Microstructure, Oxidation and Tribological Properties of TiAlCN/VCN Coatings Deposited by Reactive HIPIMS

摘要

2.5μm thick TiAlCN/VCN coating was deposited in industrial size machine equipped with HIPIMS power supplies. Prior to the coating deposition the substrate surface was pretreated by bombardment with V~+ ions generated in a HIPIMS discharge. A 300 run thick TiAIN base layer was deposited by operating one magnetron in HIPIMS mode in Ar+N_2 atmosphere. TiAlCN/VCN was deposited in mixed Ar+N_2+CH_4 reactive atmosphere utilising two opposing magnetrons furnished with TiAl and V targets operated in HIPIMS mode. XTEM analysis of the as deposited coating revealed the formation of three zones with different nanostructures across the film thickness. In the initial stages of deposition a TiAlCN/VCN nanoscale multilayer structure was formed (first zone) followed by a nanocomposite structure comprising TiAlCN/VCN crystalline grains surrounded by a carbon rich tissue phase (second zone). The grain size ofthe crystalline phase gradually decreased with thickness from diameter of 10~(-15) nm to complete dissolution in the third zone where Me- carbon with XRD amorphous structure was formed. Raman spectra with UV eτ_citation (A,=325 nm) taken from the top zone 3 ofthe coating revealed the graphitic nature of the coating showing clearly the G and D peaks at 1577 cm~(-1) and 1396 cm~(-1) respectively with IG/ID intensity ratio of about 0.94. This unique three zone nanostructure is believed to develop due to the progression ofthe target poisoning effect during the HIPIMS deposition. In dynamic oxidation conditions, thermogravimetric analysis determined the temperature of the onset of rapid oxidation to be 800°C. Compared to UBM deposited TiAlCN/VCN coating, the oxide mass gain of the HIPIMS coatings was less than 50 %. High temperature pin-on-disc tests revealed that the COF of HIPIMS deposited TiAlCN/VCN initially increases to μ=0.8 at 200°C followed by reduction to μ=0.45 at 650°C. Owing to their denser microstructure and enhanced oxidation resistance, HIPIMS deposited TiAlCN/VCN show superior performance at elevated temperatures of 650°C, (Kc=1.0 × 10~(-13) m~3N~(-1)m~(-1)) over the UBM deposited ones (Kc=5.8 × 10~(-13) m~3N~(-1)m~(-1)).