Papers by Keyword: Cast Structure

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Authors: Mitra Basirat, Hasse Fredriksson
Abstract: Dendritic segregation in deformed samples remains in the form of band structure, which is a high-strained region. The present work investigates the effect of the uphill diffusion process, occurring during deformation, on the dissolution of carbide particles in the band structure. A series of hot compression tests are performed on the cast structure of bearing steel by using a hydraulic testing machine, MTS 810. Cylindrical specimens are deformed in a temperature range of 800°C to 900°C and at strain rates of 5s-1 and 0.5s-1. In order to eliminate the recovery process, samples are immediately quenched after the compression. The microsegregation of Cr, Mo, Mn and Si are investigated in the band structure, which shows a tendency of uphill diffusion during deformation process. The results show that the volume fraction of carbides varies with the increased straining. The results also show that deformation causes the fragmentation, dispersion of pearlite in the dendrites and the dissolution of spheroidized carbides in the band structure.
Authors: A.G. Svyazhin, Liudmila M. Kaputkina
Abstract: Cast structure of ferric, austenitic and dual-phase high-nitrogen alloys and steels saturated with nitrogen at pressures of up to 3.2 MPa and solidified at cooling rates of 2 to 4•104 K/s has been investigated. Increasing the nitrogen concentration in the alloy and decreasing the cooling rate results in smaller nitrogen content in α and γ solutions and in larger content of crystallization nitrides.
Authors: Peter Müllner, Xue Xi Zhang, Yuttanant Boonyongmaneerat, Cassie Witherspoon, Markus Chmielus, David C. Dunand
Abstract: Grain boundaries hinder twin boundary motion in magnetic shape-memory alloys and suppress magnetic-field-induced deformation in randomly textured polycrystalline material. The quest for high-quality single crystals and the associated costs are a major barrier for the commercialization of magnetic shape-memory alloys. Adding porosity to polycrystalline magnetic-shape memory alloys presents solutions for (i) the elimination of grain boundaries via the separation of neighboring grains by pores, and (ii) the reduction of production cost via replacing the directional solidification crystal growth process by conventional casting. Ni-Mn-Ga foams were produced with varying pore architecture and pore fractions. Thermo-magnetic training procedures were applied to improve magnetic-field-induced strain. The cyclic strain was measured in-situ while the sample was heated and cooled through the martensitic transformation. The magnetic field-induced strain amounts to several percent in the martensite phase, decreases continuously during the transformation upon heating, and vanishes in the austenite phase. Upon cooling, cyclic strain appears below the martensite start temperature and reaches a value larger than the initial strain in the martensite phase, thereby confirming a training effect. For Ni-Mn-Ga single crystals, external constraints imposed by gripping the crystal limit lifetime and/or magnetic-field-induced deformation. These constraints are relaxed for foams.
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