Mechanical properties and fracture toughness of multilayer hard coatings using nanoindentation

The nanoindentation fracture of multilayer hard coatings of TiN/Ti(C,N)/TiC, Al2O3/TiC/Ti(C,N)/TiC, TiN/Ti(C,N)/TiC/Ti(C,N)/TiC and TiN/Ti(C,N)/TiC/Ti(C,N)/TiC/Ti(C,N)/TiC, deposited on cemented carbide using a CVD technique was studied. Based on an analysis of the energy released in cracking, the calculated fracture toughness values of these coatings were 2.18, 1.74, 3.40 and 3.90 MPa m(1/2), respectively. Both load-penetration depth and load-penetration depth squared plots have been demonstrated to be necessary if a more complete understanding of the coating system behaviour is to be gained. The interfacial failure and the critical load of interfacial failure of these coatings were also discussed. a step was found in the force-displacement curves at the onset of coating fracture. A straight line segment in the load-penetration depth squared curves was discussed. The hardness, fracture toughness and anti-wearability of these coatings were compared. The results show that the fracture toughness and anti-wearability are getting higher with the layers increasing. (C) 2000 Elsevier Science S.A. All rights reserved.