Tribological Properties of Mo-N Hard Coatings on Ti6Al4V by Double Glow Discharge Technique

Mo-N hard coatings on Ti6Al4V were formed using double glow discharge technique. The fundamental coating properties, such as the phase, hardness and elastic modulus were investigated. The tribological performances of the coatings in dry wear condition were studied by means of ball-on-disc wear machine. The experimental results showed that the thickness of the Mo-N hard coating was about 10 µm. The coating was single fcc γ-Mo2N phase with (200) preferred orientation. The hardness and the elastic modulus of the coating was 13.80 GPa and 261.65 GPa respectively. The surface treatment enhanced the hardness and elastic modulus of the surface of Ti6Al4V base greatly. With GCr15 slider ball, the friction coefficient of the Mo-N hard coating was in the range of 0.56~0.65 at the steady state. Though the coating did not show friction reducing effect, it improved the wear resistance of Ti6Al4V greatly.     

Nanomechanical and nanotribological characterization of noble metal-coated AFM tips for probe-based ferroelectric data recording

Probe-based data recording is being developed as an alternative technology for ultrahigh areal density. In ferroelectric data storage, a conductive atomic force microscope (AFM) probe with a noble metal coating is placed in contact on lead zirconate titanate (PZT) film, which serves as the ferroelectric material. A crucial mechanical reliability concern is tip wear during contact of the ferroelectric material with the probe. To achieve high wear resistance, the mechanical properties (such as elastic modulus and hardness) of the metal-coated probe should be high. Nanoindentation experiments were performed in order to evaluate the mechanical properties of four commercial noble metal coatings, namely, Pt, Pt-Ni, Au-Ni and Pt-Ir, deposited on AFM probes. The effective hardness and elastic modulus were evaluated, using a contact mechanics model that accounts for the effect of the underlying silicon substrate. The Pt-Ir coating was found to exhibit the highest hardness, highest elastic modulus and lowest creep resistance. Nanoscratch studies reveal that the noble metal coatings are removed primarily by plastic deformation. The Pt-Ir and Pt coatings show the highest and lowest scratch resistance, respectively, which is consistent with results obtained from wear tests of the noble metal-coated AFM probes on a PZT surface.     

微弧氧化处理对钛铌合金力学及摩擦磨损性能的影响

采用微弧氧化的方法于磷酸盐电解液中在二元β型TiNbx(x=5,10,15,20,25)合金表面制备了微弧氧化涂层。利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)表征各合金表面微弧氧化涂层的物相组成和微观形貌。采用纳米压痕仪、球-盘摩擦磨损实验仪分析了微弧氧化处理对钛铌合金力学性能、耐磨性的影响。结果表明,通过微弧氧化处理可以有效的在各基体表面制备出氧化涂层,表面微孔数目及大小无明显差别,拥有相似的致密度,氧化涂层主要由TiO₂相组成。随着基体Nb含量的增加,各基体表面微弧氧化涂层的硬度值与弹性模量表现出相同的变化趋势,Ti-15Nb合金表面微弧氧化涂层的硬度值和弹性模量值最大。经过微弧氧化处理后,Ti-5Nb和Ti-15Nb表面摩擦系数与基体相近,并无减摩效果;Ti-10Nb、Ti-20Nb和Ti-25Nb表面摩擦系数下降了55%以上,主要磨损机制由磨粒磨损变为粘着磨损,改善了合金的耐磨性能。     

Effect of Aging Treatment on Microstructural and Mechanical Characteristics of PEO Coatings on Mg-Al Alloy

Cast Mg-6 wt pct Al alloy solution-treated at 683 K for 16 h and aged at 498 K was coated by plasma electrolytic oxidation （PEO） method.The Mg-6 wt pct Al alloy aged for 16 h exhibited the highest microhardness and wear resistance.After PEO coating,however,the microhardness and wear resistance of coatings on Mg- 6 wt pct Al alloy showed a tendency to decrease with increasing aging time,which was in aggrement with the change of thickness with aging time.In addition,the coatings on solution-treated Mg-6 wt pct Al alloy had better microhardness and wear resistance than those on aged Mg-6 wt pct Al alloys.Consequently,it can be understood that the aging treatment has a deleterious influence on the mechanical properties of coatings on Mg-6 wt pct Al alloy.     

铝合金专用黑色耐磨涂料的研制

针对黑色阳极氧化膜层的修复研制了一种专用耐磨涂料，该涂料可直接喷涂在原阳极氧化膜层上，热固化成膜，膜层硬度高、耐磨性好，具有较优良的综合性能，解决了表面修复的难题，该涂料也可应用在其他金属材料的表面防护上。     

Structure, mechanical and tribological properties of diamond-like carbon films on aluminum alloy by arc ion plating

The low hardness and poor tribological performance of aluminum alloys restrict their engineering applications. However, protective hard films deposited on aluminum alloys are believed to be effective for overcoming their poor wear properties. In this paper, diamond-like carbon (DLC) films as hard protective film were deposited on 2024 aluminum alloy by arc ion plating. The dependence of the chemical state and microstructure of the films on substrate bias voltage was analyzed by X-ray photoelectron spectroscopy and Raman spectroscopy. The mechanical and tribological properties of the DLC films deposited on aluminum alloy were investigated by nanoindentation and ball-on-disk tribotester, respectively. The results show that the deposited DLC films were very well-adhered to the aluminum alloy substrate, with no cracks or delamination being observed. A maximum sp³ content of about 37% was obtained at −100 V substrate bias, resulting in a hardness of 30 GPa and elastic modulus of 280 GPa. Thus, the surface hardness and wear resistance of 2024 aluminum alloy can be significantly improved by applying a protective DLC film coating. The DLC-coated aluminum alloy showed a stable and relatively low friction coefficient, as well as narrower and shallower wear tracks in comparison with the uncoated aluminum alloy.     

Improved Tribocorrosion Properties of Ti6Al4V Alloy by Anodic Plasma Electrolytic Oxidation

Ti6Al4V alloy has good corrosion resistance due to the formation of the passive oxide films on the surface of Ti6Al4V alloy. However, Ti6Al4V alloy has poor tribocorrosion resistance in the seawater environment. Herein the present work, plasma electrolytic oxidation (PEO) with the electrolyte of glycerol and sodium borate is used to generate PEO coatings on the surface of Ti6Al4V alloy to improve its tribocorrosion properties. The microstructure and tribocorrosion properties of PEO coatings are investigated by using scanning electron microscopy, X-ray diffraction, and tribometer, respectively. The growth kinetics and the tribocorrosion mechanisms of PEO coatings are discussed in detail. It is shown in the results that PEO coatings deposited on the surface of Ti6Al4V alloy are composed of rutile and anatase phases. The surface hardness and thickness of PEO coatings are enhanced with the increase of the voltage and time. The wear rate of Ti6Al4V alloy with PEO coatings is significantly reduced in artificial seawater.     

Microstructure and properties of zirconia-alumina nanolaminate sol-gel coatings

Zirconia-alumina multilayer nanolaminate coatings were applied on stainless steel 316 substrates by a sol-gel dipping method. The coatings were characterised using X-ray diffraction, optical and scanning electron microscopy. The hardness and elastic modulus, the wear resistance and the oxidation resistance of the coatings were measured and assessed. It was observed that the coatings possessed fine grains, fine pores and high retention of tetragonal zirconia phase. The coatings exhibited high hardness and elastic modulus as well as good resistance to oxidation at high temperatures. However, these properties may be influenced by the interactions at the coating/substrate interface.     

Cr3C2 incorporation into an Inconel 625 laser cladded coating: Effects on matrix microstructure,mechanical properties and local scratch resistance

There is an increasing industrial demand for metal alloys with high wear resistance under severe operating conditions. Ni-based alloys, such as Inconel superalloys, are an excellent option for these applications; however, their use is limited by their high cost. Ni-based coatings deposited onto carbon steel substrates are being developed to achieve desired surface properties with reduced cost. Laser cladding deposition has emerged as an excellent method for processing Ni based coatings. In this work, microstructure, mechanical properties and local wear behaviour have been investigated in response to the addition of Cr₃C₂ ceramic particles into an Inconel 625 alloy deposited onto a ferritic steel substrate by laser cladding. Using this deposition technique, a homogeneous distribution of Cr₃C₂ particles was observed in the coating microstructure. The addition of ceramic particles to the starting powder resulted in the formation of hard precipitates in the coating microstructure. The partial dissolution of Cr₃C₂ particles during the laser cladding process increased the hardness of the Inconel 625 matrix. Depth sensing indentation and scratch tests were performed to study the local wear behaviour and scratch resistance of the cermet matrix compared with the conventional Inconel 625 alloy. Finally, the effect of Cr₃C₂ on mechanical properties was correlated with the observed microstructure modifications.     

高硬度耐磨损电弧喷涂涂层研究

采用电弧喷涂方法制备的高硬度耐磨损JCW-B涂层可广泛应用于工业零部件耐磨表面.对涂层的组织、孔隙率、硬度、结合强度及耐磨粒磨损性能进行分析,对比研究该涂层与Ni60喷熔层的耐冲蚀性能.结果表明JCW-B涂层组织致密,孔隙率低于4%,显微硬度HV0.1高于1200,平均结合强度大于50MPa.研究了涂层的耐磨损机理,XRD结果显示涂层中主要含有Fe3B硬质相,对涂层起到弥散强化的作用.     

Characterization of Plasma Nitrided and PVD-TiN Duplex Treated Armco Iron and En40B Steel by Nanoindentation

The nanoindentation test has been applied to evaluate the mechanical properties such as hardness, elastic moduli and deformation behaviors of Fe₄N iron nitride layers produced on Armco iron and En40B steel by plasma nitriding, and PVD-TiN coatings deposited on En40B with or without prior plasma nitriding treatment. Results showed that the Fe₄N layer produced on En40B exhibits higher hardness than that on Armco iron. This is attributed to the effect of the alloy compositions, especially Cr element. However, similar elastic modulus values to that of bulk ferrous alloys have been found for Fe₄N layers produced on both Armco iron and En40B. Under lower loads, TiN coatings on nitrided substrate behave quite the same in hardness and elastic modulus as TiN coatings on untreated En40B. Whilst with increasing indentation load and depth, duplex treated (i.e., combined plasma nitriding and PVD-TiN coating) En40B possesses higher composite hardness, elastic modulus and load bearing capacity than TiN coated base material.     

Electrodeposited composite coating of Ni-W-P with nano-sized rod- and spherical-shaped SiC particles

In this research, Ni-W-P-SiC nanocomposite coatings are electrodeposited from the plating solution containing suspension of nano-sized spherical- and rod-shaped SiC particles. The influence of SiC particle charge, applied current density, surfactant addition and the particle shape on the SiC incorporation rate has been studied. The phase structure, microhardness and wear resistance of Ni-W-P-SiC nanocomposite coatings were evaluated using X-ray diffraction (XRD), microhardness tester and wear test apparatus. The surface morphology of the produced coatings and worn surfaces has been investigated using scanning electron microscope (SEM). Additionally, the composite coating exhibited higher hardness and wear resistance than the pure Ni-W-P alloy. Regardless the particle shape, the mechanical characteristics of composite coatings are improved with increasing of SiC wt.% into the matrix. The corrosion behavior of the produced coatings was studied using anodic polarization measurements. The nanocomposite coating incorporating SiC rods exhibited higher mechanical and corrosion performance compared with deposits with spherical SiC nano-particles.     

Influence of Ar/N2 Flow Rate on Structure and Property for TaN/NbN Multilayered Coatings

TaN/NbN multilayered coatings with nanoscale bilayer periods were synthesized at different Ar/N2 flow rates by RF （radio frequency） magnetron sputtering. XRD （X-ray diffraction） and Nano Indenter System were employed to investigate the influence of Ar/N2 flow rate （FAr：FN2） on microstructure and mechanical properties of the coatings. The low-angle XRD pattern indicated a well-defined composition modulation and layer structure of the multilayered coating. All multilayered coatings almost revealed higher hardness than the rule-of-mixtures value of monolithic TaN and NbN coatings. At FAr：FN2=10, the multilayered coating possessed desirable hardness, elastic modulus, internal stress, and fracture resistance, compared with ones synthesized at other Ar/N2 flow rates. The layered structure with strong mixture of TaN （110）, （111）, （200） and Nb2N （101）textures should be related to the enhanced mechanical properties.     

CrNi3MoVA钢表面电火花沉积W-Ni-Fe-Co涂层的摩擦磨损性能

为进一步拓展火炮身管内膛强化手段,采用粉末冶金技术制备了W-Ni-Fe-Co合金,利用电火花表面沉积技术在CrNi3MoVA钢表面沉积了W-Ni-Fe-Co涂层,同时利用电镀技术在CrNi3MoVA钢表面制备了硬Cr涂层与之进行比较,用纳米压痕仪和摩擦磨损试验机研究了涂层的摩擦磨损性能,并利用XRD、SEM和EDS研究了沉积态和磨损后涂层的相结构、形貌及成分。结果表明电火花沉积W-Ni-Fe-Co涂层由α-W、γ-Fe和NiWO4组成,α-W在涂层中呈白亮带分布;W-Ni-Fe-Co涂层的硬度较电镀硬Cr涂层降低了18%,弹性模量较电镀硬Cr涂层提高了4%;W-Ni-Fe-Co涂层的磨损机制为轻微的粘着磨损,而电镀硬Cr涂层为严重的粘着磨损;CrNi3MoVA钢表面沉积W-Ni-Fe-Co涂层较电镀硬Cr涂层具有明显的减摩耐磨效果,随着摩擦速度的增加,W-Ni-Fe-Co涂层的摩擦系数降低,其原因是磨损表面氧化加剧,氧化物的自润滑作用加大。     

铝合金微弧氧化陶瓷层微观形貌与力学性能的不均匀性

利用直流脉冲微弧氧化电源于硅酸盐系电解液中对尺寸为200mm×200mm×1mm的LY12铝合金样品进行表面处理,采用扫描探针显微镜和纳米金刚石压头观察并测定了样品表面中心区域和边缘区域陶瓷层的微观形貌、弹性模量、硬度及抗擦伤性能的差异。结果表明:铝合金微弧氧化陶瓷层的弹性模量和硬度平均值不仅较Al2O3的理论值有较大差距,且样品平面内陶瓷层的形貌和性能也不均匀,中心区域陶瓷层的微孔密度大而孔径小,同时陶瓷层的厚度、弹性模量、硬度以及临界载荷平均值分别较边缘区域减小约25.0%、27.7%、25.6%和8.50%。     

Mechanical properties of conventional and nanostructured plasma sprayed alumina coatings

The hardness and the elastic modulus measured by microindentation of three different types of plasma sprayed alumina coatings have been compared. Usually, such coatings present porosity and heterogeneity which affect the measurement of the mechanical properties. To take such effects into account along with the indentation size effect which is relevant to all hardness studies, the Proportional Specimen Resistance model is applied. The three alumina coatings show closely similar mechanical properties at indentation loads exceeding 1 N, i.e., macrohardness around 5.7 GPa, indentation size effect parameter around 5.5 MPa mm and elastic modulus around 160 GPa. For loads below 1 N, the extrapolated values of the macrohardness of crushed and agglomerated alumina coatings increased to 8.5 GPa, while the indentation size effect parameter has the same value, and the elastic modulus increased to 320 GPa. However, no significant change in the measured values of hardness and the elastic modulus of the nanostructured alumina coating has been observed. This result is attributed to porosity and the bimodal microstructure of the nanostructured coating where a semimolten phase coexists along with the fully molten phases.     

Investigating the wear characteristics of engineered surfaces: low-temperature plasma nitriding and TiN + MoS x hard-solid lubricant coating

Significant progress has been made in the past decade in plasma nitriding with a majority of the research work focusing on improving hardness and wear resistance of the nitrided surface through the reduction of nitriding temperature, pressure or time. Hard-solid lubricating coatings have also been extensively studied for lowering the wear rate and coefficient of friction of traditional hard coatings such as TiN by the combined effect of hardness and solid lubrication. In this study, the wear characteristics of low-temperature plasma-nitrided steel substrate performed using a Saddle-field fast atom beam source and TiN + MoS _x hard-solid lubricant coating deposited by a closed-field magnetron-sputtering technique have been investigated. The thin hard layer in plasma-nitrided substrates exhibited much higher hardness and lower wear compared to the untreated substrate in pin-on-disc wear testing. In addition, the study of the wear track morphology of the nitrided samples evidenced significant reduction of deeper ploughing and plastic deformation due to higher hardness and load supporting of the nitrided layer. On the other hand, due to the incorporation of MoS₂ in TiN coating, the wear resistance and coefficient of friction were greatly improved in TiN + MoS _x coating compared to pure TiN coating. In contrast to TiN coating, a relatively smoother wear track with less abrasive wear also supported the beneficial effects of adding MoS₂ in TiN coating.     

碳弧熔覆工艺对熔覆层组织及性能的影响

为获得高硬度、高耐磨性的表面合金层,将镍基自熔合金粉末预先涂覆在Q235钢表面,利用碳弧热源进行熔覆制备熔覆层。通过金相显微镜、硬度计及磨粒磨损试验机对熔覆层表面的组织及性能进行测试,研究焊接电流和涂覆层厚度对熔覆层组织和性能的影响。结果表明:焊接电流相同,增加涂覆层厚度,熔覆层的表面硬度和耐磨性呈现先增加后降低的趋势;涂覆层较薄时,熔覆层硬度、耐磨性随电流增大而下降,涂覆层较厚时,熔覆层硬度、耐磨性随电流增大而呈上升趋势;当涂覆层厚为4 mm,焊接电流为200 A时,组织为镍基固溶体加共晶物,共晶组织为镍基固溶体与多种碳化物、硼化物共晶,硬度最高,为54.3 HRC,耐磨性最好。     

Indentation modulus extrapolation and thickness estimation of ta-C coatings from nanoindentation

Coatings used in tribological applications often exhibit high hardness and stiffness to achieve high wear resistance. One coating characterization method frequently used is nanoindentation which allows the determination of indentation hardness and indentation modulus among other material properties. The indentation modulus describes the elastic surface behavior during indentation and is, among hardness, a direct indicator for wear resistance. To obtain the true indentation modulus of a coating, it must be measured with varying loads and then extrapolated to zero load. Current recommendation of the standard ISO 14577-4:2016 is a linear extrapolation which fits poorly for nonlinear curves. Such nonlinear curves are commonly found for high hardness mismatches between coating and substrate, for example, superhard tetrahedral amorphous carbon coatings (ta-C) on a steel substrate. In this study, we present a new empirical fit model, henceforth named sigmoid. This fit model is compared to several existing fit models described in the literature using a large number of nanoindentation measurements on ta-C coatings with wide ranges of indentation modulus and coating thickness. This is done by employing a user-independent and model agnostic fitting methodology. It is shown that the sigmoid model outperforms all other models in the combination of goodness of fit and stability of fit. Furthermore, we demonstrate that the sigmoid model’s fit parameter directly correlates with coating thickness and thus allows for a new approach of determining ta-C coating thickness from nanoindentation.

     

Improving sliding and abrasive wear behaviour of cast A356 and wrought AA7075 aluminium alloys by plasma electrolytic oxidation

An important limitation of aluminium alloys for mechanical applications is their poor tribological behaviour. In this study, surface treatment by plasma electrolytic oxidation (PEO) has been applied to two widely used aluminium alloys: A359 (hypoeutectic Al–Si–Mg) cast alloy and AA7075 (Al–Zn–Mg–Cu) wrought alloy, in order to improve their wear resistance, under sliding and abrasive wear conditions. The main aim of this work was the comparison of the properties and wear resistance of the oxide layers grown under the same PEO treatment conditions on two different aluminium alloys which might be coupled in engineered components. Significant differences in the phase composition, microstructure and mechanical properties measured by microindentation were observed in the oxide layers grown on the two substrates, and were ascribed to the effects of the different compositions and microstructures of the substrate alloys. Abrasion tests were carried out in a micro-scale abrasion (ball-cratering) test, with both alumina and silicon carbide abrasive particles. The results demonstrated the influence of the abrasive material on wear behaviour: whereas relatively aggressive SiC particles gave comparable results for both PEO treated and untreated samples, with the less aggressive Al₂O₃ abrasive the wear rates of the PEO treated samples, for both substrates, were significantly lower than those of the untreated substrates. In unlubricated sliding the PEO treatment significantly increase the wear resistance of both the aluminium alloys, at low applied load. In this condition the wear behaviour of the PEO treated alloys is strongly influenced by the stability of a protective Fe–O transfer layer, generated by wear damage of the steel counterpart. Under high applied loads however, the transfer layer is not stable and the hardness of the PEO layer, as well as the load bearing capacity of the substrate, become the main factors in influencing wear resistance.