外文文獻(xiàn)翻譯-ni-ptfe化學(xué)復(fù)合材料鍍層的研究（英文）

1、Studies on electroless nickel–PTFE composite coatingsK. N. Srinivasan* and S. JohnElectroless deposition of nickel based composites produces outstanding tribiological behaviour.These composite coatings are formed by addi

2、tion to the electroless nickel solution of the materialto be codeposited, in powder form, and by maintaining it in suspension during the depositionprocess so that it is incorporated into the deposit. The most commonly us

3、ed hard dispersedcompounds are SiC, diamond powder, alumina, TiC, BN, chromium carbide or WC. Recently,electroless nickel containing PTFE as a composite material has been used because it is uniform,highly adherent, hard

4、wearing, dry lubricating, non-galling, has a lower coefficient of friction andgood corrosion resistance properties. The present paper studies the effect of PTFE in anelectroless Ni–acid bath on the rate of deposition, in

5、corporation of PTFE and phosphorouscontent in the deposit, wear and corrosion resistance.Keywords: Electroless composites, Chemical deposition, Nickel–phosphorous–PTFE composites, Composite coatingIntroductionAn electrod

6、eposited composite plating is a uniform dispersion of small discrete particulate matter deliber- ately codeposited within a metallic coating.1–3Electroless nickel phosphorous coatings have many properties that are superi

7、or to those of electrodeposited nickel.4 Because of the phosphorous content, electroless nickel is harder and has better corrosion resistance.5Electroless nickel composites combine the unique properties of conventional e

8、lectroless nickel deposits such as uniformity of deposition over complex geome- tries, high hardness and good corrosion resistance with that of abrasive materials possessing high temperature resistance and other tribiolo

9、gical properties. It is interesting to note that in electroless deposition it is possible to achieve a high percentage of incorporation even at low concentrations of particles in the bath, in contrast to electroplating,

10、where a large concentration of particles must be present to get a high percentage of incorporation. In recent years, composite materials have gained importance in engineering industries, especially for high technology ap

11、plications such as aero engines, modern gas turbine engines, automobiles, etc.6 In electroless composites, the matrix is not pure nickel, but it can be either Ni–P or Ni–B, depending upon the nature of the reducing agent

12、s used in the bath. The most commonly used hard dispersed compounds are SiC, diamond powder, alumina, TiC, BN and WC.1–9 The latest development in electroless codeposition is the incorporation of polytetrafluoroethylene

13、(PTFE) withnickel. PTFE particles are added to the solution in the form of a water dispersion.10,11The properties of electroless Ni–PTFE coatings such as wear resistance, corrosion resistance, friction coeffi- cient, mic

14、rohardness and all other properties are excellent.12–18 The production, properties and applica- tions of composite electroless Ni/PTFE coatings are good.19,20 Uniform dispersibility of PTFE particles is obtained in elect

15、roless nickel composite plating.21,22Duncan13 deposited coatings which contain 10–30 vol.-%, 0.3–0.4 mm diameter particles of PTFE with 5–10 wt-%P. The coefficient of friction is typically 0.1–0.2 for non- lubricated con

16、ditions. It was also found from micro- hardness tests and wear tests that the hardness of composite coatings with 14–16%PTFE was typically 250–400 HV, while the hardness of those with 26%PTFE had only 275 HV. After heat

17、treatment at .300uC hardness values were increased to 625–700 HV and 400 HV, respectively. Hadley and Harland17described a coating containing up to 25 wt-%PTFE uniformly distributed in chemical Ni–P containing 84.6 Ni–7P

18、–8.4PTFE (wt-%) and with a specific gravity 6.5. They also found that hardness depends on heat treatment. Nishira et al.23 found that suspension of PTFE particles in an electroless Ni–P bath was affected by non-ionic and

19、 cationic surfactants. Matsuda et al.24found that PTFE particles were codeposited in electro- less Ni–P plated film. This codeposition depends on surfactant type, i.e. zeta potential of particle surface in the plating so

20、lution and content of particles in films. PTFE has been used as a versatile material to protect parts from corrosion and wear.25 Daniels and Harme26found that the Ni–PTFE coating increases service life and product qualit

21、y in plastic manufacture.26Zhengshan et al.27 reported the morphology and structure of Ni–P–PTFE coatings. This imparts con- siderable non-galling, dry lubricant properties to theCentral Electrochemical Research Institut

22、e, Karaikudi–630 006, TamilNadu, India*Corresponding author, email k_n_srinivasan@yahoo.com? 2005 Institute of Materials, Minerals and Mining Published by Maney on behalf of the Institute Received 13 September 2004; acce

23、pted 8 November 2004 156 Surface Engineering 2005 VOL 21 NO 2 DOI 10.1179/174329405X40902Determination of hardnessThe cleaned mild steel panels were plated with EN/ PTFE and the hardness was measured using the Vicker’s h

24、ardness method. The diagonal of the diamond shaped indentation made by applying a known load through a diamond indentor for a definite time was measured using a microscope fitted with a calibrator eyepiece. The Vicker’s

25、hardness was calculated from the length of the diagonal.Determination of abrasion resistance using Taber abraserThe EN/PTFE plated specimen was weighed, then placed under a pair of weighted abrading wheels (each 500 g) o

26、f closely controlled composition in such a manner as to cause side slip between the abrading wheels and the surface of the test specimen. The wheels rotated on the specimen for 1000 revolutions, after which the panel was

27、 weighed again. The difference in weights was the wear index (Taber index) or rate of wear. The experiments were repeated twice, and the average value was taken. The same experiment was carried out using a specimen which

28、 was plated with electroless nickel only, and the abrasion resistance properties of both the specimens, with and without PTFE, were compared.Effect of heat treatment on hardnessTwo similar panels were taken. One was plat

29、ed with nickel alone and the other with nickel/PTFE composite. Both were heat treated at 400uC for 1 h and then tested for abrasion resistance using the Taber abraser.Analysis of nickel and phosphorous in depositStainles

30、s steel panels were deposited with EN/PTFE deposit in various conditions. The panel was etched in concentrated hydrochloric acid for 1–2 min and acti- vated in palladium chloride solution. Then it was plated with EN/PTFE

31、 composite. The deposit was removed from the panel, weighed, dissolved in 20 ml of 40% nitric acid and increased to 100 ml in a standard measuring flask. Nickel content in the solution was analysed volumetrically by the

32、EDTA method and phosphorous by the ammonium phosphomolybdate method.Corrosion measurements by potentiostatic polarisationTwo mild steel samples were cut to 75615 mm, mechanically polished, degreased with trichloroethylen

33、e and etched in 20% sulphuric acid at 60uC or 2 min. One specimen plated with nickel alone and the other with EN/PTFE composite for 2 h at 90uC and pH 5.5. Polarisation measurements were carried out potentios- tatically

34、by exposing a 1 cm2 area of each plated specimen (both with and without PTFE) using apotentiostat. Platinum was used as an auxilliary electrode and a saturated calomel electrode as the reference electrode. The electrolyt

35、e used in the study was 3% sodium chloride. Both anodic and cathodic polarisations were carried out. A graph was drawn with current density against potential. Using the Tafel extrapolation method, the corrosion current a

36、nd corro- sion potentials were determined. The corrosion rate in millilitres per year was calculated.Results and discussionsEffect of temperatureThe effect of temperature on the rate of deposition is shown in Table 1. Th

37、e rate of deposition increases with temperature. An increase in solution temperature increases the flow of the solution towards the electrode by convection. Because the electroless plating of metals invariably involves a

38、 reaction proceeding at a rate limited by diffusion, increasing the temperature of the solution favours more nickel ion movement towards the electrodes, which leads to a high rate of deposition. The volume percentage of

39、PTFE codeposited was also found to increase with rising temperature.Effect of deposition timeTable 2 shows the change in thickness of the deposit with increase in deposition time. It was found that, as the deposition tim

40、e increases, the thickness of the deposit also increases.Effect of concentration of PTFE in bathThe PTFE content in the bath was varied from 5 g L–1to 20 g L–1, and the nickel and phosphorous content in the deposits was

41、analysed. The analysis showed that the hypophosphite added to reduce Ni2z produced a phosphorous content of 8%. The amount of nickel in the deposit was found to decrease as the PTFE concentration increased. This confirms

42、 that there is an increase in the volume percentage of PTFE with an increase in its concentration. The volume percentage of PTFE attained a constant value from 15 g L–1 onwards. The effect of concentration of PTFE is giv

43、en in Table 3.Table 1 Influence of temperature of bath on rate of deposition at pH 5.5Temperature, uC Rate of deposition, mm h–160 3.7 70 5.0 80 8.0 90 10.5Table 3 Effect of concentration of PTFE in bathConcentration of

44、PTFE, g L–1 PTFE in EN/PTFE deposit, vol.-%5 18.0 7 20.8 9 22.6 11 24.0 13 24.8 15 24.9 17 25.0 19 25.0Table 2 Effect of plating time on thickness of deposit at bath temperature 90uC and pH 5.5Thickness of deposit, mm Ti