Investigation of the residual stresses and mechanical properties of (Cr,Al)N arc PVD coatings used for semi-solid metal (SSM) forming dies

In many cases, high compressive stresses are an unwanted side effect of deposited PVD coatings, because they are known to reduce the adhesive strength of the coating on the substrate. However, in some applications a main focus of the PVD coatings consists of bringing the surface of a substrate into a compressive state. A surface being in a compressive state is more likely to withstand thermal and mechanical alternating stresses within the surface and has a higher resistance against forming cracks and increases the life span of semi-solid metal forming (SSM) dies. Arc ion plating is a PVD process, which is known to cause high compressive stresses in coatings due to its high ionisation rate and the applied bias voltage to the substrate. Therefore, the arc ion plating process is suitable for bringing a surface of a substrate into a compressive state. The investigated (Cr,AI)N coatings were deposited in such an arc ion plating PVD process and the thickness varies from 2.7 to 17 mum. The correlation of thickness vs. residual stresses of these coatings was investigated. In order to determine these residual stresses a stripe bending test is backed up and compared with a XRD stress analysis. Additionally, the coatings were exposed to impact tests to determine the influence of compressive stresses on the wear behaviour caused by alternating stresses. (C) 2002 Elsevier Science B.V. All rights reserved.