Coating Bores of Light Metal Engine Blocks with a Nanocomposite Material using the Plasma Transferred Wire Arc Thermal Spray Process

Engine blocks of modern passenger car engines are generally made of light metal alloys, mostly hypoeutectic AlSi-alloys. Due to their low hardness, these alloys do not meet the tribological requirements of the system cylinder running surface—piston rings—lubricating oil. In order to provide a suitable cylinder running surface, nowadays cylinder liners made of gray cast iron are pressed in or cast into the engine block. A newer approach is to apply thermal spray coatings onto the cylinder bore walls. Due to the geometric conditions, the coatings are applied with specifically designed internal diameter thermal spray systems. With these processes a broad variety of feedstock can be applied, whereas mostly low-alloyed carbon steel feedstock is being used for this application. In the context of this work, an iron-based wire feedstock has been developed, which leads to a nanocrystalline coating. The application of this material was carried out with the Plasma Transferred Wire Arc system. AlMgSi0.5 liners were used as substrates. The coating microstructure and the properties of the coatings were analyzed.     

Thermal spraying of cylinder bores with the Plasma Transferred Wire Arc process

Engine blocks of passenger cars made of hypoeutectic AlSi-alloys are generally equipped with cast iron liners in order to provide cylinder running surfaces that meet the tribological requirements. Thermally sprayed cylinder running surfaces are a promising alternative to cast iron liners. APS sprayed cylinder running surfaces made from low alloyed C steel have already proven their ability to reduce friction losses within the engine. Additional potential to reduce friction losses is offered by novel, and highly alloyed iron based surface building materials. This work describes the development of such materials and their application by the Plasma Transferred Wire Arc internal diameter coating process. The feedstocks lead to partially amorphous coatings with embedded boridic nanoscale precipitations if processed by thermal spraying. The coatings were applied onto the inner diameters of test liners made of aluminium EN AW 6060 and onto cylinder bore walls of an in-line 4 cylinder engine. Prior to coating, all surfaces to be coated were pre-treated by a novel fine boring process in order to create a surface topography which enables the adherence of the coatings. The coatings microstructures were analysed by light optical microscopy, hardness measuring and transmission electron microscopy. Furthermore the oil storage capacities of the honed surfaces were determined.     

Solidification and microstructural characterisation of iron-chromium based hardfaced coatings deposited by SMAW and electric arc spraying

The microstructure and solidification of shielded metal arc welding (SMAW) hardfaced Fe-Cr-C deposits used in the sugar industry as well as electric arc-sprayed Fe-Cr-B coating have been determined using a combination of optical microscopy, image analysis, SEM and XRD. The aim of this study was to examine the morphology, microstructure and chemical composition of the coating. The weld microstructures consisted primarily of (Fe,Cr,Mn)₇C₃ carbides, austenite (γ) and ferrite (α), while the arc-sprayed coating was composed of two metallic phases, α (Fe,Cr) and Fe_1.1Cr_0.9B_0.9, which were intermingled with oxides of iron and chromium. The highest average hardness (850 kgf/mm²) occurred in weld coating A80, compared to the 730 kgf/mm² measured in the arc-sprayed coating. The results of the study also showed that different welding electrodes as well as weld procedure variation produced significant differences in the morphology of the carbides, structure of the deposit and microhardness. Although the microhardness of the welded deposits was higher than the arc-sprayed coating, the arc-sprayed coating exhibited a more consistent hardness value. Porosity and oxide inclusions were more evident in the arc-sprayed coating: 1% and 3% in the weld coatings S80 and A80, respectively, and 6.5% in the arc-sprayed coating. The implications of the result with respect to solidification and microstructure are discussed.     

变极性等离子电弧稳定性及其控制

以变极性等离子电弧稳定性机理及其控制方法为研究对象,自行研制了80C196KC单片机为控制核心,主电路为双逆变型电路拓扑结构的VPPA1型变极性等离子焊接电源.重点分析小电流过零再引燃机理及其在大规范焊接条件下变极性等离子弧焊接系统及其电弧的稳定性.分别提出了在小电流焊接时通过程序设定方法将变极性等离子电弧由正极性变反极性之前提高过零电流,而大规范焊接条件下则控制过零电流的新观点,对科学认识变极性等离子电弧特性及其焊接过程控制有重要的指导意义.     

Composition Gradient Hard Coatings by Arc Ion Plating

TIN is the major hard coatings developed since1980s.In the past20years,more hard coatings have beensynthesized.Strafford et al.m classified the availablecoatings into3generations.The first generation is TiN;the second is TiCN and TiAIN etc.;and the third iscomposite coatings that contain multiple elements andlayers.The typical examples of this generation areTi/TiN,TiN/TiCN,TiN/TiAIN,TiN/CrN etc.The mostpromising multi-layered coatings are gradient coatings.The concept of functiona…     

Abrasive wear behaviour of laser clad and flame sprayed-melted NiCrBSi coatings

In this work, the influence of the processing conditions on the microstructure and abrasive wear behaviour of a NiCrBSi hardfacing alloy is analysed. The hardfacing alloy was applied in the form of coatings onto a mild steel substrate (Fe–0.15%C) by different techniques: laser cladding (LC) and flame spraying (FS) combined with surface flame melting (SFM). In both cases, the appropriate selection of the process parameters enabled high-quality, defect-free NiCrBSi coatings to be obtained. The microstructure of the coatings was analysed by scanning electron microscopy (SEM), with attached energy dispersive spectroscopy (EDS) microprobe, and by X-ray diffraction (XRD). Their tribological properties were evaluated by micro-scale ball cratering abrasive wear tests using different abrasives: diamond, SiC and WC. Microstructural characterisation showed that both coatings exhibit similar phases in their microstructure, but the phases present differ in morphology, size distribution and relative proportions from one coating to another. Wear tests showed that in three-body abrasive conditions, despite these microstructural differences, the wear behaviour is comparable for both coatings. Conversely, in two-body wear conditions with diamond particles as the abrasive, it was observed that the specific wear rate of the material is sensitive to microstructural changes. This fact is particularly apparent in LC coatings, in which the zones of the layers with higher proportions of very small hard particles present a lower wear resistance. These results indicate that it is important to have good microstructural control of this material, in order to obtain coatings with an optimized and homogeneous tribological behaviour.     

The role of torch instabilities in the suspension plasma spraying process

In spite of the fact that plasma spraying is a commonly used technique for coating elaboration, it remains important to follow in time the characteristics of the arc jet delivered by the plasma torch. Arc voltage and heat loss measurement could be used, together with the control parameters such as arc current and plasma gas flow rate, to investigate the global behavior of the torch in association with a simple analytical model. It is shown that the specific enthalpy and the isentropic coefficient of the plasma gas have a strong influence on the jet velocity, this latter being also significantly modified by the drift of the torch performance. This work is completed by the analysis of the plasma jet instabilities that are responsible for the discrepancy in particle thermal histories. The rear part of the torch is involved in self sustained oscillations, so that the torch shows the characteristics of a Helmholtz resonator, giving rise to periodic variations of the torch voltage, higher in amplitude than the commonly admitted restrike mode. It is also evoked, that the generated acoustic waves are interacting with the solvent vaporization.     

Effect of carbide degradation in a Ni-based hardfacing under abrasive and combined impact/abrasive conditions

Within this work, the effect of carbide degradation in a WC/W₂C reinforced Ni-based hardfacing was assessed under abrasive and combined impact/abrasive conditions. In view of the above, a WC/W₂C reinforced Ni-based hardfacing was deposited by plasma transferred arc (PTA) welding using different welding currents. Microstructure was characterised by quantitative metallography to determine specific structural parameters: mean carbide diameter and carbide area fraction. Scanning electron microscopy (SEM, EDS) and X-ray diffraction (XRD) were also used to characterise carbide dissolution mechanism. Tribological behaviour was determined with a 3-body abrasion test according to ASTM G65 and with a cyclic impact/abrasion test (CIAT). Results showed significant carbide degradation with increasing welding current, resulting in a significant reduced primary carbide content and carbide diameter. Reduced carbide content indicated a significantly wear rate increase under pure 3-body abrasion conditions. Specific wear energy was determined under pure abrasive condition and showed significant dependence on the primary carbide content. However, wear rates under combined impact/abrasion were at constant level due to the reduction of the brittle primary carbide content.     

Protection of cobalt-based refractory alloys by chromium deposition on surface: Part I: Sub-surface enrichment in chromium by pack-cementation and diffusion

The feasibility of surface chromium enrichment by pack-cementation was assessed for different low chromium-containing cobalt alloys, in order to improve their resistance against high temperature oxidation. A binary Co-10Cr alloy, two ternary Co-10Cr-0.5C and Co-10Cr-1.0C alloys and two TaC-containing Co-10Cr-based alloys were elaborated by foundry for the study. 7.5 h-long and 15 h-long cementations at 1050 °C, followed or not by a 75 h-long heat treatment at 1200 °C were performed on these alloys. Microstructure examinations performed using a Scanning Electron Microscope and concentration profiles using Electron Probe Micro Analysis-Wavelength Dispersion Spectrometry were realized in order to analyze the level of Cr-enrichment of the sub-surface region, with as studied criteria: the nature of the external Cr-enriched zone, the maximal chromium content on surface and the depth of chromium enrichment. The Cr-enrichment of the sub-surface succeeded for the Co-10Cr alloy and for the two tantalum-containing alloys, with the formation of an external metallic zone containing around 30 wt.% Cr. In contrast the chromium carbides-containing alloys were effectively enriched in chromium in surface but in the form of a continuous chromium carbide layer which can induce other problems such as spallation and then possible fast oxidation of the denuded alloy. Finally it appeared that only the carbon-free alloys, and the alloys reinforced by carbides more stable than chromium carbides, are potentially able to be successful enriched in chromium in their sub-surface by pack-cementation.     

直流氢电弧等离子体蒸发法制备Cu-Ni纳米复合粉体

在一定工艺参数下,采用双枪直流氢电弧等离子体的方法制备了产率较高的Cu-Ni复合纳米粉体,分析结果表明:该纳米复合粉体为两种金属单质的混合,且混合均匀、洁净度高,分散性好,其平均粒径为53.68 nm,具有较好的市场应用前景.     

直流氢电弧等离子体蒸发法制备纳米Cu粉

采用99.99%的高纯Cu,通过自行设计的直流电弧等离子体蒸发设备实现了高产率纳米Cu粉的制备.系统研究了电流、氢氩比、充气压力3个工艺参数对纳米Cu粉产率及粒度的影响.利用X射线衍射（XRD）、透射电子显微镜（TEM）和选区电子衍射（ED）以及Simple PCI软件对试样的成分、形貌、晶体结构和粒径分布进行了分析.结果表明,电流和氢氩比（H2/Ar）分别是对粉体产率和平均粒径影响的显著性因素;所制备的纳米铜粉为多晶结构,平均粒径在29～116 nm范围内;在试验参数相近的情况下,产率比同类研究结果提高了26.65倍.     

等离子喷涂Ag-SnO2涂层的微观结构和性能

采用等离子喷涂技术在铜基体表面制备了Ag-SnO2涂层,应用XRD和SEM对涂层的相结构和微观组织进行了表征,通过拉伸和硬度实验测定了涂层的力学性能,并采用电弧侵蚀实验测试了涂层的耐电弧侵蚀性能。结果表明,所得涂层结构均匀致密,涂层内纳米级SnO2颗粒均匀分布在银基体中;涂层的力学性能和电弧侵蚀性能与块体合金接近;电弧侵蚀试验后,涂层表面阴极斑点分散,烧蚀轻微,表明所制备的Ag-SnO2涂层具有良好的耐电弧侵蚀特性。     

超音速等离子制备多元铝青铜合金涂层的组织

采用超音速等离子喷涂技术将新型多元铝青铜合金粉体喷涂在45号钢基体表面。运用XRD、SEM、EDS、EPMA等手段分析了涂层的组织特点及元素分布情况。结果表明,超音速等离子喷涂层主要由Cu9Al4、AlFe3、AlFe等相组成;涂层元素分布均匀;超音速等离子喷涂层硬度高于传统等离子喷焊层;涂层的结合强度为59.3MPa。可见,经过工艺参数的优化,超音速等离子喷涂可以制备出类似于多元铝青铜合金的易氧化涂层。     

脉冲偏压占空比对电弧离子镀TiAlN涂层的影响

通过优化电弧离子镀工艺参数改善TiAlN涂层结构及性能对TiAlN涂层应用具有重要的实用价值。本文利用脉冲偏压电弧离子镀制备了TiAlN涂层,研究了偏压占空比对TiAlN涂层结构及性能的影响,结果发现：随着占空比增加,涂层表面缺陷密度和表面粗糙度先降低后增大,占空比为70%时,制备的涂层表面缺陷密度和表面粗糙度最低。随着占空比增加,涂层的硬度和耐磨性得到明显改善,但占空比超过50%后继续增加占空比反而降低了涂层的硬度和耐磨性。TiAlN涂层与Si3N4球对磨时的主要磨损机制为黏着磨损和氧化磨损。     

Non-wetting behaviour of tungsten carbide powders in nickel weld pool: new loss mechanism in GMAW overlays

This paper presents a new mechanism, observed directly for the first time, to explain low carbide fractions in Ni–WC overlays produced with GMAW. In this loss mechanism, a significant amount of powder loss is a consequence of the non-wetting behaviour of tungsten carbide. High speed videography and quantitative metallography of weld deposits are used to identify this mechanism. The non-wetting mechanism found acts simultaneously with the carbide dissolution mechanism, which until now was the only suggested cause of low carbide fraction in GMAW Ni–WC overlays. The non-wetting behaviour is observed in both short circuit and free flight metal transfer, accounting for carbide losses between 20 and 70% in the experiments performed. Low carbide fraction has prevented the mainstream use of GMAW for Ni–WC overlays, despite the advantages of simplicity, capability of in situ repair, and low capital costs. The findings presented here have a potential large impact for further consumable and process development.     

Ni/Al Intermetallics Plasma Transferred Arc Processing

TAILORING COMPONENT SUFACES for elevatedtemperature operations has been a goal of researchersduring the last century.Process and material selectionare the key factors for this development.In particularlythe latter can be described to have started with thedevelopment of stainless steels.Ni and Co based alloys,the superalloys,attended the increasing technologicaldemands for higher service temperatures(1).Morerecently the higher operating temperatures ofequipments,such as gas turbines,r…