Preparation And High Temperature Oxidation Behavior Of Several Nano-multicomponent Nitride Coatings

With the rapid development of high-speed machining technology in China, demand for difficult-to-cut materials are increasing dramatically, such as cast iron, hardened steel, titanium alloys, stainless steel, etc., which leads increasingly requirements for selecting cutting tool’s materials. Besides, needs for increasing machining efficiency and environmental protection, people hope to machine with minimum or no cooling liquid. The temperature of the local cutting surface reaches to900-1000℃in the high speed machining, exceeding the temperature which ternary TiAIN、CrAlN coated tools can stand. Ternary coatings turn into nanosrystalline by addition of B and Si elements. The ability to withstand high temperature oxidation was improved significantly. At present, most studies are focusing on the impact of process parameters on the structure and mechanical properties of nano-composite and nano-multilayer coatings. However, research related to high temperature oxidation resistance is relatively lack.In order to further reveal the relationship between structure and coating properties, this research involves three kinds of coating:1) Based on TiAlN coating deposited by cathodic arc ion plating system, Si target is used for deposition of nano-composite TiAlSiN coating by using bipolar pulse power.2) CrTiAlN nano-multilayer coatings prepared by closed field unbalanced magnetron sputtering ion plating.3) CrAIN coating deposited using cathodic arc system is the research object, and AlTiSi target is used for deposition of CrTiAlSiN nano composite coating by arc target. High temperature oxidation behaviors of TiAlSiN, CrTiAlN and CrTiAlSiN coatings was investigated. Influence of Cr and Si content on high temperature oxidation behavior was studied. Surface morphology, composition and microstructure before and after high temperature oxidation was evaluated by SEM, EDX and XRD. Hardness of the composite coatings is evaluated using a nano-indentation system and vickers instrument. Adhesion of coatings was tested by rockwell indentation and scratch instrument qualitatively and quantitatively, respectively. Friction coefficient is estimated by wear tester.From the experimental results, the following phenomena can be observed: 1) Surface of TiAIN coatings were covered with loose TiO2oxide film after oxidation, Dense Al2O3scale layer formed on TiAlSiN coatings after oxidation. Si addition can reduce oxidation rate. TiAlSiN coatings showed higher oxidation resistance at high temperatures than TiAIN coatings.2) CrTiAIN coatings was deposited by closed filed unbalance magnetron sputtering ion plating. Uniform surface morphology and dense microstructure was observed. It was revelaed to be nano-multilayer columnar structure by TEM. The coating was mainly composed of fcc-CrN phase. CrTiAIN coatings showed excellent mechanical properties: hardness of2996Hv, interface adhesion being HF1, critical load>60N, friction coefficient as low as0.29. Mainly Cr2O3and Al2O3oxide layer formed on CrTiAIN coating after high temperature oxidation.3) At high oxidation temperatures, most of CrAIN coatings oxidized into Cr2O3at1000℃, while CrTiAlSiN coatings maintained structure stability. CrTiAlSiN coatings possessed excellent thermal stability at high temperature. It is expected that CrTiAlSiN coatings is a good candidate for industrial applications under harsh environments, such as high-speed dry machining.