Papers by Keyword: Fine Grained Microstructure

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Authors: Kinga Rodak, Jacek Pawlicki, Krzysztof Radwański, Rafal M. Molak
Abstract: In this study, commercial Cu was subjected to plastic deformation by compression with oscillatory torsion. Different deformation parameters were adopted to study their effects on the microstructure and mechanical properties of Cu. The deformed microstructure was characterized by using scanning electron microscopy (SEM) equipment with electron backscattered diffraction (EBSD) facility and scanning transmission electron microscopy (STEM). The mechanical properties were determined on an MTS QTest/10 machine equipped with digital image correlation. Can be found, that process performed at high compression rate and high torsion frequency is recommended for the refining grain size. The size of structure elements: average grain size (D) and subgrain size (d) reached 0.42 m and 0.30 m respectively, and the fraction of high angle boundaries was 35%, when the sample was deformed at a torsion frequency f= 1.6 Hz and compression rate v=0.04 mm/s. Deformation at these parameters leads to an improvement in strength properties. The strength properties are about two times greater than the initial state.
Authors: Tao Ma, Zhong Min Zhao, Long Zhang, Xue Gang Huang, Liang Xiang Liu
Abstract: Large-bulk TiB2-TiC composite ceramics were prepared by combustion synthesis under high gravity. XRD, SEM and EDS results showed TiB2-TiC composites were mainly composed of the fine-grained microstructures of TiC matrix in which a large number of the fine TiB2 platelet grains were dispersed uniformly, whereas there discontinuously dispersed the ε-carbides with the enrichment of Ti atoms, and a few of isolated, irregular α-Al2O3 grains and Al2O3-ZrO2 colonies were also observed at the boundaries of the eutectic microstructures. The results of properties indicate that with increasing mass fraction of B4C+Ti+C in combustion systems, the relative density and fracture toughness of TiB2-TiC composites are all among 97%~99% and 6.5~7.1 MPa·m1/2, respectively, and the Vickers hardness and flexural strength are increased gradually to the maximum values of 28.6GPa and 615MPa, respectively. The achievement of full-density TiB2-TiC composites benefited from the design of full-liquid SHS products and the introduction of high-gravity field, and high hardness of the composite ceramics resulted from the absence of intermediate borides and the achievement of stoichiometric TiC phases due to rapid solidification, whereas high flexural strength of the composite ceramics benefited from the homogenization and refinement of the microstructures due to the rapid separation of the liquid oxides and the rapid coupled growth of TiB2-TiC.
Authors: Andrey Belyakov, Yuuji Kimura, Kaneaki Tsuzaki
Abstract: The annealing behaviour of an Fe – 22%Cr – 3%Ni ferritic stainless steel processed by bar rolling/swaging to total strain of 4.4 at an ambient temperature was studied in the temperature range of 400 ~ 700oC. The annealing behaviour was characterised by the development of continuous recrystallization involving recovery processes followed by a normal grain growth. The large strain deformation caused the very fast recovery resulting in the development of almost equiaxed polygonized microstructure in place of the highly elongated deformation (sub)grains. The polygonization development was accompanied by some increase in the transverse (sub)grain size and the formation of many low-angle subboundaries. The latter ones could be composed from the dislocations, which were emitted by the strain-induced deformation (sub)boundaries. In spite of relatively large fraction of low-angle subboundaries, such polygonized microstructure was essentially stable against a discontinuous grain coarsening. Upon further annealing, therefore, the microstructure evolution was considered as a normal grain growth.
Authors: Xue Gang Huang, Long Zhang, Zhong Min Zhao, Chun Yin
Abstract: By using combustion synthesis under high gravity, TiC-TiB2 fine-grained composite ceramics with hypoeutectic, eutectic and hypereutectic microstructures were prepared through rapid solidification. XRD, FESEM and EDS results show that with increasing TiB2 content, TiC-TiB2 composite ceramics transform the microstructures consisting of fine TiB2 platelets from ones composed of fine TiC spherical grains, whereas when TiB2 content reaches 50mol%, the ceramics develop the eutectic microstructures that small aspect-ratio TiB2 platelets were embedded in TiC matrix. Mechanical properties show that relative density, Vickers hardness and flexural strength of TiC-50mol%TiB2 all reach the maximum values (respectively as 98.6 % ,18.4 GPa, 840 MPa) due to eutectic reaction during solidification, meanwhile TiC-50mol%TiB2 has the maximum fracture toughness of 11.5 MPa∙m0.5 due to the cooperative action of crack deflection, crack-bridging and pull-out toughening by fine TiB2 platelets.
Authors: Kinga Rodak, Tomasz Goryczka
Abstract: Polycrystalline Cu has been deformed at room temperature by oscillatory compression method to true reduction εh = 0.6 and 1. Microstructure by using transmission electron microscopy (TEM) and texture evolution after deformations was investigated. Oscillatory compressed microareas contains two distinctive regions: fine grains inside banded microstructure with large misorientation and surrounding matrix with submicrometer subgrains with a fraction of both low and high angle boundaries. Moreover nucleation of new grains under recrystallization takes place at the local-regions. The study of the crystal orientation distribution during applied deformation showed that the pole figure registered for the sample after compression shows ring of pole density, which concentrates around projection of <011>. Oscillatory compression causes formation of two axial texture components: <001> and <011>.
Authors: Jean Jacques Blandin
Abstract: Superplastic forming (SPF) of magnesium alloys has received increasing attention in the recent past. The aim of this presentation is to review recent works dealing with SPF of Mg alloys with a three-fold objective: i. How to produce fine or ultra fine grained (UFG) microstructures? ii. Are there specifities in superplastic deformation mechanisms? iii. How SPF Mg alloys resist to cavitation? Deformation mechanisms as well as damage variations in the superplastic regime will be preferentially discussed in relation with grain size, content in intermetallic particles and diffusion kinetics. For the sake of illustration, some results concerning the superplastic behaviour of UFG magnesium alloys produced by severe plastic deformation will be presented since such microstructures exhibit particularly attractive superplastic properties at quite low temperatures.
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