Abstract
Engine pistons are working components subjected to very high wear actions, mechanical and thermal stresses; moreover they can suffer damages due to pinking. Many solutions have been proposed, but there is still a large margin of improvement and strong efforts are made for improving performances and service life, taking into account for the requirements of fuel composition and of environment. Advantages can be obtained by the utilization of thermal spray coatings as protection against corrosion and pinking damages; on this matter the evolution of thermal spray processes and techniques offers suitable means. The aim of this paper is to evaluate the possibility to coat with NiCr alloys or with austenitic stainless steel (AISI 316L) the surface of engine pistons made by Al alloys. Coating layers, with thickness in the range of 200 ÷400 µm, have been sprayed, using Plasma Spray processes, on samples for metallographic investigation end test and on pistons directly. Optical and Scanning Electron Microscopy analyses were carried out on the cross sections to examine the microstructural features, while the hardness properties have been evaluated by means of both surface and cross-sectional measurements. Bend test is in progress to get information about the coating strain as well as about adhesion of the coating to the substrate. Finally the tested coatings have been applied directly on pistons and these are being tested on the test bench, evaluating the improvement of the service life.
