等离子熔覆多元镍基涂层-基体的力学性能研究

目的在FV520B不锈钢基体上,采用等离子熔覆技术制备多元镍基涂层,研究不同成分配比涂层-基体协同作用下的力学性能。方法通过扫描电子显微镜分析涂层的表面及界面形貌,并对涂层-基体进行了拉伸及高温压缩性能测试,得到各涂层的抗拉强度及高温变形抗力,对比分析组织、相分布特征及涂层成分对涂层-基体系统力学性能的影响。结果等离子熔覆涂层组织致密,界面处呈现良好的冶金结合,这种结合方式可提高涂层-基体的综合力学性能;涂层-基体协同作用可显著提高材料的抗拉强度及变形抗力,且涂层的成分、组织及相分布特征是影响涂层-基体协同形变行为的关键因素。其中,Ni60+20%Ti涂层材料的抗拉伸性能最好,抗拉强度高达921 MPa,较基体材料提高了19.6%。Ni60+30%Ti+10%WC涂层-基体的高温力学性能最好,高温变形抗力达687.87 MPa。结论等离子熔覆多元镍基涂层使基体材料的抗拉强度有所提高,且高温变形抗力提高显著。     

Cracking behaviour of PVD tungsten coatings deposited on steel substrates

Tungsten coatings have been deposited on steel substrates by magnetron sputtering. For the same processing conditions, the increase of the coating thickness enhances the (111) component of the crystallographic texture whereas the residual stress level decreases. Tensile and four-point bending tests, associated with an acoustic emission analysis, have been performed inside a SEM chamber in order to study the cracking mechanisms. When the residual stresses are taken into account, an intrinsic critical cracking stress and the associated energy release rate can be determined; the obtained values suggest an intergranular cracking mechanism. No debonding has been observed at the interface despite the large plastic deformation of the substrate at the crack tips. The observed strain localisation modes in the substrate near the interface have been shown to have a major influence on the limit crack density.     

几种硬质履层体在滑动接触时的性能比较

在运用有限元软件,分别对在受相同表面载荷作用下的单覆层体、三明治覆层体及梯度覆层体的滑动接触进行了弹一塑性计算。结果表明梯度硬覆层体在改善界面附近应变、应力场及裂纹应力分布场等方面比其它覆层体具有较明显的优点。三明治层能有效地减小膜层与基体间的应力值,且在界面处裂纹尖端处的应力也很小,但接近界面处的应力、应变梯度却很大。普通多层膜与单层膜相比,应力、应变分布没有很大的改进。     

The effect of substrate composition on the electrochemical and mechanical properties of PEO coatings on Mg alloys

Plasma electrolytic oxidation (PEO) is a unique surface treatment technology which is based on anodic oxidation forming ceramic oxide coatings on the surface of light alloys such as Mg, Al and Ti. In the present study, PEO coatings prepared on AZ91D, AZ31B, AM60B and AM50B Mg alloys have been investigated. Surface morphology and elemental composition of coatings were determined using scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS). SEM results showed that the coating exhibited a porous top surface layer and a subsequent dense layer with micro-pores and shrinkage cracks. Phase analysis of coatings was carried out by X-ray diffraction (XRD). XRD analyses indicated that PEO coatings on AZ alloys had higher amount of Periclase (MgO) followed by the presence of Spinel (MgAl₂O₄) e.g. on the AZ91D alloy compared to that on AM series alloys. In order to examine the effect of substrate composition on adhesion strength of PEO coating scratch tests were carried out. Electrochemical corrosion tests were undertaken by means of potentiodynamic polarization technique in 3.5% NaCl solution at room temperature (20 ± 2 °C). Corrosion test results indicated that the corrosion rates of coated Mg alloys decreased by nearly two orders of magnitude as compared to bare Mg alloys. PEO coatings on AZ series alloys showed better corrosion resistance and higher adhesion properties than AM series alloys. In addition to the PEO processing parameters, such are mainly attributes of the compositional variations of the substrate alloys which are responsible for the formation, phase contents and structural properties of the PEO coatings.     

The effect of oxide coatings on fatigue properties of 7475-T6 aluminium alloy

The effect of hard anodic oxide and plasma electrolytic oxide coatings on the fatigue strength of 7475-T6 aluminium alloy has been investigated. The coated aluminium alloy was tested using constant load uniaxial tensile fatigue machine. Hard anodising led to an appreciable reduction in the fatigue strength of 7475-T6 alloy of about 75% for a 60 μm thick coating. Further, plasma electrolytic oxidation resulted in reduction of the fatigue strength of about 58% for a 65 μm thick oxide coating. The decrease in fatigue strength of the hard anodic oxide coatings was associated with the stress concentration at the microcracks in the coating. The better fatigue performance of the PEO coatings was attributed to the development of the compressive residual internal stress within the coatings. The reduction in the fatigue strength of the PEO coatings as compared to the uncoated material was associated with the development of the tensile residual internal stress within the substrate. This may cause an early crack initiation in the substrate adjacent to the coating.     

几种金属基板上冷喷涂铜涂层的试验与模拟

采用自主研制的冷喷涂设备在三种典型基板上进行喷涂试验,相同的工艺参数下,在铜和铝基板上得到良好的铜涂层,而在钢基板上则没有沉积.实验结果表明:涂层与基板界面、涂层内部颗粒界面结合良好,铜涂层组织致密,显微硬度高达150HV0.1;从涂层表面形貌扫描电镜(SEM)照片中可以观察到射流状的金属,说明颗粒发生了巨大变形,经计算知颗粒在碰撞中压缩率达69%;粉末和涂层的X射线衍射(XRD)结果表明铜粉末在冷喷涂过程中没有发生氧化.同时,数值模拟了铜颗粒与三种基板的碰撞过程,讨论了形成有效结合的判断准则,根据该准则,计算出铜颗粒在铜、铝、钢基板上的临界沉积速度分别为600m/s,500m/s,800m/s,从而解释了铜颗粒在三种基板上不同的沉积行为.     

Growth mechanism and corrosion behavior of ceramic coatings on aluminum produced by autocontrol AC pulse PEO

Ceramic coatings are produced on aluminum alloy by autocontrol AC pulse Plasma Electrolytic Oxidation (PEO) with stabilized average current. Transient signal gathering system is used to study the current, voltage, and the transient wave during the PEO process. SEM, OM, XRD and EDS are used to study the coatings evolution of morphologies, composition and structure. TEM is used to study the micro profile of the outer looser layer and inner compact layer. Polarization test is used to study the corrosion property of PEO coatings in NaCl solution. According to the test results, AC pulse PEO process can be divided into four stages with different aspects of discharge phenomena, voltage and current. The growth mechanism of AC PEO coating is characterized as anodic reaction and discharge sintering effect. PEO coating can increase the corrosion resistance of aluminum alloy by one order or two; however, too long process time is not necessarily needed to increase the corrosion resistance. In condition of this paper, PEO coating at 60 min is the most protective coating for aluminum alloy substrate.     

锆合金Cr涂层包壳管在环向压缩作用下的裂纹行为EI北大核心CSCD

金属Cr涂层是事故容错燃料(ATF)包壳候选涂层之一,在各方面具有优异的性能。在实际工况下,包壳管会受到环向外压力的作用而导致涂层破裂,研究锆合金Cr涂层膜基界面裂纹萌生和扩展行为很有意义。使用多弧离子镀技术在锆合金基体表面制备Cr涂层,利用电子力学试验机对锆合金Cr涂层包壳管进行不同变形量的环向压缩试验。采用扫描电子显微镜(SEM)、能谱仪(EDX)、XRD和纳米压痕仪等测试设备对锆合金Cr涂层试样的微观组织进行表征,研究并分析Cr涂层表截面裂纹的微观行为。结果表明,试样的变形分为弹性变形-裂纹萌生阶段和塑性变形-裂纹扩展阶段两个阶段,发现锆合金Cr试样界面裂纹的产生有两种形式:①裂纹从膜基界面处萌生,原因是Cr涂层和锆合金基体材料的不同使得膜基界面发生涂层应力集中;②表面萌生裂纹,由于Cr涂层存在微缺陷。没有发现涂层的剥落现象,说明其界面结合性能较佳。采用多个变形量研究锆合金Cr涂层包壳管膜基界面裂纹的萌生与扩展过程,为ATF包壳涂层结构完整性和稳定性提供试验依据。     

Influence of process parameters on electrolytic plasma discharging behaviour and aluminum oxide coating microstructure

In this study, a plasma electrolytic oxidation process (PEO) was used to produce oxide coatings on commercially pure aluminum (Al 1100) at two different current modes, pulsed unipolar and bipolar modes. Optical emission spectroscopy (OES) in the visible and near ultraviolet (NUV) band (285 nm-800 nm) was employed to investigate the PEO plasma. The emission spectra were recorded and plasma temperature profile versus processing time was constructed using line intensity ratios method. Scanning Electron Microscopy (SEM) with energy dispersive x-ray analysis (EDS) was used to study the coating microstructure and coating cross section. It was found that the plasma discharge behavior significantly influenced the microstructure and the morphology of the oxide coatings. The main effect came from the strongest discharges which were initiated at the interface between the substrate and the coating. Through manipulation of process parameters to control or reduce the strongest discharge, the density and quality of the coating layers could be modified. This work demonstrated that by adjusting the ratio of the positive to negative pulse currents as well as their timing in order to eliminate the strongest discharges, the quality of the coatings was considerably improved.     

变形温度对核电用锆包壳管表面Cr涂层开裂行为的影响

Cr涂层能够有效提高核电反应堆锆包壳管的事故容错能力，但在高温下其内部可能会萌生裂纹导致涂层开裂失效，现有Cr涂层开裂行为研究多针对常温，因此研究不同温度下Cr涂层的开裂行为对于其应用具有重要的理论和工程价值。采用多弧离子镀技术在N36锆合金包壳管外表面制备厚度为14μm左右的Cr涂层，采用WDW-100C万能试验机对涂层管分别进行室温（25℃）与高温（100、200、300、400℃）拉伸试验，并通过超景深显微镜和扫描电镜（SEM）观察涂层的裂纹表面与截面形貌，对Cr涂层在不同温度下的开裂行为与开裂机理进行研究。结果表明，随着温度升高，涂层管的屈服强度从（400±5）MPa下降到（150±5）MPa，涂层管的总体塑性变化不大；室温下裂纹萌生于涂层内部，其开裂方式为脆性沿晶断裂；100℃时涂层开裂方式不变，但表面裂纹数量减少，裂纹尖端出现钝化，由V字形转变为U字形；随着温度进一步升高，涂层的塑性变形能力提高，其表面呈流线形塑性变形；200℃及以上温度下，涂层表面无明显开裂，仅出现少量微裂纹，塑性的升高导致拉伸过程中涂层的变形量与基体存在差异，裂纹开始萌生于界面处，其断裂方式也由脆性断裂...     

Investigation of Plasma Electrolytic Oxidation (PEO) coatings on a Zr-2.5Nb alloy using high temperature/pressure autoclave and tribological tests

A Plasma Electrolytic Oxidation (PEO) process was used to produce thin oxide coatings on a Zr-2.5 wt% Nb alloy. Effects of current density on surface morphologies and wear properties of PEO coatings were investigated and compared to the uncoated substrate and a commercially used black oxide coating. Corrosion properties at ambient and high temperature/pressure conditions were studied using potentiodynamic polarization tests and autoclave tests, respectively. Up to 30-day autoclave experiments were carried out in an aqueous condition of 300 °C and 10 MPa in 0.05 M LiOH solutions. It was found that most of the micro-pores which were produced during the PEO treatment were closed after the autoclave experiments. PEO coatings had larger weight gains in the first 10 exposure days than the black oxide coating. However, after 10 days, the corrosion rate of black oxide coating accelerated and exhibited a similar weight gain to PEO coatings after 30 days. PEO coatings prepared at low current densities had lower weight gains. Although the black oxide coating exhibited a good corrosion resistance, it had a much lower wear resistance than the PEO coatings. Compared with the uncoated substrate, all PEO coatings had a higher corrosion resistance, lower weight gain during autoclave tests and better wear resistance.     

H13热作模具钢微弧氧化复合陶瓷层的组织和性能

通过热浸镀铝/微弧氧化复合工艺对H13模具钢进行表面改性以提高模具表面质量。在热浸镀铝过程中,将H13钢基体浸入710℃纯铝液6 min,得到了以Fe2Al5为主中间合金层,使得镀层与基体紧密结合。经过微弧氧化处理后,镀铝试样表面铝层转化为氧化铝陶瓷,主要由α-Al2O3和γ-Al2O3相组成。用带有能谱分析装置(EDX)的扫描电镜(SEM)、X射线衍射(XRD)分析了膜层的形貌、成分和相组成。微弧氧化陶瓷层主要由Al、O、Si元素组成,其中O、Si主要来源于硅酸盐电解液。     

Fe粒子参数对低温超音速火焰喷涂层构建的影响

应用LS-DYNA大应变有限元耦合算法,研究了低温超音速火焰喷涂Fe粒子参数对喷涂层构建的影响.结果表明,随着粒子温度或者速度的升高,粒子所含内能的增加,使得涂层界面温度不断升高,粒子的沉积塑性应变发生变化.粒子在不同基体上的沉积特征表明基体硬度将影响沉积粒子与基体界面的结合状态.随着涂层的构成,后续粒子对已沉积粒子的高速撞击使得先沉积的粒子产生二次塑性变形,并引发温变.先沉积的粒子塑性变形引起的粗化作用将降低后续粒子沉积的临界速度.这些将导致涂层在拉应力作用下发生脆性断裂.     

Interface fracture toughness and fracture mechanisms of thermal barrier coatings investigated by indentation test and acoustic emission technique

Interface fracture toughness and fracture mechanisms of plasma-/sprayed thermal barrier coatings (TBCs) were investigated by interfacial indentation test (IIT) in combination with acoustic emission (AE) measurement. Critical load and AE energy were employed to calculate interface fracture toughness. The critical point at which crack appears at the interface was determined by the IIT. AE signals produced during total indentation test not only are used to investigate the interface cracking behavior by Fast Fourier Transform (FFT) and wavelet transforms but also supply the mechanical information. The result shows that the AE signals associated with coating plastic deformation during indentation are of a more continuous type with a lower characteristic frequency content (30-60 kHz), whereas the instantaneous relaxation associated with interface crack initiation produces burst type AE signals with a characteristic frequency in the range 70-200 kHz. The AE signals energy is concentrated on different scales for the coating plastic deformation, interface crack initiation and interface crack propagation. Interface fracture toughness calculated by AE energy was 1.19 MPam_1/2 close to 1.58 MPam_1/2 calculated by critical load. It indicates that the acoustic emission energy is suitable to reflect the interface fracture toughness.     

锆合金表面Cr涂层在高温压缩下的界面开裂行为EI北大核心CSCD

在事故条件下核反应堆的核心部件镀Cr锆合金包壳管容易受到挤压发生变形,导致Cr涂层产生裂纹影响涂层的保护性能,因此研究镀Cr锆合金在高温压缩下的裂纹扩展行为十分有必要。采用环向压缩试验研究不同厚度Cr涂层锆合金在不同温度下的开裂行为,通过扫描电子显微镜(SEM)、X射线衍射仪(XRD)和维氏硬度计等测试设备研究不同压缩试验温度下的镀Cr锆合金包壳管表截面裂纹微观形貌,并统计表截面裂纹密度及截面裂纹最大宽度。分析包壳材料的载荷-位移曲线和裂纹扩展行为,评价温度和涂层厚度对镀Cr锆合金包壳管力学性能的影响。研究结果表明:镀Cr锆合金包壳管在高温工况下,抗压强度会下降,断裂韧性增加;当涂层厚度增加时,表截面裂纹密度减少,裂纹张开尺寸增大;裂纹首先在表面产生,然后逐渐向基体扩展,并随着变形量的增加逐渐向基体扩展,最终在膜基结合处停止;试样变形量从10%压缩到50%时,截面裂纹的新增主要来自表面主裂纹分叉,且在压缩过程中Cr涂层并不会剥落,Cr涂层与锆基体结合性能良好。研究不同厚度锆合金Cr涂层包壳管在高温压缩下的膜基界面裂纹的扩展行为,可为锆合金包壳管的涂层制备提供数据支持。     

等离子喷涂ZrO2—NiCoCrAlY梯度热障涂层的抗热震性及失效机理

研究了ZrO2-NiCoCrAlY热障涂层的抗热震性和热震失效机理。实验结果表明,梯度热隙涂层能明显延缓热震裂纹的形成和扩展,具有较高的抗热震性。热震裂纹形成与扩展主要在粘结层与基体的界面处。随热循环次数的增加,热震裂纹可在表面陶瓷层内和陶瓷层与过渡层的界面处形成。实验表明热障涂层热震失效的过程主要是裂纹形成、扩展及涂层剥落,粘结层的氧化是导致涂层剥落失效的重要原因。     

Thermal Performance and Microstructure of Vacuum Plasma Sprayed Tungsten Coatings under Cyclic Heat Load

采用真空等离子喷涂技术在铜基体表面制备了钨涂层,分别通过NiCrAl和W75Cu25涂层作为中间层。5 MW/m2, 2 s的高热负荷电子束实验表明NiCrAl中间层提高了涂层的热导率并降低了热应力和残余应力值。W75Cu25涂层作为中间层则表现出较差的热疲劳性能。高热负荷电子束真空等离子喷涂钨涂层表现出侵蚀和微裂纹。因热应力导致涂层发生塑性变形,在高温情况下裂纹起源于熔融的钨颗粒,但是,裂纹被钨涂层塑性变形和孔洞所抑制     

Analysis of a wedge impression test for measuring the interface toughness between films/coatings and ductile substrates

The adhesion between thin elastic films/coatings and ductile substrates can be measured using a wedge test, wherein a long sharp edge is impressed through the film into the substrate. The resulting plastic deformation causes delamination between the film and the substrate. The extent of the delamination can be correlated with the crack driving force to determine the toughness of the interface. Results are presented that relate the energy release rate and mode-mixity to the stresses: both residual and those induced by the impression. Numerical and asymptotic results are presented for the strain transferred to the coating. The numerical results verify that the asymptotics provide accurate closed-form solutions when the delaminations exceed about seven contact widths. An example is provided for a thermal barrier coating system.     

特征喷涂参数对等离子喷涂纳米 Al2 O3 -13%TiO2涂层微观结构及耐磨性能的影响

目的研究等离子喷涂纳米Al2O3-13%TiO2的特征喷涂参数(CPSP)对涂层微观结构及耐磨性能的影响,探索更合理的等离子喷涂工艺参数。方法采用等离子喷涂,在Q235钢表面制备过渡层为NiCrAl、陶瓷层为纳米Al2O3-13%TiO2的涂层系统。对涂层试样进行高温和常温磨损性能测试,并对比分析喷涂粉末、涂层的微观结构和相组成。结果纳米涂层为微观双模结构,由部分熔化区和完全熔化区组成,存在裂纹、孔隙等缺陷,其主要物相为α-Al2O3,γ-Al2O3和rutile-TiO2。纳米涂层磨损失效的主要原因是内部板条的分层剥落和涂层表面材料的塑性变形切削。结论随着CPSP的增大,纳米涂层的耐磨性能增强,且高温磨损性能较室温磨损性能为差。纳米Al2O3-13%TiO2涂层微观结构中部分熔化区结构和纳米晶粒的存在显著提高了涂层的耐磨性。     

Amorphous coatings deposited on aluminum alloy by plasma electrolytic oxidation

Amorphous [Al-Si-O] coatings were deposited on aluminum alloy by plasma electrolytic oxidation (PEO). The process parameters, composition, micrograph, and mechanical property of PEO amorphous coatings were investigated. It is found that the growth rate of PEO coatings reaches 4.44μm/min if the current density is 0.9 mA/mm^2. XRD results show that the PEO coatings are amorphous in the current density range of 0.3 - 0.9 mA/mm^2. EDS results show that the coatings are composed of O, Si and A1 elements. SEM results show that the coatings are porous. Nano indentation results show that the hardness of the coatings is about 3 - 4 times of that of the substrate, while the elastic modulus is about the same with the substrate. Furthermore, a formation mechanism of amorphous PEO coatings was proposed.