Characterization of mechanical properties of FeCrBSiMnNbY metallic glass coatings

This article investigates mechanical characteristics of Fe-based metallic glass coatings. A series of the coatings were fabricated by conventional wire-arc spray process. The microstructure of the coating was characterized by means of X-ray diffraction, scanning election microscopy equipped with energy dispersive X-ray analysis, transmission electron microscopy, and differential scanning calorimeter. The coating is very dense smooth, adhering well and with no cracking. The microstructure of the coating consists of amorphous phase and α(Fe,Cr) nanocrystalline phase. The nanocrystalline grains with a size of 30 to 60 nm are homogenously dispersed in the amorphous phase matrix. The crystallization temperature of the amorphous phase is about 545 °C. The mechanical properties, such as porosity, adhesive strength, microhardness, elastic modulus, and abrasive wear resistance, were analyzed in detail. The experimental results indicate that the coating has high microhardness (15.74 GPa), high elastic modulus (216.97 GPa), and low porosity (1.7%). The average adhesive strength value of the coating is 53.6 MPa. The relationship between abrasive wear behavior and structure of the coating is discussed. The relatively wear resistance of metallic glass coating is about 7 and 2.3 times higher than that of AISI 1045 steel and 3Cr13 martensite stainless steel coating, respectively. The main failure mechanism of metallic glass coating is brittle failure and fracture. The Fe-based metallic glass coating has excellent wear resistance.     

Effects of aging treatment on microstructure and tribological properties of nickel-based high-temperature self-lubrication wear resistant composite coatings by laser cladding

The NiCr/Cr₃C₂–WS₂ high-temperature self-lubrication wear resistant composite coatings were fabricated on substrate of a hot-rolled AISI304 austenitic stainless steel by laser cladding. The high-temperature phase stability of the composite coatings was evaluated by aging at 600 °C for 10 h, 30 h, 50 h, and the microstructures of the as-laser clad and aged coatings were examined by means of XRD, SEM, EDS, respectively. The sliding wear resistance of the as-laser clad and aged coatings was evaluated at 600 °C. The results show that NiCr/Cr₃C₂–WS₂ composite coating has excellent high-temperature phase stability, the γ-(Fe,Ni)/Cr₇C₃ eutectic phases, Cr₇C₃ and (Cr,W)C hard phases, CrS/WS₂ mixed solid lubricant phases all existed in the as-laser clad and aged coatings. The volume fraction of eutectic phases decreased gradually with the increasing of aged time due to their dissolution. The microhardness of the aged coating decreased slightly after aging the coating 50 h at 600 °C due to the dissolution of the eutectic phases and notable breaking or granulation of the Cr₇C₃ hard phase, but the tribological properties were not significantly affected by aging treatment.     

(Fe,Cr)7C3/Fe surface gradient composite: Microstructure,microhardness, and wear resistance

In this study, the (Fe,Cr)₇C₃/Fe surface gradient composite was produced by in situ synthesis process with subsequent heat treatment. According to the results of thermal analysis, the as-cast specimen was subjected to heat treatment at 1180 °C for 3 h in argon atmosphere. The phase composition, microstructure, microhardness, and wear resistance of the samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Vickers hardness tester, and wear resistance tester, respectively. The XRD results show that α-Fe and (Fe,Cr)₇C₃ are the predominant crystalline phases in the composite obtained. The volume fraction of (Fe,Cr)₇C₃ particulates has a gradient distribution from the surface to the matrix, and the morphology of (Fe,Cr)₇C₃ particulates changes considerably. A dense ceramic layer is formed on the upper surface of (Fe,Cr)₇C₃/Fe surface gradient composite with a volume fraction of 90%. The microhardness of the dense ceramic layer is 1484 HV_0.1, and its relative wear resistance is five times higher than that of the iron matrix.     

Evaluation of stellite coatings by µ-PTA powder,laser, and PTA deposition processes

This article presents comparative evaluation of microplasma-transferred arc powder deposition (µ-PTAPD), laser deposition, and plasma-transferred arc deposition (PTAD) processes for sound quality and cost-effective deposition of Stellite 6 on AISI 4130 steel substrate. Dilution, deposition thickness, microstructure, secondary dendritic arm spacing (SDAS), microhardness, and abrasive wear resistance have been used for comparative evaluation. Analysis of morphology of Stellite deposition revealed that µ-PTAPD process and laser deposition processes could produce a coating of less than 1?mm thickness having good deposition quality, smaller dilution, and SDAS as compared with PTAD process. Analysis of X-ray diffraction patterns revealed that the Stellite coatings manufactured by all three processes had a lamellar structure consisting of Co phases, chromium-rich carbides (Cr₂₃C₆ and Cr₇C₃), and tungsten-containing compounds (W₂C). Analysis of microhardness and abrasive wear resistance found that the Stellite coatings manufactured by µ-PTAPD and laser deposition processes exhibited a lower coefficient of friction, wear volume, and higher microhardness as compared with the coating manufactured by PTAD process, this imparting them with higher abrasive wear resistance. This work proves that µ-PTAPD process has a capability to offer an economical and sustainable solution for good-quality thin coating of Stellite on metallic substrates.     

Nonequilibrium microstructures and their evolution in a Fe–Cr–W–Ni–C laser clad coating

The laser-solidified microstructural and compositional characterization and phase evolution during tempering at 963 K were investigated using an analytical transmission electron microscope with energy dispersive X-ray analysis. The cladded alloy, a powder mixture of Fe, Cr, W, Ni, and C with a weight ratio of 10:5:1:1:1, was processed with a 3 kW continuous wave CO₂ laser. The processing parameters were 16 mm/s beam scanning speed, 3 mm beam diameter, 2 kW laser power, and 0.3 g/s feed rate. The coating was metallurgically bonded to the substrate, with a maximum thickness of 730 μm, a microhardness of about 860 Hv and a volumetric dilution ratio of about 6%. Microanalyses revealed that the cladded coating possessed the hypoeutectic microstructure comprising the primary dendritic γ-austenite and interdendritic eutectic consisted of γ-austenite and M₇C₃ carbide. The γ-austenite was a non-equilibrium phase with extended solid solution of alloying elements and a great deal of defect structures, i.e. a high density of dislocations, twins, and stacking faults existed in γ phase. During high temperature aging, in situ carbide transformation occurred of M₇C₃ to M₂₃C₆ and M₆C. The precipitation of M₂₃C₆, MC and M₂C carbides from austenite was also observed.     

Laser cladding composite coatings by Ni–Cr–Ti–B4C with different process parameters

To investigate the effect of laser process parameters on microstructure and properties of composite coating, the composite coatings were manufactured by laser cladding Ni–Cr–Ti–B₄C mixed powder on Q235 mild steel with different process parameters. The coatings are bonded with the substrate by remarkable metallurgical binding without cracks and pores. The composite coatings are consisted of in situ synthesized solid solution Ni–Cr–Fe, intermetallic compound (IMC) Ni₃Ti, Cr₂Ti, and ceramic reinforcements TiB₂, TiC. Results of scanning electron microscopy (SEM) revealed that the ceramic reinforcements became coarser with higher specific energy (E_s). There were independent ceramics TiB₂, TiC, eutectic ceramic TiB₂–TiC in coatings, and eutectic alloy–ceramic was detected. Compared with the substrate, the microhardness of coatings was increased significantly, and the maximum microhardness of coatings was approximately five times as high as the substrate. The wear resistance of coatings was improved dramatically than the substrate. Compared to the coatings with lower E_s, higher E_s led to lower microhardness and worse wear resistance ascribing to more Fe diffused into the coating from the substrate.     

Effect of silicon content on the microstructure and properties of Fe–Cr–C hardfacing alloys

In this study, the surface of St52 steel was alloyed with preplaced powders 55Fe39Cr6C, 49Fe39Cr6C6Si, and 45Fe39Cr6C10Si using a tungsten-inert gas as the heat source. Following surface alloying, conventional characterization techniques, such as optical microscopy, scanning electron microscopy, and X-ray diffraction were employed to study the microstructure of the alloyed surface. Microhardness measurements were performed across the alloyed zone. Room-temperature dry sliding wear tests were used to compare the coatings in terms of their tribological behavior. It was found that the as-deposited coatings contained higher volume fractions of carbides (Cr₇C₃). The presence of 6%Si in the preplaced powders caused an increase in microhardness and wear resistance.     

Effects of high temperature treatment on microstructure and mechanical properties of laser-clad NiCrBSi/WC coatings on titanium alloy substrate

Laser-clad composite coatings on the Ti6Al4V substrate were heat-treated at 700, 800, and 900 °C for 1 h. The effects of post-heat treatment on the microstructure, microhardness, and fracture toughness of the coatings were investigated by scanning electron microscopy, X-ray diffractometry, energy dispersive spectroscopy, and optical microscopy. The wear resistance of the coatings was evaluated under dry reciprocating sliding friction at room temperature. The coatings mainly comprised some coarse gray blocky (W,Ti)C particles accompanied by the fine white WC particles, a large number of black TiC cellular/dendrites, and the matrix composed of NiTi and Ni₃Ti; some unknown rich Ni- and Ti-rich particles with sizes ranging from 10 nm to 50 nm were precipitated and uniformly distributed in the Ni₃Ti phase to form a thin granular layer after heat treatment at 700 °C. The granular layer spread from the edge toward the center of the Ni₃Ti phase with increasing temperature. A large number of fine equiaxed Cr₂₃C₆ particles with 0.2–0.5 μm sizes were observed around the edges of the NiTi supersaturated solid solution when the temperature was further increased to 900 °C. The microhardness and fracture toughness of the coatings were improved with increased temperature due to the dispersion-strengthening effect of the precipitates. Dominant wear mechanisms for all the coatings included abrasive and delamination wear. The post-heat treatment not only reduced wear volume and friction coefficient, but also decreased cracking susceptibility during sliding friction. Comparatively speaking, the heat-treated coating at 900 °C presented the most excellent wear resistance.     

Development of Ni-based and CeO2-modified coatings by microwave heating

In the present investigation the microwave hybrid heating process was used to develop coatings on P20 tool steel substrates. The experiments were carried out in a domestic microwave oven of 900?W and 2.45?GHz frequency for a duration of 360?s. Ni-based clads/coatings without cerium oxide (CeO₂;unmodified coating) and with the addition of CeO₂ (modified coating) with varying wt.% of 1–3 were developed by the microwave hybrid heating process. The effect of CeO₂ addition on the microstructure, X-ray diffraction, and Vickers hardness, and the abrasive wear behavior of the developed clads was studied under varying sliding speeds and grit sizes. Investigation showed that the optimal addition of CeO₂ (1?wt.%) can effectively improve the microstructure, hardness, and abrasive wear behavior of the coatings. The Vicker’s microhardness of the modified coating with 1?wt.% of CeO₂ was 30% higher than the unmodified coating. Abrasive wear resistance of the modified coatings was found higher with an optimal addition of 1?wt.% CeO₂ at varying sliding speeds and grit sizes.     

Effects of La2O3 on microstructure and wear properties of laser clad γ/Cr7C3/TiC composite coatings on TiAl intermatallic alloy

The effects of La₂O₃ addition on the microstructure and wear properties of laser clad γ/Cr₇C₃/TiC composite coatings on γ-TiAl intermetallic alloy substrates with NiCr–Cr₃C₂ precursor mixed powders have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive spectrometer (EDS) and block-on-ring wear tests. The responding wear mechanisms are discussed in detail. The results are compared with that for composite coating without La₂O₃. The comparison indicates that no evident new crystallographic phases are formed except a rapidly solidified microstructure consisting of the primary hard Cr₇C₃ and TiC carbides and the γ/Cr₇C₃ eutectics distributed in the tough γ nickel solid solution matrix. Good finishing coatings can be achieved under a proper amount of La₂O₃-addition and a suitable laser processing parameters. The additions of rare-earth oxide La₂O₃ can refine and purify the microstructure of coatings, relatively decrease the volume fraction of primary blocky Cr₇C₃ to Cr₇C₃/γ eutectics, reduce the dilution of clad material from base alloy and increase the microhardness of the coatings. When the addition of La₂O₃ is approximately 4 wt.%, the laser clad composite coating possesses the highest hardness and toughness. The composite coating with 4 wt.%La₂O₃ addition can result the best enhancement of wear resistance of about 30%. However, too less or excessive addition amount of La₂O₃ have no better influence on wear resistance of the composite coating.     

Untersuchungen zur Beständigkeit thermisch gespritzter Schichten im Vergleich zu Hartchromschichten bei durch Abrasion dominierter tribologischer Beanspruchung

Investigations on thermal spray coatings resistance against abrasion dominated tribological load in comparison to hard chromium coatings HVOF iron and nickel based hard alloy as well as WC/Co(Cr) and Cr₃C₂/Ni20Cr coatings are compared to APS Al₂O₃/TiO₂ and Cr₂O₃, powder flame sprayed and fused composite coatings consisting of NiCrBSi and WC/Co and electrolytically deposited hard chromium coatings concerning their wear behavior for tribological load by lose abrasive particles (ASTM G65 and ASTM G75). Thereby the influence of newly developed HVOF torch combustion chambers with reduced critical diameter and divergent expansion nozzles that both permit increased combustion gas and therefore also particle velocities on microstructure and wear resistance of the produced coatings is studied. While there is no improvement of wear resistance for hard alloy coatings compared to mild steel substrates for the specific tribological boundary conditions of these tests, especially the carbide reinforced coatings permit improvement by more than one order of magnitude in ASTM G65 tests and even more than two orders of magnitude in ASTM G75 tests. Also, for both types of tribological load HVOF coatings with WC as reinforcing phase are clearly superior to electrolytically deposited hard chromium coatings. Both use of the combustion chamber with reduced critical diameter and the expansion nozzles with divergent contour result in improved wear resistance of the thereby produced coatings. The specific wear mechanisms are deduced based on SEM examination of worn specimen surfaces.     

Microstructure and mechanical properties of copper–titanium–nitrogen multiphase layers produced by a duplex treatment on C17200 copper–beryllium alloy

In this study, a copper–titanium–nitrogen multiphase coating was fabricated on the surface of C17200 copper–beryllium alloy by deposition and plasma nitriding in order to improve the surface mechanical properties. The phase composition, microstructure and microhardness profiles of the as-obtained multiphase coating were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM) and Vickers microhardness measurements, respectively. Pin-on-disk tribometer and SEM equipped with energy dispersive spectrometer (EDS) were applied to measure tribological properties and analyze wear mechanisms involved. The XRD results show that the phase composition changes with nitriding temperature. The Ti₂N layer is replaced by a Cu–Ti intermetallic layer when the nitriding temperature is higher than 700 °C. The Cu/Ti ratio in the multiphase coatings remains at a constant value of 2:1 due to the incorporation of nitrogen atoms. The surface hardness achieves a maximum value of 983 HV at 650 °C, and decreases as the nitriding temperature increases. The increased hardness corresponds to the improved wear resistance and decreased frictional coefficient and the surface hardness is proportional to the wear rates. The wear mechanism depends on the phase composition of the multiphase coatings. With the nitriding temperature increasing, the oxidative wear mechanism changes to adhesive and abrasive mode.     

Microstructure and properties of in‐situ vanadium carbide phase reinforced nickel based coating by laser cladding

Laser cladding has been applied to fabricate in‐situ vanadium carbide phase on the surface of C45E (according to ISO 683‐1:2016 (E)) using a preplaced powder consisting of 55 wt.% Ni35 and 45 wt.% (FeV50 + graphite), meanwhile, pure Ni35 has also been cladded for comparison. The microstructure and phases analysis were carried out by means of optical microscope, X‐ray diffractometer, scanning electron microscope, energy dispersive spectroscopy, and electron probe microanalysis. The microhardness and wear resistance were tested through the microhardness tester and ring‐on‐block wear tester respectively. The results show that there are many kinds of microstructure such as cellular and columnar crystals for the pure Ni35 cladding coating, and lots of cellular or dendritic vanadium carbide and reticular Cr₂Fe₁₄C₃ phases distribute over the Fe₃Ni₂ matrix in the coating cladded with 55 wt.% Ni35 and 45 wt.% (FeV50 + graphite). Vanadium carbide phase is uniformly distributed and bonded metallurgically to the matrix very well, which increases the hardness and wear resistance. The wear resistance of coating cladded with 55 wt. % Ni35 and 45 wt. % (FeV50 + graphite) alloy powder is 5.16 times as high as C45E, and is higher 139.7% than that of the pure Ni35 clad layer.     

A study on the abrasive and erosive wear behavior of arc-deposited Cr-N-O coatings on tool steel

In this study, the cathodic arc evaporation technique, by using the chromium target and controlling the flow rate of nitrogen/oxygen reactive gases, was utilized to deposit three different Cr-N-O coatings (CrN, CrN/Cr(N,O), CrN/Cr₂O₃) on AISI M2 tool steel. Two types of wear tests were applied to evaluate the abrasive and erosive wear behavior of the coated and uncoated specimens. One was the ball-on-disk abrasion test to measure the friction coefficient of these specimens. The other was the erosion test using Al₂O₃ particles (~ 177 µm in size and Mohr 7 scale) of about 5 g, and then the surface morphologies of the eroded specimens were observed. To further understand the coating effects on the two wear behaviors of M2 steel, coating structure, morphology, and adhesion were analyzed using XRD, SEM, and TEM, respectively. The results showed that surface roughness and adhesion of the double-layered coatings (CrN/Cr(N,O) and CrN/Cr₂O₃) were inferior to those of monolithic CrN, but their hardness and elastic modulus were superior to those of CrN. In the abrasive behavior, Cr-N-O coatings reduced the friction coefficient of M2 substrate. In particular, the CrN/Cr₂O₃ has the highest hardness/elastic (H/E) modulus ration, therefore the lowest friction coefficient, among all the coated-specimens tested. In the erosive behavior, the coated specimens exhibited better erosion resistance as compared to the uncoated ones, at the impingement angles of either 30^o or 90^o. Moreover, the erosion resistance of CrN/Cr(N,O) coatings was superior to that of CrN/Cr₂O₃ coatings due to its better adhesion.     

Surface modification of Cr3C2–NiCr cermet coatings by direct diode laser

Thermal spraying has emerged as an important tool of increasingly sophisticated surface engineering technology, and it is being used widely to repair and surface modification in metallic parts. The Cr₃C₂–NiCr sprayed coatings are frequently used as wear resistant coatings against abrasion and erosion at high temperature up to 1173 K, and in corrosive environments. Hardness and microstructure of Cr₃C₂–NiCr cermet coatings fused by direct diode laser process was compared with that formed by high-velocity oxygen fuel spraying (HVOF) process. The effect of beam characteristics (power density, power, scanning speed, etc.) was examined on the surface modification of sprayed coatings. In this study, we treated Cr₃C₂–25%NiCr cermet coatings by laser irradiation process and examined its hardness compared with that formed by HVOF process. Consequently, the average hardness of laser-treated Cr₃C₂–25%NiCr cermet coatings has been found out to be higher than that of HVOF coatings. Laser remelting improved markedly the wear resistance of HVOF sprayed Cr₃C₂–25%NiCr cermet coatings.     

Carbide surface coating of Co-Cr-Mo implant alloys by a microwave plasma-assisted reaction

A technique to grow a hard carbide surface coating on Co-Cr-Mo implant alloys used in artificial joints was developed. The carbide surface coating was applied to as-cast and forged Co-Cr-Mo alloys to improve their wear properties. The surface carbide layers were produced by reactions between the alloy surface and a methane-hydrogen mixed gas by a microwave plasma-assisted surface reaction. The new carbide layers showed brain coral-like surface morphology and appear to consist of mixed phases including Cr₃C₂, Cr₂C, Cr₇ C₃, Cr₂₃C₆, and Co₂C. The Vickers microhardness of thin carbide coatings (3 m thick) was about HV 1100 regardless of the test location. The Vickers microhardness of thick carbide coatings (10 m thick) showed a wide range of hardnesses from HV 1000 to HV 2100. Co-deposition of soot and diamond films occured on a small area of the forged alloy substrates and diamond particles were sparsely dispersed on as-cast alloy substrates. The carbide surface layer has the potential to increase the wear resistance of the Co-Cr-Mo alloy as a wear resistant coating.     

高速电弧喷涂FeAlNbB非晶纳米晶涂层的组织与性能

为了提高钢铁材料的耐磨性和硬度,利用高速电弧喷涂技术在45钢基体上制备了FeAlNbB非晶纳米晶涂层.采用扫描电镜(SEM)、能谱分析仪(EDAX),透射电镜(TEM)和X射线衍射仪等设备对涂层的组织结构和相组成进行了分析,研究了非晶纳米晶的形成机制.实验结果表明:FeAlNbB非晶纳米晶涂层是非晶相、α-Fe、FeAl纳米晶和Fe3Al微晶共存的多相组织,涂层中非晶相含量约36.2%,纳米晶尺寸约14.1 nm;涂层组织均匀,结构致密,平均孔隙率约2.3%;非晶纳米晶涂层具有较高的硬度,其耐磨性是相同实验条件下制备的3Cr13涂层的2.2倍.     

Fabrication of Co-Based Coatings on Titanium Alloy by Laser Cladding with CeO2 Addition

In this study, Co-based laser cladding coatings reinforced by multiple phases were fabricated on titanium alloy. Co42 Co-based self-fluxing alloy, B₄C, and CeO₂ mixed powders were used as the precursor materials. The coatings were mainly composed of γ-Co/Ni, CoTi₂, CoTi, NiTi, TiC, Cr₇C₃, TiB₂, and TiB phases. A typical TiB₂/Cr₇C₃/TiC composite structure was chosen. It was found that CeO₂ did not influence the phase types of the coating significantly, but was effective in refining the microstructure and enhancing the microhardness and dry sliding wear resistance. Compared with the Ti-6Al-4V titanium alloy, the microhardness and wear resistance of the composite coatings were enhanced by 3.44–4.21 times and 14.26–16.87 times, respectively.     

Influence of heat treatment on microstructure and mechanical properties of iron-based coating

Iron-based alloys were deposited on the low carbon steel by plasma cladding process. Furnace annealing was conducted at 600 °C for 40 min. Resulting microstructure and phases were observed and investigated by scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS) and X-ray diffraction (XRD). Effect of post heat treatment on the mechanical properties of coatings was also studied by instrumented indentation technique. It was found that solid solution γ-(Fe, Ni, Cr) and carbide reinforced phases Cr₇C₃ were the main phases of as-cladding coatings while iron carbide became the main carbide reinforced phase for annealed coatings. For all coatings, hardness and reduced elastic modulus showed obvious load dependence, namely decreased with the indentation load increasing. It was found that calculated values of annealed coatings were generally lower than those of as-cladding coatings as a result of the dissolution of the eutectic structure which decreased the effect of dispersion strengthening.     

Microstructural characterisation of nanocomposite nc-MeC/a-C coatings on oxygen hardened Ti-6Al-4V alloy

Nanocomposite coatings are novel, important systems composed of two or more nanocrystalline, or nanocrystalline and amorphous, phases. Such coatings offer a possibility of tailoring the coating microstructure and achieving new improved properties of coated materials. In this work a duplex surface treatment, consisting of an oxygen diffusion treatment and deposition of low friction nanocomposite nc-MeC/a-C (Me = transition metal, Ti, W or Cr) coatings, was applied for improvement of the Ti-6Al-4V alloy properties. The coatings composed of nanocrystallites of transition metal carbides (TiC or Cr_xC_y or WC) embedded in hydrogen-free amorphous carbon (a-C) matrix were deposited onto the surface of an oxygen hardened Ti-6Al-4 V alloy substrate by means of a simple DC magnetron sputtering. A nano/microstructure of the substrate material and coatings has been examined by scanning- and transmission electron microscopy complemented with the results of X-ray diffraction analyses.It was found that the nanocomposite coatings are composed of different carbide nanocrystals (with sizes of a few nanometres) embedded in an amorphous carbon matrix. The results of qualitative and quantitative analyses of the nanocrystalline phase in the coatings with use of high-resolution transmission electron microscopy combined with image analysis are given in the paper.An effect of the nano/microstructure parameters of the coated alloy onto its micro-mechanical (nanohardness and Young's modulus) and tribological properties (wear resistance and friction coefficient) is discussed in the paper.