Kensuke Sassa

Control of Crystal Orientation of Hydroxyapatite by Imposing a High Magnetic Field

The controlled development of texture microstructure in ceramics is one effective way to improve their properties, such as electrical, mechanical properties and biocompatibility. A bioceramics with oriented crystal structure has attracted great interest. In bone reparations, Hydroxyapatite (HAp)-based biomaterials were frequently used. And HAp is the main mineral constituent of the hard tissue of human bodies, which occurs with a hexagonal crystal. A HAp crystal turns out to have different surface properties in a- (or b-) plane and c-plane. In this regard, to get highly oriented HAp is very important before using HAp as a biomaterial. And the crystal orientated HAp is useful not only as biomaterials but also as protein absorbents. In this research, two different kinds of HAp-based biomaterial with oriented structure (HAp bioceramics and HAp-coated titanium composite) were studied.

Formation of c-Axis Aligned Hydroxyapatite Sheet by Simultaneous Imposition of High Magnetic Field and Mold Rotation During Slip Casting Process

A high magnetic field is a useful tool to control the crystal alignment of non-magnetic materials such as ceramics and polymers. In the case of Hydroxyapatite crystal, the a,b-axis is aligned parallel to the direction of an imposed magnetic field. This fact implies that the alignment of the c-axis is not controllable only using a high static magnetic field due to the freedom of the c-axis in a plane perpendicular to a magnetic field direction. In this study, a high static magnetic field and mold rotation was simultaneously so applied during a slip casting process as to align the c-axis of HAp poly crystals.

Enhancement of Press Formability of Rolled Mg Alloy Sheet by Using Cross Rolling Processes

In this study, two different cross rolling processes, which are effective rolling processes for a reduction of (0002) plane texture, are introduced. In the first cross rolling process, a sheet specimen is rotated around the rolling plane normal after each pass. In the second cross rolling process, the roll axis is tilted against the transverse direction (TD) in the rolling direction (RD) - TD plane. The two cross-rolling processed were carried out on a AZ31 alloy, and the press formability of cross-rolled sheets was compared with that of unidirectionally rolled sheets determined by Erichsen tests at 433 – 493 K. Both the cross-rolled specimens exhibited a high press formability, compared to an unidirectionally rolled alloy. The high press formability of the specimen by the first cross rolling was due to a reduction in (0002) texture intensity. The high press formability of the specimen by the second cross rolling was due to not only a reduction in (0002) texture intensity but also grain refinement.

Mechanical Properties and Press Formability of Mg Alloy Processed by Cross-Roll Rolling

Cross-roll rolling with different rolling routes (unidirectional rolling and reverse rolling) was carried out on a commercial Mg alloy sheets. In the cross-roll rolling, the roll axis was tilted by 7.5 degrees against the transverse direction. As a result of the Erichsen tests at 433 – 493 K, the stretch formability of the reverse cross-rolled specimen was higher than that of the unidirectional cross-rolled specimen. The reverse cross-rolled specimen showed lower average Lankford value compared with the unidirectional cross-rolled specimen. This is likely to be responsible for the enhanced stretch formability of the reverse cross-rolled specimen. The higher stretch formability was attributed to reduction of (0002) texture intensity, which was originated from random grain distribution.

Crystal orientation in high magnetic field

A new technology relating to crystal orientation and structure alignment has emerged by the development of superconducting technologies. Now, a high magnetic field covering a rather large space is available even in small-scale laboratories. Under this circumstance it has been found that the crystal orientation in materials can be controlled by imposition of the high magnetic field. This principle due to a magnetization force can be applied not only to magnetic materials but also to non-magnetic materials with asymmetric unit cells. In this paper, three novel processes for the crystal orientation of ceramics and metals are described.