| At the background of the rapid development of high-speed and high-efficiency process technology, ceramics materials (mainly Al2O3-based and Si3N4-based ceramics) become one of most promising cutting tool material because of its excellent wear resistance and high temperature stability. But there are still some technical difficulties which limit the wide application of ceramic cutting tool. For example, the strength and thermal shock resistance of alumina ceramic are weak, and it would get tipping or even fragmentation easily under strong cutting impact. Silicon nitride ceramic has good affinity with Fe in the workpiece, which would decrease chemical stability of the tool and c lead to sharp wear of the cutting tools.With the development of hard coating technology, it is a feasible method to cover the tool surface with a thin hard and wearable coating to improve their cutting performances. Among them, the physical vapor deposition (PVD) method, which has low process temperature requirements and no pollutant emissions, is an environmentally friendly science and technology. And the coatings which deposited by PVD method possess high hardness, low friction coefficient, excellent wear resistance and chemical stability, could improve the cutting performance and cutting life of ceramic tools obviously.In order to study the cutting performance and wear mechanism of PVD coated ceramic tools, cathodic arc evaporation (PVD-CAE) was adopted to produce TiN, TiSiN coatings on alumina tools; TiAlN, TiAlSiN and CrAlN, TiAlN coatigs on silicon nitride tool, respectively. The microstructure, hardness and adhesion evaluation of the coatings were studied by scan-ning electron microcopy (SEM), micro-hardness tester and scratch test. Cutting tests were carried out on both uncoated and coated tools in gray cast iron machining under dry environment to investigate the cutting performance, wear mechanism. The cutting life, wear mechanism and machining quality of cutting tools under different cutting method and cutting speed were also investigated in this thesis using PVD-CrAIN, TiAlN coated silicon nitride ceramic cutting tools.The results showed that:1) The coatings which deposited by PVD method have dense structure, good combination with the matrix, and can improve the tool hardness effectively, thus improve the cutting life.2) The main wear mechanism of TiN, TiSiN and uncoated alumina cutting tools machining gray cast iron were abrasive wear, moreover, chipping appears on the uncoated tools. The main wear mechanism of TiAlSiN and uncoated silicon nitride tools were abrasive wear and few adhesive wear. The TiAIN coated silicon nitride tools showed the same wear mechanism with other experimental tools in the early stage of cutting, and then turn into serious adhesive wear rapidly.3) In the continuous turning process, the cutting life of PVD coated silicon nitride tools decreases rapidly with the increase of the cutting speed. And there was no obvious difference in the wear mechanism of PVD coated ceramic cutting tool under different cutting speed.4) In the process of high speed face milling, the service life of PVD-coated Si3N4 cutting tool first decreases with the the enhancement of cutting speed, and when the cutting speed rises to a certain value, the service life will increases with the enhancement of cutting speed. The wear mechanism of the coating tool is essentially the same-under different cutting speed, but the extent of adhesive wear of the cutting tool is different. The change of machining quality with the cutting speed is similar to the change of tool life in face milling process. |
