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The effect of applied load on the tribological behaviors of single DLC coating and DLC/Cr 3 C 2 –NiCr duplex coating was explored in the paper experimentally, and the role of cermet interlayer on the duplex coating tribological behavior was analyzed from the perspective of carbonaceous transfer film formation. Results proved that the duplex coating wear rate under 20 N was the lowest, about 1/6 of that of the single coating. The existence of Cr 3 C 2 –NiCr interlayer can prevent the top DLC film from being damaged in high load friction, reduce the fluctuation and vibration of the friction interface, and help the friction-induced graphitized carbonaceous transfer film to maintain on the friction counterpart, thus realizing the low-friction of the duplex coating. Furthermore, the critical conditions under which the friction-induced carbonaceous transfer film of a single coating maintains on the friction counterpart are explored by designed experiments. Results show that the carbonaceous transfer film derived from the single coating can only maintain on the friction counterpart under conditions of low load, low sliding frequency, and high humidity, which indirectly confirms the excellent tribological performance of the duplex coating. [ABSTRACT FROM AUTHOR]

To supply wear-resistant coatings on AISI 310 austenitic stainless steel for harsh industry applications, Ni3Al intermetallic compound coatings were prepared by high-velocity oxygen fuel (HVOF) spraying. Ni3Al coatings were deposited under different oxygen/fuel ratios of 4.45, 4.89 and 5.34. The phase structure, microstructure, mechanical and tribological properties of the coatings at 25 °C were investigated firstly. As a result, the HVOF oxygen/fuel ratio of 4.89 was chosen to get the best physical properties of an average porosity 1.0 vol.%, thickness 290 μm, hardness 527 ± 16 HV, friction coefficient 0.75 and wear rate 1.74 × 10− 5 mm3/(N·m). Then tribological tests across a wide temperature range from 25 to 800 °C were carried out on the optimized coating: the coating presented the highest anti-friction and wear resistance at 600 °C, a continuous and dense oxide layer comprised of NiO, Ni2O3, Al2O3 and NiAl2O4 was formed and acted as a solid lubricant, and contributed a relatively low friction coefficient of 0.57 and wear rate of 8.91 × 10− 5 mm3/(N·m). The wear mechanisms were mainly tribo-oxidation wear and slight abrasive wear. [ABSTRACT FROM AUTHOR]

A Fe-based amorphous coating was successfully deposited on an AZ31B magnesium alloy substrate by detonation spraying. The microstructure and sliding wear behavior of the coating were investigated in detail under dry conditions in ball-on disk mode by using a Si3N4 ball as the counterpart. It was found that the Fe-based amorphous coating presents an almost perfect amorphous structure, and the thickness, microhardness, porosity and amorphous content are 200 ± 30 μm, 825 ± 15 Hv0.1, 1.0% and 89.3 ± 2%, respectively. The dry sliding wear tests indicate that the Fe-based amorphous coating presents a fairly low dry sliding wear rate of 3.14-11.5 × 10−6 mm3 N−1 m−1, which is two orders of magnitude lower than that of the AZ31B substrate under a normal load of 5 N and at a sliding speed of 0.25 m/s. This distinguished wear resistance is mainly attributed to the fact that the Fe-based amorphous coating prepared by detonation spraying has an extremely low porosity and high amorphous phase content. Moreover, as the increase in load and sliding speed, the dry sliding wear mechanism of the Fe-based amorphous coating changes from fatigue wear and oxidative wear to delamination wear and oxidative wear. [ABSTRACT FROM AUTHOR]

Preparation of duplex coating is an innovative way to improve components surface in terms of mechanical and tribological properties by the combination of high velocity oxy-fuel (HVOF) and physical vapor deposition (PVD) technologies. The present work focused on the construction, mechanical properties and high temperature tribological behaviors of the duplex coating consisting of a thick HVOF Cr3C2-NiCr interlayer and a thin PVD TiN top layer, as well as compared it with the Cr3C2-NiCr coating and the single TiN film. The results showed that the Cr3C2-NiCr/TiN duplex coating exhibited higher hardness, elastic modulus, H/E and H3/E2 ratios and superior load-bearing capacity than the single TiN film. The introduction of Cr3C2-NiCr intermediate layer did not affect the microstructure of TiN film but significantly improved the adhesion strength between TiN film and substrate, as well as the wear resistance sliding against WC ball at different temperatures. In addition, the friction and wear mechanism of the Cr3C2-NiCr coating, TiN film and Cr3C2-NiCr/TiN duplex coating was revealed by investigating the friction-induced morphological and structural evolutions of the sliding surface at elevated temperature. [ABSTRACT FROM AUTHOR]

To improve the corrosion resistance of Q235 carbon steel in 3.5 wt.% NaCl solution, an Fe-based amorphous coating was deposited on the surface of Q235 carbon steel by detonation gun (D-gun) spraying method. It was found that the coating showed a typical amorphous phase with hardness of about 850 Hv. The morphology of the microdomains showed that the coating was dense, contained no visible defects, and its porosity was about 0.7%. The micro-regional element analysis indicates the formation of Cr7C3 during the spraying process. Compared with Q235 carbon steel, electrochemical tests show that the coating has higher pitting corrosion potential (− 296 versus − 914 mV for Q235 carbon steel), and lower corrosion current density (1.7 versus 24.6 μA/cm2 for Q235 carbon steel), and larger polarisation resistance (11,306.8 versus 1,821.1 Ω cm2 for Q235 carbon steel), indicating that the coating is more resistant to corrosion. XPS analysis shows that the coating forms a passivation film, rich in Cr and Mo, in the 3.5 wt.% NaCl solution. It exhibits excellent corrosion resistance, and limits the severity of corrosion, of carbon steel. [ABSTRACT FROM AUTHOR]

Duplex coating consisting of a Cr 3 C 2 -NiCr interlayer and a top DLC film was prepared using the high-velocity oxyfuel (HVOF) spraying and a closed field unbalanced magnetron sputtering (CFUBMS). The electrochemical behaviors of the Cr 3 C 2 -NiCr/DLC duplex coatings in 3.5 wt% NaCl solution was investigated by comparing it with a single DLC film and a single Cr 3 C 2 -NiCr coating. Then the role of cermet interlayer on the anticorrosion mechanism of the duplex coatings was explored. Results showed that introducing the cermet interlayer increased the surface roughness of DLC films without changing its microstructure. In the dynamic potential polarization test, duplex coatings maintained high surface integrity even after corrosion, and corrosion only occurs in localized areas. The inclusion of an interlayer avoided substrate corrosion caused by penetrating cracks and therefore provided excellent corrosion resistance. • The top DLC film covers the pores of the Cr 3 C 2 -NiCr coating. • The corrosion occurs the island boundaries, but duplex coating remains dense surface. • Oxide of Cr and Ni protects the coating system from diffusion of corrosive ions. [ABSTRACT FROM AUTHOR]

Effects of carbide content on the mechanical and tribological properties of DLC/Cr 3 C 2 –NiCr duplex coatings were systematically investigated. Results revealed that cermet coating with high carbide content provided strong support for the top DLC film by bearing most of the contact stress, thus improving its hardness, load-bearing capacity, and adhesion strength. The increased carbide content increased the contact and shear stresses on duplex coating during the friction process, intensifying the graphitization of the top DLC film but inhibiting the formation of a graphitized transfer film on the counterpart, thus slightly increasing its friction coefficient. However, the predominant wear mechanism changed from high-efficiency abrasive wear to low-efficiency adhesive wear for low to high carbide content, superior wear resistance was thereby achieved. [Display omitted] • Effects of carbide content on mechanical and tribological properties of duplex coatings was systematically studied. • Contact stress distribution in duplex coatings during the load-bearing process was clarified by FEM analysis. • Tribological mechanisms were revealed from many aspects of energy description, phase transition and contact mechanics. [ABSTRACT FROM AUTHOR]

Nanomultilayered WC/a-C coatings with modulation period raning from 1.3 to 11.5 nm were successfully fabricated using unbalanced magnetron sputtering process and the evolution of their microstructure, mechanical and tribological properties with the modulation period were systemically investigated. It has been demonstrated that the columnar structure in WC/a-C nanomultilayers originates from the surface irregularities of intermediate Cr/WC/C layer and the column diameter is correlated with the initial Cr layer thickness in this intermediate stage. Hardening and toughening through the nanomultilayer structure design have been achieved and particularly pronounced when the modulation period ranges from 5.8 to 10 nm. The enhanced hardness and fracture toughness are mainly attributed to dislocation/crack pinning effect from the thin individual layer and the heterointerfaces between WC and a-C layers. It is also found that the more heterointerfaces, the lower internal stress. What's more, the WC/a-C nanomultilayers with small modulation period (≤5.8 nm) exhibit low COF about 0.05 and good wear resistance due to the interfacial sliding between a WO 3 -rich tribofilm and a carbon-rich wear surface; once the modulation period above 5.8 nm, it fails to build up such a low friction interface between the tribopairs, which combining with the high intrinsic friction caused by its own structure characteristics result in high COF about 0.18–0.2 and poor wear resistance. [ABSTRACT FROM AUTHOR]

To promote the application of Fe-based amorphous coating (AMC)-protected magnesium alloys in fretting wear conditions, a Fe-based AMC with a thickness of about 164 μm was deposited on AZ31B magnesium alloy substrate by detonation spraying. The microstructure and fretting wear behaviors against GCr15 counterpart ball in different frequencies of the Fe-based AMC were studied in detail. The results show that the Fe-based AMC has a substantially complete amorphous structure, the porosity and surface hardness are ≤1.2 vol %, and 764.7 ± 37.5 Hv 0.1 , respectively. Therefore, the Fe-based AMC presents excellent fretting wear resistance, and its wear rate is almost 1/10 of that of AZ31B magnesium alloy, and 1/5 of that of high-velocity oxygen-fuel sprayed 316L stainless steel coating on AZ31B magnesium alloy substrate. The fretting wear behavior of Fe-based AMC was found to be sensitive to the fretting frequency: as the frequency increases from 5 to 100 Hz, the average steady-state friction coefficient increases from 0.77 to 1.07, but the wear rate exhibits an anomalous phenomenon, decreasing from 5.26 × 10−5 mm3N−1m−1 to 3.47 × 10−5 mm3N−1m−1. The improvement in wear rate is mainly attributed to the formation of an oxygen-rich river-like friction layer on the worn surface as the transient contact temperature increases with frequency, effectively suppressing delamination wear. Additionally, the occurrence of high transient frictional temperatures at high frequencies leads to evident crystallization within the coating, accompanied by the formation of nanocrystals, oxide films, and a large area river-like friction layer consisting of debris-compacted layers, which strengthens the Fe-based AMC. Consequently, the wear mechanism changes from delamination wear and abrasive wear at low frequencies to oxidative wear and adhesive wear at high frequencies, resulting in superior fretting wear resistance of the Fe-based AMC at high frequencies. • The synergistic effect of crystalline and oxidized phases increase the average microhardness of the worn surface. • The friction coefficient is positively correlated with fretting wear frequency, while the wear rate is opposite. • The wear mechanism transitions from delamination and abrasive wear to adhesive wear and oxidative wear. [ABSTRACT FROM AUTHOR]

• Steel was coated with Fe-based amorphous coating (AMC) by detonation spraying • This technique worked well: the coating was thick, hard, smooth, and dense • We performed nanoindentation creep tests on the Fe-based AMC • Viscoplastic and anelastic creep responses varied with indentation loading rate • There were two kinds of anelastic creep, corresponding to two relaxation processes A very thick (∼1 mm) coating of Fe-based amorphous material was applied to a Q235 steel substrate by detonation spraying. The rate-dependent anelastic and viscoplastic deformations of the coating were investigated through nanoindentation creep experiments with loading rates of 0.1∼5 mN s−1; the results were analyzed using the Maxwell-Voigt model with two Kelvin units. Creep deformation in the Fe-based amorphous coating was found to be sensitive to loading rate; the nanohardness, creep-stress exponent, and viscosity lessened with increased loading rate during viscoplastic deformation. The presence of two characteristic peaks in the relaxation-time spectrum shows that the anelastic deformation was related to the activation of two types of defects. Low loading rates promoted the activation of defects in the soft region with long relaxation times; larger loading rates promoted the activation of defects in the hard region with shorter structural relaxation times, allowing plastic deformation. This resulted in lower creep resistance at higher loading rates. [ABSTRACT FROM AUTHOR]

A top DLC film was deposited on the surface of Cr 3 C 2 -NiCr coated 38CrMoAl steel substrate, and the effect of Cr 3 C 2 -NiCr cermet interlayer thickness on the mechanical and tribological properties of the duplex coating was investigated by experimental analysis and finite element modeling (FEM). Results shown that, compared with single DLC film, the load-bearing capacity and tribological performance of DLC/Cr 3 C 2 -NiCr duplex coating were significantly improved, especially its anti-wear performance was nearly ten times higher than that of the single DLC film. Moreover, the duplex coating with an optimum cermet interlayer thickness of 100 μm showed the best comprehensive performance. FEM analysis also shown that the presence of Cr 3 C 2 -NiCr cermet interlayer limited the stress concentration area within the interlayer, which made the stress concentration area far away from the interface of DLC film and cermet interlayer, thus improved duplex coating durability. What's more, the cermet interlayer thickness increase resulted in the contact stress on DLC film increase, which contributed to the improvement of its tribological performance. • C100 duplex coating achieved superior mechanical and tribological properties. • C100 duplex coating anti-wear rate is ten times higher than single DLC film. • Stress concentration in C100 is the farthest against film/cermet interlayer interface. • Thickened interlayer increased contact stress and intensified DLC graphitization. [ABSTRACT FROM AUTHOR]

The Fe-based amorphous amorphous coating with a thickness of 150 μm was prepared by detonation spraying. Under a constant strain rate (0.01 s−1 and 0.50 s−1) and a holding time of 50 s, the Fe-based amorphous coatings were subjected to room temperature nanoindentation creep tests with the penetration depth varying from 50 nm to 500 nm, then the depth-dependent creep deformation mechanism of Fe-based amorphous coating during nanoindentation tests were investigated in detail. The results show that the creep responses of coating obviously depend on the indentation penetration depth (h p) and the indentation load rate, i.e., the creep displacement of coating increases with the increase of h p and loading strain rate. This is mainly due to the rapid increase in the shear transition zone volume of the coating as the h p increases, making it easier for the shear band to be excited to nucleate, and results in an obvious creep deformation. Moreover, at high strain rates, the initiation rate of the free volume in the amorphous coating far exceeds its annihilation rate, resulting in a large amount of excess free volume in the amorphous coating, which makes it easier to excite multiple shear bands in the amorphous coating and cause creep plastic deformation. • Fe-based amorphous coatings were deposited by detonation spraying. • The amorphous coating displays a very significant indentation size effect. • Lager shear transition zone volume induces the multiple initiations of shear bands. • Free volume is more likely to accumulate and promote creep at high strain rates. [ABSTRACT FROM AUTHOR]

Fe-based amorphous coating is deposited on invar steel substrates using detonation spray and then through the cryogenic cycling (CCT) treatment from 0 to 60 cycles with the interval 10 cycles. Effects of CCT on microstructure, thermal properties, mechanical and tribological properties were investigated. It was found that, all the coated samples with CCT are still well bonded with the invar steel substrate, except for the surface of C60 appears local cracks. Moreover, it also found that although CCT did not significantly change the phase structure of the amorphous coating, CCT promoted the rejuvenation behavior in the amorphous coating, which also led to the heterogeneity of the internal structure. Attributed to this heterogeneity, it promotes the generation of a large amount of free volume in the amorphous coating, which results in a significant change in the toughness and resistance to crack propagation of the amorphous coating. And after 50 CCT cycles, the amorphous coating has undergone an obvious ductile-brittle transition, which has the highest fracture toughness K IC and plastic work W p value. The COF and wear rate of coatings increased initially, then followed by a decrease, but then again increased with the increase of CCT cycles. The 50-cycles coatings exhibited the lowest COF (0.60) and wear rate (0.56 × 10−5 mm3N−1 m−1). The wear mechanism of all the samples is mainly delamination wear with oxidative wear, but the degree of delamination wear is obviously different, showing a trend corresponding to the tribological behavior of the amorphous coating. Therefore, the CCT method could be an effectively strategy to ameliorate the toughness and then enhance the wear performance of the Fe-based amorphous coating. • Fe-based amorphous coatings were deposited by detonation spraying. • The coated samples were treated by cryogenic thermal cycling from 0– 60 cycles. • The cryogenic thermal cycling treated samples undergo a brittle-tough transition. • C50 coatings exhibit the best friction and wear properties. [ABSTRACT FROM AUTHOR]