Effects Of Content And Structure On High-Temperature Behavior Of Cr-Al-N Coatings

Advanced machining and processesing technology calls for coating tools with highhardness, strong adhesion and excellent oxidation performance. In recent years, much moreattention has been paid on Cr-Al-N hard coating over the world. In this paper, using pure Cr,Al, Ti and Cr30Al70（at.%） alloy targets, Cr-Al-N hard coatings with different structurearchitectures and composition modulation were deposited on M2high speed steel substratesby means of multi-arc ion plating. The microhardness, the adhesion strength between thecoating and substrate were tested by multi function tester of materials surface properties,microhardness tester. Eelectron microscopy, X-ray diffraction and electron probe analysissystem were used to characterize the constituent phases and microstructure of the coatingsbefore and after annealing. The main conclusion can be made:1. When substrate negative bias voltage and N₂pressure are fixed to be80V （duty cycle50%）,3.0×10^-1Pa repspectively, the Al content （x） in Cr_1-xAl_xN coatings can be modulatedin the range from0to0.60by controlling pure Cr, Al target currents in this paper. With thetarget current ratio I_Al/I_Crincreasing, the Al content in coatings almost increases linearly.2. Both monolayer CrAlN and graded CrAlN coatings exhibited dense columnar fractograph.Usually a columnar grain tranvers through the coating for the monolayer coating, while300nm thick short fiber-like columnar grain appears on the fracture surface of gradedCrAlN coatings.3. As compared to Cr_0.30Al_0.70N monolayer coating, the gradient structure architecyure ofgaraded CrAlN coatings is beneficial to mechanical properties. It is found that the hardessand adhesion force of Cr_1-xAl_xN/Cr_0.30Al_0.70N graded coating are improved by6.08%,16.70%respectively， and they are improved by4.78%,14.20%for Cr_1-xAl_xN/TiN/Cr_0.30Al_0.70N graded coatig.4. The mechanical properties of the CrAlN coatings decrease with increasing the annealingtemperature. When annealed below800℃, the Cr-Al-N coatings can hold2600³106HV0.01microhardness, and41⁶1N adhesion force. However, the mechanical propertiesdecline sharply when the annealing temperature is beyond800℃.5. As far as the oxidation resistance is concerned, the graded structure coatings are superior to the monolayer coatig. The oxidation behavior of all coatings obeys a parabolic law ofoxidation weight gain. It is found that the gradient structure pay much more contribution toimprove oxidation resistance of CrAlN based coating than the Al contentin the coatings. Itis the inward diffusion of Al in the graded coatings that depress the outward diffusion ofTi/Fe species, which improve the oxidation resistance of graded CrAlN coatings.