High-strength Alumina Research Articles

Fabrication of Hybrid Material by Coating of Bioactive Glass-Ceramic on Alumina Substrate through Porcelain Enamel Process.

In artificial bones, a steady bioactivity over long-term service, no dissolution of harmful ions and a sufficient mechanical strength are required, though the relative importance of the above factors depends upon the implantation place. In general, bioactive materials have no sufficient mechanical strength and, on the other hand, materials with high mechanical strength are not bioactive. In the present study, a porcelain enamel technique was applied to produce a hybrid material whose both bioactivity and high mechanical strength, which merely consists of inorganic materials. High-strength alumina and bioactive glass-ceramics were used as substrate and coating material, respectively, and an adhesion-glass was employed to achieve a tight bond between alumina and the bioactive glass-ceramic. Appropriate heat-treatments of the alumina, adhesion-glass and bioactive glass-ceramic composite resulted in the successful production of a hybrid material that has about 2.5 times stronger in bending-strength than that of an apatite precipitation-type glass-ceramic. This technique gives a useful process on production of ceramic-ceramic hybrid materials with high mechanical strength and bioactivity for bone substitution.

高速遠心成形法による高純度アルミナセラミックスの切削性能

Using a high-speed centrifugal compaction process (centrifugal force : 1×104-2×104 G) developed by the authors, a slip prepared from alumina powder with a purity of 99.99 % and an average particle size of 0.22 μ m was compacted, and sintered at 1230°C for 1.5 hours in the atmosphere. The sintered compact has superior mechanical properties, including a 3-point bending strength of 1330 M Pa and a Vickers hardness of 2100.The cutting performance of this high-strength alumina sintered compact was studied in this experiment. The results show that tools manufactured using the subject high-speed centrifugal compaction process have relatively high wear resistance and toughness as compared with commercially available high purity alumina ceramic tools.

Testing of High‐Strength Ceramics with the Split Hopkinson Pressure Bar

The split Hopkinson pressure bar was used to study the failure of a high‐strength alumina at strain rates on the order of 103 s‐1. There appears to be a critical strain rate above which the traditional method of using the transmitter bar signal to calculate the stress in the specimen is no longer valid. To compute the correct stress in the specimen it was necessary to use the strain signal from a gage mounted directly on the specimen.

高純度アルミナのスリップキャスティング成形とその焼結体

Slip casting method for submicron high purity alumina was developed by optimizing the concentration of slip and dispersant, and using resin mold as a substitute for plaster and apparatus with vacuum⋅pressure system. The results obtained were summarized follows:1) High density green body (>60%) was obtained.2) High strength alumina (700-800MPa) was obtained after sintering the body at 1250-1300°C. This value is equal to that of alumina sintered under HIP and HP at 1500-1600°C.3) This high strength comes from uniformally controlled small grain size(1-3μm) of sintered body which results in grain fracturing instead of grain boundary fracturing of conventional alumina ceramics.