The NiTi alloys are generally considered hard-to-deform materials when processing by equalchannel angular pressing (ECAP) at room temperature. Nevertheless, it is shown by experiment that a NiTi alloy may be successfully processed by ECAP for up to two passes using a core-sheath configuration. Three-dimensional finite element simulations were used to more fully evaluate the flow behavior after the first and second pass of ECAP. The values of the microhardness were recorded across transverse directions within the cores and the results show that the imposed strain both decreases by comparison with the processing of conventional sheath-free NiTi billet and increases by increasing the dimensions of the core. The lower areas of the cores undergo less deformation than the upper areas after successful ECAP processing but the imposed strain, and thus the microhardness values, become homogeneously distributed on the longitudinal planes after two passes of ECAP.
Severe plastic deformation (SPD) methods are developed to produce highly strained materials while 7 experiencing no dimensional changes. Several parameters have to be considered to develop a SPD 8 process such as industrial applicability. In this study, the repetitive corrugation and straightening by 9 rolling (RCSR) method, is used. Process parameters, sample thickness, and rollers design and gap, are 10 optimized according to deformation mode simulated by Abaqus software. The results are verified using 11 DIC (digital image correlation) experiments, which are in good agreement with the simulations. 12 Analytical modeling is also used to estimate accumulated strain after one cycle and the results show a 13 similar trend. Microhardness tests show that deformation homogeneity and hardness are increased 14 after each step of RCSR. 15
A new design of billet, based on a core–sheath configuration, was used for the processing of Ni, Fe, and a NiTi alloy by equal‐channel angular pressing (ECAP) at room temperature. This configuration involves inserting metal cores within Fe sheaths prior to processing and it is designed especially for use with hard‐to‐deform materials. Billets were processed through one or two ECAP passes at room temperature and the microhardness values were recorded across the transverse directions within the cores to evaluate the flow process. As in conventional ECAP, the hardness increased significantly after the first pass and there were regions of lower hardness along the bottom surfaces of each core. The gradient of hardness decreased with increasing core diameter but the average microhardness values remained unchanged. Three‐dimensional finite element simulations were used to evaluate the flow behavior after one pass of ECAP using different core metals. These simulations show the lower areas of the cores undergo less deformation than the upper areas and the homogeneity increases with increasing levels of friction at the core–sheath interface.
A novel severe plastic deformation (SPD) technique entitled Multi-Axial Incremental Forging and Shearing (MAIFS) has been introduced and the preliminary evaluation of this technique by characterizing the material flow has been described in this paper. The MAIFS process is the combination of incremental forging (or incremental back extrusion) followed by angular pressing. The streamline visualized data of a tin-based alloy as the representative of the soft deformable metals was utilized to predict the strain distribution experienced by material during deformation induced by MAIFS process. It was demonstrated that acceptable deformation homogeneity can be achieved after pass two of the process, and the workpieces were deformed up to four passes of MAIFS without any crack or discontinuity. The first results of numerical simulations of proposed process after four consecutive passes proved its general feasibility, and comparison of acquired data with the simulation results of same specimen processed by four passes ECAP through route B c confirmed the capability of MAIFS process. An attempt has also been made to primarily investigate the potential of the process for grain refinement.
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