美国西南研究院_SwRI_等离子全方位离子镀膜技术_PIID_研究及实际应用

1、DOI：CNKI:11-3905/TG.20120213.2223.011 Published online：2012-02-13 22:23URL：美国西南研究院（SwRI）等离子全方位离子镀膜技术（PIID）研究及实际应用魏荣华1，李灿民2（1.西南研究院，圣安东尼奥，德克萨斯州，美国 78238；2.合肥永信等离子技术有限公司，合肥230061）摘要：文中介绍了美国西南研究院（Southwest Research Institute - SwRI）等离子全方位离子镀膜技术（PIID）的最新研究成果。SwRI在等离子表面工程领域为实际应用开发了一些新的技术，PIIDSwRI关注的重点是类金

2、刚石（DLC）涂层的高速率沉积，超厚DLCDLC涂层和长管道内表面的镀膜技术。与传统的辉光（PGD）放电技术不同，SwRI基于空心阴极放电（HCD文中讨论了HCD技术的原理，使用HCD和PGD技术制备DLCDLC研究的未来展望进行了探讨。关键词: DLC; 脉冲辉光放电; 空心阴极放电; 管道内壁镀膜; 冲蚀; 磨损; 中图分类号：TG135+.5 文献标识码：Abstract：This paper reviews the Southwest Research Institute (SwRI) in PlasmaImmersion Ion Deposition (PIID). new in p

3、lasma surface engineering for practical -like carbon cess, eseKeywords:0 promise of treating large components without the need of sample manipulation, thereby potentially reducing the processing cost 1,2. Later the process has been commonly referred as plasma immersion ion implantation (PIII) 3-5. A

4、fter over two decades of effort, even though the research is still active 6-10, PIII has not been widely accepted by industry for its intended tribological applications due to its inherent shortcoming, i.e. the implanted species can only penetrate to a depth no more than 200 nm. This treated layer i

5、s deemed to be too shallow for most mechanical components.收稿日期：2011-12-17 修回日期：作者简介：魏荣华(1952),男（汉），美籍华人，原籍辽宁省鞍山人，博士。However, along with the research in PIII came another process from the late 1990s plasma immersion ion deposition (PIID) 11-14. Using this process, 3-D components can be deposited with

6、 a much thicker layer of hard coatings. In particular, diamondlike carbon (DLC) coating obtained using PIID has become the focal point by the research community because it can be readily deposited on a variety of surfaces. Due to its high hardness (10-25 GPa) and sufficient thickness (0.5-2 m), DLC

7、has found practical applications particularly for automotive and biomedical industries 15-21. It should be pointed out, although many techniques can be used to prepare DLC coatings including direct ion beam deposition, magnetron sputtering deposition, cathodic arc deposition, and RF plasma depositio

8、n 22-24, the pulsed glow discharge (PGD)-based PIID, a variation of plasma enhanced chemical vapor deposition (PECVD), offers a much simpler approach and hence a potential for lowerprocessing cost 11, 12, 25-28. In addition, the deposition system hardware is also quite simple; therefore the capital

9、investment is also low. In this paper, we will briefly discuss the PGD process; then we will focus on the latest development in the PGD process and other novel technologies. During the discussions of these technologies, we will present practical application examples. 1Pulsed Glow Discharge Depositio

10、nThe PIID process can be understood using the schematic shown in Figure 1a. After parts are placed in a vacuumchamber and the chamber is pumped down to a low pressure (10-6 Torr), a gas is fed into the chamber to reach 10-15 millitorr. When a train of pulses of negative voltage typically around 5 kV

11、 is applied to the parts, pulsed glow discharge (PGD) plasma is generated in the entire vacuum chamber. The same pulsed voltage also draws the ions out of the plasma so that they are accelerated towards the component surfaces. Dependingon the ion species (precursor gases), either ion sputter cleanin

12、g (when Ar is used) or deposition of DLC (when a carbonaceous gas such as C2H2 is used) can be performed. These two steps are generally performed sequentially by simply switching the gas supply without breaking the vacuum. To ensure a good adhesion of the DLC to the substrate made of metallic materi

13、als, in particular steels, typically a Si or Si-C bond layer is used before the deposition of the DLC. This may be accomplished by feeding the deposition system with silane (SiH4) or trimethylsilane (TMS). It should be pointed out that SiH4 is pyrophoric and needs special handling, while TMS is much

14、 safer. Shown in Figure 1b is a cross-sectional image 2.5m in Figure 2 are a few (b)图1 （a）原理图（b）西南研究院试验装置(a)(b) (c)Figure.2 Components coated with DLC(a) Multi-components processed in one batch, (b) various components in onebatch, and (c) components coated with DLC.图2 工件的DLC镀膜（a）一次加工同种多个工件 （b）一次加工多种

15、工件 （c）镀过DLC的工件2 DLC Deposition using a Mesh Method2.2 Coating uniformity, thickness and deposition rate As shown in Figure 3b, a number of the parts are being coated with DLC, including a tube of 58 mm in diameter by 110 mm long representing 3-D components. After the deposition, by sectioning the tu

16、be longitudinally and using SEM, the coating thickness distribution along the ID surface and the OD surface is shown in Figure 3c. As can be seen, the coating thickness varies from 2 to 9 m. The coating on the ID is thicker than the OD due to the hollow cathode effect even if the tube was in the mes

17、hed cage. The coating does not seem to be uniform. However, considering both 2.1 Principle of meshed PIIDShown in Figure 3a is a schematic of the meshed PIID process 29. Parts are installed inside a metal mesh cage. Usually the parts are electrically connected to the metal cage. When the voltage pul

18、ses are applied to the cage, plasma is generated inside the cage. The pulsed negative voltage also draws ions from all directions to the surfaces of the parts. As a result, a DLC coating canphotograph of the process in progress, and (c) Coating thickness distribution on both sides of the tube.图3 加网P

19、IID技术及涂层的厚度分布(a)加网PIID技术的原理图（b）利用PIID技术正在镀膜的照片（c）管子内外DLC的厚度分布2.3 Microstructural characteristics of DLC coatings Quantitative Raman spectroscopic analyses on the DLC films showed that the Id/Ig is about 1.2 and 0.8 for the conventional PIID and meshed PIID, respectively, indicating an increase in th

20、e sp3/sp2 ratio for the DLC prepared using the meshed PIID 32-34. 2.4 Tribological characteristics of DLC coatingsBall-on-disc tribotests were conducted on 1018 carbon steel deposited with DLC films using both methods in ambient environment, dry sliding with 1 N load against an alumina ball. Shown i

21、n Figure 4a are the coefficients of friction (COF) of the DLC films. Both DLC films show much lower COF than the uncoated 1018 steel (not shown, = 0.6-0.7), while the DLC prepared using the meshed PIID shows slightly higherCOF ( = 0.12) than the PGD DLC, which may be the result of a higher sp3 conte

22、nt in the meshed PIID. DLC films may be used for the protection of components under two-phase flow situations such as air and sand. The erosion resistance of the DLC films was determined using a micro sand blaster with alumina powder of an average grain size of 50 m at an incident angle of 15 and a

23、back pressure of 5 psi. Shown in Figure 4b is the mass loss for selected DLC films prepared using the PGD and the meshed-PIID methods. The total erosion time was 2 min. The mass loss of the PGD DLC is slightly lower than that for the uncoated steel but the mass loss for2.5. Corrosion resistanceCorro

24、sion resistance of the deposited samples was evaluated using electrochemical impedance spectroscopy. Equivalent circuit models were used to calculate the polarization and pore resistance values. The results are shown in Figure 4c. Higher polarization resistance implies better corrosion resistance. A

25、s can be seen, the DLC deposited using the meshed PIID method has much higher corrosion resistance than the standard DLC and the uncoated steel. An increase of 4 orders of magnitude is obtained. One of the reasons may be that the meshed 图4 1018（c3. DLC and PipesBesides advantage of typical size of t

26、ubes (20 100 mm in diameter by 0.1 3 m long), the ID can be deposited with DLC using various methods including hollow cathode discharge 35-37. If the ID is very small and the material is paramagnetic, magnetic field may be used to generate plasma inside the tube 31. Because DLC coatings are hard and

27、 chemically inert, they may be deposited on the ID of tubes forwith a small diameter (25 mm), while Figure 5b two short tubes with a larger diameter (100 mm) in a DLC deposition process. In general the smaller the diameter, the higher the pressure is needed to generate plasma inside the tube. For a

28、tube of 25 mm in diameter by 300-400 mm long, the breakdown pressure is about 50 millitorr either for Ar or acetylene.(a)(b)short tubes with large ID图5使用空心阴极放电PIID技术细管和管道内壁沉积DLC (a) 3.2. Deposition of long pipesLong pipe may also be deposited with DLC films. Shown in Figure 6 is a large diameter (15

29、0 mm), long curved carbon steel pipe (2 m) being deposited with DLC inside the SwRI large PIID chamber. If a pipe is too long, no vacuum chamber can be used to hostusing tubular to the pipe, be generated inside the a be deposited on the inner Shown 7 is a photograph of the HCD PIID process.图6 使用空心阴极

30、放电PIID技术对长管道内径镀DLC膜3.3. Morphology of DLC in long pipesFigure.7 Deposition system for long pipes图7 长管道的镀膜系统conformal. Even though the steel pipe surface is very rough, the DLC coating covers everywhere and adheres well to the substrate. Certainly, our systematic studies indicate that, in some cases,

31、 if the substrate surface is too rough with deep cuts or kinks, the DLC film will have discontinuities. The discontinuities or cracks in the coating are detrimental to the corrosion resistance. Therefore, it is necessary to polish the surface to reduceTo study the DLC coating morphology, a long pipe

32、 was sectioned and the samples were studied suing SEM. Shown in Figures 8a and 8b are the low and high magnifications of cross-sectional SEM images of the DLC coating on the steel pipe surface. In this deposition a Si-C bond layer was used first; then the DLC coating was deposited on top. As can be

33、seen, the coating is quitethe surface roughness and hence to reduce the number ofdefects.ification.in air for Alfor as-Surface C2H2 is (WCA). It is surface energy is hydrophobic. of 117. To surface from revealed that entical to achieve high WCA for is also can hold air to with super applications. hy

34、drophobic from lenses in can be accumulation. 6CAAASAACS(DCCD图9 未处理（AS）和喷砂(SB)后的Al表面镀各种 4.2. Deposition of large components and large number of componentsIn an early publication, the PIID process was demonstrated for depositing DLC on a large number of pistons 37, 38. At SwRI, the deposition of larg

35、e components or a large number of small components are pursued which may be found in Ref 39a few more examples will be given.Shown in Figure 10a is a large to the impellers. In addition, may also adhere to the worst scenario, best, only is the DLC resistant and inside the at the Yongxin Plasma SwRI

36、has helped Yongxin Sample Type(a) (b) (c)DDCS(Figure.10 Deposition of large components and large number of components (a) one large impeller at SwRI, (b) three impellers in mesh at Yongxin Plasma Technology, and (c) ten large water pump parts at Yongxin Plasma Technology.图10大型工件和大批量工件的镀膜 (a)西南研究院大型叶

37、轮的镀膜（b）永信等离子科技在网内同时镀三个叶轮（c）永信等离子科技一次镀10个潜水泵部件(a)(c) (d)图11使用PIIDDLC镀膜, （b、c）汽车部件和试样的DLC镀膜， (d)In this paper, we an research mesh PIID of friction, erosion resistance over the conventional PIID method include the high deposition rate (up to 6.5 times), capability for thick coating (up to 20 m) and mu

38、ch conformal coating coverage. Beside the “standard” DLC coatings derived from a carbonaceous gas such as C2H2, other DLC coatings including the hydrophobic DLC coatings derived from Si-DLC F-DLC and Si-O-DLC were also discussed. In addition, we presented the technique on the deposition of tubes and

39、 pipes of various shapes and sizes. The PIID process may be the easiest way to the coating of ID of tubes and pipes. Up to 12 m long pipes have been deposited with a fairly uniform coating. Finally, the deposition of large components or a large number ofcomponents was also discussed with actual appl

40、ication examples.For the future research, first, the development of coatings with super hydrophobic properties (WCA150) will find many practical applications. Second, deposition of longer pipes is challenging and needs more work. Third, high rate deposition is an important research area. Fourth, the

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