钛合金表面粗化对WC-17Co涂层结合性能的影响

研究Ti-6Al-4V合金表面不同粗糙度对超音速火焰喷涂(HVOF)碳化钨(WC-17Co)涂层结合性能的影响. 采用不同喷砂工艺对钛合金表面进行粗化预处理,得到1,2和3号试样的表面粗糙度分别为22.003,20.845和14.765 μm. 利用超音速火焰喷涂技术在粗化后的钛合金表面制备WC-17Co涂层,厚度为0.3 mm. 对WC-17Co/Ti-6Al-4V试样进行三点弯曲试验,利用扫描电镜观察界面形貌. 结果表明,3号试样的界面裂纹扩展最严重并引起了部分涂层脱落,2号试样结合最好;采用四点弯曲法测试涂层与基体的结合界面的断裂能量释放率分别为239.7,259.0和200.1 J/m2.     

钛合金与WC-17Co涂层界面结合性能分析

采用超音速火焰喷涂技术在Ti-6Al-4V合金表面制备WC-17Co涂层,从显微形貌、界面氧化行为、裂纹扩展形式等方面系统分析了WC-17Co涂层与Ti-6Al-4V基体界面断裂失效原因,并利用四点弯曲法测量了WC-17Co与Ti-6Al-4V合金的平均断裂能量释放率.结果表明,热喷涂过程使Ti-6Al-4V的表面氧化相含量显著提高.氧化后Ti-6Al-4V的表面显微硬度达到322.4 HV,熔融粒子撞击到Ti-6Al-4V表面很难对基体造成明显的塑性变形,不能形成有效咬合,使得钛合金与WC-17Co涂层的结合性能偏低.     

Interface fracture property of PEO ceramic coatings on aluminum alloy

This paper combines the four-point bending test, SEM and finite element method to study the interface fracture property of PEO coatings on aluminum alloy. The interface failure mode of the coating on the compression side is revealed. The ceramic coating crack firstly along the 45° to the interface, then the micro crack in the coating deduces the interface crack. The plastic deformation observed by SEM shows excellent adhesion property between the coating and substrate. The plastic deformation in the substrate is due to the interfacial crack extension, so the interface crack mode of PEO coatings is ductile crack. The results of FEM show that the compression strength is about 600 MPa.     

离子束增强沉积工艺对镀层表面粗糙度的影响

研究了不同界面共混工艺对精密轴承镀层表面粗糙度的影响。结果表明 ,用氮离子进行界面反冲共混 ,在动态反冲共混过程中 ,随着氮离子能量的增高 ,氮离子选择溅射和界面碳富集造成界面上沉积的镀层表面粗糙度相应增大 ,而对于在工件表面预先沉积一层纯钛的静态反冲共混工艺 ,镀层具有较低的表面粗糙度。当氮离子能量为 40keV时 ,静态反冲共混界面具有高的镀膜基体结合力。     

Fracture dynamics of sprayed and laser-glazed titania by an inverse processing of elastic waves

A new elastic wave (EW) or acoustic emission (AE) monitoring and signal processing system has been developed and used to elucidate the fracture behavior of sprayed and laser-glazed ceramic coatings. The system measures the minute surface displacements excited by the propagation of elastic waves. It enables elucidation of the fracture dynamics (fracture mode and kinetics) of stressed coatings. The surface displacement at the sensor position was computed by the convolution integral of an assumed source wave with the dynamic Green’s function until signals resembled the measured wave. This new signal processing method was used to determine the fracture strength and dynamics of microcracks in sprayed and laser-glazed titania subjected to four-point bending. It was found that mode II shear cracking along the interface between the coating and substrate occurred prior to mode I cleavage cracking. The fracture strength of laser-glazed titania was higher than that of as-sprayed titania in most cases; however, this depended on the coating structure. This article introduces the principle of source inversion processing of elastic waves, the monitoring system, laser glazing of sprayed titania, and experimental work on the fracture behavior of titania coatings.     

涂覆WC-17Co涂层的Ni718合金在不同环境温度中的疲劳性能

利用超音速火焰喷涂技术在Ni718合金表面制备WC-17Co涂层.利用反复弯曲试验分析25,150,300℃条件下涂覆WC-17Co涂层Ni718合金疲劳性能,利用扫描电镜、X射线衍射仪分析涂层的断口形貌和相组成,并利用剥层法测量涂层中残余应力分布.结果表明,相同应变量条件下试样的疲劳寿命随着温度的升高而降低;循环载荷作用下裂纹由涂层表面产生,向基体方向扩展,最终形成整体断裂;室温至300℃温度范围内,涂层不会发生相变,但是随环境温度上升涂层中的残余压应力呈现下降趋势,这种趋势使得涂层中裂纹的扩展速度增加,最终导致疲劳寿命下降.     

四点弯曲条件下热障涂层断裂模式的声发射表征

采用声发射技术实时监测喷涂态8% Y₂O₃稳定的ZrO₂（8YSZ）在四点弯曲载荷下的损伤断裂行为。采用特征参数分析、聚类分析和小波包变换分析声发射信号结合涂层的微观形貌和应力状态,从而推测出热障涂层系统的失效形式。结果表明：内弯和外弯两种加载模式下,均各有4种失效行为。宏观断裂对应的剥落信号无明显频带,而基底变形、表面垂直裂纹、张开型界面裂纹和剪切型界面裂纹信号对应的主频带可清晰区分为：0~156.25 kHz、156.25~234.375 kHz、312.625~390.625 kHz和390.625~468.75 kHz。热障涂层在外弯载荷下,表面垂直裂纹不断出现,随后扩展到粘结层-陶瓷层界面处并转化为张开型界面裂纹;而在内弯载荷下,则在粘结层-陶瓷层界面附近产生剪切型界面裂纹,仅出现少量的表面垂直裂纹。两种界面裂纹均会引起热障涂层的宏观裂纹和剥落。     

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.     

Microstructure and adhesion of 100Cr6 steel coatings thermally sprayed on a 35CrMo4 steel substrate

Thermally sprayed of 100Cr6 steel coatings are widely used to combat degradation of components and structures due to mechanical wear. In this paper, the microstructure and adhesion energy of 100Cr6 steel coatings thermally sprayed on a 35CrMo4 steel substrate are investigated. The microstructure characteristics of the deposits are studied using the combined techniques of X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM) including energy-dispersive spectroscopy (EDS). The practical work of adhesion of flame-sprayed 100Cr6 on steel substrate is determined using a four-point delamination bending test. The influence of a molybdenum bond coat on the adhesion is also studied. Microstructure suggests that the coating is mainly constructed by splats of γ-phase (fcc) and FeO. Phase analysis also confirms that during spraying process, a stable α-phase (bcc) was transformed into a new γ-phase (fcc). The highest values of the fracture energy are obtained for the 35CrMo4 substrate/100Cr6 steel deposit type samples. On the contrary, when a molybdenum bond coat is introduced (composite system 35CrMo4 substrate/Mo bond coat/100Cr6 steel deposit), the fracture energy decreases in a ratio of approximately three. So, the presence of a Mo bond coat as a barrier between the coating and the substrate has a negative role on the adhesion.     

Interface fracture behavior of electroplated coating on metal substrate under compressive strain

The inducement of interface fracture is crucial to the analysis of interfacial adhesion between coating and substrate. For electroplated coating/metal substrate adhering materials with strong adhesion, interface cracking and coating spalling are difficult to be induced by conventional methods. In this paper an improved bending test named as T-bend test was conducted on a model coating system, i.e. electroplated chromium on a steel substrate. After the test, cross-sections of the coated materials were prepared to compare the failure behaviors under tensile strain and compressive strain induced by T-bend test. And the observation results show that coating cracking, interface cracking and partial spalling appear step by step. Based on experimental results, a new method may be proposed to rank the coated materials with strong interfacial adhesion.     

塑性变形导致的镀锌板基体表面粗糙化现象

以热镀锌板单向拉伸试验为基础,运用化学退镀以及随后的基体表面粗糙度测量和横截面标记观测等试验手段,比较了塑性变形前后基体表面及界面的形貌,得出,塑性变形过程中,基体表面作为界面的一部分会产生粗糙化现象,但这种粗糙化会受到镀锌层的抑制,因此界面并不会出现明显的形貌变化,然而这种基体表面粗糙化所产生的应力,可能导致界面失效。     

Study of fracture behaviour of bond coats on nickel superalloy by three-point bending of microbeams

A microbeam testing geometry is designed to study the variation in fracture toughness across a compositionally graded NiAl coating on a superalloy substrate. A bi-material analytical model of fracture is used to evaluate toughness by deconvoluting load–displacement data generated in a three-point bending test. It is shown that the surface layers of a diffusion bond coat can be much more brittle than the interior despite the fact that elastic modulus and hardness do not display significant variations. Such a gradient in toughness allows stable crack propagation in a test that would normally lead to unstable fracture in a homogeneous, brittle material. As the crack approaches the interface, plasticity due to the presence of Ni₃Al leads to gross bending and crack bifurcation.     

钛基 / TiN 涂层接触应力有限元分析

目的研究在接触载荷作用下,钛基/TiN涂层的应力变化规律。方法利用ABAQUS软件建立可靠有限元模型,分析涂层厚度不同的钛基/TiN涂层系统在球压头作用下的接触应力。结果钛基/TiN涂层系统最大Mises应力出现在距表面约0.4a(a为接触半径)处的亚表层或者亚表层附近的界面处。在接触应力和弯曲应力作用下,涂层弯曲变形会影响涂层的径向应力和剪应力分布。结论在接触载荷作用下,涂层内存在接触应力和自身弯曲两种应力作用。分析结果有利于理解钛基Ti N涂层的失效机理。     

热喷涂涂层界面断裂韧性的反向三点弯曲法试验

以热喷涂NiCrBSi涂层/钢基体为材料模型,利用将涂层置于受压侧的反向三点弯曲法试验,对热喷涂涂层界面断裂现象进行分析并建立相应的界面断裂韧性计算模型。结果表明,界面裂纹起始于三点弯曲试样中部,对应于加载压头与涂层接触区域正下方的界面上,并向两侧扩展,伴随涂层屈曲,形成分层屈曲的破坏形貌。根据分层屈曲形貌建立计算模型,通过分层屈曲几何参数与屈曲临界应力、涂层内真实应力以及界面断裂韧性的关系,获得界面断裂韧性值。     

加热温度对Al-Si涂层热成形钢组织及性能的影响

利用粗糙度仪、扫描电镜、硬度计、辉光放电原子发射光谱仪等检测方法,研究分析了热冲压成形工艺过程中的加热温度对Al-Si涂层22MnB5热成形钢组织及性能的影响。结果表明,随着加热温度的升高,Fe沿垂直于表面方向由热成形钢基体向Al-Si涂层表面的迁移量逐渐增大,O沿垂直于表面方向由Al-Si涂层表面向热成形钢基体的迁移量逐渐增大,且迁移的最大深度约为2.80 μm。Fe沿垂直于表面方向由热成形钢基体向Al-Si涂层表面的迁移量直接决定了Fe-Al-Si相的形态、生成位置及界面结合层厚度。随着加热温度的升高,Al-Si涂层表面粗糙度R_a、峰值计数R_pc值先增大后减小;当加热温度为930 ℃时,涂层表面粗糙度R_a达到最大值1.89 μm,峰值计数R_pc值达到最大值218。随着加热温度的升高,Al-Si涂层总厚度从27.78 μm增加至40.46 μm,界面结合层厚度从1.08 μm增加至15.11 μm。当加热温度为930 ℃时,热成形钢基体的硬度达到最大值505 HV0.2。     

AZ31B镁合金表面微弧电泳复合膜层微观结构及耐蚀性表征

采用微弧氧化技术在AZ31B镁合金表面制备陶瓷层,利用其表面多孔结构借助电泳技术沉积有机膜层,对比研究陶瓷层和复合膜层表面粗糙度、表面及截面形貌、电化学性能及划伤腐蚀特性。结果表明:陶瓷层表面放电微孔被电泳层完全填充并形成均匀膜层,复合膜层表面粗糙度明显降低;微弧电泳复合膜层腐蚀电流密度与陶瓷层和基体相比分别降低2个和4个数量级,极化电阻分别增大2个和4个数量级,腐蚀倾向降低;微弧电泳复合膜层电化学阻值与陶瓷层相比增加4个数量级,同时电容值降低4个数量级,耐蚀性显著提高;由于陶瓷层与电泳层的机械嵌合作用,复合膜层划伤腐蚀过程表现为基体腐蚀及陶瓷层与基体界面的破坏,复合膜层界面处结合完好。     

盐雾环境下X70管线钢等离子喷涂铝涂层的腐蚀行为

目的研究X70管线钢的防腐工艺,以延长其使用寿命。方法采用等离子喷涂方法在X70管线钢基体表面制备铝涂层,通过扫描电镜(SEM)和能谱仪(EDS)对涂层表面、界面质量和微观形貌进行分析。利用盐雾腐蚀试验,对比分析涂层对基体的保护作用机制。结果涂层为富铝层,主要以富铝脆性物相存在,并受环境空气的影响,涂层出现孔洞、裂纹和未熔颗粒等缺陷。涂层表面因铝粉颗粒尺寸差异,颗粒间熔融状态不同,导致表面铝元素呈波浪式分布。涂层界面结合处,铁、铝元素相互渗透,形成Fe-Al冶金结合,增加了涂层结合强度。热处理后,未熔颗粒及部分金属氧化物熔化并填充涂层缺陷,减小了表面粗糙度和孔洞率,提高了涂层质量。盐雾腐蚀16h后,未喷涂涂层试样表面出现了严重的点蚀现象,影响了管线钢的使用寿命。喷涂铝涂层试样在盐雾腐蚀试验120h后,表面出现了轻微腐蚀现象。结论涂层表面形成了致密氧化膜,避免了腐蚀介质和基体直接接触,提高了X70管线钢的耐腐蚀性。     

基板表面粗糙度对合金化热镀锌板镀层组织的影响

利用扫描电镜和电感耦合实验观察了不同基板粗糙度的合金化热镀锌钢板表面形貌，测定了镀层中的Fe含量。结果表明，在相同的合金化工艺条件下，基板表面粗糙度越大，合金化镀层中的Fe含量越高。较大的基板粗糙度使镀层中的微裂纹增多，镀层均匀性变差。     

喷砂预处理对HVOF喷涂TiAl-Nb/NiCrAl涂层结合强度的影响

采用不同的喷砂压力对基体表面进行喷砂预处理,研究了基体表面状态的变化对HVOF喷涂TiAl-Nb/NiCrAl涂层结合强度的影响。结果表明：随着喷砂压力的增大,基体粗糙度及表面凹坑的深度和宽度增大,NiCrAl层与基体结合界面处孔洞等缺陷增多,同时基体表面残余砂粒的面积分数增加;涂层结合强度随基体粗糙度的增大,先增大后减小,当基体粗糙度为8.33μm时,结合强度达到最大值44.5 MPa。     

Tribological properties of thin hard coatings: demands and evaluation

Thin hard coatings are currently being used in a large number of tribological applications. Some important examples are tools for metal cutting and forming, and machine elements like sliding bearings, seals, valves, etc. The present paper deals with the problems of identifying the limiting factors in given tribological applications of coating composites, and how to experimentally determine their tribological responsse, with special attention given to wear.

As a means for coating development, the intricate relations between coating deposition parameters and the triboological response of the coated composite are indicated by a flow chart of relevant coating and substrate properties. It is demonstrated how the general characteristics (topography, composition, microstructure, etc.) and fundamental properties (chemical, thermal, mechanical, etc.) of coating and substrate combine to generate the tribological properties (resistance against abrasion, erosion, sliding wear, etc.), which given the tribological loading, determines the tribological response in terms of friction and wear.

A number of different test methods for tribological evaluation of coating composites are presented together with illustrative examples. The test range from four-point bending for evaluating coating fracture strength, to designated tribological tests to determine the resistance against abrsion, particle erosion, and sliding wear.