Study on production of modified MCrAlY powder with nano oxide dispersoids as HVOF thermal spray feedstock using mechanical milling

Abstract

This paper investigates NiCoCrAlY-CeO 2 nanocomposite powders prepared by mechanical milling process. At first, micron-sized ceria powder was pre-milled to obtain nano-sized powders and then 1 wt% CeO 2 was mixed with the conventional NiCoCrAlY powder and milled under three sets of parameters. The conventional and milled powders were deposited on low carbon steel substrates by HVOF thermal spray technique. X-ray diffraction (XRD), scanning electron microscopy (SEM), fieldemission scanning electron microscopy (FESEM) and image analyzing method were used to characterize the prepared powders and coatings. Microstructural characterization showed that the milled powders underwent morphological and phase transitions. Through the microstructural and compositional analyses, it was found that a homogeneous distribution of CeO 2 nano-dispersoids in the NiCoCrAlY matrix was obtained. The resulting coatings showed that by using optimized milling parameters, required particle size and suitable morphology for thermal spray can be achieved.

A comprehensive study on the microstructure evolution and oxidation resistance of conventional and nanocrystalline MCrAlY coatings

“…Meanwhile, following increasing the milling these low-angle grain boundaries were transformed into the random-oriented nanostructures. Thus, by increasing milling time the crystalline size of the powder was progressively decreased until the final stage of milling (15 h) that the saturated particle size for the powder mixture was achieved 22 , 40 , 42 , 43 .…”

Effect of powder manufacturing process on characteristics of nanostructured MCrAlY coatings: dry vs. wet ball milling

“…Compared to the original spherical morphology, severe particle deformation can be clearly observed with the morphological transformation to the flaky particles. Despite the fact that the NiCoCrAlY powder is consisted of a ductile g-matrix with FCC crystal structure, the typical tendency for cold-welding was inhibited, primarily due to the active presence of ethanol [14]. Also, some micro-cracks were observed on the surface of particles (Fig.…”

“…This is mostly true for the larger particles which do not get as easily melted as the smaller ones. It is worth noting that the surface particles lack the impact pressure from the subsequent deposition pass; therefore, there is a higher possibility for the particles to experience a minor degree of deformation [14]. Moreover, splashed regions were also observed on the coating surface, as a result of molten particle impingement.…”

“…MCrAlY-type alloys (M: Ni and/or Co) are considered the state-of-the-art materials for thermal spray coatings and have proven to be effective in most engine applications [13]. Fur-thermore, it has been shown that MCrAlY coatings can be deposited by HVOF process, which enjoy equivalent, and sometimes superior, protection properties compared to the plasma-sprayed counterparts [14][15][16].…”

“…In this regard, some routes have been proposed and pursued by other researchers, some good examples of which are: powder processing, laser treatment, and shot peening [18][19][20][21]. Among these approaches, the powder processing via mechanical milling technique has been widely adapted due its simplicity and versatility [14,22].…”