چكيده به لاتين
The goal of the present research is to develop a wear-resistant Ti-Al-C-N coating using the plasma-assisted chemical vapor deposition (PACVD) and evaluate of the effects of various parameters; such as the ratio of the precursors and the deposition temperature on the structure, mechanical and wear properties of the prepared coatings. In addition, the relationship between the structure and the properties of the coatings was studied. In this study, H13 hot work tool steel substrates (DIN; 1.2344) were used. The steel substrates were subjected to plasma nitriding at 470 ˚C for 2 hours after the heat treatment. Then, the TiAlCN nanostructured coatings were deposited on the as-nitrided substrates using PACVD with the different chloride precursors’ ratio of AlCl3 to TiCl4 (x=AlCl3/TiCl4) and the different deposition temperatures. The coatings were deposited for 3 hours with a duty cycle of 33% and a frequency of 10 kHz. Then the deposited coatings were characterized by the XRD, FESEM, SEM, FT-IR, XPS, Raman spectroscopy, TEM and AFM. The microhardness and nanohardness of the coatings were measured by microhardness and nanoindentation test, respectively and the wear properties of them were investigated through the pin-on-disc wear test method. The results of the GIXRD, XRD, XPS, FT-IR, TEM and Raman analysis showed that the deposited coatings were consisted of the crystalline phases of fcc-TiN, fcc-(Ti,Al)(C,N), and w-AlN in addition to an amorphous carbon phase. Increasing x from 0.5 to 1 at a constant temperature of 350 ˚C led to the formation of a more grain-refined (by a reduction of 40 %) structure. It seems that decreasing the grain size can be related to the formation of a higher amount of the w-AlN phase, which can act as the heterogeneous nucleation sites for the formation of the fcc-TiN phase. Then, increasing x from 1 to 3 led to an increased grain size due to the formation of a higher amount of the w-AlN phase. Moreover, it was observed that the thickness of the coating was affected by three competing phenomena with increasing x at 350 °C: 1) the effect of decreasing the reaction rate owing to saturation of the surface with more TiCl4 and AlCl3 molecules, which results in decreasing the coating’s growth rate; 2) the decreasing effect of etching of chlorine molecules due to increasing the amount of the chloride precursors, and 3) the grain size effect. So that, the maximum coating thickness was 2.3 μm at x=0.5 and the minimum thickness was about 300 nm at x=1. In addition, the highest hardness value of about 3840±40 HV0.01 was measured for the sample with x=0.5 among the deposited coatings at the deposition temperature of 350 °C. Increasing the deposition temperature from 350 °C to 500 °C resulted in the increased amount of free carbon in the coatings and increased intensity ratio of the disordered peak to the graphite peak (ID/IG) in the Raman curve, which can be related to decreased amount of sp3 bonds of the free carbon phase. Also, increasing the deposition temperature from 350 to 425 °C resulted in decreasing of the crystallite size from 11 to 9 nm probably due to the further formation of the w-AlN and amorphous carbon phases. In fact, these phases, which locating at the grain boundaries of fcc-(Ti,Al)(C,N) grains, inhibit the crystallite growth. A further increase in the deposition temperature resulted in increasing the crystallite size to 13 nm. This increase can be related to the grain growth phenomenon at higher temperatures. Moreover, the thickness of the coatings changed with increasing the deposition temperature at x=0.5 due to two competing phenomena: first, the higher sputtering of the coating surface, which occurs due to the higher ion bombardment caused by increasing the voltage (which occurs due to higher temperature) in the plasma environment. Second, the grain size variation. So that the maximum coating thickness (about 2.3 μm) and the minimum coating thickness (about 1.7 μm) were achieved at 350 °C and 425 °C, respectively. Also, it was found that the maximum microhardness value of 4040±53 HV0.01 was obtained at 425 °C among the coatings deposited at x=0.5. According to the FESEM images, it seems that the mechanism of nucleation and growth of the deposited coatings is layered-island. However, for the coating deposited at the temperature of 425 °C, only a limited number of islands formed on the initial layer whereas, for the ones deposited at the temperatures of 350 °C and 500 °C, the islands covered the whole initial layer. The change of the chloride precursors’ ratio and deposition temperature affected the wear behavior of deposited coatings. The results showed that increasing x in the constant temperature of 350 °C, decreased the wear resistance of coatings due to the hardness and the thickness reduction. The delamination mechanism of deposited coatings by various chloride precursors’ ratio was recognized as fatigue type. The least specific wear rate of 1.8 × 10-4 mg/(N.m) was measured for the coating deposited at 350 °C with the x of 0.5. Also, the highest specific wear rate of 3.3 × 10-4 mg/(N.m) was related to the deposited coating at 350 °C with the x of 3. Besides, the smallest coefficient of friction of 0.16 was attained for the coating deposited at 500 °C and the x of 0.5.
