Studies On The Nanostructure,Mechanical Properties And Self-sharpening Phenomenon Of The Teeth From Acanthochiton Rubrolineatus

Firstly, the nanostructure of the magnetite cap in the teeth from Acanthochiton rubrolineatus was studies with SEM, and we also analyzed the major elements and their distribution in the whole teeth by EDS. The SEM observation showed that three microstructurally distinct regions were recognized:one is close to the anterior surface of the cusp and composed of thick rod microstructure units, one is close to the posterior surface and composed of fine fibers and the other one is sandwiched between the above two regions and composed of thin sheets. The microstructure units in the three regions are perpendicular to each other, but smoothly convert in the transition zones. These microstructure units constitute a continuous and integrated architecture component. In addition, in the study of the immature teeth of Acanthochiton rubrolineatus, the result showed that the three structure units were composite of magnetite nanocrystals these in the posterior region is smaller than those in the anterior region. Besides, the chemical composition analysis by EDS indicated that the teeth have two regions:the outer layer is rich in Fe-O elements (magnetite cap) and the inner core is rich in Fe-P elements. The further study on immature teeth demonstrated that the magnetite cap was formed earlier than the Fe-P core region.Secondly, the hardness of magnetite cap in teeth from Acanthochiton rubrolineatus has been measured by Nanoindentation and Vickers hardness. The result showed that the hardness and modulus increase from the anterior region to the posterior region of the teeth, and from the longitudinal section of the teeth, the hardness in the posterior region remains small change in400-500Hv.Lastly, based on the SEM observation on the wear patterns and the microstructure observation, the abrasive behavior and microstructural mechanism of self-sharpening of the chiton tooth were discussed in the paper. The self-sharpening was attributed to the combined effect of the hardness and the texture orientation of the microstructure units in the posterior and the anterior regions. On the one side, it is due to the difference in hardness between the posterior and the anterior regions, causing the harder posterior region wear more slowly than the softer anterior region, so the tooth maintains a sharp corner on the front tip of the posterior region. On the other side, it is due to the texture orientation of the microstructure units. The column structure in the anterior regions is paraller to the frictional force, which makes the materials lose quickly in the manner of peelling off. But in the posterior region, the sheet structre perpendicular to the frictional force causes materials lose slowly, which also makes the tooth keep a sharp cutting edge in the front of the posterior region.