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.     

Vacuum tribological behaviour of self‐lubricating quasicrystalline composite coatings

High‐temperature‐resistant self‐lubricating coatings are needed in space vehicles for components that operate at high temperatures and/or under vacuum. Thick composite lubricant coatings containing quasicrystalline alloys as the hard phase for wear resistance can be deposited by a thermal spray technique. The coatings also contain lubricating materials (silver and BaF₂ CaF2 eutectic) and NiCr as the tough component. This paper describes the vacuum tribological properties of TH103, a coating of this type, with a very good microstructural quality. The coating was deposited by high‐velocity oxygen fuel spraying and tested under vacuum using a pin‐on‐disc tribometer. Different loads, linear speeds, and pin materials were studied. The pin scars and disc wear tracks were characterised using a combination of scanning electron microscopy and energy dispersive spectrometry. A minimum mean steady friction coefficient of 0.32 was obtained when employing an X750 Ni superalloy pin in vacuum conditions under 10 N load and 15 cm/s linear speed, showing moderate wear of the disc and low wear of the pin.     

等离子喷涂WC/Co Fe基涂层摩擦与磨损性能

以普通铸铁为基体,碳化钨陶瓷粉末WC 12Co为热喷涂材料,采用大气等离子法制备WC/Co Fe复合涂层.通过SEM、EDS、XRD等手段对WC/Co Fe涂层微观组织与结构进行表征,并对WC/Co Fe复合涂层耐磨损性能进行测试.结果表明,等离子喷涂制备的WC/Co Fe涂层物相以WC相为主;WC涂层摩擦因数波动小于铸铁材料摩擦因数,表明WC复合涂层具有良好的抗摩擦性能.WC涂层耐磨损性能高于铸铁,主要归因于WC颗粒韧性好、硬度高、抗冲击及抗磨损性能强,与基体金属的结合性好.     

Microstructure and Wear Behaviors of Plasma-Sprayed FeCrNiMoCBSi Coating with Nano-Grain Dispersed Amorphous Phase in Reciprocating Sliding Contact

A novel FeCrNiMoCBSi amorphous/nanocrystalline coating was fabricated using a plasma spraying process. The coating was dense with a low porosity of approximately 0.99%. The coating consisted of a 67.8 vol% amorphous phase coupled with many nanocrystalline grains that were approximately 5?nm in diameter. The mechanical properties of the as-sprayed coating were determined by nanoindentation measurement, and the tribological behaviors were systematically investigated in a reciprocating sliding contact. The results show that FeCrNiMoCBSi coatings possess superior wear resistance compared to other typically similar Fe-based amorphous coatings. The tribological behaviors evolve with the combination of normal load and sliding velocity. Herein, the dominant wear mechanisms are delamination wear and oxidation wear. With an increase in normal load and sliding velocity, the abrasive wear is gradually weakened, the formation of oxide films on the worn surfaces is facilitated, and wear debris is ground to powder. The oxide films suffer from fatigue wear with induced cracks undergoing reciprocating sliding effects.     

Abrasive wear behavior of sprayed hydroxyapitite coatings by gas tunnel type plasma spraying

Hydroxyapatite (HA) coatings were sprayed using gas tunnel type plasma spraying at different arc currents. Abrasive wear test was carried out for the coatings sprayed at different arc currents under unlubricated conditions in air atmosphere. The abrasive wear rate was measured at different coatings thickness to study the effect of coating thickness on the anti-abrasion resistance of HA coatings. The results showed that the abrasive wear resistance of HA coatings increases as the operating arc current of the plasma torch increases. On the other hand, the abrasive wear rate reaches a minimum value near the substrate with coating thickness less than 50 μm. The results showed that the coating hardness increases in the region near the substrate and increases as the arc current increases. The experimental results indicated that there is a relation between the abrasion resistance and hardness properties of HA coatings.     

Wear behaviour of laser cladded and plasma sprayed WCCo coatings

The usefulness of WCCo cermets as wear resistant material for coatings is determined by the cladding technique employed. This paper compares the features of an 83% WCCo coating on an AISI 1043 steel substrate using two different application techniques: plasma spraying and laser cladding. Results show significantly less porosity, improved coating hardness and better layer-substrate adherence in laser cladded than in plasma sprayed coatings. This causes them to have different wear behaviour which was determined using a method developed on the basis of the PV factor theory using sliding linear contact of flat-cylinder type. The method proved that wear rate (V_d′) is directly proportional to the product of coefficient of friction (μ), load (C) and applied speed (V), V_d′ = KμCV, where proportionality constant, K, is different for every material and depends on conditions such as lubrication, temperature, etc. To study wear behaviour, laser cladded and plasma sprayed 83% WC-Co coatings, under extreme lubrication, were placed against a hardened and tempered AISI 1043 steel, at different load and sliding speed rates. As a result constant K was estimated for each coating. The tests also showed that wear rate in laser deposited coatings is approximately 34% lower than in plasma sprayed coatings.     

Wear study of Ni–WC composite coating modified with CeO2

In the present investigation, Ni–WC composite powder was modified with the addition of CeO₂ in order to form a new composition of Ni–WC–CeO₂. The Ni–WC and Ni–WC–CeO₂ compositions were used for coating deposition by high-velocity oxy-fuel (HVOF) spraying process so as to study the effect of CeO₂ addition on microstructure, distribution of various elements, hardness, formation of new phases, and abrasive wear behavior. Further, the effect of load, abrasive size, sliding distance, and temperature on abrasive wear behavior of these HVOF-sprayed coatings was investigated by response surface methodology. To investigate the abrasive wear behavior of HVOF-sprayed coatings four factors such as load, abrasive size (size in micrometers), sliding distance (meters), and temperature (°C) with three levels of each factor were investigated. Analysis of variance was carried out to determine the significant factors and interactions. Investigation showed that the load, abrasive size, and sliding distance were the main significant factors while load and abrasive size, load and sliding distance, abrasive size and sliding distance were the main significant interactions. Thus an abrasive wear model was developed in terms of main factors and their significant interactions. The validity of the model was evaluated by conducting experiments under different wear conditions. A comparison of modeled and experimental results showed 4–9% error. The abrasive wear resistance of coatings increases with the addition of CeO₂. This is due to increase in hardness with the addition of CeO₂ in Ni–WC coatings.     

Microstructure and tribological characteristics of ZrO2–Y2O3 ceramic coatings deposited by laser-assisted plasma hybrid spraying

ZrO₂–Y₂O₃ ceramic coatings were deposited on AISI 304 stainless steel by both a low-pressure plasma spraying (LPPS) and a laser-assisted plasma hybrid spraying (LPHS). Microstructure and tribological characteristics of ZrO₂–Y₂O₃ coatings were studied using an optical microscope, a scanning electron microscope, and an SRV high-temperature friction and wear tester. The LPHS coatings exhibit distinctly reduced porosity, uniform microstructure, high hardness and highly adhesive bonding, although more microcracks and even vertical macrocracks seem to be caused in the LPHS coatings. The ZrO₂ lamellae in the LPHS coatings before and after 800°C wear test consist mainly of the metastable tetragonal (t′) phase of ZrO₂ together with small amount of c phase. The t′ phase is very stable when it is exposed to the wear test at elevated temperatures up to 800°C for 1 h. The friction and wear of the LPHS coatings shows a strong dependence on temperature, changing from a low to a high wear regime with the increase of temperature. At low temperatures, friction and wear of the LPHS coatings is improved by laser irradiation because of the reduced connected pores and high hardness in contrary to the LPPS coating. However, at elevated temperatures, the friction and wear of the LPHS coatings is not reduced by laser irradiation. At room temperature, mild scratching and plastic deformation of the LPHS coatings are the main failure mechanism. However, surface fatigue, microcrack propagation, and localized spallation featured by intersplat fracture, crumbling and pulling-out of ZrO₂ splats become more dominated at elevated temperatures.     

Tribological study of NiCrBSi coating obtained by different processes

Thermal spraying offers a wide range of coatings with very different composition and properties. NiCrBSi is a Ni-base superalloy widely used to obtain high wear resistant coatings. This coating is usually heat treated after thermal spraying to improve their tribological properties. In this work a tribological comparison between NiCrBSi coatings obtained by spray&fuse and as-sprayed coatings obtained by Atmospheric Plasma Spraying (APS) and High Velocity Oxy Fuel (HVOF) spraying is carried out. Ball on Disk (BOD) tests are performed with a martensitic plain steel as counterface and wear parameters are calculated by means of Scanning White Light Interferometry (SWLI). Main wear mechanisms are investigated by the characterisation of the coating wear track and debris using Scanning Electron Microscopy (SEM). It is observed that different wear mechanisms take place in the coatings obtained by the diverse processes.     

镁合金表面再制造AlCoTi非晶涂层组织及力学性能研究

采用高速电弧喷涂技术在AZ91镁合金表面制备了高非晶含量AlCoTi涂层,研究了涂层显微组织、力学性能、摩擦磨损及电化学腐蚀性能。结果表明,涂层呈典型的层状结构,其结构紧凑,与镁合金基体结合良好,孔隙率约为1.63%。涂层的组织主要由非晶相、纳米结构的α-Al和Al3Ti相组成。相比于AZ91镁合金,AlCoTi非晶涂层具有更高的显微硬度和耐磨性能：涂层的显微硬度约为511.3Hv0.1,远高于AZ91镁合金(62Hv0.1);在相同的磨损条件下,非晶涂层相对耐磨性约为晶体结构AZ91镁合金的3.9倍,其主要磨损机制为脆性剥落。在0.6 mol/L NaCl溶液中,非晶涂层自腐蚀电位、自腐蚀电流密度和电荷转移电阻分别为-0.696V、0.741 8μA/cm²和33 660?·cm²,明显优于AZ91镁合金的-1.392V、769.3μA/cm²和1 914?·cm²。通过对镁合金表面不同防护涂层的电化学腐蚀性能和显微硬度比较分析,本研究为镁合金提供一种低成本、高性能的涂层材料及再制造关键技术。     

TiB2陶瓷颗粒增强电弧喷涂涂层滑动磨损性能的研究

采用电弧喷涂含TiB2陶瓷粉末的粉芯丝材,在低碳钢基体上制备了NiCr-TiB2和304L-TiB2金属基复合涂层,在摩擦磨损试验机上研究了按环/块线接触方式作往复运动条件下无润滑时室温下的摩擦磨损性能,利用光学显微镜、扫描电子显微镜和X射线衍射仪对涂层的显微组织结构、磨损表面及其相组成进行分析。结果表明,涂层的相对耐磨性能远高于碳钢基体,约为9到11.5倍。304L-TiB2涂层的低磨损率除了与硬质相有关,还和涂层具有较高的硬度有关。NiCr-TiB2涂层的耐磨性能好,细小的TiB2陶瓷相在局部涂层中连成网状,与基体结合良好,有效提高了涂层的磨损性能。     

Friction and Wear Characteristics of C/Si Bi-layer Coatings Deposited on Silicon Substrate by DC Magnetron Sputtering

The tribological behavior of carbon/silicon bi-layer coatings deposited on a silicon substrate by DC magnetron sputtering was assessed and compared to that of amorphous carbon and silicon coatings. The motivation was to develop a wear resistant coating for silicon using thin layers of amorphous carbon and silicon. Wear tests were conducted by sliding a stainless steel ball against the coating specimens under applied normal loads in the range of 20?~?50?mN. Results showed that the wear rate of the bi-layer coating was strongly dependent on the ratio of thickness between the carbon and silicon layers. The wear rate of the bi-layer coating with 25?nm thick carbon and 102?nm thick silicon layers was about 48 and 20 times lower than that of the single-layer amorphous carbon and amorphous silicon coating, respectively. In addition, the steady-state friction coefficient of the bi-layer coating could be decreased to 0.09 by optimizing the thickness of the layer. Finally, a model for the wear reduction mechanism of the carbon/silicon bi-layer coating was proposed.     

High temperature fretting wear behavior of WC-25Co coatings prepared by D-gun spraying on Ti-Al-Zr titanium alloy

Detonation gun (D-gun) spraying is one of the most promising spraying techniques for producing wear-resistance coatings. A thick layer (about 0.3 mm thickness) of WC-25Co with high hardness was covered on Ti-Al-Zr titanium alloy by D-gun spraying and the fretting wear behavior of WC-25Co coatings was studied experimentally on a high precision hydraulic fretting wear test rig. An experimental layout was designed to perform fretting wear tests at elevated temperatures from room temperature (25 °C) to 400 °C in ambient air. In the tests, a sphere (Si₃N₄ ceramic ball) was designed to rub against a plane (Ti-Al-Zr titanium alloy with or without WC-25Co coatings). It was found that the fretting running regimes of WC-25Co coatings were obviously different from those of Ti-Al-Zr titanium alloy. The mixed fretting regime disappeared in WC-25Co coatings, and the boundaries in the running condition fretting map (RCFM) showed hardly any change as temperature increased. The worn scars were examined using a laser confocal scanning microscope (LCSM), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The results showed that the coefficients of friction (COF) of WC-25Co coatings at elevated temperatures were nearly constant in the partial slip regime and very low in the steady state. The fretting damage of the coatings was very slight. In the slip regime, the WC-25Co coatings exhibited a good wear resistance, and the wear volume of the coatings obviously decreased with increasing tested temperature. The fretting wear mechanisms of WC-25Co coatings were delamination, abrasive wear and oxidation wear at elevated temperature. The oxide debris layer formed at higher temperature was denser and thicker on top of WC-25Co coatings, thus providing more surface protection against fretting wear, which played an important role in the low fretting wear of the coatings.     

A DOE nano-tribological study of thin amorphous carbon-based films

A design of experiment (DOE) matrix of 150 nm non-hydrogenated amorphous C and Cr doped amorphous C films was produced to investigate the effect of four key coating process parameters (use of an adhesion layer, Cr magnetron current, cathodic substrate bias voltage and Ar flow to the chamber) using a new rapid method of nano-scale wear test under conditions relevant to MEMS and similar devices. The condition of nano-wear was produced by controlled oscillation of the sample mounting within a nanoindentation system under ultra-low normal load. Specific wear rates were low, typically in the range 6-24×10⁻¹⁷ m³ N⁻¹ m⁻¹. The results were processed using an analysis of variance (ANOVA) procedure which showed that: hardness was reduced in the Cr containing films whilst specific wear rate and data scatter increased, increasing the cathodic substrate bias voltage reduced the specific wear rate due to increased coating hardness, the use of a Cr adhesion layer reduced the specific wear rate and scatter of results with Cr doped films but had no effect on pure a-C films, and Ar flow rate had no significant effect on specific wear rate but strongly interacted with the effect of the cathodic bias voltage.     

Effects of Thickness and Roughness Variations on the Abrasiveness of a Thin Boron Carbide Coating

Boron carbide (B₄C) is well known for its high hardness and favorable wear resistant properties. In dry sliding wear contact, it polishes its mating surface and provides fatigue resistance to coated parts. Employing such run-in coatings demands a thorough understanding of the parameters which directly influence the changes that occur in the coating abrasiveness during the polishing process. In this study, the effects of the overall coating thickness, overall coating roughness, substrate roughness and substrate roughness orientation are examined in connection with abrasiveness. The coating thickness only influences the initial abrasiveness, whereas the coating roughness drastically affects the rate at which the abrasiveness decreases. Finally, no significant changes are observed in the abrasiveness due to substrate roughness or substrate roughness orientation effects. This work provides further insight into the design of a finite-life run-in coating.     

AlNiZr非晶纳米晶复合涂层的腐蚀磨损行为研究

为提高海洋极端环境下钢结构材料的耐腐蚀磨损性能,采用高速电弧喷涂技术制备了一种AlNiZr非晶纳米晶复合涂层,并研究了该涂层在质量分数为3.5%的NaCl溶液中的腐蚀磨损行为。结果发现,AlNiZr涂层组织较为均匀,致密性较好,相结构由非晶、纳米晶及晶化相共同组成,涂层非晶体积分数约为64.93%,平均显微硬度值为363HV0.1,与45钢基体之间的平均结合强度约为30.8 MPa;在干摩擦条件下其平均摩擦因数约为0.125,磨损体积约为0.134 mm3,磨痕宽度约为882.4 μm,磨损失效机制以氧化磨损和脆性剥层磨损为主,并伴有轻微磨粒磨损;在腐蚀介质条件下,由于受到腐蚀介质的润滑减摩作用,导致涂层的平均摩擦因数、磨损体积、磨痕宽度均有明显减小,其平均摩擦因数约为0.058,磨损体积约为0.02216 mm3,磨痕宽度约为314 μm,腐蚀磨损失效机制主要表现为剥层磨损形式,同时磨损起主导作用、腐蚀次之。与纯铝涂层相比,AlNiZr涂层表现出优异的耐腐蚀磨损性能。     

高速电弧喷涂Al-Ni-Mm-Co涂层在脂润滑下的摩擦磨损性能

针对铝合金硬度低、耐磨性差的问题,采用电弧喷涂分别在6061铝合金基体表面喷涂Al和Al-Ni-Mm-Co涂层,采用显微硬度计、扫描电子显微镜、X射线衍射仪分别对涂层硬度、涂层显微结构、涂层成分进行分析。采用球-盘式往复摩擦试验机考察涂层在脂润滑下的摩擦学性能,并对磨痕形貌和表面主要元素进行观察。结果表明,Al-Ni-Mm-Co涂层的减摩性和抗磨性能均优于6061铝合金和Al涂层,其优异的摩擦学性能归结为摩擦表面形成的Al2O3、NiO、CoO等氧化保护层,主要的磨损形式为疲劳磨损。     

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.     

Sliding wear characteristics of plasma-sprayed Al2O3 and Cr2O3 coatings against copper alloy under severe conditions

Al₂O₃ and Cr₂O₃ coatings were deposited by atmospheric plasma spraying and their tribological properties dry sliding against copper alloy were evaluated using a block-on-ring configuration at room temperature. It was found that the wear resistance of Al₂O₃ coating was superior to that of the Cr₂O₃ coating under the conditions used in the present study. This mainly attributed to its better thermal conductivity of Al₂O₃ coating, which was considered to effectively facilitate the dissipation of tribological heat and alleviate the reduction of hardness due to the accumulated tribological heat. As for the Al₂O₃ coating, the wear mechanism was plastic deformation along with some micro-abrasion and fatigue-induced brittle fracture, while the failure of Cr₂O₃ coating was predominantly the crack propagation-induced detachment of transferred films and splats spallation.     

Tribological Dependence of the High-Performance Ferrous-Based Coating on Different Coating Counterparts in Engine Oil

A ferrous-based coating with significant chromium was fabricated on aluminum alloy substrate using a plasma spray technique. The tribological performance of the as-fabricated ferrous-based coating sliding against different coatings including Cr, CrN, TiN, and diamond-like carbon (DLC) in an engine oil environment were comparatively studied. Results showed that the high hardness of the sprayed ferrous-based coating was achieved due to the dispersion strengthening effect of Cr₇C₃ phase embedded in the austenite matrix. The ferrous-based coating exhibited low friction coefficients when coupled with these four coating counterparts, which could be attributed to the boundary lubricating effect of engine oil. However, both friction and wear of the ferrous-based coating were different when sliding against these different coating counterparts, which might be closely related to the surface roughness, self-lubricating effect, and mechanical properties of the coupled coatings. Ferrous-based coating sliding against CrN and DLC coatings exhibited good tribological performance in engine oil. The best coating counterpart for the ferrous-based coating in an engine was DLC coating.