Structure and properties of ceramic coatings formed on aluminum alloys by microarc oxidation

The thick and hard ceramic coatings were deposited on 2024 AI alloy by microarc oxidation in the electrolytic solution. Microstructure, phase composition and wear resistance of the oxide coatings were investigated by SEM, XRD and friction and wear tester. The microhardness and thickness of the oxide coatings were measured. The results show that the ceramic coating is mainly composed of α-Al2O3 and γ-Al2O3. During oxidation, the temperature in the microarc discharge channel is very high to make the local coating molten. From the surface to interior of the coating, microhardness increases gradually. The microhardness of the ceramic coating is HV 1 800, and the microarc oxidation coatings greatly improve the antiwear properties of aluminum alloys.     

Effects of sodium tungstate on characteristics of microarc oxidation coatings formed on magnesium alloy in silicate-KOH electrolyte

Oxide coatings on AM60B magnesium alloy were prepared using the microarc oxidation（MAO） technique in silicate-KOH electrolyte with addition of 0-6.0 g/L Na2WO4. The MAO processes in base electrolyte with different concentrations of Na2WO4 were studied. The microstructure, compositions and mechanical tribological characteristics of the oxide coatings were also investigated by SEM, XRD, XPS, microhardness analysis and ball-on-disc friction testing, respectively. It is found that the addition of Na2WO4 into the base electrolyte has direct effect on the characteristics of voltage-time curves and breakdown voltage in MAO process. The number of micropores at top of the coating surface is increased by the addition of Na2WO4. The fraction of forsterite Mg2SiO4 in the oxide coating increases with increasing concentration of Na2WO4 in base electrolytes. Furthermore, the microhardness and wear resistance of oxide coatings are enhanced as well.     

Sliding wear behavior of high velocity arc sprayed Fe-Al coating

The friction and wear behavior of Fe-Al intermetallics based coating produced by high velocity are spraying technique under dry sliding at room temperature were investigated using a ball-on-disc tribotester. The effect of sliding speed on friction coefficient and wear of the coating was studied. The worn surface of the coating was analyzed by scanning electron microscope (SEM) to explore sliding friction and wear mechanism. The results show that the variations of friction coefficient can be divided into three distinct steps during the trail. Both the friction coefficient and the wear of the coating increase with increased sliding speed due to accelerated crack propagation rate and lamellar structure with poor ductility of the coating. The coating surface is subjected to alternately tensile stress and compression stress during sliding wear process, and the predominant wear mechanism of the coatings appears to be brittle fracture and delamination.     

Wear resistance of Zr/WC composite coatings on Cr12MoV steel surface by electric spark deposition

Zr/WC composite coating was prepared on the surface of Cr12MoV steel by electric spark deposition technology to change its surface properties. The surface and worn surface morphology of the coating were observed using scanning electron microscope. Dry friction and wear tests of the coatings were carried out at room temperature. The results show that the coating is continuous and uniform, and the thickness was about 50-60 μm. The microhardness of the coating surface was highest at 1140 HV_(200g), which was significantly higher than that of the substrate. The ear tests results show that the wear weight loss, wear volume and wear rate follow the following rules: Cr12MoVWC coating Zr/WC composite coating.     

Tribological Performance of TiB2-Ni Composite Coating Deposited by APS

TiB2-Ni composite powders were prepared by pressurized hydrogen reduction cladding with different proportion of TiB2.The coatings were then prepared by APS.The microstructures and the phase composition of the powders as well as the deposited coatings were analyzed by scanning electron microscopy(SEM)and X-ray diffraction(XRD).The coatings were tested using a ring-on-disc tribometer from ambient temperature to 300°C.A sprayed Cr3C2-NiCr coating was tested as a reference.The morphologies of the worn surface of the coatings were observed and analyzed.It is found that the TiB2-Ni composite coatings present higher friction coefficient than that of the Cr3C2-NiCr coating at room temperature due to the adhesive wear mechanism,whereas the main wear mechanism of Cr3C2-NiCr coating is rupture and exfoliation.However,at high temperature,the friction coefficient of the TiB2-Ni composite coating decreases as a result of B2O3 solid lubricant,which alleviates the adhesive wear on coatings.Furthermore,the TiB2-Ni composite coating greatly reduces the mass loss of the boron cast iron.     

Effects of Cr interlayer on mechanical and tribological properties of Cr-Al-Si-N nanocomposite coating

Cr-Al-Si-N coatings were deposited on SUS 304 substrate by a hybrid coating system. A Cr interlayer was introduced between Cr-Al-Si-N coating and SUS 304 substrate to improve the coating adherence. The effects of Cr interlayer on the microhardness, adhesion, and tribological behavior of Cr-Al-Si-N coatings were systematically investigated. The results indicate that the microhardness of the Cr-Al-Si-N coatings gradually deceases with increasing thickness of Cr interlayers. The adhesion between Cr-Al-Si-N and SUS 304 substrate is improved by addition of the Cr interlayers. A peak critical load of ~50 N is observed for the coating containing Cr interlayer of 60 nm as compared ~ 20 N for the coating without Cr interlayer. The thicker Cr interlayers result in reduced critical load values. Moreover, the wear resistance of the Cr-Al-Si-N coatings is greatly enhanced by introducing the Cr interlayer with thickness of 60 nm in spite of the decreased microhardness. The friction coefficient of the coating system is also moderately reduced.     

Characterization of micro-arc ceramic coatings on Ti-2Al-2.5Zr alloy substrates

Titanium oxide coatings were synthesized on Ti-2Al-2.5Zr alloy substrates by micro-arc oxidation （MAO） technique. The surface features of the coatings were studied by scanning electron microscopy. The micro-arc discharge channels of the Ti-2Al-2.5Zr alloy decrease while the discharge channel size increases clearly with an increase in treating time. With an increase of the coating thickness the porous layer thickness increases apparently. Phase composition of the surface layers of the coatings was evaluated by X-ray diffraction and X-ray photoelectron spectroscopy. The results of XRD and XPS analysis show that the MAO coating mainly consists of anatase and rutile TiO2.     

Microstructure and Wear Resistance Evolution of HVOFSprayed WC-（W,Cr）2C-Ni Coating with Post Heat Treatment In Air Atmosphere

WC-(W,Cr)2C-Ni coating was prepared on 1Cr18Ni9Ti stainless steel and C-276 Ni-base Hastelloy by high velocity oxy-fuel(HVOF)spraying.The effect of post heat treatment in air atmosphere on the microstructure,phase composition,microhardness,fracture toughness,and wear resistance of HVOF-sprayed WC-(W,Cr)2C-Ni coating was investigated.The microstructure and phase composition of the coatings were analyzed by means of field emission scanning electron microscopy(FESEM)and X-ray diffraction(XRD).The microhardness and fracture toughness of the coatings were measured using a microhardness tester and a Vickers hardness tester.Moreover,dry friction and wear behavior of the coatings sliding against Si3N4 ball was investigated using an oscillating friction and wear tester;and the worn surfaces of the coatings were analyzed by means of scanning electron microscopy(SEM).It was found that heat treatment within 500-800°C resulted in crystallization of amorphous phase in as-sprayed coating,generating nanoscale new phases such as NiWO4,CrWO4 and Cr2WO6.Besides,heat treatment led to increase of the microhardness of as-sprayed coating,and the highest microhardness was obtained after heat treatment at 800°C.The fracture toughness and wear resistance of the as-sprayed coating increased with increasing heat treatment temperature up to 700°C but tended to decrease with further elevating temperature.In other words,the mechanical properties and wear resistance of the as-sprayed coatings were worsened owing to excessive growth of oxidation grains and depletion of ductile Ni binder after heat treatment above 700°C.Thus it was suggested that as-sprayed ceramic composite coating should be post heat treated in air at a moderate temperature of 700°C so as to achieve the optimized mechanical properties and wear resistance.     

Wear resistance of ceramic coating on AZ91 magnesium alloy by micro-arc oxidation

The ceramic coating formed on AZ91 magnesium alloy by micro-arc oxidation （MAO） was characterized. The results show that the ceramic coating （3.4-23 μm in thickness）on the surface ofAZ91 alloy was attained under different micro-arc oxidation treatment conditions, which consist mainly of MgO, Mg2SiO4 and MgSiO3 phases. Nano-hardness in a cross-sectional specimen was determined by nano-indentation experiment. The MAO coatings exhibit higher hardness than the substrate. Dry sliding wear tests for the MAO coatings and AZ91 alloy were also carded out using an oscillating friction and wear tester in a ball-on-disc contact configuration. The wear resistance of the MAO coatings is improved respectively under different treatment time as a result of different structures of ceramic coatings formed on AZ91 alloy.     

Microstructure and Tribological Behavior of Cr-Cu-N Coatings Deposited by Ion Beam Assisted Magnetron Sputtering

Cr-Cu-N coatings with copper content from 0 at%to 6.8 at%were deposited on silicon and M2 steel by ion beam assisted magnetron sputtering.The microstructure and composition of the coatings were characterized using SEM,GDOES,XRD and XPS.The mechanical properties of the coatings were tested on a standard hardness tester.The tribological behavior of the coatings in dry wear condition was studied by means of ball-on-disc wear test.The experimental results show that addition of copper can restrict the columnar crystal growing to a certain degree.XRD and XPS analysis indicate that coatings are mainly composed of Cr and CrN phase.Cu is mainly existed in a free state in the coatings.Copper adding has no obvious effects on the hardness of the coatings.However,the coatings fracture toughness can be improved by doped copper.The coefficient of friction of the coatings against bearing steel is in the range of 0.25-0.6 changing with the copper content.The coating with 2.6 at%copper shows the lowest coefficient of friction about 0.25 and wear rate which is about one tenth of that of the coating with 6.8 at%copper.The higher coefficient of friction and wear rate of the coating with 6.8at%copper may be attributed to its lower bonding strength.     

铝合金表面Al2O3-Ni涂层的制备及耐磨性研究

目的研究Al2O3含量对Al2O3-Ni复合涂层摩擦磨损性能的影响。方法采用大气等离子喷涂技术,在6082-T6铝合金基体表面分别制备Al2O3含量为30%、50%和70%的30%Al2O3-70%Ni、50%Al2O3-50%Ni、70%Al2O3-30%Ni复合涂层。对三种涂层的显微硬度和摩擦磨损性能进行对比研究,并分析原始粉末和涂层的相组成、涂层组织结构、磨损形貌和磨损机制。结果原始粉末中的部分α-Al2O3相在急冷条件下转变成γ-Al2O3新相,涂层中各衍射峰出现明显的宽化现象,有Al2O3非晶相生成。三种试样均由基体、打底层、涂层组成,基体与打底层之间有明显的分界面,打底层因与涂层化学成分相似使分界面不明显,层与层之间结合良好。涂层的显微硬度明显高于基体,约为基体硬度的4~5倍,且其随着Al2O3含量的增加而增加。在试验条件下,涂层的摩擦系数、磨痕宽度、磨损率均随着Al2O3含量的增加而减小,相较于30%Al2O3-70%Ni涂层,70%Al2O3-30%Ni涂层的摩擦系数降低了13%,磨损率降低了66.7%。30%Al2O3-70%Ni涂层磨损最严重,磨痕表面剥落明显,而50%Al2O3-50%Ni涂层与70%Al2O3-30%Ni涂层磨损后,磨痕表面产生大量即将剥落的"橘皮状"氧化物,磨损机制均为氧化磨损与粘着磨损的混合。结论 Al2O3-Ni复合涂层中增加Al2O3含量可以提高复合涂层的耐磨性。     

Thickness effects on corrosion and wear resistance properties of micro-arc discharge oxide coatings on AZ91D magnesium alloys

The microarc oxidation coatings with difference thickness were synthesized on AZ91D magnesium alloy. The microstructure and phase structure of the coatings were analyzed using SEM and XRD, the tribological properties and corrosion resistance behaviour of the coatings were also investigated. The results show that the coating contains two layers, a porous outer layer and relatively dense inner layer. The microhardness of the MAO coatings is four to six times higher than that of the magnesium alloy substrate. The MAO coatings have much better wear-resistance and corrosion resistance abilities than those of magnesium alloy substrate, but possess higher friction coefficient. The results further indicate that there is an optimization thickness for corrosion and wear resistance.     

超音速火焰喷涂Fe基非晶合金涂层材料的摩擦磨损性能研究

目的通过优化涂层制备工艺,制备致密的Fe基非晶合金涂层,以提高非晶合金涂层的耐磨性。方法采用活性燃烧高速燃气超音速火焰喷涂(AC-HVAF)技术,通过工艺优化,制备了组织致密的Fe基非晶合金涂层。利用场发射扫描电子显微镜、X射线衍射仪、维氏显微硬度计、摩擦磨损试验机、三维光学轮廓仪等设备,对非晶合金涂层的组织结构、摩擦性能和磨损机制进行了深入分析。结果 Fe基非晶合金涂层呈现典型的非晶结构,涂层厚度在300μm左右,涂层的平均显微硬度值高达1000HV0.1。在干摩擦试验条件下,Fe基非晶合金涂层的磨损量远低于304不锈钢材料,磨损率是304不锈钢基体的1/3~1/2。Fe基非晶合金涂层的磨损机制以疲劳磨损为主,伴随着氧化磨损。氧化磨损主要是由干摩擦过程中产生的摩擦热导致,氧化磨损加速了片层剥落。结论 Fe基非晶合金涂层孔隙率的降低和非晶相含量的提高,有利于稳定摩擦系数和改善涂层的耐磨损性能。     

阴极微弧电沉积表面处理钛的高温氧化行为

在0.4 mol/l Al(NO3)3乙醇溶液中,采用阴极微弧电沉积方法在纯钛表面制备出80 μm厚的氧化铝涂层.研究了钛及其镀膜样品在973 K的高温氧化行为,并分析了它们恒温氧化后的组织、成分和相组成.结果表明,具有氧化铝涂层的钛在973K的氧化速率降低了4倍,恒温氧化后涂层的形貌和相组成几乎保持不变.涂层/钛界面附近的较薄氧化铝致密层对抑制氧和钛原子的扩散起重要作用.阴极微弧电沉积是提高钛抗氧化性能的有效方法之一.     

钛合金表面微弧氧化膜层磨损性能研究

采用微弧氧化技术,以硅酸钠、磷酸钠溶液为电解液,在TC4钛合金表面制备出高硬度、高耐磨的微弧氧化膜层。用扫描电镜观测了膜层的显微结构,用X射线衍射分析其相组成,并对膜层进行了耐磨损和摩擦学性能实验。结果表明,膜层由过渡层、致密层和疏松层3层组成。其相组成主相为Al2TiO5,其次为Al2SiO5,并含有少量无定型SiO2。膜层的维氏硬度为8470MPa,是基体硬度的2倍多。采用45#钢作对磨副,载荷为5kg,磨损时间20min条件下,膜层的失重为0.25mg,仅为基体的8%左右。     

镁合金在硅酸盐体系中微弧氧化膜层的性能研究

利用交流微弧氧化装置对AZ91D镁合金在硅酸盐体系中进行了微弧氧化处理,并通过扫描电镜、电化学测试技术和表面性能测试仪等研究了氧化时间和电流密度对微弧氧化膜层表面形貌、厚度、耐蚀性、摩擦磨损性能和结合力的影响.结果表明：随氧化时间和电流密度的增大,镁合金微弧氧化膜层中微孔的数量减少,但微孔的直径和表面粗糙度增大.膜层厚度随氧化时间和电流密度的增加呈线性增大,但与基体的结合力明显降低.镁合金微弧氧化膜层的耐蚀性和耐磨性随氧化时间和电流密度的增大呈先增大后减小的趋势.镁合金在硅酸盐体系中微弧氧化处理的最佳工艺为氧化时间40min、电流密度0.20A/cm2.     

反应等离子喷涂AlNbO4-Al2O3-NbOx复合涂层的研究

目的研究等离子喷涂Al-Nb_2O_5铝热体系制备的AlNbO_4-Al_2O_3-NbO_x复合涂层的组织、力学性能和摩擦磨损性能。方法以Nb_2O_5粉和Al粉为原料,通过喷雾造粒制备复合粉,采用等离子喷涂技术喷涂Al-Nb_2O_5复合粉体,利用复合粉的自反应制备出含有AlNbO_4、Al_2O_3和NbO_x的复合陶瓷涂层。利用扫描电镜、EDS和XRD检测和分析复合涂层的组织和物相。用显微硬度计测定复合涂层的硬度,并用硬度压痕法测量裂纹扩展能(Gc)。用销盘式磨损试验机测定涂层在无润滑条件下的摩擦磨损性能。结果 XRD分析可知,复合涂层由AlNbO_4、Al_2O_3和NbO_x相组成,SEM显示涂层为交替分布的层片状组织。在28~32 k W功率范围内,随着喷涂功率的升高,涂层的硬度增加,喷涂功率为32 k W时,涂层硬度最高,为912HV0.1。随着喷涂功率的升高,涂层的裂纹扩展能先升高后降低,喷涂功率为30 k W时,涂层的裂纹扩展能最大,为14.14J/m2。摩擦系数随功率的升高先降低后保持不变,28 k W时,涂层的摩擦系数为0.7~0.8,30 k W和32 k W时,涂层的摩擦系数为0.5~0.6。磨损量随喷涂功率的增加先降低后升高,喷涂功率为30 k W时,涂层的磨损量最小。磨损后的试样进行SEM检测发现有明显的犁沟、凹槽和剥落。结论涂层具有由AlNbO_4、Al_2O_3和NbO_x相组成的交替分布的多相层片状组织。喷涂功率为30 k W时,复合涂层的性能最好。复合涂层的主要磨损机制为磨粒磨损和疲劳磨损。     

CrAISiN涂层与不同材料配副时的摩擦学特性

目的 研究CrAlSiN涂层分别与304不锈钢、TC4钛合金、Al2O3陶瓷和GCr15钢四种不同材料配副时的摩擦学特性.方法 采用阴极电弧离子镀技术在M35高速钢上制备了CrAlSiN涂层,采用扫描电镜(SEM)、显微硬度计、划痕仪、球-盘式摩擦磨损试验仪和3D轮廓仪分别测试了涂层的结构和性能.结果 CrAlSiN涂层与304不锈钢、TC4钛合金和GCr15钢配副时的磨损形式为粘着磨损和磨粒磨损,其中与亲和性高的304不锈钢、TC4钛合金粘着磨损严重.CrAlSiN涂层与不锈钢对磨时,摩擦系数最高,达到0.71;与GCr15钢对磨时,摩擦系数最低,但摩擦系数波动大;与钛合金对磨时,摩擦系数介于两者之间.CrAlSiN涂层与亲和性较差的Al2O3陶瓷之间的磨损形式为磨粒磨损,随着磨损的进行,摩擦系数逐渐降低.结论 CrAlSiN涂层与亲和性较高的材料对磨时,磨损形式为粘着磨损和磨粒磨损,与亲和性较差的Al2O3对磨时为磨粒磨损.     

微弧氧化表面处理对铝合金拉伸性能的影响

研究了微弧氧化表面处理对LY12CZ铝合金拉伸性能的影响,并用扫描电镜(SEM)观察了拉伸断口及氧化膜形貌。结果表明,LY12CZ铝合金表面生长一层陶瓷氧化膜后拉伸性能变化不大。屈服强度、抗拉强度、弹性模量下降量都小于5%,伸长率也略有降低。试样表面氧化膜经过抛光后,拉伸性能有所改善。已拉伸试样的表面均匀地残留大量氧化膜碎片,显示氧化膜与基体结合状况良好。