Wear protection potential of TiN coatings for 304 stainless steels used in rotating parts during olive oil extraction

The aim of this study is to determine the damage mechanisms affecting 304L Stainless Steel (SS) parts used in olive oil production, and to evaluate the performance of TiN coatings in improving their resistance to these effects. Tribological behavior of 304L SS parts was investigated through pin on disc tests against olive seed counter bodies, both in uncoated state and after TiN coating via cathodic arc physical vapor deposition. Further assessment of tribological behavior was carried out through the means of an in house centrifugal testing setup, designed to simulate the environment encountered during the de­seeding step of oil production, and cavitation erosion tests with an ultrasonic probe. The results of pin on disc tests showed considerable wear damage of uncoated SS while TiN coated samples exhibit excellent wear resistance, with no visible damage to the coatings. Further results obtained from centrifugal tests indicated a damage mechanism related to impact from olive seed particles. Plastic deformation of the SS substrate surface was observed via SEM, both for uncoated and TiN coated samples, leading to fracturing of the TiN coatings and their subsequent removal in the latter. This observation is supported by the results of cavitation erosion tests, in which similar damage can be observed on TiN coated SS samples. The same test carried out on TiN coated high speed steel samples which have a higher substrate hardness than SS showed better resistance to fracture of the coating.