Multilayer-Forming Behavior of Cr Nitrides and Carbides for Thermoreactive Deposition

Abstract

The effect of a nitride layer on the forming behavior of CrN and (Cr, Fe) 7 C 3 multilayers for thermoreactive deposition (TRD) was investigated. Plasma nitriding followed by TRD (PN-TRD) produced a larger coating thickness than the case of direct TRD with no plasma nitriding. For PN-TRD, an Fe 2-3 N layer of 10 µm in thickness was produced on AISI 52100 steels using plasma nitriding, followed by TRD using a mixed powder composed of 30 wt % Cr, 2 wt % NH 4 Cl, and 68 wt % Al 2 O 3 . During TRD at 800 • C, a CrN layer of 2 µm in thickness was formed along with a thin layer of mixed carbide (Cr 7 C 3 ) and nitride (CrN) on top. As the deposition temperature was increased to 950 • C, a new layer of Cr 7 C 3 was formed underneath the outermost layer composed of mixed Cr 7 C 3 and CrN. At 950 • C, a Cr-rich zone indicated a thickness of~7 µm. As the deposition time increased to 3 h at 950 • C, a new layer of (Cr, Fe) 7 C 3 was produced at the interface between the CrN formed at 800 • C and the base metal. This layer formed because of the abundant resources of Cr and C provided from the TRD powder and base metal, respectively. The multilayer and interface were concretely filled without the formation of voids as the TRD time increased to 6 h at 950 • C. The TRD process on a pre-nitrided layer was successfully applied to produce multilayers of CrN and Cr 7 C 3 .coating surface was deflected at the interface between the layers. However, PVD has the disadvantages of high cost and low adhesion compared to other coating technologies, such as CVD and TRD. CVD also has many process variables and a complicated device configuration. By contrast, TRD has the advantages of excellent bonding strength, simple equipment, and capability of mass production. TRD coating is performed in a heat treatment furnace at 800-1250 • C using carbonitride-forming powders, such as vanadium, niobium, tantalum, chromium, molybdenum, and tungsten. There are several process techniques incorporating salt baths, fluidized beds, and pack cementation [16]. In the surface treatment based on TRD, factors affecting the growth of the coating layer include temperature, time, powder composition, and base metal. The longer the time, the thicker the coating layer becomes, and the higher the temperature, the more the growth is promoted. The composition of the powder depends on the ratio of the mixed powders and the catalyst used [16][17][18][19][20][21]. To form a carbide, it is necessary for the base metal to contain at least 0.3 wt % C [18,22], and the carbide thickness becomes thicker as the C content increases [20,23]. Therefore, a multilayer having high hardness formed using TRD is more likely to be applied to the material that requires wear resistance, than that by PVD and CVD.In this study, we applied PN to increase the nitrogen content of the base material and a Cr-carbonitride multilayer with high hardness, corrosion, and wear resistance was formed on high-carbon steel through TRD coating [24,25]. In the TRD process, the integrity of the coating layer and ...

Surface Treatment Technology of Metals and Alloys

“…Technology of Metals and Alloys. All the presented subjects are multidisciplinary, and include shot peening treatment [1], electropolishing [2], low-pressure carburizing [3], oxi-nitrocarburization [4], abrasive blasting [5], hydrothermal treatments [6], laser cladding [7], plasma modification [8], low-temperature vacuum carburization [9], plasma electrolytic oxidation [10], and thermoreactive deposition [11].…”

“…This layer formed because of the abundant resources of Cr and C provided from the TRD powder and base metal, respectively. The multilayer and interface were concretely filled without the formation of voids as the TRD time increased to 6 h at 950 • C. The TRD process on a pre-nitrided layer was successfully applied to produce multilayers of CrN and Cr 7 C 3 [11].…”