Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《材料研究学报》
Abstract： FEM calculation for the preparation process of SiC fiber and SiC/Ti-6Al-4V composite was carried out to investigate the effect of different processing parameters on the residual stress of the SiC fiber as well as the densification behavior and residual stress of the composite. The results show that, for the fabrication process of fibers, the axial thermal stress of the WC layer decreases with the decrease of deposition temperature and thickness of C layer. For the densification of composites, HIP temperature and sheath thickness have greater impact on the density, but HIP time and fiber volume fraction have smaller impact; with the increasing HIP temperature and decreasing sheath thickness, the density of the composite could be enhanced; the radial residual stress on the matrix greatly increases with the increase of HIP temperature and fiber volume fraction and decrease of sheath thickness appropriately; the hoop residual stress on the matrix greatly decreases with the increase of HIP temperature and sheath thickness, while decrease of HIP time appropriately. Finally the following processing parameters were recommended for preparation of SiC/Ti-6Al-4V composite with good quality: HIP temperature 950-960℃, HIP time 9 h and sheath thickness 70-80 mm and fiber volume fraction 45%-50%. FEM calculation results show some differences with those measured in the experiment for the residual stress of the composite, but with similar variation tendency.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Homogeneous distribution of primary dendritic arm spacing (PDAS) is required to achieve uniform mechanical properties in final product of single-crystal superalloys. In this work, the dendrite characterization and orientation of Ni-based single-crystal DD6 superalloy have been deeply investigated using different methods, which include minimum spanning tree (MST), Voronoi polygon- based approach, fast Fourier transform (FFT), as well as EBSD and RO-XRD. The investigation results indicate that the mean PDAS of DD6 superalloy is about 325.7 mm and its variation ratio is 7.38%. The measured Voronoi polygon parameters suggest that the number of nearest-neighbor dendrite ranges from 5.87 to 5.93, approximating six nearest neighbors in the spatial distribution of dendrite microstructures. However, the change in ratio of six nearest number proportion has exceeded 30% for the twenty specimens. The MST method shows that the change in branch length measured from the twenty specimens achieves 26.95%. Also, the analysis results of FFT imply that the dendrite microstructures of DD6 superalloy evolve apparently. These results give the proof that the dendrite microstructures of DD6 superalloy vary with the solidified distance. Additionally, the deviation angles between preferential orientations of DD6 with the axial direction of specimen were measured by EBSD and RO-XRD, respectively. The deviation angle values of DD6 superalloy in this experiment are both within 10�. The reason for the deviation angle measured by RO-XRD being smaller is well explained due to the fact of selecting the diffraction intensity maximum angles. Furthermore, the EBSD results indicate that the orientations of DD6 superalloy prepared by grain selector can be well controlled along the Z-axial direction, but do not work in other two X and Y directions.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Tensile properties and fracture mechanisms of SiCf/TC17 composites at room temperature and 773 K were studied. The results show that fiber elastic deformation and matrix yielding contributed to the shapes of the stress-strain curves of SiCf/TC17 composites, which were the bilinear appearance at 298 K and the slight curvature at 773 K. Major fracture mechanism of SiCf/TC17 composites at room temperature were as follows: multiple fractures of the interfacial reaction layer, single fiber fracture, matrix brittle fracture etc.. Typical fracture mechanism of SiCf/TC17 composites at elevated temperature were as follows: multiple fiber fracture, matrix plastic fracture, interface debonding etc.. Fiber cumulating damage theory was proved to be suitable for estimation of the fracture strength of this composite. The calculations of local loading sharing model while taking three or more fibers failure into account and global loading sharing model were close to the experimental values of room temperature and elevated temperature respectively. In addition, according to fracture mechanisms and strength prediction, tensile fracture process of SiCf/TC17 composites at room and elevated temperature were explained in detail. At room temperature, multiple fractures of the interfacial reaction layer started at first, and then the weak fiber fractured gradually and randomly. After critical fiber cluster has been formed by nearby broken fibers, the crack extended into the matrix from these fibers. With the increase of load, the fibers and the matrix at the tip of crack gradually destroyed. At the same time, the cracks from other critical fiber clusters were also expanding and connecting to each other. When the crack area has reached the critical level, the remaining fiber and matrix quickly fractured. However, at elevated temperature the matrix yielded firstly, and then multiple fracture randomly of the interfacial reaction layer and the weak fiber occurred sequentially. The crack from broken fiber deflected at interface between fiber and matrix, caused interface debonding. With the increasing of broken fiber number, the micro- cavities of matrix emerged gradually in the stress concentration area. When the total crack area accumulated by the broken fibers and micro-cavities of matrix has reached the critical level, the remaining fiber and matrix quickly fractured.
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-15 Cooperative journals: 《金属学报》
Abstract：本文简述了近年来国内外SiC纤维增强钛基复合材料的发展进程和应用进展情况，从纤维批量化生产、复合材料界面、主要力学性能、无损检测和结构件研制与考核五个方面对该类材料的研究进展进行了回顾。在纤维批量化生产和结构件研制方面，重点介绍了中国科学院金属研究所的研究工作，并对该类复合材料未来的发展趋势进行了展望
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