Wear Analysis of Thermal Spray Coatings on 3D Surfaces

Even though the application of thermal spray coatings on complex geometries gained a greater interest in the last decade, the effect of different geometrical features on the wear behavior is still ill-defined. In this study, the wear resistance of FTC-FeCSiMn coated 3D surfaces was investigated. The wear test was carried out by means of two innovative testing procedures. The first test is a Pin-on-Tubes test where the rotating motion is realized by a lathe chuck. The specimens in the second test were fixed on the table and a robot arm operated the pin. This wear test was applied on specimens with concave or convex surfaces. The residual stresses, which were determined by means of an incremental hole-drilling method, show a dependency on the substrate geometry. The obtained stresses were put in relation to the different radii. After the wear test, a 3D-profilometer determined the wear volume and the sections of the coatings were characterized by a scanning electron microscope. The results indicate that the wear resistance is strongly influenced by the geometry of the substrate.     

Intermetallic Al-, Fe-, Co- and Ni-Based Thermal Barrier Coatings Prepared by Cold Spray for Applications on Low Heat Rejection Diesel Engines

Conventional thermal barrier coating (TBC) systems consist of a duplex structure with a metallic bond coat and a ceramic heat insulating topcoat. They possess the desired low thermal conductivity, but at the same time they are very brittle and sensitive to thermal shock and thermal cycling due to the inherently low coefficient of thermal expansion. Recent research activities are focused on the developing of multilayer TBC structures obtained using cold spraying and following annealing. Aluminum intermetallics have demonstrated thermal and mechanical properties that allow them to be used as the alternative TBC materials, while the intermetallic layers can be additionally optimized to achieve superior thermal physical properties. One example is the six layer TBC structure in which cold sprayed Al-based intermetallics are synthesized by annealing in nitrogen atmosphere. These multilayer coating systems demonstrated an improved thermal fatigue capability as compared to conventional ceramic TBC. The microstructures and properties of the coatings were characterized by SEM, EDS and mechanical tests to define the TBC material properties and intermetallic formation mechanisms.     

Thermal Spray Coatings for Fusion Applications—Review

Thermonuclear fusion is a potential source of cleaner and safer energy for the future. Its technological realization depends on the development of materials able to survive and function in extreme conditions. This article reviews the applications of thermally sprayed coatings for fusion reactor materials. First, the principle and purpose of fusion is briefly introduced, and technological objectives are mentioned. Material-environment interactions are summarized, together with materials requirements and the role of coatings. Then, specific applications—e.g., the plasma facing components—are reviewed, focusing on application issues as well as issues related to thermal spray processing and specific properties of the respective materials. An overview of specific materials testing methods is also provided.     

Quality Considerations for the Evaluation of Thermal Spray Coatings

Revealing the true structural and mechanical properties is of utmost importance for the optimized use of thermal sprayed coatings. Only the true properties can be expected to correlate to the spray parameters. During the recent decade, the gas turbine industry has experienced a focus on the laboratory procedures being the weakest link in a frozen and robust process. This article will show several results indicating that the laboratory procedures are more essential to the evaluation results than the spray parameters themselves. With new and robust laboratory techniques, the true properties of thermal spray coatings are revealed, causing a major problem with respect to the quality standards developed 30-40 years ago. In many cases, these old specifications need updates, which is a difficult task from a cost, time, and quality perspective for OEM’s. Coatings that have been successfully used for almost half a century no longer conform to the specification they were optimized to, because of these new appropriate laboratory techniques and procedures. What is actually meant when stating the following? (1) The coating has 5% porosity; (2) No cracks are allowed; (3) Tensile bond is 50 Mpa; (4) Hardness is 1000 HV; and (5) Coating thickness is 100 μm. This article also initiates a discussion on the measurement inaccuracies, for testing of thermally sprayed coatings, with respect to the commonly used general international standards (such as QS9000, ISO17025, AS9003, and ISO10012), as well as with respect to recommendations from the Six Sigma methodology.     

中等功率柴油机缸体和缸盖制芯工艺

总结了中等功率柴油机缸体、缸盖制芯工艺的要点,包括:缸体缸筒砂芯设计应尽量避免实心制芯;在湿砂造型生产线大批量生产缸盖的情况下,应尽量采用底座砂芯;水套砂芯应尽量设计成整体;缸体、缸盖砂芯一次涂料一般用水基涂料,特别部位的二次涂料一般用醇基涂料;缸体、缸盖砂芯必须采用组芯胎具和夹具来完成组芯和下芯工序;等。最后指出:近精确制芯技术是中等功率柴油机铸造业的发展方向。     

Indentation of Metallic and Cermet Thermal Spray Coatings

Indentation methods are presented by which the elastic and inelastic stress-strain characteristics of metallic thermal spray (TS) coatings on substrates may be extracted. The methods are based on existing techniques for brittle solids, and adapted for the finite geometry associated with coatings. Basic assumptions and derivations are given, along with guidelines for experimental measurement. Using these, indentation inelastic stress-strain curves are generated for NiCrAlY and Ni-Al bondcoats, as well as WC-Co cermet coatings. Elastic moduli are extracted for CoNiCrAlY coatings. Results are briefly discussed in the context of the effect of feedstock material, process and post-process heat treatment on the intrinsic properties of splats as well as their in-coating cohesion. The methods presented are attractive, particularly for the TS industry, due to the minimal specimen preparation and lack of intricate equipment required for measurement.     

大型船用柴油机缸套的细长孔铸造

分析了大型船用柴油机缸套铸件的细长孔铸造方案，介绍了采用镶铸钢管的方法来形成铸件内弯曲细长孔，它具有制作方便、孔的圆度和平直度好、孔内表面光洁等优点。同时在铸造过程中，必须采取措施解决镶铸管因受热膨胀而产生弯曲变形、被液态金属熔穿和减少铸件的热应力等问题。     

S20CrMoVS钢船用柴油机气缸盖锻件材料研究

对98机型S20Cr Mo VS材质的船用柴油机气缸盖锻件进行解剖,在气缸盖内部不同位置取样进行力学性能、硬度、组织、疲劳性能等相关试验,通过试验数据对整个气缸盖综合力学性能进行评定。     

Wear Behavior of Thermal Spray Coatings on Rotavator Blades

A rotavator is a motorized cultivator, popularly used to decrease the total time and human efforts in soil preparation. However, under dynamic loading, rotavator blades are subjected to extreme abrasive wear. The objective of this study was to enhance the working life of the rotavator blade in order to decrease the idle time required to reinstate the blade periodically during cultivation. The objective was carried out by means of thermal spray coatings, where the effect of the coatings on the extent of wear and the wear characteristics of the rotavator blades were examined. Three different detonation gun sprayed coatings, namely WC-Co-Cr, Cr₃C₂NiCr and Stellite-21 were compared in this study on high tensile steel rotavator blades. The wear rates of Cr₃C₂NiCr and Stellite-21 coated blades showed significant superiority over the uncoated blade, but not as much as shown by WC-Co-Cr coated blade.     

Infrared Thermography as a Non-destructive Testing Solution for Thermal Spray Metal Coatings

In this work, an infrared (IR) thermographic procedure was evaluated as a non-destructive testing tool to detect damage in thermal spray metallic coatings. As model systems, polished HVOF- and HVAF-sprayed Fe-based layers deposited onto steel plates were employed. Damage by external-object impingement was simulated through a cyclic impact-test apparatus, which induced circumferential and radial cracks across all model systems, and interface cracks of different sizes in distinct samples. Damaged and undamaged plates were bulk-heated to above 100 °C using an IR lamp; their free-convection cooling was then recorded by an IR thermocamera. The intentionally induced defects were hardly detectable in IR thermograms, due to IR reflection and artificial “hot” spots induced by residuals of transfer material from the impacting counterbody. As a micrometer-thin layer of black paint was applied, surface emissivity got homogenized and any artifacts were effectively suppressed, so that failed coating areas clearly showed up as “cold spots.” This effect was more apparent when large interface cracks occurred. Finite-element modeling proved the physical significance of the IR-thermography approach, showing that failed coating areas are cooled by surrounding air faster than they are heated by conduction from the hot substrate, which is due to the insulating effect of cracks.     

Hierarchical Formation of Intrasplat Cracks in Thermal Spray Ceramic Coatings

Intrasplat cracks, an essential feature of thermally sprayed ceramic coatings, play important roles in determining coating properties. However, final intrasplat crack patterns are always considered to be disordered and irregular, resulting from random cracking during splat cooling, since the detailed formation process of intrasplat cracks has scarcely been considered. In the present study, the primary formation mechanism for intrasplat cracking was explored based on both experimental observations and mechanical analysis. The results show that the intrasplat crack pattern in thermally sprayed ceramic splats presents a hierarchical structure with four sides and six neighbors, indicating that intrasplat crack patterns arise from successive domain divisions due to sequential cracking during splat cooling. The driving forces for intrasplat cracking are discussed, and the experimental data quantitatively agree well with theoretical results. This will provide insight for further coating structure designs and tailoring by tuning of intrasplat cracks.     

大中功率船用柴油机气缸套振动时效工艺研究

在大中功率船用柴油机离心浇铸合金铸铁气缸套时效处理工艺中,采用振动时效替代传统热时效,结果表明其精度稳定性达到或超过热时效的效果,而且环保、节能、降耗,工效高.     

Determination of Interfacial Fracture Toughness of Thermal Spray Coatings by Indentation

Adhesion is an important and basic property for thermal spray coatings. The standard tensile test method “ISO 14916” is usually used to evaluate the adhesive strength of coatings. On the other hand, the indentation test method has some advantages to evaluate the interfacial fracture toughness as the adhesive strength, arising from the following reasons: the test procedure and the specimen preparation are easy in comparison with the typical testing method. Collaborative research has been conducted by “Committee on Standard Development” in the Japan Thermal Spray Society to establish a standard test method for evaluating interfacial fracture toughness of thermal spray coatings using a conventional Vickers indenter. This article reports the differences among collaborators in round-robin tests performed in this committee and discusses the validity of the test method and test conditions with respect to the test results and finite element analyses. Comparison among collaborators reveals that interfacial fracture toughness can be obtained with a small scattering from the indentation test under constraints found on the basis of the results.     

热喷涂工艺对涂层摩擦磨损性能的影响

采用超音速火焰喷涂和爆炸喷涂法在金属表面制备了WC-Co单层涂层和NiCrAl／WC-Co梯度涂层,对涂层的室温干摩擦磨损性能进行了测定和分析。结果表明,超音速火焰喷涂WC-Co单层涂层具有最好的综合磨损性能。梯度涂层较好的结合力对摩擦磨损性能的影响只有在轻载时表现明显。涂层中原有的孔隙和摩擦过程中形成的孔洞可以在一定程度上减轻磨损,而不同条件下形成的磨屑对涂层的摩擦性能亦有较大影响。     

柴油机缸套-活塞环摩擦副耐磨性研究

对衡量作为摩擦系统的缸套-活塞环摩擦副的耐磨性提出了判据。根据这种判据，对国内生产的合金铸铁缸套、硼磷缸套及激光淬火缸套与镀铬球铁活塞环及其渗陶活塞环进行了配套试验。结果表明：和套与活塞环所组成的摩擦副应作为一个系统来考虑，并且用配副性这个特征量来评价其耐磨性是合理的；渗陶镀铬环与激光淬火缸套的配副性最好。     

Laser Processing of Multilayered Thermal Spray Coatings: Optimal Processing Parameters

Laser processing offers an innovative approach for the fabrication and transformation of a wide range of materials. As a rapid, non-contact, and precision material removal technology, lasers are natural tools to process thermal spray coatings. Recently, a thermoelectric generator (TEG) was fabricated using thermal spray and laser processing. The TEG device represents a multilayer, multimaterial functional thermal spray structure, with laser processing serving an essential role in its fabrication. Several unique challenges are presented when processing such multilayer coatings, and the focus of this work is on the selection of laser processing parameters for optimal feature quality and device performance. A parametric study is carried out using three short-pulse lasers, where laser power, repetition rate and processing speed are varied to determine the laser parameters that result in high-quality features. The resulting laser patterns are characterized using optical and scanning electron microscopy, energy-dispersive x-ray spectroscopy, and electrical isolation tests between patterned regions. The underlying laser interaction and material removal mechanisms that affect the feature quality are discussed. Feature quality was found to improve both by using a multiscanning approach and an optional assist gas of air or nitrogen. Electrically isolated regions were also patterned in a cylindrical test specimen.     

Insulated Piston Heads for Diesel Engines

Widely studied in the 1980s, the insulation of pistons in engines aimed at reducing the heat losses and thus increasing the indicated efficiency. However, those studies stopped in the beginning of the 1990s because of NO _x emission legislation and also because of lower oil prices. Currently, with the improvement of exhaust after treatment systems (diesel particulate filter, selective catalytic reduction, and diesel oxidation catalyst) and engine technologies (exhaust gas recirculation), there are more trade-offs for NO _x reduction. In addition, the fast rise of the oil prices tends to lead back to insulation technologies in order to save fuel. A 1 mm thick plasma sprayed thermal barrier coating with a graded transition between the topcoat and the bondcoat was deposited on top of a serial piston for heavy-duty truck engines. The effects of the insulated pistons on the engine performance are also discussed, and the coating microstructure is analyzed after engine test.