Narrow Results

The biocompatibility of titanium implants with different surface properties is investigated. We prepared three types of specimens, one ground by the newly developed ELID grinding system, another ground by conventional ELID grinding, and the other polished by SiO₂ powder. These surfaces were characterized and, the number of cell and cytotoxicity in in-vitro were measured. Energy Dispersive X-ray Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscope (TEM) revealed that the modified ELID system can create a significantly thick oxide layer and a diffused oxide layer, and also can control the thickness of a modified layer. The results of cell number and cytotoxicity showed that the sample ground by the modified system had the highest biocompatibility. This may have been caused by improvement of chemical properties due to a surface modified layer. The above results suggest that this newly developed ELID grinding system can create the desirable surface properties. Consequently, this system appears to offer significant future promise for use in biomaterials and other engineering components.

To investigate the possibility of developing a new surface modification method by the combined process of ELID grinding and high-temperature oxidization, we treated ELID finished specimens and polished specimens by high-temperature oxidization in the atmosphere and performed detailed analysis to determine how the treatment would change the specimen surfaces. The ELID-series showed high quality surface roughness and excellent tribological characteristics as compared with the polished-series. The improved surface properties of the ELID-series seem to result from formation of fine, uniform structures of spinel-type multiple oxides FeCr₂O₄ and Cr₂O₃ on the surface by high-temperature oxidization.

One of the authors has pioneered a novel grinding technology that incorporates in-process dressing of metal bonded superabrasive wheels known as electrolytic in-process dressing (ELID). This technology provides dressing to metal bonded wheels, during the grinding process, for continuous protrudent abrasive from superabrasive wheels. ELID grinding was performed on two types of silicon nitride materials with various grit sized diamond grinding wheels. A mirror surface finish with a R_a(center line average) value of 3.2 run was achieved when ELID grinding was performed with a # 8000 grit sized (average grain size = 1.76 µm) wheel.

ELID-Lap Grinding is an extension of the ELID grinding technology. It is a method of constant pressure grinding which employs the electrically conductive bonded wheel and electrolytic in-process dressing (ELID). ELID-Lap Grinding was performed on brittle materials such as silicon and glass BK 7 with wheels of different grit sizes. The results of experiments showed that stable grinding can be achieved with the # 8000 to # 3000000 (average grain size = 5 nm) metal resin bonded diamond wheels (MRB-D). With the # 3000000 MRB-D wheel, a very smooth surface finish was obtained for silicon (2.8 nm) and for glass (2.5 nm) (peak to valley). The results of this investigation will be reported in this paper.