Authors: J.W. Paek, Beom Seob Kim, Deug Joong Kim
Abstract: Ceramic foams containing MoSi2 were prepared by a self-blowing process of poly-silsesquioxane with MoSi2 as filler. Ceramic foams prepared by polymer pyrolysis were composed of MoSi2 and silicon oxycarbide glass matrix. Densities, pore sizes and mechanical properties of ceramic foams were depended on the filler content and heating rate for curing of polymer. Depending on the foaming condition, ceramic foams with a density of 1.2∼0.4 and a compressive strength of 3∼30 MPa were obtained.
129
Authors: Young Seok Song, M.R. Lee, Jeong Tae Kim
Abstract: Alloy 718 ingot with a diameter of 400mm was made by the vacuum melting process ;
VIM followed by VAR. Compression tests were conducted on samples collected from columnar
zone of the VIM/VAR-processed Alloy 718 ingot in wide temperature and strain rate ranges, i.e.
750~1,200OC and 10~0.001s-1 in order to understand the deformation behavior and evolution of
microstructure. Tensile tests at high temperature were also conducted on samples in temperature
ranges, i.e. 750~1,100OC. Effects of process parameters on the flow behavior as well as on the
microstructure evolution during compression tests at high temperatures are considered.
As a result of the deformation simulation, The VIM/VAR ingot was heat-treated for
homogenization, and casting structure of the ingot was broken down for uniform microstructures
and mechanical properties by controlled cogging process using a hydraulic press.
The observation of the microstructure and grain size distribution was carried out to evaluate the
effects of optimum process parameters during cogging and mechanical property tests were
performed in this study.
3124
Authors: Roberta M.C. Sasahara, H.N. Yoshimura, Cátia Fredericci, Alberto Calasans, Paulo Francisco Cesar, André Luiz Molisani
Abstract: The aim of this work was to establish a route to produce pre-sintered blocks of Y-TZP
(yttria stabilized tetragonal zirconia polycrystal) suitable to be machined in a commercial CADCAM
system, used to manufacture crowns and bridge frameworks for dental applications. Two
commercial Y-TZP powders were investigated. The powders were pressed with different
compaction pressures (40 to 500 MPa) and pre-sintered at temperature ranging from 900 to 1100°C.
Vickers hardness, biaxial flexural strength, and linear shrinkage could be correlated to the relative
density of pre-sintered samples. Using an empirical equation, pre-sintered blocks with a pre-defined
density could be prepared. The blocks withstood the machining in a CAD-CAM system, and the
machined and sintered crowns presented good adaptation.
712
Authors: Qiang Shen, Chang Lian Chen, Fei Chen, Qi Wen Liu, Lian Meng Zhang
Abstract: Porous calcia stabilized zirconia ceramics (CSZC) with closed pores were presurelessly sintered by adding different contents of zirconia hollow balls. CSZC FGM with porosity gradient structure was then fabricated by laminating five layers with designed contents of zirconia hollow balls. The porosity, microstructure, and bending strength of the obtained CSZC samples were characterized. The results show that the hollow balls distribute uniformly and are well bonded with the matrix, and the porous structure is mainly composed of closed pores. The porosity of the CSZC increases linearly from 5.7 % to 31.6 % when the content of zirconia hollow balls increases from 0 % to 30 %, and the bending strength decreases rapidly from 297 MPa to 30 MPa. The thermal shock behavior of the CSZC and FGM was evaluated using air-quenching technique. It is shown that the residual bending strength of the quenched samples increases after several quenching cycles, and the samples are damaged by thermal shock after eight thermal cycles because of the production of monoclinic zirconia. FGM samples with porosity gradient structure can endure above twelve thermal shock cycles and exhibits better thermal shock resistance.
435
Authors: Yi Wen Hu, Xin Zhang, Yin Wu, Wen Jie Si
Abstract: Zirconia ceramics are now widely used in dental restorations. The veneering porcelain chipping happens sometimes in zirconia-porcelain all-ceramic system. The objective of this study was to evaluate the bonding strength between the zirconia core and various commercial veneering ceramics. The shearing and bending methods were used to evaluate the bonding strengths of zirconia core and four veneering ceramics. Meanwhile, as surface treatment will play an important role for the bonding strength, the influence of 3 kinds of surface treatment was investigated. The results indicated that both the shearing and bonding strengths of Cercon ceram kiss is better. Moreover sand blasting is the most useful method of surface treatment.
528
