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排序方式: 共有606条查询结果,搜索用时 15 毫秒
1.
《Journal of the European Ceramic Society》2022,42(11):4429-4435
Here we design a novel multi-principal element carbide system (Ti,Zr,Hf,W)C with a miscibility gap using computational tools and report on the formation of a single-phase (Ti,Zr,Hf,W)C after spark plasma sintering. The (Ti,Zr,Hf,W)C shows high nanohardness (32.7 GPa) and fracture toughness (5 MPa·m1/2). Aging studies at 1350 °C for 100 h show that the single-phase carbide solid solution is quite stable even though this temperature is within the predicted miscibility gap of the system. Detailed electron microscopy characterization shows that phase separation has initiated with minor decomposition after aging by forming rock-salt (Ti,W)C- and (Zr,Hf)C-rich phases as well as hexagonal WC precipitates. We show that the (Ti,W)C- and (Zr,Hf)C-rich phases form a lamellar structure upon aging and the interlamellar spacing is considerably coarser than what has been previously found for the binary (Ti,Zr)C system. The decomposition kinetics, on the other hand, is sluggish due to the reduced driving force for phase decomposition. 相似文献
2.
3.
First-principles study on the dissolution and diffusion behavior of hydrogen in carbide precipitates
Yifan Li Xingming Zhang Tiantian Wu Jianfeng Tang Lei Deng Wei Li Liang Wang Huiqiu Deng Wangyu Hu 《International Journal of Hydrogen Energy》2021,46(42):22030-22039
To understand the hydrogen (H) behavior in the carbide precipitates, the dissolution and diffusion properties of interstitial H in the transition metal carbide (TMC; TM = Hf, Nb, Ta, Ti, V, and Zr) were studied by first-principles calculations. In these carbides, it can be seen that H tends to occupy the trigonal site (tri2-site) surrounded by three transition metal atoms and one carbon atom rather than the face center (fc-site) and the body center (bc-site) which with the larger space. We found that the bonding interaction between H atom and the nearest-neighbor (1NN) carbon atom is the dominant influence on the stability of H dissolution. Besides, we obtained the temperature-dependent solubility and diffusion coefficients of H in TMC and pure vanadium through Sievert's law and transition state theory. Compared with pure vanadium, H shows the worse solubility in TMC, and it is more difficult for hydrogen to migrate in TMC, but segregate toward the interface. Furthermore, it is interesting to note that, the diffusion barrier and the H solution energy show a linear relationship for transition metal carbides in the same period. These results can help us deepen the understanding of H behavior in vanadium alloys strengthened by carbide precipitates, and furtherly providing the theoretical guidance for the design of alloys with excellent performance. 相似文献
4.
《Ceramics International》2022,48(9):12790-12799
The ablation behavior of high-entropy ceramics (HECs) was investigated in this study using an oxyacetylene flame at 2000 °C. Spark plasma sintering was used to construct a dense HEC (TiZrHfNbTa)C with a 20 vol% of SiC addition (HEC-20SiC). The densification of HEC-20SiC can be improved to a certain extent by adding SiC particles, increasing the hardness of HEC-20SiC to up to 24.6 GPa, and the crack deflection observed through the addition of SiC particles were considered to be the strengthening and toughening mechanisms. After ablation, Hf6Ta2O17, Ti5.1Ta4.9O20, Nb2Zr6O17, TaZr2.75O8, and SiO2 can be detected on an ablated surface and HEC-20SiC possesses the minimum mass ablation rate (?1.9 mg s?1) and line ablation rate (2.1 μm s?1) among the comparative ceramics. On the one hand, the SiC phase forms gaseous CO, CO2, and SiO as well as viscous SiO2 during ablation and some part of the heat can be dissipated by the evaporation of gaseous CO, CO2, and SiO; further, pore defects can be healed by viscous SiO2, thus inhibiting the diffusion of reactive oxygen species. On the other hand, the HEC phase with a lattice-distortion caused by single-phase solid-solution can effectively inhibit the invasion of reactive oxygen species and the outward migration of metal atoms. The invasion rate of reactive oxygen is considered to be the main step during HEC-20SiC ablation, and it is believed that higher principal component HECs can improve ablation performance even further. 相似文献
5.
钨白口铸铁成本低,但共晶碳化物呈连续网状分布,脆性大,在承受冲击载荷的工况下使用易断裂,使用范围受到严格限制。研究了Ce、K、Na复合变质处理对其组织和性能的影响,还提出了评价碳化物变质效果的圆度概念。变质处理后,钨合金白口铸铁的共晶碳化物形态发生了显著变化,在常规热处理条件下,共晶碳化物变成了团球状,使之冲击韧性提高了72.2%、耐磨性提高了49.9%。对共晶碳化物团球化机理进行了深入分析,并讨论了共晶碳化物团球化对力学性能和耐磨性能的影响。变质处理的钨合金白口铸铁轧辊使用寿命比高铬铸铁轧辊提高20%以上,生产成本降低30%以上,推广应用变质钨合金白口铸铁具有较好的经济效益。 相似文献
6.
7.
Yafei Wang Guangxu Cheng Mu Qin Qing Li Zaoxiao Zhang Kang Chen Yun Li Haijun Hu Wei Wu Jianxiao Zhang 《International Journal of Hydrogen Energy》2017,42(38):24549-24559
In this paper, the effects of high temperature deformation on the microstructure, mechanical properties and hydrogen embrittlement (HE) of the 2.25Cr–1Mo-0.25 V steel was investigated by a scanning electron microscope (SEM), a transmission electron microscope (TEM) and tensile tests. The SEM and TEM images demonstrated that high temperature plastic deformation (HTPD) led to the coarsening of carbides and the dislocation density increase. The tensile tests displayed that the HTPD resulted in the cracking susceptibility increase, as indicated by the increased numbers and sizes of cracks at the fractured surface. This was attributed to the coarsening of carbides during high temperature deformation. In contrast, the HTPD highly decreased the loss of ductility compared to the un-deformed specimens, although the amount of ductility losses (elongation or reduction of area) did not change significantly as the HTPD increased. The correlations among carbides, hydrogen and cracks were discussed. 相似文献
8.
M. J. Zhan F. C. Wang J. W. Lang W. Z. Shi 《Tribology - Materials, Surfaces & Interfaces》2015,9(3):137-143
WC-Fe composite coatings were prepared on IC45/080A47 steel substrates by argon arc cladding technique. Minute amounts of La were added into the coating, and the microstructure was investigated to find the relation to rare earth. Results show that RE does not change the categories of phases, and the main components remain α-Fe, Fe3W3C, WC and W2C. However, the distribution of carbide particles is optimised. It reduces the agglomeration and bridging in the cladding layer's structure, makes the particles distribute homogeneously and restrains the dissolution of WC and the formation of fishbone shaped dendritic carbides. It promotes the formation of granular carbide and refines grains. It also reserves the WC particles in the composite coating and improves the average hardness and wear resistance. 相似文献
9.
Rolling contact fatigue in bearing steels is manifested by dark-etching regions, which are attributed to deformation induced tempering. In order to quantitatively explain this phenomenon, a model is suggested for martensite tempering assisted by dislocation glide during rolling contact fatigue. In the model, dislocations transport carbon from the matrix to carbide particles, provided that the carbon is located at a certain distance range from the dislocation contributing to the tempering process. By calculating the amount of carbon in the matrix, the kinetics of carbide thickening and hardness reduction are computed. It is found that the dark-etching region kinetics can be controlled by both bearing operation conditions (temperature and deformation rate) and microstructure (type, size, and volume fraction of carbides). The model is validated against tested bearings, and its limitations are discussed. 相似文献
10.
Antonio Camarano Javier Narciso Donatella Giuranno 《Journal of the European Ceramic Society》2019,39(14):3959-3970
Reactivity between SiC and Ir as a function of SiC-crystallinity was investigated by diffusion bonding technique under a vacuum and over the temperature range of 1200–1450 °C. As reaction products, various Ir-silicides and free unreacted-C were detected. Reactivity is strongly affected by the temperature and SiC-crystallinity involving a series of interactions, from “no reaction” to “massive exothermic reactions”. In particular, interfacial phenomena are more pronounced by the presence of defects and grain boundaries.Solid state reactions result in formation of fine C-precipitates rearranged in a quasi-periodic microstructure. On the contrary, clustering of highly ordered C-precipitates (C-graphitized) occurs after “massive reactions” take place.A relationship between the degree of graphitization (from 1 to multi-layers of graphene), temperature and SiC crystallinity was found by Raman spectroscopy. 2D-layering phenomenon is enhanced in polycrystalline SiC at high temperature. 相似文献