Abstract
This study reports the high temperature erosion-oxidation (E-O) behavior of conventional and nanostructured Cr3C2-25(Ni-20Cr) coatings prepared by high velocity oxygen fuel (HVOF) spraying. As-received and nanostructured Cr3C2-25(Ni-20Cr) powders with mean crystallite sizes of 145 nm and 50 nm respectively, were used to prepare 120 - 200 µm thick coatings on AISI 310 samples. The E-O behavior of the coatings prepared with the as-received (AR) and nanostructured (NS) powders was determined as weight change in a custom designed rig at room temperature, 450, 700 and 800 oC. The Vickers microhardness, Young's Modulus and fracture toughness of the AR and NS coatings were determined, and the NS coatings exhibited higher values compared with the AR coatings. The E-O resistance of the NS coating was higher than that of AR coating at all temperatures, and particularly at 800 oC. The increase in E-O resistance of the NS coatings is due to its superior mechanical properties as well as to the presence of some heterogeneities in the AR coatings. The E-O mechanisms of both types of the coatings are discussed, with special attention to that at high temperatures. The results suggest that at 800 oC the E-O process is controlled by erosion of the oxide.
Highlights
In many engineering fields there has been a steady increase in demand for materials with enhanced physical properties
The coatings revealed a uniform structure with good distribution of the carbides in the binder phase and the typical lamellar structure often observed in coatings produced by the high velocity oxygen fuel (HVOF) process
It is important to note that the oxide films which form between “splats” during the coating process - quite distinct from the oxide layer that forms on the surface upon exposure to high temperatures - weaken the microstructure in terms of the erosion process, given that the regions close to the oxide films are more susceptible to de-cohesion during impact of erodent particles
Summary
In many engineering fields there has been a steady increase in demand for materials with enhanced physical properties. In this context, the pioneering work of Benjamin et al[1,2] that established the process which became globally known as “Mechanical Alloying” has produced materials with superior mechanical properties, and this process has since evolved considerably. A variety of techniques have been used to prepare chromium carbide based coatings and the high velocity oxygen fuel (HVOF) process is widely used, as it produces smooth, low porosity, dense and adherent coatings, without altering significantly the integrity of the carbide particles[11,15,16]. Brandt[17] investigated the effects of different HVOF spraying parameters on the fatigue resistance
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