primary factor responsible for the delayed onset of exfoliation corrosion.

Abstract: We introduce a polarization superimposed phase contrast microscope (PS-PCM) for wide-gap semiconductor wafers as a new analytical technique that enables non-destructive and three-dimensional characterization of threading dislocations; TSDs and TEDs in SiC epilayers and substrates, such as discrimination each other or detection of their inclination in the depth direction.

Abstract: In this study, we investigated how bar-shaped 1SSF (Single Shockley-type stacking fault) in a chip of a SiC (Silicon Carbide) epitaxial wafer expanded with UV (ultraviolet) irradiation and observed it with PL (Photoluminescence) imaging and demonstrated early detection of bar-shaped 1SSF with an algorithm for automatic detection for the initial shape of bar-shaped 1SSF. Furthermore, we estimated that it was 83% how much UV irradiation time could be reduced.

Abstract: This work studies the variation of the defects density of in situ doped 3C-SiC layers during heteroepitaxial Chemical Vapour Deposition (CVD). A review on the evolution of defects density as a function of 3C-SiC grown thickness, for different N doping concentrations is offered. The doping range spanned in the experiment suits the realization of power devices.The outcome of this work provides an explanatory picture of the significant drop in stacking faults density by roughly an order of magnitude through the N doping at concentrations of the order of ~2.9×10¹⁹ cm^-3 during the growth. Conversely, N doping shows to favor the development of dislocation-like defects within the crystalline matrix. However, in few um, the crystal is able to display an effective dislocation closure mechanism, which rapidly recovers crystal quality.

Abstract: In this work the relationship between changes in wafer center bow after thinning process and the wafer morphology has been shown. KOH wet etching allowed the observation and counting of dislocation in 4H-SiC substrate. In deep a correspondence between changes in wafer center bow and the dislocation density of the SiC substrate has been observed. By using a counting software, a relationship with the basal plane dislocation and center bow has also been observed.

Abstract: The influence of electrolysis parameters on the structure and properties of iron coatings is shown. The dependencies of hardness of iron coatings upon the parameters of metal microstructure characterized by dilatation are established. It is shown that dilatation can be used as a checkup parameter for iron strength properties. The influence of some factors on the properties of iron deposits obtained under non-stationary deposition regimes is analyzed.

Abstract: Geometric aspects of the shear processes in hexagonal metals are analysed. They can be divided into three groups: those localized essentially between neighbouring atomic planes, occurring in narrow slabs along particular atomic planes, or covering a large crystal volume. Obviously, dislocation glide and deformation twinning are principal types of such processes. On the geometrical level, the dislocation slip as well as twin propagation are controlled by Schmid factors. Since the sample loaded by external stress can sometimes give way to fracture (cleavage) under tensile stress, it has to be also mentioned. The main aim of this work is to show only on geometrical grounds for which sample orientation which process is more likely to occur. More complex shear processes that take place during double twinning are also briefly considered. In polycrystals, the shear phenomena lead to texture formation when the processes that control the behaviour of materials may be those that act in a similar way in single crystals.

Abstract: Tensile tests of Mg-Y single crystals with different yttrium concentrations: 0.07 and 0.3 at.% were carried out to investigate effects of yttrium on pyramidal <c+a> slip system. In Mg-0.07at%Y alloy single crystals, {11 2}< 23> second order pyramidal <c+a> slip was activated and yield stress increased, compared to pure Mg single crystals. On other hand, in Mg-0.3at%Y alloy single crystals, {10 1}< 23> first order pyramidal <c+a> slip was activated and yield stress increased, compared to Mg-0.07at%Y alloy single crystals. The change in slip system by yttrium addition would be caused by increasing critical resolved shear stress (CRSS) for second order pyramidal slip.

Abstract: 17-7PH stainless steel is high age-hardening property due to precipitate NiAl intermetallics by aging heat treatment after the deformation induced martensitic transformation by cold working. In this study, the effect of aging conditions on stress relaxation behavior of 17-7PH stainless steel was investigated, and the mechanism of the stress relaxation was discussed. The 0.2% proof stress after aging at 753K for 180s-18ks is about 450MPa, and then decreases after 18ks. On the other hand, the stress relaxation ratio decreases by long time aging at 753K. The dislocation density of 17-7PH decreases by long time aging at 753K. The formation of NiAl clusters around 5nm by 3D-AP analysis is observed in 17-7PH aged at 753K for 1.8ks. It is suggested that the reduction of the stress relaxation ratio after long time aging at 753K is caused by NiAl clusters and decreasing mobile dislocation density.

Abstract: Microstructure and dislocations were observed for Ti-600 alloy crept at the temperature of 600°C with the stress of 200MPa and 300 MPa. The results indicate that more precipitation phases could be found both in β phases and at phase boundaries for the alloy after creep tests, and the width of the phase boundary become broader obviously. Also more dislocations could be seen at or around the precipitation phases for the alloy crept at 600°Cwith the stress of 200MPa. Dislocation density is rather big in some regions, dislocations aggregate in precipitation phases, phase boundaries and sub-grain boundaries. Some tangled dislocations or regular arranged dislocations could also be found around precipitation phases. Condensed three-dimensional dislocation meshes could be found in the alloy crept for the alloy crept at 600°Cwith two stresses. For the alloy crept at 600°Cwith the stress of 200MPa, faults originated from boundaries of α lamellar could be found in α lamellar. Some of these faults extend to boundaries of α lamellar, and some stop or end off in α lamellar. While for the alloy crept at 600°Cwith the stress of 300MPa, dislocation tend to arrange in dislocation walls, form bamboo-like structure along the direction of α lamellar, which would expand and penetrate the whole grain of elongated dislocation walls, and at last stop at grain boundaries.