| Summary: | 博士 === 國立成功大學 === 機械工程學系碩博士班 === 94 === This study utilizes the closed-field unbalanced magnetron sputtering system to develop the Cr-W-N, Ti-W-N and Cr-W-C nano-multilayered coatings for industrial applications. Effect of tungsten, crystallite size, surface roughness and modulation period on the nano-structure and nano-mechanical properties of CrN, TiN and CrC coatings was discussed in this dissertation. Mechanical and tribological properties of these nano-multilayered coatings were investigated by the nanoindentation technique and nano-wear test. The microstructure of these nano-multilayered coatings was examined by AFM, SEM, TEM and XRD in terms of crystal structure and crystallite size. Finally, the cutting performance of the Cr-W-N, Ti-W-N and Cr-W-C coated cemented carbide tools was analyzed in the turning and PCB micro-drilling test.
Results of the experiments show that adding 3~8 at.% tungsten into the Cr-N coating influence the hardness significantly. The hardness rises steeply and a maximum of 67.2 GPa is reached approximately 6 at.% W of the Cr-W0.06-N coating. Upon further increasing the tungsten content, the hardness drops rapidly to approximately 36 GPa at 16 at.%. The hardness is increasing with an increase of the tungsten content for the Ti-W-N coatings. The Ti-W0.38-N coatings with 38 at.% tungsten possess the highest hardness of 46.3 GPa. For the Cr-W-C coatings, adding 12~15 at.% tungsten does not influence the hardness significantly. The optimum Cr-W-N and Ti-W-N coatings for sliding against spherical diamond indenter in the nano-wear test are the Cr-W0.06-N and Ti-W0.14-N coatings. For the Cr-W-C coatings, the 60V2 coating obtains the lowest wear depth and friction coefficient among all Cr-W-C coatings. The wear depth decreases with an increase of the H/E factor (elastic strain to failure) in the nano-wear test. The H/E factor is a more suitable parameter for predicting wear resistance than is hardness alone.
With increasing the tungsten content, the microstructure of Cr-W-N and Ti-W-N coatings can be divided into three types. The first type, Cr-W0.03-N and Ti-W0.01-N coatings, is nanocrystalline/amorphous and the surface topography is featureless and very smooth. The second type has the slender columnar grain structure and surface topology changes into crystalline, and can be found in the Cr-W0.06-N, Cr-W0.08-N, Ti-W0.06-N and Ti-W0.14-N coatings. Moreover, the third type is coarse columnar and the surface topology is rough crystalline structure and we can found in the Cr-W0.13-N, Cr-W0.16-N, Ti-W0.29-N and Ti-W0.38-N coatings. An obvious evolution from dense columnar to loose amorphous-like microstructure in the Cr-W-C coatings is observed with increasing the flow rate of methane gas from 2 to 6 sccm at 35V. There is no significant evolution of the microstructure with an increase in the substrate bias. The 40V2, 60V2 and 80V2 coatings show dense and well-developed columnar structures.
The crystallite sizes of the Cr-W-N, Ti-W-N and Cr-W-C coatings are increasing with increase of the tungsten concentration. The surface roughness of the Cr-W-N, Ti-W-N and Cr-W-C coatings is obviously increased with increase of the crystallite size. The surface roughness and the wear behavior of the Cr-W-N, Ti-W-N and Cr-W-C coatings in the nano-wear test have strong correlation. The higher the surface roughness of the coatings is, the greater the coefficient of friction and wear depths of the coatings are. An obvious increase in crystallite size is observed in the case of the Cr-W-N and Ti-W-N coatings as the modulation period is increased, whereas only minor change in the crystallite size is observed in the case of the Cr-W-C coatings.
The Cr-W0.06-N, Ti-W0.14-N and 60V2 coatings have the best wear resistance for Cr-W-N, Ti-W-N and Cr-W-C coatings in the turning and PCB micro-drilling test, respectively. By drilling the same number of 20,000 holes, the 60V2 coated micron-drill has the smallest corner wear among all nano-multilayered coatings in PCB micro-drilling test.
|
|---|
