The crystalline structure, hardness and thermal stability of AlN/CrN superlattice coating prepared by D.C. magnetron sputtering

AlN/CrN nanoscale multilayered superlattice coatings have been deposited on M2 HSS by reactive D.C. magnetron sputtering with Al and Cr targets under Ar and N2 atmosphere. The bilayer period of the coatings was controlled from 2.0 nm to 11.7 nm by changing rotation speed of the substrate holder. The crystalline structures of the AlN and CrN single layer were würtzite and B1, respectively, whereas the AlN/CrN nanoscale multilayered superlattice coatings were stabilized to B1 structure, irrespective of bilayer period within the experimental parameter range. The maximum hardness, 40 GPa, could be obtained for the AlN/CrN nanoscale multilayered superlattice coating with the bilayer period of 3.8 nm, which is much higher than those of AlN and CrN single layer coatings. After heat-treatment at high temperatures in air, the AlN/CrN nanoscale multilayered superlattice coatings have shown excellent oxidation resistance compared with AlN and CrN single layers.