Study of the Splat Microstructure, Splat-Substrate Interface, and the Effects of Substrate Heating on the Splat Formation for Ni-Cr Particles Plasma Sprayed on to Aluminum Substrates

Abstract

This study investigates the mechanisms of formation of plasma-sprayed coatings, through the study of splat morphology and the splat-substrate interface of NiCr single splats sprayed onto Al substrates, at both micro-and nano-scale levels, using a range of electron microscopy techniques. This study provides direct observation of extensive substrate melting, together with chemical inter-mixing with the splat and the formation of metastable interfacial phases (including both non-equilibrium phases and metallic glasses). In addition, voids and a range of oxide phases were observed. The mechanisms of formation of these features are discussed. Two aluminum alloys (with and without Mg additions) and three different sets of substrate surface conditions (polished, and heat treated prior to and during spraying) were used to investigate the variations in splat morphologies induced by the different preparation conditions. It was found that the heating of substrate during spraying significantly reduced splashing.

Effects of Substrate Roughness on Splat Formation for Ni-Cr Particles Plasma Sprayed onto Aluminum Substrates

“…However, from the EDS maps (3), it can be concluded that such layers may be composed mainly of alumina and a mixture of spinel (NiAl 2 O 4 and/or NiCr 2 O 4 ). Chromium oxide, notably Cr 2 O 3 , was often reported to form as a thin dense layer on top of NiCr splats in previous studies (Ref 5,8). Here, it was not observed on the TEM cross sections prepared; however, the possibility of its formation on other splats should not be ruled out.…”

“…Effects of a thermal treatment prior to plasma spraying on the substrate surface chemistry, roughness, and splat formation, were discussed in previous papers (Ref 8,39). In summary, it was found that such heat treatment increased the c-Al 2 O 3 content of the oxide layers already present on the surface, partially dehydrating them (reducing the hydroxide content), and increasing the thickness (a few nanometers), and roughness (slightly from about 7 to 8 nm).…”

“…Many studies have investigated these mechanisms by studying single splats sprayed onto smooth substrates ( . In particular, it was noted that localized melting of the substrate from the heat provided by the sprayed particle may occur, which may then lead to the formation of intermetallic compounds or the generation of nonequilibrium microstructures (Ref 4,8). In such cases, metallurgical bonding is achieved, and assuming that the interfacial phase is not brittle, this is then beneficial for adhesion strength ( Ref 1,2).…”

Research Progresses of Atmospheric Plasma Sprayed Splat

“…7 Surface topologies of stainless steel surfaces either non-oxidized or preoxidized at different temperatures, images of nickel splats after solidification and cooling curves of splats [39] 研究中遭到了否定。Li 等 [44] [28] Fig. 8 Grain size in a cross-section of the splat obtained in different ambient pressures [28] (a) on stainless steel in atmospheric pressure; (b) on gold-coated stainless steel in atmospheric pressure; (c) on stainless steel under low pressure; and (d) on gold-coated stainless steel under low pressure 特定体系和条件下才可能出现的现象, 如 Li 等 [47] 在大功率(>80 kW)喷涂条件下, 沉积在不锈钢表面 的钼金属熔滴会使下方的基体局部融化, 进而引起 熔滴在铺展过程中液态物质前进方向的改变, 使单 片层呈现溅射状。Brossard 等 [48] 在研究铝表面 Ni-Cr 熔滴铺展时发现界面处形成了中间相, 这种现象…”

Plasma-sprayed nickel splats on chromium substrates: The role of substrate preheating and thermal conductivity

“…In addition, during substrate preheating, the composition of surface oxides formed on the outer surface of the substrate may be modified in the process of vaporizing surface moisture/adsorbates [19][20][21][22][23][24][25]. Such changes in surface chemistry are critical because it is this very thin substrate surface layer that first interacts with the molten droplets.…”