Papers by Keyword: Elongated Grains

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Authors: Bin Zou, Chuan Zhen Huang, Jun Wang, Bing Qiang Liu
Abstract: An effect of nano-scale TiN grains on the mechanical properties and microstructure of Si3N4 based ceramic tool materials is investigated at the different sintering temperature. Compared to monolithic Si3N4 ceramic tool materials, the sintering temperature is decreased and mechanical properties is enhanced when only one percent of nano-scale TiN in term of mass is added into the Si3N4 matrix. The optimum mechanical properties are achieved when Si3N4/TiN nanocomposites tool materials were sintered at the sintering conditions of 1650, 30MPa and holding time of 40min. The flexural strength, fracture toughness and hardness are 1018.2MPa, 8.62MPa⋅m1/2 and 14.58GPa respectively. SEM micrographs indicate that microstructure is composed of the elongated and equiaxed β-Si3N4 grains, and some nano-scale TiN grains are enveloped into matrix grains.
Authors: G.H. Liu, Ke Xin Chen, He Ping Zhou, Xiao Shan Ning, José Maria F. Ferreira
Abstract: In this paper, Yb a-sialon powders with elongated grains have been prepared by combustion synthesis. The effects of diluents, nitrogen pressure, adding a-sialon seeds and NH4F on the phase transformation and microstructure development of the samples are discussed systematically. The experimental results show that the addition of diluents, proper nitrogen pressure and additive NH4F can facilitate the nitridation of Si. It was also found that the added a-sialon seeds and NH4F are beneficial to the nucleation and growth of elongated grains.
Authors: Yong Chang Zhu, Shou Fan Rong, Ji Wei Guo, Jun Gang Li
Abstract: The elongated grain evolution of alumina ceramics doping with Al2O3-CaO-SiO2(CAS), Nb2O5, and 3Y-TZP was studied under pressureless sintering. From in-situ growth elongated grain cooperating with second phase to toughen the alumina ceramics, microstructure and sintering properties were firstly studied systematically. The effect of additives on the alumina ceramics with columnar grain were analyzed by means of TEM, SEM, XRD, etc. Basing on the analyzed sintering process by the principle of dynamics, the elongated grain growth mechanism was further studied.
Authors: Paul F. Becher, Gayle S. Painter, Naoya Shibata, Hua Tay Lin, Mattison K. Ferber
Abstract: Silicon nitride ceramics are finding uses in numerous engineering applications because of their tendency to form whisker-like microstructures that can overcome the inherent brittle nature of ceramics. Studies now establish the underlying microscopic and atomic-scale principles for engineering a tough, strong ceramic. The theoretical predictions are confirmed by macroscopic observations and atomic level characterization of preferential segregation at the interfaces between the grains and the continuous nanometer thick amorphous intergranular film (IGF). Two interrelated factors must be controlled for this to occur including the generation of the elongated reinforcing grains during sintering and debonding of the interfaces between the reinforcing grains and the matrix. The reinforcing grains can be controlled by (1) seeding with beta particles and (2) the chemistry of the additives, which also can influence the interfacial debonding conditions. In addition to modifying the morphology of the reinforcing grains, it now appears that the combination of preferential segregation and strong bonding of the additives (e.g., the rare earths, RE) to the prism planes can also result in sufficiently weakens the bond of the interface with the IGF to promote debonding. Thus atomic-scale engineering may allow us to gain further enhancements in fracture properties. This new knowledge will enable true atomic-level engineering to be joined with microscale tailoring to develop the advanced ceramics that will be required for more efficient engines, new electronic device architectures and composites.
Authors: Zhang Fu Yang, Hao Wang, Xin Min Min, Wei Min Wang, Zheng Yi Fu
Abstract: Ca-α-sialons with low oxygen content were fabricated at 1800°C by hot pressing. The phase and microstructure were characterized by XRD and SEM. The calculated lattice parameter reveals that 20~30% Ca2+ ions still exist in the grain boundary phase of Ca-α′. A large amount of Ca-containing liquid phase efficiently promotes the anisotropic growth of α′ grains in Ca-rich composition. Reinforced only by elongated α′ grains, the fracture toughness of Ca-α′ can reach 4.96 MPa•m1/2.
Authors: Chun Feng Liu, Feng Ye, Yu Zhou, Qing Chang Meng, Yong Liang Wang
Abstract: The densified α-sialon ceramics with the compositions RE0.333Si10Al2ON15 (RE= Yb,Y, Dy, Sm and Nd) were prepared by a two-step hot-pressing sintering. The ceramics doped with smaller cations (Yb3+, Y3+ and Dy3+) are fully composed of α-sialon, while the larger cation-doped ceramics (Sm3+ and Nd3+) exist a few M′ (RE2Si3-xAlxO3+xN4-x) phases. A small amount of β-sialon phases are also found in the Nd-doped sialon. Microstructure observation indicates that Yb-α-sialon consists of equiaxial grains, but when increasing the radius of the doped cations, the elongated α-sialon grains form and the aspect ratio of grain increases slightly. TEM observation indicated that almost no intergranular phases exist in the α-sialon doped with smaller cations, but a few exist in Sm- and Nd-doped α-sialon. Some elongated α-sialon grains with grain core were found. EDX results suggest that the compositions of the grain shell and that of the core are different. Surrounding the grain core, some misfit dislocations were seen.
Authors: Wen Bin Dai, Xin Li Wang, Peng Zhao, Jing Kun Yu
Abstract: The effect of 1mol% calcia additive on sintering of yttria was investigated, and a yttria with elongated grains and micro-pores was developed in present work. The results showed that in calcia added samples heated at 1600°C, calcia contained yttria solid solution grains were formed and distributed among pure yttria grains. With the prolonging soaking time, they were concentrated into rod- or plate-like elongated grains and some of them were embedded into pure coarse yttria grains. Furthermore, in calcia added samples, grain growth was much faster and lots of micro-pores were left in coarse pure yttria grains. Water quench test revealed that thermal shock resistance of calcia added sample was greatly improved by elongated grains and micro-pores.
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