Fabrication And Properties Of Al₆₂Cu_25.5Fe_12.5 Quasicrystalline Grinding Materials

Al stable icosahedral quasicrystals (QCs) show a hardness/Young’s modulus ratio(HIE) of0.059, which is about2to3times as large as those of industrial Al alloys and steels. The QCs thus can be classified as a family of high hardness/Young’s modulus ratio materials. The material property of Al QCs would imply a unique match in the degree of defromation between the ealstic deformation of QC particles themselves and the plastic one of the soft friction pair material. The sample surface is thus expected to the greatest extent to be free of fatal scratching. The powders of Al QCs are therefore promising additives in the abrasive polish paste for soft metals. In the present work, high purity Al62Cu25.5Fe12.5QC powders by means of a sequence of metallurgical procedures of arc melting, ball milling and annealing. By taking the commercial diamond metal polishing paste into comparison, a comparative study has been made on the surface polishing treatment for pure Al. The performance of the QC particles as grinding agent and the underlying mechanisms are studied. The experimental results are summarized in the following.(1) At the nominal composition of Al62Cu25.5Fe12.5, alloy powders composed of a single icosahedral phase were made by arc melting, followed by annealing at800℃for8h. The icosahedral phase is very stable and preserves its strucutre during ball milling. The powder of a particle size of less than15μm were screen separated for making the QC polishing paste. The ingridient formula reads:30wt.%QC powder-30wt.%fatty acid mixed-10wt.%geoline-distilled water.(2) After polishing with the QC paste, the sample surface of pure Al metal showed a good roughness (Ra=0.306) and was free of fatal scratch marks, which meets the general requirement of precise surface grinding. For diamond paste on the other hand, the surface roughness was found much better, but the presence of secondary scratch marks are hardly unavoidable.The QC paste was found to follow a mechanism of surface rolling and squeezing, wherease cutting became the operative mechanism in the process of diamond particles grinding. Due to the large separation in hardness, seconday scratch marks were readily produced on A1metal surface by hard diamond particles. (3) Our polishing experiments also revealed that the QC particles showed an evident repairing effect on the Al metal surface. The unique tolling and squeezing mechanism as taken by the QC polishing material has an interesting implication for obtaining good surface roughness in soft metal polishing.