Effect of in-flight particle behavior on the morphology of flame sprayed Er2O3 splats

The morphology and microstructure of splats impact the comprehensive capability of a new coating methodology called chelate flame spraying (CFS). This study addresses the quantitative characterization of the spread morphologies of flame sprayed Er₂O₃ splats directly deposited under different spray conditions on aluminum alloy substrates with a mirror finish. The influence of the in-flight particle temperature and velocity, carrier gas type, and carrier gas ratio on the solidification mechanism of molten droplets was investigated. Image analysis methods were employed to identify single splats from the morphology observed with field-emission scanning electron microscopy (FE-SEM). In addition, Er₂O₃ films were synthesized on an Al–Mg alloy (A5052) substrate using N₂ or O₂ as the carrier gas. When O₂ was used as the carrier gas, 109-μm-thick films were deposited on the A5052 substrate. The cross-sectional porosity of the films was 3.8%. In contrast, films with 101-μm thickness were synthesized on the A5052 substrate when N₂ was used as the carrier gas. The cross-sectional porosity of these films was 13.8%. The results showed that the carrier gas type (N₂) and carrier gas ratio had a significant effect on the flattening behavior of the molten droplets. A spraying method combined with multidimensional modes is proposed to control the morphology of the splats.     

Role of Lamellae Morphology on the Microstructural Development and Mechanical Properties of Small-Particle Plasma-Sprayed Alumina

The influence of spray parameters on the microstructure and flexural strength of plasma-sprayed alumina was investigated. Coatings were applied using a small-particle plasma spray (SPPS) method, which is a recently patented process that allows submicrometer-sized powders to be sprayed. Using identical starting powders, coatings that were produced using two distinctly different spray conditions exhibited significant differences in both microstructure and strength. Scanning electron microscopy investigations of single lamellae (or splats) revealed that, for one spray condition, melted alumina particles will splash when they contact the substrate. The morphology of the splats that comprised the subsequent layers of the coating also were highly fragmented and thinner than lamellae formed under "nonsplashing" spray conditions. The surface roughness was strongly dependent on the morphology of the lamellae; increased roughness was noted for fragmented splats. Thick coatings that were comprised of splashed splats developed a unique microstructural feature that was responsible for the observed increase in roughness. These microstructural differences greatly influenced the flexure strength, which varied from 75 ± 21 MPa for the nonsplashing spray condition to 17 ± 2.4 MPa for the "splashing" condition.     

Microstructural evolution and mechanical properties of atmospheric plasma sprayed Y2O3 coating with state of in-flight particle

Y₂O₃ coating on Al₂O₃ substrate was prepared by atmospheric plasma spray (APS). Computational fluid dynamics (CFD) was carried out to predict the state of in-flight Y₂O₃ particles at different powder feeding rates. Microstructure and mechanical properties were found to be affected by the spray distance and powder feeding rate. In this study, the hardness was calculated using a field emission-scanning electron microscope (FE-SEM) because the indentation in the coating is too small to measure using a hardness test machine. The formation of pores causes a decrease in the mechanical property, and the pore length of over 10 μm substantially decreases the hardness. Meanwhile, the solidification behavior is affected by the maximum temperature of the in-flight particles. Based on computational fluid dynamics (CFD) analysis, the maximum temperature of the in-flight particles was found to decrease with increase of the powder feeding rate at the same spray distance. At the powder feeding rate of 60 g/min, a lower adhesion strength was confirmed than that at feeding rate of 30 g/min because splats were insufficiently spread due to the lower maximum temperature of the in-flight particles. The roughness and height of the coating surface were evaluated by confocal microscopy and atomic force microscopy(AFM) analyses. The roughness is the resultant of accumulated splats and the accumulation mechanism of splats is affected by the state of the in-flight particles. Furthermore, there were nano-scale differences of height on the splat surface, on which the nucleation looks like ‘rugged bark’ during solidification of splats when the in-flight particles impact the substrate.     

Fe/Al2O3梯度涂层的制备与性能

采用喷涂法和溶胶-凝胶法相结合的工艺制备钢基Fe/Al2O3梯度涂层复合材料,并对其性能进行分析。结果表明：Fe/Al2O3梯度涂层与钢基体的界面结合强度较高,达21.2MPa;涂层与基体以及涂层与涂层之间没有明显的界面,实现了良好结合。涂层的表面硬度要比钢基体高4-5倍;Fe/Al2O3梯度涂层主要由α-Al2O3、AlFeO3、Al2Fe2O3和Al3Fe5O3物相组成。     

High performance tribological coatings on a secondary cast Al–Si alloy generated by Plasma Electrolytic Oxidation

Due to their outstanding properties, including low density or high-strength-to-weight ratio, cast Al–Si alloys are attractive materials. Nevertheless, their low wear and corrosion resistance still remain a critical issue for several applications. The present work is focused on the obtention of PEO coatings on a secondary cast Al–Si alloy (EN AC-46500) and the in-depth study of the properties derived from the use of two developed aluminate-based electrolytes.All the obtained PEO coatings have been characterized in terms of their thickness and roughness, morphology, and composition. Reciprocal wear tests have been performed in order to evaluate the tribological behavior of the PEO layers, while their anti-corrosion properties have been analyzed throughout Potentiodynamic Polarization and Electrochemical Impedance Spectroscopy.Our findings suggest that the aluminate-based electrolytes led to an increase in coating thickness of density, while providing a notable improvement on the surface hardness in comparison with the uncoated Al–Si alloy. All the PEO coatings tested exhibited excellent wear resistance and an improved anti-corrosion behavior compared with the uncoated Al–Si alloy. Furthermore, K₂TiF₆-containing electrolyte promoted the obtention of PEO coatings that provided the highest protection against wear and corrosion to the cast Al–Si alloy treated.     

Friction behavior of PTFE-coated Si3N4/TiC ceramics fabricated by spray technique under dry friction

PTFE coatings were deposited on the Si₃N₄/TiC ceramic substrate by using spray technology. The surface and cross-section micrographs, adhesive force of coatings with substrate, surface roughness and micro-hardness of the coated ceramics were examined. The friction and wear behaviors of ceramic samples with and without coatings were investigated through carrying out dry sliding friction tests against WC/Co ball. The test results indicated that the coated ceramics exhibited rougher surface and lower micro-hardness, and the PTFE coatings can significantly reduce the surface friction and adhesive wear of ceramics. The friction performance of PTFE-coated sample was affected by applied load due to the lower surface hardness and shear strength of coatings, and the main wear failure mechanisms were abrasion wear, coating delamination and flaking. It can be considered that deposition of PTFE coatings is a promising approach to improve the friction and wear behavior of ceramic substrate.     

Al2O3-CoCrAlY 复合陶瓷激光熔覆层的组织与性能

研究了Ａｌ２Ｏ３－ＣｏＣｒＡｌＹ复合陶瓷涂层的组织结构、成分分布及其耐磨性能。结果表明：等离子喷涂层的组织呈层片状,面层由α－Ａｌ２Ｏ３和少量的γ－Ａｌ２Ｏ３组成,层间为机械结合界面,涂层平均硬度为８９７ＨＶ０．２。经激光重熔后的组织为单一的α－Ａｌ２Ｏ３柱状晶,在ＣｏＣｒＡｌＹ与基体间有界面相形成,其界面为冶金结合,层间存在着平缓的成分过渡;Ａｌ２Ｏ３与ＣｏＣｒＡｌＹ间的界面结合状况得到了明显的     

载重汽车销轴表面改性及其摩擦磨损性能的研究

在载重汽车销轴基材40Cr钢表面制备Ni-WC纳米复合镀层,实现表面改性,以期提高销轴表面的摩擦磨损性能。观察并分析了纳米复合镀层的表面形貌和微观结构,检测了纳米复合镀层的结合强度、硬度及摩擦磨损性能。结果表明:纳米复合镀层表面较平整、结构致密,与基材结合牢固,其硬度平均值为6 081MPa,约为基材的1.3倍;其平均摩擦因数约为0.35,磨损失重约为1.83mg,均比基材的低。低孔隙率、致密结构和高硬度,使纳米复合镀层具有良好的摩擦磨损性能。     

Influence of Spray Angle on the Pore and Crack Microstructure of Plasma-Sprayed Deposits

To understand the influence of processing parameters on the microstructure of plasma-sprayed deposits, smallangle neutron scattering measurements were made of the processing-parameter-dependent specific surface area of the voids in gray alumina deposits. These studies indicate that the voids are in the form of pores between the splats and around inclusions or unmelted particles, and are also in the form of cracks within the splats which may develop during cooling. The porous volume increases as the angle between the spray gun and the substrate (the "spray angle") decreases. This study also indicates that the cracks are preferentially oriented, and that the crack orientation also depends on the spray angle. The interlamellar pores, however, are preferentially oriented parallel to the substrate surface, and the orientation of the pore is independent of the spray angle.     

汽车活塞销镀Ni-Co合金镀层表面改性及性能研究

利用电镀技术,在汽车活塞销表面制备Ni-Co合金镀层实现表面改性。概述了活塞销表面改性的工艺过程,观察了表面改性后活塞销的形貌,检测了Ni-Co合金镀层与活塞销基体的结合强度以及表面改性后活塞销的硬度、抗拉强度及耐摩擦磨损性能。结果表明,Ni-Co合金镀层与活塞销基体结合牢固,表面改性后活塞销的表面平整均匀,硬度和抗拉强度均提高,表现出较好的耐摩擦磨损性能。Ni-Co合金镀层有效改善了活塞销的表面状况,使活塞销的硬度提高约17%,抗拉强度提高约7.2%,磨损量和磨损速率分别下降17.5%和17.9%。     

Modification of electrophoretically deposited nano-hydroxyapatite coatings by wire brushing on Ti–6Al–4V substrates

In the present study, after successful synthesis of nano-HA powders by chemical precipitation method, wire-brushing (WB) treatment was effectively employed on Ti–6Al–4V substrates for the modification of electrophoretically deposited nano-hydroxyapatite coatings. The precipitated nano-HA particles were characterized by XRD, FT-IR, and DLS analyses. The morphology and particle size of synthesized nano-HA particles was observed by FE-SEM. The Ti–6Al–4V plates were initially wire brushed at different times and rotational speeds. Microhardness profile and AFM analysis of substrates were then studied. It was found that WB treatment at 16,000 rpm for 60 s leads to a maximum enhancement in the hardness and roughness of surface. Then, the electrophoretic deposition of nano-HA particles was carried out at constant voltage of 30 V and after 60 s. The results of adhesion test and potentiodynamic polarization measurements showed that WB treatment on Ti–6Al–4V substrates could efficiently increase the bonding strength between coating and substrate as well as corrosion resistance.     

阳极氧化对TC4钛合金力学与耐磨性能的影响

对比分析了脉冲阳极氧化和直流阳极氧化工艺对TC4钛合金表面形貌、拉伸性能、疲劳强度和耐磨性的影响。结果表明,脉冲阳极氧化和直流阳极氧化膜的粗糙度相较于TC4钛合金更大,而表面硬度从高至低为:脉冲阳极氧化膜>TC4钛合金>直流阳极氧化膜。虽然阳极氧化后试样的力学性能都相较于处理前有不同程度的减小,但是耐磨性有较大的提升。脉冲阳极氧化试样的疲劳强度接近TC4钛合金基材,且明显高于同样膜厚的直流阳极氧化试样,它的强度、断后伸长率和耐磨性也更优。     

Influence of in-flight particle state diagnostics on properties of plasma sprayed YSZ-CeO2 nanocomposite coatings

This article describes the influence of controlling in-flight hot particle characteristics on properties of plasma sprayed nanostructured yttria stabilized zirconia (YSZ) coatings. This article depicts dependence of adhesion strength of as-sprayed nanostructured YSZ coatings on particle temperature, velocity and size of the splat prior to impact on the metallic substrate. Particle temperature measurement is based on two-color pyrometry and particle velocities are measured from the length of the particle traces during known exposure times. The microstructure and adhesion strength of as-sprayed nano-YSZ coatings were studied. Field emission scanning electron microscopy results revealed that morphology of coating exhibits bimodal microstructure consisting of nano-zones reinforced in the matrix of fully melted particles. The coating adhesion strength is noticed to be greatly affected by the melting state of agglomerates. Maximum adhesion strength of 42.39 MPa has been experimentally found out by selecting optimum levels of particle temperature and velocity. The enhanced bond strength of nano-YSZ coating may be attributed to higher interfacial toughness due to cracks being interrupted by adherent nano-zones.     

镁合金化学复合镀Ni-P/纳米SiC工艺的研究

在AZ 91D镁合金表面制备Ni-P/纳米SiC化学复合镀层.探讨镀液中纳米SiC微粒的质量浓度对镀速、复合镀层性能等的影响.利用扫描电镜观察镀层表面形貌,采用能谱分析仪进行镀层表面成分的定性分析,采用显微硬度计测试镀层硬度,并对不同工艺下获得的镀层进行快速磨损实验.结果表明:镀液中添加适量的纳米SiC微粒,镀速和镀层硬度都有显著的提高.当镀液中纳米SiC的质量浓度为9 g/L时,镀速可达到25.6 μm/h;当镀液中纳米SiC的质量浓度为7 g/L时,镀层的维氏硬度可达到9 380 MPa;同时镀层的耐磨性能相比于Ni-P合金镀层的也有显著提高.     

Effect of the powder particle structure and substrate hardness during vacuum cold spraying of Al2O3

In this paper, the effect of the powder particle structure and substrate hardness during vacuum cold spraying (VCS) of Al₂O₃ is investigated. Our results help understand the underlying deposition mechanism during VCS in more detail and enable the tailoring and improving of the resulting coatings. Two structurally different alumina feedstocks were used for this study. We find that the loosely agglomerated powder bonds to the substrate primarily through coordinated deformation of the nano-sized powder particles. The sintered powder, on the other hand, bonds to the substrate through severe fracture and deformation of the particles. High-resolution transmission electron microscopy (HR-TEM) was employed to observe details in the interfacial microstructure of the coatings on the two substrates with differing hardness. The hard steel substrate facilitates particle fracture, which leads to cohesive particle/particle-bonding in the coating region close to the substrate. The softer aluminum substrate leads to strong interfacial coating/substrate-bonding because the particles are embedded into the substrate. In summary, the fracture and deformation of the feedstock as well as the substrate hardness affect both adhesion (coating/substrate bonding) and cohesion (particle/particle bonding) considerably.     

SiC颗粒对镀铁层表面形貌和结构的影响

采用自制的不对称交直流电镀电源,在氯化亚铁镀铁液中加入S iC颗粒制备了Fe-S iC复合镀层。研究了S iC颗粒对镀铁层表面形貌和镀铁层结构的影响,并对复合镀层的硬度和耐磨性进行了评定。研究结果表明,加入S iC颗粒可以减少镀铁层中的微裂纹,提高镀铁层的硬度和耐磨性。     

Nano-scratch and fretting wear study of DLC coatings for biomedical application

The generation of wear particles is now considered one of the most important failures in total arthroplasty. It is especially needed to study damage process of the particles at slight movement and lower load for long-term service of implanted materials. The wear and abrasion behavior of particles on Ti–6Al–4V coated with diamond-like carbon (DLC) were appropriately simulated in the present paper by fretting wear and nano-scratch test. The coatings with a thickness of 2.5 μm were deposited with an r.f.-plasma enhanced chemical vapor deposition method. The analytic techniques employed to assess DLC coatings characterization include SEM, AFM, Raman and IR spectroscopy. Assessment of hardness, elastic modulus, abrasion and adhesion of the coatings were performed using a Nano Indenter XP system with attachments of continuous stiffness measurements (CSM) and lateral force measurements (LFM). Tribological properties of the coatings were evaluated by a fretting wear test. It was concluded that the DLC coatings had a smooth surface morphology with a rms of 6.8 nm and possessed good adhesion to the substrate, they recovered fully elastic at lower load (60 mN) and were ploughed and delaminated only partially at higher load (400 mN). Nevertheless, there was wear debris concurrently generated during the nano-scratch and fretting test, which was more evident at high loads for a definite coatings, indicating an essential necessity of the work to improve the wear resistant of the coatings to avoid the generation of wear debris. The friction coefficient of DLC coatings against corundum obtained by fretting test decreased with the increase of relative humidity, it was below 0.1 in an aqueous condition, this may be beneficial to their biomedical applications in body fluids.     

Wear behavior of graded Cr-CrN-Cr(1−x)Al(x)N coatings synthesized by closed-field unbalanced magnetron sputtering for advanced machining operations

Graded Cr-CrN-Cr_(1?x)Al_(x)N coatings were synthesized onto M42 HSS substrates used in advanced machining operations by closed-field unbalanced magnetron sputtering (CFUBMS). The tribological behavior of these graded coatings was explored in detail by advanced electron microscopy, confocal laser scanning microscopy, nanoindentation and dry sliding wear tests. The presence and magnitude of residual stresses in these coatings were determined by the XRD – sin²ψ method, which revealed increasing compressive stresses with increasing Al content. The coating surface morphology, mechanical properties were determined prior to dry sliding wear by atomic force microscopy (AFM) and nanoindentation methods, which yielded decreasing surface roughness (R_a) as well as enhancement of hardness and modulus along with increase in H/E and H³/E² ratios with increasing Al content. Tribological investigation was performed with a pin-on-disc arrangement by keeping the sliding velocity (0.2?ms^?1) and normal axial load (10?N) constant and varying the sliding distance. Specific wear rates of the order ~ 10^–17 m³ N^?1 m^?1 were encountered for all coatings with the wear rates increasing as the Al content increased implying a decrease of wear resistance of the coatings. Abrasive wear has been found to be the dominant wear mechanism during dry sliding wear. Increasing modulus mismatch between coating and substrate can be mainly attributed to a decrease in wear resistance of the coatings.     

Microstructure,adhesion, and tribological properties of conventional plasma-sprayed coatings on steel substrate

A variety of metallic and oxide coatings were deposited under various conditions on 1020 mild steel substrate by conventional plasma spraying. The coating thickness, microhardness, cohesion and adhesion failure loads, friction coefficient, and abrasive wear resistance were evaluated. The coatings were classified as follows, in order of decreasing microhardness and wear resistance: alumina, chromia, 316 stainless steel, Ni-5% Al, elemental aluminum and aluminum-polyester. Wear resistance increased with increasing microhardness and decreasing friction coefficient. The microhardness and wear resistance of high-velocity oxy-fuel (HVOF) diamond jet (DJ)-sprayed aluminum were found to be superior to those of plasma-sprayed aluminum. Plasma or flame-sprayed metallic coatings adhered well to the substrate. The cohesion, adhesion, microhardness, and wear resistance of alumina coatings exceeded those of equally thick chromia coatings.     

Mechanical behavior of YSZ coatings co-deposited with Al and Ag on AISI 316L via RF sputtering

This article presents nanohardness, coefficient of friction (COF), and wear of Yttria-stabilized zirconia coatings (YSZ) deposited on 316L steel substrates and co-deposited with Al and Ag. YSZ coatings were deposited via RF sputtering reactive phase technique. It is widely known that the RF sputtering technique produces stoichiometric coatings with high homogeneity and density. The average thickness of the coatings was 200 nm, and the X-ray diffraction study (XRD) showed the formation of alumina alpha (α-Al₂O₃) and metallic silver in the YSZ coatings deposited with Al and Ag, respectively. The mechanical properties were evaluated by means of nanoindentation, and the wear resistance was studied with pin-on-disk technique. The addition of Ag to the YSZ coatings led to decreased hardness, while the YSZ coatings deposited with Al presented an increased hardness. Finally, YSZ coatings deposited with aluminum and silver had the lowest friction coefficient, while Ag-YSZ coatings had a COF very similar to that obtained in YSZ coatings. The wear resistance test showed that YSZ coatings deposited with Al had lower volume loss compared to YSZ coatings deposited with Ag. The wear mechanism in the deposited coatings is analyzed.