This paper aims to clarify the development and characterization of cold-sprayed aluminum coatings on a non-regular medium-carbon steel surface. The work is carried out with a two-fold purpose: to optimize the deposition process and coating thickness and to learn how substrate defects and imperfections influence coating performance and the corrosion resistance of the coated material.

Invar alloy (Fe – 36%Ni) is used in industrial applications which require high dimensional stability because of its exceptionally low thermal expansion coefficient. Purpose of this work is to enhance the performance of molds for the production of carbon fiber reinforced plastic (CFRP) components. Four different kinds of commercial powders were coated on an Invar substrate: Al 2 O 3 - 12TiO 2 , Cr 2 O 3 and ZrO 2 - 8Y 2 O 3 by Air Plasma Spray (APS) and WC - CoCr by High Velocity Oxygen Fuel (HVOF). Metallographic microscopy observation and SEM analysis were carried out and microhardness and fracture toughness were evaluated by means of the micro - indentation method. Friction behaviour and wear resistance were evaluated in dry sliding conditions with Pin On Disk apparatus for not coated Invar substrate and for the different coated substrates. Chromium oxide and tungsten carbide coatings exhibited higher mechanical characteristics respect to the other coatings: chromium oxide had the higher hardness value and tungsten carbide the higher fracture toughness. Tungsten carbide coating had the lower average coefficient of friction and together the chromium oxide the lower wear mass loss and wear rate. Among APS ceramic coatings, Cr 2 O 3 exhibited the best mechanical and tribological behavior while the HVOF cermet coating exhibited the best behavior among all the coatings.

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.

The degradation of materials, connected to ageing and wear, can be limited by suitable treatments aimed at the increase of surface properties Among the surface modification techniques thermal spraying processes allow a lot of advantages improving the performance and extending the life of materials and components. The convenience for the substitution of nodular cast iron with coated steel for the manufacture of rolls to be employed in a rod mill plant was studied by means of disk on disk wear tests on plain carbon samples coated with the fuse and spray technology, using 7 different type of nickel or cobalt based powders, comparing their wear resistance with the behaviour of nodular cast iron specimens. On the basis of the wear tests, the most promising coating materials were applied to steel rolls and their behaviour and duration on a rod rolling plant were compared with those of nodular cast iron rolls. The rolls coated with nickel based alloy admixed with WC-Co powder reached the best performance, with a duration about 40 % higher than the cast iron ones.