Subjects: Other Disciplines >> Synthetic discipline submitted time 2023-03-28 Cooperative journals: 《中国科学院院刊》
Abstract： An overview is presented of the status of pressure-resistant structural materials and structural functional materials for application in marine observation and exploration platform. The key roles of new materials in facilitating high performance marine equipment are highlighted. The most in-demand observation tasks concern the upper ocean and low cost materials must be developed to manufacture affordable equipment. For deep ocean observations, future challenges are identified for developing next-generation high strength titanium alloys, buoyancy materials, lighting materials, and lubricating and sealing materials. Recommendations are proposed regarding project organization and research paradigm update, and emphasis is placed upon identifying and solving scientific problems underlying the technical advance of the materials.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： The history of research and development of g-TiAl intermetallic alloys was outlined and divided into 4 stages: starting (1974~1985), revolutionary (1986~1995), emerging (1996~2005) and specialty materials (2006~). Major events and landmarks at the different stages were recounted to provide a framework for understanding scientific and technological progress. Key advances in the following 6 areas were reviewed: alloying, microstructure type, primary processing (melting), secondary processing (hot working), properties (including creep, fracture and fatigue, and oxidation), and tertiary processing (forming, covering both investment casting and near- net shape powder metallurgy). Future challenges were identified as follows: improvement of centrifugal casting technology, low-cost wrought process, development of third-generation alloys that meet design specifications, new applications based on new technologies, and viability of new forming routes such as additive manufacturing.
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 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： Pre-alloyed powders of Ti-47Al-2Cr-2Nb-0.15B (%, atom fraction) were prepared by an electrode induction melting gas atomization process, and powder metallurgy (PM) γ-TiAl alloys were prepared by hot isostatic press (HIP). Pre-alloyed powders of γ-TiAl were characterized. A comparison study was made between vacuum degassed and not degassed for the pre-alloyed powders and the PM alloys were subjected to tensile and rupture life test at different temperatures. Infrared spectrum analysis showed that the powders would absorb H2O when exposed in air. By getting rid of the absorbed H2O and O2 through a carefully designed vacuum degassing pre-treatment, the numbers of voids in the prepared PM γ-TiAl alloys decreased obviously, correspondingly the rupture life, as well as the consistency of room temperature tensile elongation, was also improved. In order to find out the influence of container materials on the microstructure and mechanical properties of the PM γ-TiAl alloys, two different container materials (CP-Ti and mild steel) were adopted. Experimental results showed that a lot of obvious voids appeared in the reaction zone due to severe reaction diffusion between the mild steel container and the PM γ-TiAl alloys when HIPed at 1260oC. The shielding effect of the mild steel container was stronger than that of the CP-Ti container, thus the densification shrinkage process of the CP-Ti canned PM γ-TiAl alloys would be more fully completed when HIPed at 1230oC compared with that of the mild steel canned PM γ-TiAl alloys, and thereby both of the yield and tensile strength were both improved. The γ-TiAl alloys prepared by powder metallurgy route present more uniform microstructure, finer grain and better properties compared with the casting alloys. Furthermore, the PM γ-TiAl alloys had no texture which was very common for the casting alloys.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： Powder metallurgy (PM) Ti2AlNb alloy of Ti-22Al-24Nb-0.5Mo (atomic fraction, %) was prepared from pre-alloyed powder using hot isostatic pressing (HIPing). Compression tests of PM Ti2AlNb alloy, heat treated PM Ti2AlNb alloy and wrought Ti2AlNb alloy with the same chemical composition were conducted on Gleeble-3800 testing machine. The testing temperatures were from 930oC to 1050oC, strain rates varied from 0.001 s-1 to 10 s-1, and engineering strain was about 50% for each compression. The results show that the deformability of PM Ti2AlNb alloy is comparable to that of wrought alloy, and heat treatment has no obvious effect on the hot workability of PM Ti2AlNb alloy. The high temperature flow behavior of Ti2AlNb alloys prepared by different fabrication routes is similar in this work, while processing windows for PM Ti2AlNb alloy is broader than casting alloys especially at low temperature or relative high strain rate. PM Ti2AlNb billets for hot deformation were prepared by a typical powder metallurgy process, and were upset or drawn out to different deformation in two-phase region. Macrostructure of deformed PM Ti2AlNb billets were observed, no macro crack was found in deformed PM Ti2AlNb billets and the deformation was uniform. The results of tensile tests show that the deformed PM Ti2AlNb alloy after heat treatment presents better tensile properties.
Subjects: Materials Science >> Materials Science (General) submitted time 2017-11-21 Cooperative journals: 《金属学报》
Abstract：本文采用第一性原理的方法系统研究了在不同六角结构金属中这种新的孪晶方式的形成过程，以及合金化对形成过程的影响。结果表明在不同的六角结构金属中，形成这种基面/柱面的垂直界面需要不同的激发能，其中Mg的激发能最低，而Os最高；基面/柱面垂直界面的形成由“剪切变形”和“原子重排”两部分构成。在典型六角金属，如Mg中“原子重排”贡献了一个激发能的主要部分，而在Ti中，当“剪切变形”足够大时，随后的“原子重排”过程是一个能量下降的过程；合金化在Mg合金中主要影响纯“剪切变形”部分的激发能，而在Ti合金中主要影响“原子重排”部分的激发能；在一定的“剪切变形”或“原子重排”下，合金化对后续激发能的影响依赖于体系和合金元素。
Subjects: Materials Science >> Materials Science (General) submitted time 2017-03-31 Cooperative journals: 《金属学报》
Abstract：利用XRD、SEM和TEM等手段分析了TC16钛合金辊模拉丝变形过程中的相组成和显微组织的变化情况，并对不同应变的辊模拉丝变形丝材进行了室温拉伸性能与显微硬度测试。结果表明：在辊模拉丝变形过程中，TC16钛合金丝材主要由α相和β相组成，部分β相发生应力诱发α〃马氏体相变；随着辊模拉丝真应变的增加，TC16钛合金丝材的显微组织明显细化，当真应变达到2.14时，横截面和纵截面中的α相和β相纤维状组织厚度均约为0.3μm，两相衍射斑点已经近似环状，表明两相显微组织也明显细化；随着辊模拉丝真应变的增加，TC16钛合金丝材的抗拉强度和显微硬度大幅提高，当真应变达到2.14时，TC16钛合金丝材的显微硬度由初始的266HV提高到365HV。
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
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-04 Cooperative journals: 《金属学报》
Abstract：利用第一原理平面波赝势方法，计算了含不同过渡族合金原子时Al2O3和TiO2的氧化能，据此分析了合金化对Al2O3和TiO2相对稳定性的影响。计算结果表明，几乎所有合金元素均增加Al2O3和TiO2的氧化能，使它们的稳定性下降。Al2O3和TiO2氧化能的差值表明，Nb、Mo、W、Re等显著降低Al2O3相对于TiO2的稳定性，因此，可抑制γ-TiAl中Al组分的内氧化，提高γ-TiAl的高温抗氧化性能。
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