Optimization of Mechanical Properties of Cr3C2-Ni20Cr/Graphite Cold Sprayed Coatings

Abstract

This study analyzed the mechanical properties of cold-sprayed Cr3C2-25(Ni20Cr) blended with Ni-graphite as a solid lubricant deposited on 7075 aluminum alloy substrate. To optimize the coating properties, different sets of parameters (graphite content in feedstock, process gas composition, spraying distance, and traverse gun speed) were tested in the frame of the Taguchi experiment. The cold-sprayed coatings were evaluated for their chromium carbide and graphite content, hardness, and coefficient of friction. Analysis of the microstructure of the deposited coatings revealed that graphite as a soft and brittle component fills all voids in the coating and its quantity depends on its content in the feedstock. The experimental results show that the composition of the process gas has the greatest impact on the Cr3C2 content in the coating and the proportion of graphite in the sprayed blend directly affects its hardness. In the case of the coefficient of friction, the most significant parameters were the graphite content in the sprayed blend, the spraying distance, and process gas composition. The conducted verification experiment with the optimum parameter values allowed a coating with the highest hardness and the lowest coefficient of friction to be obtained.

The Effect of the Substrate on the Microstructure and Tribological Properties of Cold Sprayed (Cr3C2-25(Ni20Cr))-(Ni-graphite) Cermet Coatings

“…The results corresponded to the higher content of the ceramic phase and lower amount of the graphite built in these deposits and, thus, a greater strain hardening Ni20Cr matrix. This microhardness corresponds with that obtained by Żórawski et al [ 19 ], who investigated the same type of deposits, albeit cold sprayed from the feedstock powder containing a different graphite content, as well as using various spray parameters and working gas combinations. It was also in the range of microhardness (227 HV0.3 to 875 HV0.3) of cold sprayed Cr 3 C 2 -25(Ni20Cr) coatings produced with different parameters of the cold spraying process, but with the use of a powder of the same manufacturer [ 14 , 16 , 17 , 22 ].…”

“…The absence of discontinuities in deposits confirmed the good adhesion of the coatings to the substrates. The above-indicated microstructure features of (Cr 3 C 2 -25(Ni20Cr))-5(Ni25C) composite coatings were observed in the papers of Góral et al [ 16 ] and Żórawski et al [ 19 ], who described in detail the cermet deposit formation during the cold spray process. Image analysis performed using ImageJ software showed that the coatings deposited on the Al alloy substrate had 31.5 ± 1.9 vol.% Cr 3 C 2 and 1.6 ± 0.4 vol.% C, while the coatings deposited on the steel substrate had 32.3 ± 1.3 vol.% Cr 3 C 2 and 1.3 ± 0.2 vol.% C in their structure.…”

“…Cermet coatings containing ceramic particles embedded in a metallic matrix meet criteria such as anti-wear, high hardness, and compact microstructure with good adhesion [ 1 , 2 , 3 , 4 ]. Protective Cr 3 C 2 -NiCr deposits are manufactured mainly using plasma spraying and HVOF; however, cold spraying is increasingly becoming popular [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ]. This type of coating has been deposited on various substrates, usually on low-carbon steel [ 5 , 6 , 7 , 8 ], corrosion-resistant steel, and aluminium alloys [ 21 ], depending on the application of the working element.…”

“…The use of ceramics in the coating material allows the properties of the coatings to be improved. The literature data describing cold sprayed cermet Cr 3 C 2 -NiCr coatings show that, depending on the used substrates, they reveal various amounts of Cr 3 C 2 embedded in their structure and mechanical properties [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. For cold sprayed Cr 3 C 2 -25(Ni20Cr), the carbide content built in the deposit was in the range of 22.8–33.8 vol.%, whereas the hardness changed from 449 HV0.3 to 875.7 HV0.2.…”

“…They possess self-lubricating properties and improve the anti-wear properties of substrates. So far, there is limited data on Cr 3 C 2 -25(Ni20Cr) deposits containing graphite as a solid lubricant obtained in the cold spray process [ 18 , 19 ]. Therefore, a detailed examination of these coatings will fill the knowledge gap in this field and show how the used substrates affect the microstructure and properties of these cermet deposits.…”