Wear behavior of PVD titanium nitride-coated tool steels

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Wang, Xihong
Oregon Health & Science University
Tool-steel; Ceramic coating; Mechanical wear
thesis / dissertation description
Titanium nitride films deposited by physical vapor deposition (PVD) have received great interest as wear resistant coatings. In spite of many successful applications, especially on metal cutting tools, the mechanisms by which these coatings fail or degrade are poorly understood. The wear behavior of commercial titanium nitride coatings prepared by two different PVD evaporation processes were studied using the Dry Sand Rubber Wheel (DSRW) test and wood cutting tests. Their performance was compared with an electroplated chromium coating. Titanium nitride coatings were deposited on high speed steel substrates by two commercial PVD coating vendors. One vendor used an arc evaporation PVD process while the other used electron-beam evaporation. The thickness of these commercial titanium nitride coatings varied from 0.5 to 2.4 µm depending on the side of the sample. The thicker titanium nitride coating showed a higher wear resistance than the electroplated chromium coating. However, the thinner titanium nitride coatings did not perform better than the electroplated chromium. Macroparticles distributed on the titanium nitride coating surface were found to influence the initial deterioration of the thicker titanium coating, while microcracking observed on the surface of the thinner titanium nitride coating is believed to enhance coating removal. The electroplated chromium was found to degrade by uniform grooving wear in contrast to the titanium nitride coatings which deteriorated predominately by a spalling process. There was no difference in deterioration behavior or wear resistance observed between the arc-evaporated titanium nitride coating (0.7 µm thick) and the thin titanium nitride coating (0.5 µm thick) produced by electron-beam evaporation. The ranking of wear resistance in the wood cutting test among the different types of coatings was different from that of DSRW testing; with the Cr-coated cutters having the highest wear resistance, the Multi-Arc arc-evaporated TiN coating the second highest, and the Balzers electron beam evaporated TiN coating the lowest wear resistance. Coating deterioration was also found to be different from that observed in the DSRW test. Microcracking was not observed on the coating surface. The higher hardness of the abrasives used, the higher shear forces acting on the vicinity of the saw chain cutter tip, and substrate (AISI 8660) softening possibly accounted for the performance of titanium nitride coatings in the wood cutting testing. More extensive evaluation of the coating deterioration in both tests is recommended to realize a full understanding of these coatings and their behavior in abrasive environments.