Effect of deposition conditions on the properties and annealing behavior of cold-sprayed copper

The deposition of copper by cold gas dynamic spraying has attracted much interest in recent years due to the capability to deposit low-porosity oxide-free coatings. However, it is generally found that as-deposited copper has a signicantly greater hardness, and potentially lower ductility, than bulk material. In this article, copper was deposited by cold spraying using helium as the driving gas at both 298 and 523 K. Evidence is presented indicating that the material sprayed at the lower temperature exhibits a lower dislocation density throughout the grain structure than the material sprayed at the higher temperature. The low stacking fault energy of copper restricts recovery during annealing, and thus microstructural changes during annealing only proceed once recrystallization begins. The material sprayed at low temperature (with the low dislocation density) exhibited recrystallization at annealing temperatures as low as 373 K with a corresponding reduction in hardness. However, the copper sprayed with helium at 523 K was resistant to annealing at temperatures up to 473 K where the dislocations in the structure prevented recrystallization. However, at higher temperatures, recrystallization did proceed (with corresponding reductions in hardness). The fracture behavior of the copper that was cold sprayed with helium at 523 K, both in the as-sprayed condition and following annealing, was measured and explained in terms of the annealing mechanisms proposed. The original version of this paper was published in the CD ROM Thermal Spray Connects: Explore Its Surfacing Potential, International Thermal Spray Conference, sponsored by DVS, ASM International, and HW International Institute of Welding, Basel, Switzerland, May 2–4, 2005, DVS-Verlag GmbH, Düsseldorf, Germany.     

Processing of yttria partially stabilized zirconia thermal barrier coatings implementing a high-power laser diode

Several studies have been undertaken recently to adapt yttria partially stabilized zirconia (YPSZ) thermal barrier coating (TBC) characteristics during their manufacturing process. Thermal spraying implementing laser irradiation appears to be a possibility for modifying the coating morphology. This study aims to present the results of in situ (i.e., simultaneous treatment) and a posteriori (i.e., post-treatment) laser treatments implementing a high-power laser diode. In both cases, the coatings underwent atmospheric plasma spraying (APS). Laser irradiation was achieved using a 3 kW, average-power laser diode exhibiting an 848 nm wavelength. Experiments were performed to reach two goals. First, laser post-treatments aimed at building a map of the laser-processing parameter effects on the coating microstructure to estimate the laser-processing parameters, which seem to be suited to the change into in situ coating remelting. Second, in situ coating remelting aimed at quantifying the involved phenomena. In that case, the coating was treated layer by layer as it was manufactured. The input energy effect was studied by varying the scanning velocity (i.e., between 35 and 60 m/min), and consequently the irradiation time (i.e., between 1.8 and 3.1 ms, respectively). Experiments showed that coating thermal conductivity was lowered by more than 20% and that coating resistance to isothermal shocks was increased very significantly.     

Microstructure evolution of cold-sprayed coating during deposition and through post-spraying heat treatment

The microstructural features of cold-sprayed coatings were investigated using Cu, Ti and Zn feedstocks by optical microscopy, scanning electron microscopy and transmission electron microscopy to reveal the microstructure evolution mechanisms in cold spray. Four typical effects including tamping, refinement, impact-induced fusion and annealing were examined on microstrueture. It is found that the microstructure of cold spray coating is remarkably influenced by spray materials. Ti coatings consist of evident porous layer and Cu coatings present a limited porous layer only near the surface. It is clear that the successive tamping effect and dynamic refinement of grains significantly influence the microstructure evolution of cold-sprayed coating. The tamping effect leads to the densification of porous coating layer gradually and the refinement effect leads to the formation of fine microstructure. It is considered that the large difference in the formation of porous layer is attributed to the dynamic impact pressure and hardenability of materials. It is also found that the impact-induced fusion during deposition of Zn coating can also modify the interfacial microstructure between particles in cold spray coating. Moreover, the nanocrystalline phase can be formed at the interfaces among particles resulting from the localized melting of the interfaces and tamping effect. Furthermore, the annealing treatment can modify the microstructure and property of a cold-sprayed coating.     

粘结剂对镍基复合粉末及涂层性能影响研究

本文对比分析了四种不同粘结剂制备的镍铬铁铝氮化硼复合粉末及涂层性能, 结果表明： A3 粘结剂的固 化性能和热降解性能与镍铬铁铝氮化硼复合粉末的粉末制备工艺及喷涂工艺匹配性良好, 制备的复合粉末的形貌 和性能较优, 以此制备的封严涂层组织均匀, 硬度为 62 HR15Y, 结合强度为 7.99 MPa, 耐盐浴腐蚀性能良好。     

等离子喷涂技术现状及发展

从等离子喷涂设备、等离子喷涂过程中的测量技术及等离子喷涂技术的应用等几个方面综合分析了近年来等离子喷涂技术的研究现状和发展概况,指出了等离子喷涂技术的发展方向.     

Cold gas dynamic spraying of aluminum: The role of substrate characteristics in deposit formation

Aluminum powder of 99.7 wt.% purity and in the nominal particle size range of −75+15 μm has been sprayed onto a range of substrates by cold gas dynamic spraying (cold spraying) with helium, at room temperature, as the accelerating gas. The substrates examined include metals with a range of hardness, polymers, and ceramics. The substrate surfaces had low roughness (R _a < 0.1 μm) before deposition of aluminum in an attempt to separate effects of mechanical bonding from other forms of bonding, such as chemical or metallurgical bonding. The cross-sectional area of a single track of aluminum sprayed onto the substrate was taken as a measure of the ease of initiation of deposition, assuming that once a coating had begun to deposit onto a substrate, its growth would occur at a constant rate regardless of substrate type. It has been shown that initiation of deposition depends critically upon substrate type. For metals where initiation was not easy, small aluminum particles were deposited preferentially to large ones (due to their higher impact velocities); these may have acted as an interlayer to promote further building of the coating. A number of phenomena have been observed following spraying onto various substrates, such as substrate melting, substrate and particle deformation, and evidence for the formation of a metal-jet (akin to that seen in explosive welding). Such phenomena have been related to the processes occurring during impact of the particles on the substrate. Generally, initiation of aluminum deposition was poor for nonmetallic materials (where no metallic bonding between the particle and substrate was possible) and for very soft metals (in the case of tin, melting of the substrate was observed). Metallic substrates harder than the aluminum particles generally promoted deposition, although deposition onto aluminum alloy was difficult due to the presence of a tenacious oxide layer. Initiation was seen to be rapid on hard metallic substrates, even when deformation of the substrate was not visible. The original version of this article was published as part of the ASM Proceedings, Thermal Spray 2003: Advancing the Sciences and Applying the Technology, International Thermal Spray Conference (Orlando, FL), May 5–8, 2003, Basil R. Marple and Christian Moreau, Ed., ASM International, 2003.     

用GA-BP算法研究超音速电弧喷涂JCW-S-AM涂层显微硬度与工艺参数间的关系

采用超音速电弧喷涂设备在不同工艺参数条件下制备JCW-S-AM涂层,利用显微硬度计测定各种涂层的显微硬度.根据测试结果,运用GA-BP算法构建涂层显微硬度与喷涂电压、喷涂电流的关系模型并进行工艺参数优化.研究结果表明:喷涂电压和喷涂电流对涂层显微硬度均有影响,呈现非线性规律,并且电压和电流之间存在交互作用;通过遗传算法优化,获得的最佳喷涂工艺参数为:喷涂电压29V,电流200A.此时JCW-S-AM涂层显微硬度最大.     

Microstructure and Sliding Wear Behaviour of Ni(Cr)-TiB_2 Coatings Deposited by HVOF Spraying of SHS Powders

THERMAL SPRAYING provides a large range ofcoatings,which increase the wear resistance ofsubstrates[1].One of the major coating families is thecermet,composed of hard ceramic particles with ametallic binder.The most commonly used cermetcoatings in industrial applications are based on eitherthe WC-Co or the Cr3C2-Ni(Cr)systems with WC-17wt%Co and Cr3C2-25wt%Ni(Cr)being typicalcompositions[2,3].Although WC-Co deposits are hardand wear resistant at ambient temperatures their rangeof ap…     

Thixoforging of continuous fiber-reinforced AlSi/AlMg-alloys

High strength in combination with low density is the key features for lightweight constructions in automotive and aerospace applications. Tailor-made fiber reinforcements in light-metal matrices could help to achieve this goal. However, the integration of fibers with conventional casting-route manufacturing techniques like squeeze casting or diffusion bonding restricts the component geometry and results in elevated process cost due to long cycle times and the need of additional fiber coatings. In the center of competence for casting and thixoforging Stuttgart (CCT), new processes for manufacturing metal matrix composites are developed. Long-fiber reinforced Al–Si alloys and components are produced by thixoforging of laminates made of alternating metal matrix layers and carbon fiber fabrics. This paper illustrates the manufacturing technology and first experimental results with special focus on fiber penetration and infiltration behavior and also on the formation of fiber-matrix interface to analyze fiber damage by mechanical or chemical attack.     

Ni－Cr－B－Si合金粉末等离子喷涂层的高温性能及其在滚锻模上的应用

研究了Ｎｉ－Ｃｒ－Ｂ－Ｓｉ合金粉末等离子喷涂层的高温抗氧化性能、耐磨性、热稳定性，并介绍了其在连杆毛坯滚锻模上的应用．结果表明，这种涂层的某些高温性能大大优于５ＣｒＮｉＭｏ钢，在冲击载荷不大的场合，可以作为热锻模的强化方法．