Influence of Heat Treatment on Microstructure and Sliding Wear of Thermally Sprayed Fe-Based Metallic Glass Coatings

Fe₆₂Ni₃Cr₄Mo₂W₃Si₆B₁₇C₃ amorphous coatings were thermally sprayed by a high velocity oxygen fuel spraying system (DJ-2700) and heat-treated at the temperatures ranges from 873 to 1,173 K in vacuum for 1 h. Differential scanning calorimetry, X-ray diffraction (XRD), and scanning electron microscopy were used to study the microstructural characteristics of the coatings. Vickers hardness tester was used to measure the hardness of the coatings. At the same time, the sliding wear behavior of the coatings was evaluated in a reciprocating ball-on-disk system. Within the resolution of XRD, amorphous structure without apparent crystalline phases was obtained in the as-sprayed coating. The heat treatments above 873 K led to the crystallization of amorphous phase. With the increase of heat treatment temperature, diffusion and sintering could occur between the layers of the coatings. The highest microhardness was obtained in the coating heat-treated at 973 K. When wear tested at a relative low load of 2 N, a direct correlation between the hardness and wear resistance of the coatings seems to be reasonable. However, at relative high loads, the wear resistance of the coatings is dependent on the resistance to crack initiation and growth between the layers rather than the hardness.     

TiC-VC颗粒增强Fe基熔敷层组织与耐磨性能

以H08A为焊芯，以钛铁、钒铁和石墨等为药皮组分，利用焊接电弧高温冶金反应，在Q235基体上制备TiC-VC复合超硬颗粒增强Fe基熔敷层。利用扫描电镜、X射线衍射仪、透射电镜、能谱分析仪及磨损试验，研究了熔敷层的组织、性能及组分加入量对熔敷层性能的影响。研究结果表明：冶金反应形成的TiC-VC颗粒尺寸细小，且弥散分布在基体上；熔敷层硬度在HRC55以上，具有很高的耐磨性和良好的抗裂性；钛铁、钒铁及石墨加入量（质量分数）分别为15％～18％、12％～14％和8％～10%时，熔敷层具有良好的耐磨性能和抗裂性能。     

Wear resistant multilayer nanocomposite WC1−x/C coating on Ti–6Al–4V titanium alloy

A significant improvement of tribological properties on Ti–6Al–4V has been achieved by developed in this study multilayer treatment method for the titanium alloys. This treatment consists of an intermediate 2 μm thick TiC_xN_y layer which has been deposited by the reactive arc evaporation onto a diffusion hardened material with interstitial O or N atoms by glow discharge plasma in the atmosphere of Ar+O₂ or Ar+N₂. Subsequently, an external 0.3 μm thin nanocomposite carbon-based WC_1−x/C coating has been deposited by a reactive magnetron sputtering of graphite and tungsten targets. The morphology, microstructure, chemical and phase compositions of the substrate material after treatment and coating deposition have been investigated with use of AFM, SEM, EDX, XRD, 3D profilometry and followed by tribological investigation of wear and friction analysis. An increase of hardness in the diffusion treated near-surface zone of the Ti–6Al–4V substrate has been achieved. In addition, a good adhesion between the intermediate gradient TiC_xN_y coating and the Ti–6Al–4V substrate as well as with the external nanocomposite coating has been obtained. Significant increase in wear resistance of up to 94% when compared to uncoated Ti–6Al–4V was reported. The proposed multilayer system deposited on the Ti–6Al–4V substrate is a promising method to significantly increase wear resistance of titanium alloys.     

Influence of aging treatment on microstructure, wear and corrosion behavior of a nickel base hardfaced coating

In this work nickel based hardfacing alloy (Colmonoy 5) was deposited on 316 L (N) stainless steel substrate to study the effects of aging treatment on coating microstructure, wear and corrosion properties. Coatings, deposited through plasma transferred arc (PTA) welding process, were aged at 923 K for 5000 h. Microstructural characterization studies carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed the coarsening of dendrites and precipitation of Cr₂₃C₆ particles in the aged coating. The wear behavior of the as deposited and aged coatings was compared in room temperature (RT) and high temperature (823 K) under dry sliding wear condition (pin-on-disc configuration). At RT, aged coating experienced more wear loss when compared to as-deposited. At high temperature, the wear loss was almost same with similar operating wear mechanisms (tribo-oxidation) for both as-deposited and aged coating. From pitting corrosion studies, it was found that aged coatings are more prone to pitting when compared to the as-deposited coatings.     

Developing an (Al,Ti)N x C y Interlayer to Improve the Durability of the ta-C Coating on Magnetic Recording Heads

In this study, a new surface pre-treatment technique has been developed to improve the durability of the ultra-thin tetrahedral amorphous carbon (ta-C) coating for magnetic tape drive read/write heads. In this technique, prior to the deposition of an 8-nm ta-C overcoat, a 2-nm thin TiN interlayer was deposited on the heads surface and bombarded with energetic Ar⁺ and C⁺ ions. X-ray photo-electron spectroscopy results revealed that this surface pre-treatment technique would lead to the formation of an atomically mixed (AlTi)N _x C _y interlayer which can chemically bond the interlayer to the overcoat and substrate. The effect of this atomically mixed interlayer on the wear resistance of the ta-C coating was investigated using ball-on-flat tests as well as a functional tape drive tester. According to the ball-on-flat test results, the application of the (AlTi)N _x C _y interlayer was able to improve the wear life of the ta-C overcoat by up to 3.3 times as compared to that of the conventional ta-C coating. The results of the wear tests in a real head/tape interface were in agreement with the ball-on-flat results, and showed that while the conventional ta-C film was completely removed from the head surface, the ta-C film with (AlTi)N _x C _y was able to protect the head surface for wear tests of about 1.6 million meters.     

Tribological behaviour and microstructure of TiCxN(1−x) coatings deposited by filtered arc

A series of macroparticle-free TiN, TiC_xN_(1−x) and TiC coatings were deposited on 316 austenitic stainless steel using a titanium target in a filtered arc deposition system (FADS) and reactive mixtures of N₂ and/or CH₄ gases. The surface topography, chemical composition and microstructure of these coatings were characterised by optical microscopy (OM), atomic force microscopy (AFM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The microhardness has been measured and the adhesion of the coatings has been evaluated. Further, the wear and friction behaviour of the coatings were assessed under controlled test conditions in a pin-on-disc tribometer.The results show a significant increase in surface roughness, microhardness and wear resistance as the CH₄:N₂ gas flow rate ratio is increased. The composition of the coatings was strongly dependent on reactive gas flow rate during deposition. Surface particles were observed on high carbon content coatings and subsequently determined to be carbonaceous particles by using OM, AFM and EDS. At lowest load (10 N), all coatings exhibited low friction and wear. At loads of 15 and 25 N, the higher carbon content TiCN and TiC coatings showed a much lower friction and wear compared to TiN and low carbon TiCN.     

Wear behavior of Ni–P and Ni–P–Al2O3 electroless coatings

In this research, hardness and wear resistance of two types of electroless coating have been investigated including Ni–P and Ni–P–Al₂O₃ coatings. These coatings were applied on AISI 1045 steel discs by electroless deposition process and then they were heat treated at 200, 400 and 600 °C for 1 h. Wear resistance of deposits was measured by the pin on disc method and wear surfaces and debris were studied by scanning electron microscopy (SEM). Also, microstructural changes were evaluated by X-ray diffraction (XRD) analysis.The results showed that the existence of alumina particles in Ni–P coating matrix led to an increase in the hardness and wear resistance of the deposits. It was also found that heat treated coatings at about 400 °C have the maximum hardness and wear resistance.     

Microstructural and abrasive characteristics of high carbon Fe–Cr–C hardfacing alloy

A series of high carbon Fe–Cr–C hardfacing alloys were produced by gas tungsten arc welding (GTAW). Chromium and graphite alloy fillers were used to deposit hardfacing alloys on ASTM A36 steel substrates. Depending on the four different graphite additions in these alloy fillers, this research produced hypereutectic microstructures of Fe–Cr phase and (Cr,Fe)₇C₃ carbides on hard-facing alloys. The microstructural results indicated that primary (Cr,Fe)₇C₃ carbides and eutectic colonies of [Cr–Fe+(Cr,Fe)₇C₃] existed in hardfacing alloys. With increasing the C contents of the hardfacing alloys, the fraction of primary (Cr,Fe)₇C₃ carbides increased and their size decreased. The hardness of hardfacing alloys increased with fraction of primary (Cr.Fe)₇C₃ carbides. Regarding the abrasive characteristics, the wear resistance of hardfacing alloys were related to the fraction of primary (Cr,Fe)₇C₃ carbides. The wear mechanism was also dominated by the fraction of primary (Cr,Fe)₇C₃ carbides. Fewer primary carbides resulted in continuous scratches worn on the surface of hardfacing alloy. In addition, the formation of craters resulted from the fracture of carbides. However, the scratches became discontinuous with increasing fraction of the carbides. More primary carbides can effectively prevent the eutectic colonies from the damage of abrasive particles.     

Microstructure and Dry-Sliding Wear Behavior of Thermal Sprayed and Fused Ni-Based Coatings with the Addition of La2O3

A Ni-based alloy with 1.5 wt% of La₂O₃ powders was thermal sprayed onto steel substrate. The microstructure and dry sliding wear behavior of the coatings were studied by XRD, field emission gun scanning electron microscope (FEGSEM) and SEM analyses. The microstructure of the coating with 1.5 wt% of La₂O₃ differs widely from the coating without La₂O₃; the typical microstructure with 1.5 wt% of La₂O₃ is composed of net-like dendrite (Cr, Fe)₂₃C₆ and Cr₇C₃, cellular-dendrite Fe₂₃(C, B)₆, γ-Ni + Ni₅Si₂ interdendritic lamellar eutectic. Interestingly, significant amounts of net-like (Cr, Fe)₂₃C₆ and Cr₇C₃ hard phases as a wear-resistant skeleton were formed and uniformly dispersed in the coating. Meanwhile, blocky and rod-like hard-phase CrB scattered in the coating can also contribute to improving the wear resistance. The novel microstructure, therefore, is beneficial for wear resistance. Friction and wear tests without lubricant show that the friction coefficients of the coating are less than 0.57. There is an approximately linear relationship between friction coefficients and sliding speed. The wear rate slightly increases with an increase of load, and the wear rate of the coating slightly decreases with sliding speed.     

Impact wear resistance of WC/Hadfield steel composite and its interfacial characteristics

A composite coating of WC/Hadfield steel was fabricated through centrifugal casting process to improve the impact wear resistance of Hadfield steel under the conditions of low or medium impact energy. The interfacial structure between WC ceramic particle and the steel matrix was analyzed with scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The impact wear tests at different impact energy were carried out on a MLD-10 type impact wear rig to investigate the wear-resistant properties of three kinds of composites with different WC particle sizes. For comparison, the wear tests of Hadfield steel were also carried out under the same conditions. The results show that WC particles are partially dissolved in the steel during centrifugal casting. The elements W, C and Fe in steel react to form new carbides such as Fe₃W₃C or M₂₃C₆, which precipitate around former WC particles forming fine particles during subsequent solidification. So the interface between WC particles and Hadfield steel matrix is a strong metallurgical bonding. The composite reinforced with smaller WC particles has better impact wear resistance than that of Hadfield steel regardless of impact energy level. Whereas, the composite reinforced with larger WC particles has better impact wear resistance property than that of Hadfield steel when the impact energy is small but an opposite result is gained when the impact energy is higher. So, it is very essential to choose suitable size of WC particles as reinforcement in Hadfield steel to make the composite material more durable in the service conditions.     

Effects of Loadings on Friction and Wear Behaviors of Cathodic Arc Ion Plating AlTiN Coating at High Temperature

A layer of AlTiN coating was deposited on YT14 cutting tool by cathodic arc ion plating (CAIP) and the coefficients of friction (COFs) of the AlTiN coating under different loads at a temperature of 800°C were investigated with a high-temperature wear tester. The wear morphologies, chemical elements, and phases of the coating after wear were analyzed with scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), and X-ray diffraction (XRD), respectively, and the contours of wear tracks were investigated with a comprehensive measurement tester for material surface performance. The effects of loads on COFs and wear resistance of the AlTiN coating were analyzed, and the wear mechanism of the AlTiN coating at high temperature is discussed. The results show that the mixed oxides of Al₂O₃ and TiO₂ are produced under high temperature to improve the lubrication performance and wear resistance of the AlTiN coating. The average COFs of the coating under loads of 5, 7, and 9 N are 0.6495, 0.5897, and 0.3898, respectively. The COFs of the coating decrease with increasing load; as a result, the AlTiN coating is suitable for heavy loads at high temperature. The friction and wear mechanisms of the AlTiN coating are primarily composed of oxidation wear and abrasive wear, accompanied by fatigue wear and adhesive wear.     

Development of nano-structured Al2O3-TiB2-TiN coatings by combined SHS and laser surface alloying

A powder mixture of aluminium (Al), titania (TiO₂) and hexa-boron nitride (h-BN) was laser-triggered to undergo SHS (self-propagating high temperature synthesis) and was subsequently laser alloyed onto a mild steel substrate surface. A nano-structured coating was formed with high microhardness (～3000 HV_0.05 at the cross-section and ～2600 HV_0.2 on the top surface). X-ray diffraction (XRD) identified the presence of aluminium oxide (Al₂O₃), titanium di-boride (TiB₂), titanium nitride (TiN), iron (Fe) and its borides (FeB, Fe₂B) in the coating. Scanning electron microscopy (SEM) and high resolution transmission electron microscopic (HRTEM) analysis of the coating revealed nano-fibrous titanium-rich reinforcements in a matrix of nano-crystalline alumina. The thickness of titanium di-boride nano-fibres was an order of magnitude higher than the size of nano-alumina crystallites.     

Dry Sliding Wear Behavior of (Cr,Fe)<Subscript>7</Subscript>C<Subscript>3</Subscript>-γ(Cr,Fe) Metal Matrix Composite (MMC) Coatings: The Influence of High Volume Fraction (Cr,Fe)<Subscript>7</Subscript>C<Subscript>3</Subscript> Carbide

The high volume fraction (Cr, Fe)₇C₃ carbide particle-reinforced metal matrix composite (MMC) coatings with different Cr/C ratios were produced by flux-cored arc welding (FCAW). The in situ synthesized effectiveness of (Cr, Fe)₇C₃ carbide in the coatings was studied by the aid of CALPHAD and differential scanning calorimeter. The microstructure of the coatings was observed by optical microscope and field emission scanning electron microscope, and their phases were determined by the X-ray diffraction. Meanwhile, the hardness and wear resistance of the coatings were measured. The results show that the (Cr, Fe)₇C₃ carbide can be in situ synthesized in the coatings. With decreased Cr/C ratio, the in situ synthesized effectiveness of (Cr, Fe)₇C₃ carbide is improved and the mass fraction of the (Cr, Fe)₇C₃ carbide is increased. The microstructure of the coatings consists of in situ synthesized (Cr, Fe)₇C₃ carbide and eutectic (Cr, Fe)₇C₃/ γ (Cr, Fe) matrix. The hexagonal-rod-form (Cr, Fe)₇C₃ carbide can be fractured and segregated from austenite-matrix under a relatively high load force (50 N), and transforms the wear state from two-body-abrasion to three-body-abrasion, which facilitates the coating be seriously abraded and even adhered. The wear resistance of the MMC coatings can be effectively improved by the formation of high volume fraction of (Cr, Fe)₇C₃ carbide.     

Microstructure and tribological properties of laser clad γ/Cr7C3/TiC composite coatings on γ-TiAl intermetallic alloy

In order to improve the wear resistance of the γ-TiAl intermetallic alloy, microstructure, room- and high-temperature (600 °C) wear behaviors of laser clad γ/Cr₇C₃/TiC composite coatings with different constitution of NiCr–Cr₃C₂ precursor-mixed powders have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive spectrometer (EDS), block-on-ring (room-temperature) and pin-on-disk (high-temperature) wear tests. The responding wear mechanisms are discussed in detail. Results show that microstructures of the laser clad composite coatings have non-equilibrium solidified microstructures consisting of primary hard Cr₇C₃ and TiC carbides and the inter-primary γ/Cr₇C₃ eutectic matrix, about three to five times higher average microhardness compared with the TiAl alloy substrate. Higher wear resistance than the original TiAl alloy is achieved in the clad composite coatings under dry sliding wear conditions, which is closely related to the formation of non-equilibrium solidified reinforced Cr₇C₃ and TiC carbides and the positive contribution of the relatively ductile and tough γ/Cr₇C₃ eutectics matrix and their stability under high-temperature exposure.     

Improvement of the Oxidation and Wear Resistance of Pure Ti by Laser-Cladding Ti<Subscript>3</Subscript>Al Coating at Elevated Temperature

Ti₃Al coating was in situ synthesized successfully on pure Ti substrate by laser-cladding technology using aluminum powder as the precursor. The composition and microstructure of the prepared coating were analyzed by transmission electron microscopy, scanning electron microscopy (SEM), and X-ray diffraction technique. Thermal gravimetric analysis was used to evaluate the high-temperature oxidation resistance of the Ti₃Al coating. The friction and wear behavior was tested through sliding against Si₃N₄ ball at elevated temperature of 20, 100, 300, and 500°C. The morphologies of the worn surfaces and wear debris were also analyzed by SEM and three-dimensional non-contact surface mapping. The results show that the Ti₃Al coating with high microhardness, high-temperature oxidation resistance, and high temperature wear resistance. The pure Ti substrate is dominated by severe adhesion wear, abrasive wear, fracture, and severe plastic deformation at lower temperature, and severe adhesion wear, abrasive wear, plastic deformation, oxidation, and nitriding wear at higher temperature, whereas the Ti₃Al coating experiences only moderate abrasive and adhesive wear when sliding against the Si₃N₄ ceramic ball counterpart. In addition, the wear debris of the laser-cladding Ti₃Al coating sliding and Si₃N₄ friction pairs are much smaller than that of pure Ti substrate and Si₃N₄ friction pairs at elevated temperature.     

Dry sliding wear behaviors of La2O3–WSi2–MoSi2 composite against alloy steel

A molybdenum disilicide (MoSi₂) matrix composite with the addition of WSi₂ and La₂O₃ (RWM) was fabricated as a wear resistant material by self-propagating high temperature synthesis (SHS) and hot pressing (HP). This composite was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The wear resistance of MoSi₂ against steel is significantly improved by the addition of both WSi₂ and La₂O₃, and it is attributed to the increase in hardness and toughness of the composite. It is found that the wear behavior of the RWM is sensitive to sliding speed, load and hardness of the counter-face material. When worn against a steel with a lower hardness (A), the wear rate of RWM increases with an increase of sliding speed, and increases initially and then decreases with an increase of load. The material removal mechanisms varied from ploughing wear at low load and speed to serious adhesive wear at high load and speed. When worn against a steel with a higher hardness (B), the wear resistance of the RWM improved and the material removal mechanism were brittle fracture wear at low speed and adhesive wear at high speed.     

The effects of welding processes on abrasive wear resistance for hardfacing deposits

In this research, four kinds of welding deposits were evaluated, applied through two different welding processes: flux cored arc welding (FCAW) and shielded metal arc welding (SMAW). The other variable of the tests was the deposited layers. The hardfacing deposits were evaluated using the dry sand-rubber wheel machine according to procedure A of the ASTM G65 standard. Optical and scanning electron microscopy was used for the characterization of the microstructure and worn surface of deposits. FCAW welds presented higher abrasive wear resistance than the SMAW deposits. The hardfacing deposit formed by uniformly distributed carbides rich in titanium presented the highest abrasive wear resistance. Abrasive wear resistance was higher when three layers were applied, except for SMAW-D deposit. It was not possible to get a clear relation between hardness and the abrasive wear resistance of the deposits. The results showed that the most important variable to improve abrasion resistance is the microstructure of hardfacing deposits, where the carbides act as barriers to abrasive particle cutting.     

Wear and friction characteristics of atmospheric plasma sprayed Cr3C2–NiCr coatings

ABSTRACT

The present work focuses on investigating the wear and friction characteristics of the Atmospheric Plasma Sprayed Cr₃C₂-NiCr coatings deposited onto the surface of die steel material. The as-sprayed specimens were characterized. The coating porosity, bond strength and microhardness values were evaluated. Wear tests were performed on the high-temperature pin-on-disc tribometer at room temperatures, 400°C and 800°C under two loads as 25N and 50N in the laboratory. The wear mechanisms of all the worn-out samples were studied by scanning electron microscopy (SEM) technique. The specific wear rates and the coefficient of friction values were analyzed. The developed coating showed better wear resistance than its uncoated counterpart. The coefficient of friction values for coated specimens decreased at elevated temperatures. At room temperatures, the wear mode was observed to be adhesive and further at elevated temperatures of testing, the wear mode was observed to be the combination of oxidative, adhesive and abrasive.     

Design of experiments approach to the study of tribological performance of Cu-concentrate-filled PPS composites

The tribological performance of copper-concentrate (CC) mineral deposit as the filler in polyphenylene sulfide (PPS) was studied as a function of the filler proportions and sliding test variables. CC is a complex mixture of CuS, Fe_xO_y, SiO₂, Al₂O₃, and other trace materials. The design of experiments based upon L₉ (3⁴) orthogonal arrays by Taguchi was used. Sliding tests were performed in the pin-on-disk configuration against a hardened tool steel (55-60 HRC) disk. The improvement in wear resistance of PPS was considerable with the use of fillers. The lowest steady state wear rate of 0.0030 mm³/km was obtained for PPS+20%CC+15%PTFE composition. It was two orders of magnitude lower than that of unfilled PPS. The variations in steady state coefficient of friction with the changes in filler proportions and sliding test variables were small. The transfer film was studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM). X-ray photoelectron microscopy (XPS) was used to detect chemical reactive species developed during sliding, especially in the interface between transfer film and its counterface. Wear particles and the polymer worn surfaces were analyzed by energy dispersive spectroscopy (EDS) for elemental distribution.     

Sliding tribological behavior of AlCrN coating

The sliding tribological behavior of the PVD AlCrN coating against Si₃N₄ ball have been investigated by using the CETR multi-functional UMT-2 test system under two sliding conditions (bidirectional and unidirectional). Reciprocating sliding tests (bidirectional) were performed under varied normal loads (5, 10 and 20 N) at sliding velocity of 0.48 m/min. Ball-on-disc tests (unidirectional) were performed at varied sliding velocities (0.48 and 5 m/min) under normal load of 5 N. The wear scars of the coating were evaluated by surface profilometer, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDX), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), and the sliding wear mechanism of the coating was consequently discussed. The results showed that AlCrN coating had excellent anti-abrasion properties. Both the normal load in reciprocating sliding test and the sliding velocity in ball-on-disc test had significant influence on the sliding tribological behavior of the AlCrN coating. The combination of abrasion and oxidation was the main sliding wear mechanism for the AlCrN coating. The wear resistant and thermally stable oxides formed by the tribo-chemical reactions of chromium and aluminum protected the AlCrN coating against wear admirably.