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Thin Films for Cutting Tools
Published in Fredrick Madaraka Mwema, Tien-Chien Jen, Lin Zhu, Thin Film Coatings, 2022
Fredrick Madaraka Mwema, Tien-Chien Jen, Lin Zhu
CrC just like its nitride equivalent is used in high temperature operations. It has high hardness, and excellent adhesive and abrasive wear resistance. The hardness of CrC thin films varies between 3.6 and 48 GPa depending on the method and processes of deposition [45]. It has been shown that the chromium carbide coating improves the tool hardness and wear resistance by close to 40% [46]. It has excellent resistance to oxidation and corrosion. It exhibits a low coefficient of friction and is therefore suitable for high abrasion conditions. The application of these coatings on working tools has greatly increased commercially, and they are currently being used in cores and mounds for die-casting of aluminium-based alloys. These coatings are also used on dies for plastic injection moulding. It has been used to coat cemented carbide tools for turning, drilling, and various operations [47].
Observations on the Role and Selection of Coatings and Surface Treatments in Manufacturing
Published in Ken N. Strafford, Roger St. C. Smart, Ian Sare, Chinnia Subramanian, Surface Engineering, 2018
Coatings produced by the TD process (see Table 13.4) are reported to exhibit many beneficial properties, including high hardness and a significant corrosion resistance, at least in cases where chromium carbide is formed as a surface layer [29]. The simplicity of its operation makes it economically favourable to many more hi-tech processes and has, in fact, been advocated as a possible alternative to PVD in tooling applications where dimensional accuracy is not paramount. Coating adhesion is reported to be superior to that of hard chromium plate. The main limitation of the process, however, is the allowance that must be made for distortion during heat treatment and the narrow range of appropriate substrate compositions. The hardening/tempering-induced volume changes, it has been suggested, can be avoided by preheating, tempering, and then final machining, presuming the size tolerance is tight enough to justify this approach.
Uranium Fuel Dissolution
Published in Reid A. Peterson, Engineering Separations Unit Operations for Nuclear Processing, 2019
Of the mineral acids required to dissolve uranium-based fuels, HNO3 also is desirable because of its compatibility with the stainless-steel equipment and compatibility with separations processing. Low carbon or carbon-scavenged austenitic stainless steels, frequently 304L, are attractive in nuclear chemical processing applications because of strength, ease of construction, relatively low cost, and broad corrosion resistance under the oxidizing conditions imposed by HNO3. The corrosion resistance is due to a passive layer of chromium oxide (Cr2O3) on the exposed metal surface (Decours et al. 1987; Fauvet et al. 2008). Carbon is always present to some extent in stainless steel. At above 0.03% carbon, chromium carbide (Cr23C6) forms during heat-treatment, such as welding, depleting the neighboring regions in the steel of chromium, preventing the formation of the protective Cr2O3 layer, and leading to enhanced corrosion in that region (Gupta 2017). Amounts of carbon in stainless steel are limited either by removal or by sequestration through carbon’s reaction with scavengers such as niobium or tantalum. Thus, for example, the dissolvers in the first reprocessing plants at the Hanford Site used 25-12 S-Cb stainless steel (DuPont 1944, 408), akin to type 309 austenitic stainless steel, with columbium (Cb; i.e., niobium) added to scavenge carbon. The Magnox fuel dissolver at Sellafield, UK, operating from 1964 until 1978, used 18-13-Nb austenitic stainless steel (18% chromium (Cr), 13% nickel (Ni), with carbon scavenged by niobium (Nb) addition). Also at Sellafield, the Thermal Oxide Reprocessing Plant (THORP) dissolver, designed for reprocessing of commercial light water reactor UO2 fuels, used nitric acid grade (NAG) low-carbon 310L stainless steel (25% Cr, 20.5% Ni, and 0.015% carbon) (Shaw 1990).
Effect of grinding on surface characteristics of HVOF-sprayed WC–10Co–4Cr coatings
Published in Surface Engineering, 2020
Parsa Pishva, Mehdi Salehi, Mohammad Ali Golozar
Nowadays, thermal spray coatings are used in various areas such as aircraft, automobile, gas turbine, steam turbine, chemical, and oil and gas industries [1,2]. The main application of thermal spray coatings, especially High-Velocity Oxygen Fuel (HVOF) coatings, is improving the wear and corrosion resistance of surfaces. Cermet coatings produced by HVOF are the most commonly used coatings for this purpose. Chromium carbide and tungsten carbide-based coatings are the appropriate replacement for hard chromium coatings, the most common coatings used to increase the corrosion and wear resistance of surfaces until a few years ago when their use was banned due to some environmental issues [3–7]. Because of the high velocity and the low temperature of powder particles during HVOF spraying, the decarburisation of the coatings produced by this process is very low. Also, the HVOF coatings have low porosity and high adhesion to the substrate [8,9].
Thermal treatment effect on structural and mechanical properties of Cr–C coatings
Published in Transactions of the IMF, 2018
M. Fellah, L. Aissani, A. Zairi, M. Abdul Samad, C. Nouveau, M. Z. Touhami, H. Djebaili, A. Montagne, A. Iost
During the last decade, transition metal carbides and nitrides with good mechanical properties have started to make their mark in surface engineering.1 They have attracted much attention due to their excellent mechanical and physical properties such as high hardness (about half that of diamond), high melting temperature, high chemical and thermal stability, good wear and corrosion resistance.2 The hard chromium carbide coatings produced by physical vapour deposition,3 chemical vapour deposition4 or by means of electrodeposition techniques5,6 with a few microns thickness, have enhanced the mechanical resistance of various parts. For example, Zhou et al.7 discovered that chromium and ternary chromium carbide films are effective in protecting steel and various alloys from chemical attack.
Corrosion behaviour of detonation gun sprayed cermet coatings on AA5083
Published in Surface Engineering, 2021
T. Arunnellaiappan, S. Baskaran, S. Arun, R. Prithivirajan
Nowadays, cermet coatings have been widely employed on aluminium alloys to protect it from localized corrosion and also improves its wear resistance. A wide range of coating techniques such as high-velocity oxygen fuel (HVOF) [5], plasma spraying [6], cold spray [7], plasma electrolytic oxidation [8], and detonation gun coating [9] have been used to produce different cermet coatings on steel and aluminium alloys. Each coating has its own merits and demerits. Among all the coating techniques, denotation gun coating offers better properties such as dense coating with least porosity (<1%), very less oxidation, and good adhesion [10]. Carbide particles such as tungsten carbide (WC), chromium carbide (Cr3C2) are preferred for cermet coatings with Co, Co–Cr, and NiCr matrix. Hard carbide particles improve the strength and hardness, while metal binders enhance the plasticity and toughness of the coatings. Cermet coatings such as WC–Co, WC–Co–Cr, and Cr3C2–NiCr are being considered as a viable replacement for toxic chromate coatings, especially in marine applications. da Silva et al. [11] investigated the mechanical and corrosion properties of WC–Co coatings, produced by cold gas sprayed on AA7075 and found that the coating produced with WC–25Co remains unaltered even after 3000 h of salt spray fog. Magnani et al. [12] fabricated WC–Co coating on AA7050 using HVOF technology and studied the influences of the spray process parameter on electrochemical corrosion properties of the coatings. Jalali et al. [13] studied the effect of spraying temperature on the corrosion resistance and wear behaviour of thermal sprayed WC–Co coatings. Based on their experimental results, it was concluded that the amorphous phase of WC–Co enhanced the corrosion resistance of the coating. Recently, the effect of Cr addition with WC–Co powder on the corrosion properties of thermal sprayed coatings is being investigated [14]. The results showed chromium-containing coatings (WC–Co–Cr) improved the corrosion resistance. Generally, the chromium-containing coating provides excellent corrosion resistance. Chromium can be added in the form of chromium carbide or as an alloying element into the cermet coating. Mudgal et al. [15] studied the corrosion properties of D gun sprayed Cr3C2–NiCr coatings and found that chromium oxide and NiCr2O3 phases were formed on the coating structure and that exhibited better corrosion resistance.