Evaluation of the interfacial bonding between fibrous substrate and sputter coated copper

The sputter coatings provide new approaches to the functionalization of textile materials. One of the key issues in the use of sputter coatings onto textiles is the interfacial adhesion between the coated layer and the fiber substrate. The interfacial bonding between polypropylene (PP) fibrous substrate and sputter coated copper was investigated and discussed by abrasion test and peel-off test in this study. It was found that the plasma pretreatment and heating during the sputter coating process obviously improved the adhesion of the coating layer to the PP fibrous substrate. The mechanism of the interfacial adhesion between copper and PP substrate was also examined by atomic force microscopy. The AFM observations revealed the surface and interfacial structures of the PP fibers.     

彩色涂层钢板时效T弯性能影响因素及规律研究

为提高彩涂板服役品质,其时效T弯性能的研究非常关键。通过对影响彩涂钢板时效T弯的主要因素,即镀锌基板表面状态、复合氧化工艺、钝化工艺进行系统研究,归纳总结了各因素对时效T弯性能的影响规律。研究结果表明:基板粗糙度R_a在1.0～1.45 μm范围内,彩板时效T弯值均满足不大于5T的技术要求,且R_a的均匀性对时效T弯性能的影响较大,R_a的相对标准偏差越小,时效T弯性能越好;基板表面峰值密度Rpc与时效T弯性能无明显相关性,时效T弯性能较好时Rpc值较小。复合氧化膜越均匀致密,膜中Co含量越高,涂层附着力越好,时效T弯值越小;钝化工艺控制Cr点数在23以上时,时效T弯(5T及以下)合格率达100%,随着Cr点数的增加,时效T弯性能明显提高。为此,提出控制基板表面粗糙度及其均匀性,控制复合氧化工艺中氧化槽碱比稳定性(碱比小于1.6),控制钝化工序Cr点数在23~25之间等措施,可提高彩板时效T弯性能。     

Interface fracture behavior of zinc coatings on steel: Experiments and finite element calculations

Hot-dipped galvanized steels are widely used in the automotive industry. The formability and damage resistance of zinc coatings depend strongly on their microstructure and adhesion to the steel substrate. In order to improve the mechanical performance of zinc coatings, the influence of their thickness, grain orientation and grain size on the zinc coating/steel substrate interface cracking behavior was studied. To this end, scanning electron microscopic observations during in situ tensile testing of zinc coated IF steel sheets were performed. After partial delamination of the zinc coating, cross sections of zinc coated steel were prepared to determine the location and extent of the interface cracking and the crystallographic orientation of the delaminated zinc grains. A two-grain model using a finite element method is proposed to analyze the zinc coating/steel substrate interface cracking behavior. In addition, the coating adhesion strength can be estimated based on this model. Both calculations and experimental observations show that: (i) a preferential zinc grain orientation with the [0001] direction parallel to the interface and (ii) a small grain size mitigate zinc coating/steel substrate interface cracking.     

Evaluation of the Interfacial Adhesion between Brittle Coating and Ductile Substrate by Cross-Sectional Indention

THE EVALUATION of the interfacia adhesion is thepredominant factor in determining the performance andreliability of coating substrate system'I There aremore than200different methods for measuringadhesion,but most of which are problematic at highadhesive strength levels[21.Cross-sectional indentation has been designed toexamine the interfacial fracture properties of thin filmon brittle substrate,whatever the film is ceramicsI3]ormetals|4'.The novelty of this indentation technique isthe u…     

Evaluation of the Interfacial Adhesion between Brittle Coating and Ductile Substrate by Cross-Secitional Indention

The cross-sectional indentation method is extended to evaluate the interfacial adhesion between brittle coating and ductile substrate. The experimental results on electroplated chromium coating/steel substrate show that the interfacial separation occurs due to the edge chipping of brittle coating. The corresponding models are established to elucidate interfacial separation processes. This work further highlights the advantages and potential of this novel indentation method.     

重载条件下钢基体表面涂层裂纹及分层失效

用有限元法分析了Hertz接触应力下钢基体表面涂层裂纹和分层失效状况,采用无预制裂纹状况下的扩展有限元(XFEM)技术和内聚力(Cohesive)模型研究了涂层的裂纹扩展和分层失效过程。分析表明:涂层的裂纹萌生于涂层表面,并向内部扩展;涂层弹性模量越大越易产生裂纹,且裂纹扩展越深。涂层的分层失效主要是由涂层-基体界面切应力造成;由于畸变应力的存在,较薄涂层(如物理气相沉积涂层),涂层越厚越易产生分层;较厚涂层(如等离子喷涂涂层),涂层越薄越易产生分层。在另一方面,涂层的裂纹和分层会相互影响,分层会使涂层更易产生裂纹,使裂纹扩展越深,影响裂纹扩展速度;涂层裂纹会使涂层更易分层,使分层区域在远离接触区域方向上不断扩展。对比分析表明,研究结果与前人的理论及实验结果吻合较好,为今后进行涂层失效数值模拟提供了依据。     

Influence of substrate microstructure on the contact fatigue strength of coated cold-work tool steels

The contact fatigue behavior of three microstructurally distinct tool steels coated with a physical vapor deposited TiN film is studied. Substrate microstructural differences come from variations in either chemical composition or processing route. Experimental procedure is based on determining critical applied loads and pressures, under both monotonic and cyclic spherical indentation loading conditions, for emergence and evolution of distinct damage modes at the coating surface: circumferential cracking, cohesive spallation and interfacial decohesion. Experimental results indicate that all coating/substrate systems evaluated are susceptible to mechanical degradation associated with repetitive contact loading. This is clearly discerned from the fact that some damage mechanisms, such as cohesive spallation at the coating and adhesion failure at the interface, are exclusively observed under cyclic loading. Substrate microstructure effects are evidenced by consideration of coating detachment as the critical damage mechanism. In this regard, crack nucleation resistance of primary carbides is pointed out as the main reason for the distinct response against decohesion observed under cyclic contact loads. Hence, finer and tougher, as well as less irregular and more homogeneously distributed primary carbides are pointed out as key microstructural features for enhancing contact fatigue strength of coated cold-work tool steels.     

Corrosion and Nano-mechanical Behaviors of Magnetron Sputtered Al-Mo Gradient Coated Steel

A gradient three-layer Al-Mo coating was deposited on steel using magnetron sputtering method. The corrosion and nano-mechanical properties of the coating were examined by electrochemical impedance spectroscopy and nano-indentation tests and compared with the conventional electroplated cadmium and IVD aluminum coatings. Electrochemical impedance spectroscopy was performed by immersing the coated specimens in 3.5% NaCl solution, and the impedance behavior was recorded as a function of immersion time. The mechanical properties (hardness and elastic modulus) were obtained from each indentation as a function of the penetration depth across the coating cross section. The adhesion resistance of the coatings was evaluated by scratch tests on the coated surface using nano-indentation method. The results show that the gradient Al-Mo coating exhibits better corrosion resistance than the other coatings in view of the better microstructure. The impedance results were modeled using appropriate electrical equivalent circuits for all the coated systems. The uniform, smooth and dense Al-Mo coating obtained by magnetron sputtering exhibits good adhesion with the steel substrate as per scratch test method. The poor corrosion resistance of the later coatings was shown to be due to the defects/cracks as well as the lesser adhesion of the coatings with steel. The hardness and elastic modulus of the Al-Mo coating are found to be high when compared to the other coatings.     

Effect of the Cold-Sprayed Aluminum Coating-Substrate Interface Morphology on Bond Strength for Aircraft Repair Application

This article is dealing with the effects of surface preparation of the substrate on aluminum cold-sprayed coating bond strength. Different sets of AA2024-T3 specimens have been coated with pure Al 1050 feedstock powder, using a conventional cold spray coating technique. The sets were grit-blasted (GB) before coating. The study focuses on substrate surface topography evolution before coating and coating-substrate interface morphology after coating. To study coating adhesion by LASAT^® technique for each set, specimens with and without preceding GB treatment were tested in load-controlled conditions. Then, several techniques were used to evaluate the effects of substrate surface treatment on the final coating mechanical properties. Irregularities induced by the GB treatment modify significantly the interface morphology. Results showed that particle anchoring was improved dramatically by the presence of craters. The substrate surface was characterized by numerous anchors. Numerical simulation results exhibited the increasing deformation of particle onto the grit-blasted surface. In addition, results showed a strong relationship between the coating-substrate bond strength on the deposited material and surface preparation.     

复合镀覆Ti—Ni金刚石的钎焊应用

镀覆技术的研究进展表明：经过真空微蒸发镀钛、钨的金刚石单晶或聚晶,可以采用化学镀或电镀的方法在钛或钨镀层上进一步镀覆镍、钴、铬等金属,这种复合镀层与金刚石界面强力冶金结合,并且可以采用各种钎焊方法实现金刚石与多种金属基体的焊接。复合镀覆的金刚石可用于各类表镶工具的制造,获得高出刃、高磨粘结合强度,使金刚石表镶工具的使用寿命和加工效率大幅度提高。     

Interfacial indentation and shear tests to determine the adhesion of thermal spray coatings

Adhesion is one of the most important parameters which influences the development of thermal spray coatings. Therefore, the level of adhesion should be known for a given application. Apart from the standardized Tensile Adhesive Test (TAT), more than 80 methods are reported to measure the coating adhesion. Most of them are energy consuming in terms of time, cost and equipment. Moreover, they do not fulfil the necessary requirements of accuracy, confidence and representation of the real delamination process observed in service. To address this problem, the interfacial indentation test is used here to initiate and propagate a crack at the interface between the substrate and the coating. Studying the extension of the crack, an interfacial toughness is defined and deduced analytically from the experimental results. The new shear test, developed in the frame of the EU-CRAFT-project “Shear Test for Thermally Sprayed Coatings”, is also employed to assess the coating adhesion. Both tests are compared to the standardized TAT for various spraying systems, materials, substrate roughness and coating thickness. Advantages and disadvantages of the three tests are discussed. Correlations between the tests results obtained for different coating-substrate combinations are presented and general trends are described.     

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.     

Study of Cr2O3 coatings Part I: Microstructures and modulus

Metallographic characterization has been used to estimate the quality and, particularly, the adhesion of plasma-sprayed Cr₂O₂ coating. This study focuses on the state of the substrate before spraying. During the process of spraying, the differential contraction generated between the various materials because of their different physical and mechanical properties determines the stresses inside the coating and at the interface between the coating and the substrate. The residual stresses thus influence the mechanical and thermomechanical behavior of the coated parts and their adhesion. These stresses are determined by a step-by-step hole drilling method (Part II of this paper), and Young’s modulus is measured by two differ-ent methods: a dynamic ultrasonic test and a static four-point bend test. Part II of this paper is devoted to the adhesion of a Cr₂O₃ deposit on a cast iron substrate.     

Investigation of delamination mechanisms during a laser drilling on a cobalt-base superalloy

Temperatures in the high pressure chamber of aircraft engines are continuously increasing to improve the engine efficiency. As a result, constitutive materials such as cobalt and nickel-base superalloys need to be thermally protected. The first protection is a ceramic thermal barrier coating (TBC) cast on all the hot gas-exposed structure. The second protection is provided by a cool air layer realized by the use of a thousand of drills on the parts where a cool air is flowing through. The laser drilling process is used to realize these holes at acute angles. It has been shown on coated single crystal nickel-base superalloy that the laser drilling process causes an interfacial cracking (also called delamination), detected by a cross section observation. The present work aims at characterizing interfacial cracking induced by laser drilling on coated cobalt-base super alloy. On the one hand, this work attempted to quantify the crack by several microscopic observations with regards to the most significant process parameters related as the angle beam. On the other hand, we studied the difference of the laser/ceramic and the laser/substrate interaction with real time observation by using a fast movie camera.     

Estimation of interfacial fracture toughness based on progressive edge delamination of a thin transparent coating on a polymer substrate

Evaluation of interfacial toughness of sub-micron-thickness layers deposited on a ductile substrate is a challenging task which has motivated different experimental approaches. Fragmentation testing was used in the present study as a means of interface characterization of a silicon–nitride-coated polyimide substrate. During the test, after an initial rapid segmentation–cracking phase, the coating fragments developed edge delaminations which propagated in a stable manner with further increase in the applied strain. The debonding process was modelled by the finite element method incorporating a cohesive zone at the front of the interfacial crack. The edge cracks were found to be dominated by mode II loading. By fitting the predicted delamination evolution to the experimental data for coating fragments of differing geometry, the mode II critical energy release rate was estimated at 30 J m^?2.     

Influence of microarc oxidation and hard anodizing on plain fatigue and fretting fatigue behaviour of Al-Mg-Si alloy

The present study compares the performance of microarc oxidation (MAO) and hard anodizing (HA) treated Al-Mg-Si alloy (AA6063) test samples under cyclic loading in uniaxial tension with a stress ratio of 0.1 (plain fatigue) and fretting fatigue loading. Fatigue test specimens were treated using MAO and HA techniques. MAO coated specimens were ground to reduce the surface roughness comparable with that in HA coated specimens. In that process the porous outer layer was removed. Characterization of coated and uncoated specimens was done with reference to the coating morphology, microhardness, surface roughness and residual stress. The specimens were tested under plain fatigue and fretting fatigue loading at ambient temperature. While the ground MAO coating exhibited relatively less amount of porosity, HA coating had through thickness cracks. MAO coating had compressive residual stress and it was very hard compared with HA coating. Both types of coated samples exhibited slightly higher friction force than that experienced by the uncoated specimens. Fretted region of the HA coated samples was rougher than that of the MAO coated specimens. Plain fatigue lives of both coated samples were inferior to those of the uncoated specimens. The inferior plain fatigue lives of MAO coated specimens compared with those of the substrate may be attributed to the tensile residual stresses supposedly present in the substrate leading to an early crack initiation in the substrate adjacent to the coating. As friction force of MAO coated samples was higher than that experienced by uncoated specimens, the fretting fatigue lives of MAO coated samples were slightly inferior to those of uncoated samples. As the anodized layer had preexisting through thickness cracks and strong adhesion with the substrate, cracks propagated from HA coating through the interface into the substrate easily. This may be the reason for the HA coated samples exhibiting inferior plain fatigue and fretting fatigue lives compared with MAO coated and uncoated samples.     

铝合金与复合材料组合构件的涂装工艺

目的解决底/面漆涂层在铝合金与复合材料基材表面经常出现剥离、起泡、开裂等缺陷问题。方法通过对问题涂层部件的结构设计合理性分析,指出了封闭式蒙皮结构部件出现的设计缺陷。对铝合金与复合材料的加工工艺进行了分析,用对比试验的方法,验证了铝合金阳极氧化处理工艺所生成的保护膜对涂层性能的影响。通过改进表面前处理工艺,验证了复合材料表层残留的脱模剂是影响涂层附着力的主要原因。以改善涂层应力变化适应能力为目的,调整了涂料韧性配方,涂覆不同的基材和相关结构部件,用可模拟产品试验考核状态的"温度冲击+振动+湿热"联合加载试验方法,验证了设计与工艺改进后的涂层性能。结果合理设计通气孔后,消除了封闭式蒙皮结构部件内部气体的膨胀效应,改进铝合金与复合材料表面前处理工艺和涂料韧性后,涂层不再出现起层开裂现象。结论封闭式蒙皮结构部件应设置内外通气工艺孔,彻底清除复合材料表面脱模剂渗透层和铝合金表面的阳极氧化膜,选用韧性好的涂料体系,能够有效提升铝合金与复合材料组合构件表面涂层的环境适应性能。     

Study of the influence of phase composition and iron content on the formability characteristics of zinc-iron electroplated sheet steel

This study focuses on the relationship between coating composition and deformation and friction behavior of zinc-iron electroplated sheet steel. The influence of phase composition and microhardness of the deposits and the electrodeposition process parameters on the mechanical properties of the material were determined. The influence of coating composition on the friction and galling behavior was also investigated. Both V-bend test and cup test were used to evaluate the influence of the iron content on the powdering and flaking behavior of the deposits. Finally, the adhesion of the coating to the substrate was studied by lap shear tests. Although the soft η phase appears to be the main component in zinc-iron coatings with less than 16 wt% Fe, Γ₁ particles were observed even at low iron contents. As the iron content in the coating increases, the Γ₁ fraction increases and the coating becomes harder and more brittle. Above 16 wt% Fe the deposits start to show substantial powdering and flaking during deformation. At iron contents above 30 wt%, bending of the coated product results in total coating delamination. At low iron contents, zinc-iron electroplated sheet steel exhibits a superior deformation behavior, and both cup tests and flat die tests proved the suitability of the coating for deep drawing.     

Formability of aluminum-silicon coated boron steel in hot stamping process

Flow behavior of the Al-Si coated boron steel was investigated with Gleeble-3500, in comparison with the uncoated one. Effect of deformation conditions on the coating integrity was characterized by optical microscopy. Facture surfaces of the coated steels were inspected under SEM. Experimental results indicate that the ultimate tensile strength and ductility of the Al-Si coated boron steel are lower than those of the uncoated steel under test conditions. Extensive cracks occur in the coating after tensile tests; the width and density of cracks are sensitive to the deformation temperatures and strain rates. The bare substrate exposed between the separate coating segments is oxidized. Appearance of the oxide degrades the Al-Si coating adhesion. Remarkable difference between formability of the coating layer and the substrate is confirmed. The formability of the Al-Si coating could be optimized by controlling the phase transformation of the ductile Fe-rich intermetallic compounds within it during the austenization.     

压痕法研究镶嵌结构界面金刚石膜粘附性能

在铜基体上沉积Cu(Cr)-diamond复合过渡层,用热丝CVD法在复合过渡层上沉积出金刚石膜。用压痕法对沉积的金刚石膜/基结合性能进行了研究。结果表明,在Cu-diamond上沉积的金刚石膜,用147 N压痕时压痕边缘出现大面积崩落,并在基体表面留下被拔出的金刚石凹坑;在Cu-diamond中掺入微量Cr,压痕边缘只形成环形裂纹,增大压痕载荷至441 N,环形裂纹区域增大,并出现部分崩落,崩落区域有被切断的金刚石残留。在Cu-diamond复合层中掺入微量Cr能显著提高金刚石膜/基结合力。