Scratch and cyclic impact testing of adhesion PLD coatings, Ti-N on SS316L substrate

ABSTRACT The paper reports about an attempt to improve the characterization modality of adhesion and cohesion of TiN coatings coated on the femoral heads of total hip prostheses. It has been used both scratch test and normal and inclined impact test, to evaluate adhesion resistance of the PLD (pulses laser deposition) TiN coatings. The assessment was made on the flat cylindrical stainless steel SS 316L TiN coated. Scratch tests were done on a tester with a spherical head of diamond, with a radius of 2 mm using a cyclic impact system developed at the Institute of Solid Mechanics of the Romanian Academy. This was seen in particular the failure mechanism of the coatings, by scratching and cyclic impact tests. For the impact test, was used a cylindrical indentor wih spherical head by Cr carbide, with 3 mm diameter. Have been tested thin TiN layers of coating deposited after 5000, 10000 and 20000 laser pulses, on flat cylindrical samples of SS316L stainless steel, medical grade. After the test, the samples were observed both on an optical microscope, through AFM, and a scanning electronic microscope to investigate the failure of the coatings. All four samples were presented in both tests, both cohesion and adhesion failures. Experimental results have highlighted the fact that the TiN coatigs, deposited to 20000 pulses have presented the best resistance to scratching and impact. Impact tests also showed pitched the fact that exercising a tangential to the scope of contacts, has major effects upon critical events faced by coating. The aims of this work was to capture the critical event of the transition from the coating elastic deformation at its exfoliation and remanent plastic deformation of the substrate.