外文翻譯--合金顯微結(jié)構(gòu)和腐蝕狀態(tài)的研究在牙科領(lǐng)域的應(yīng)用（英文）

1、Laser weld: microstructure and corrosion study of Ag–Pd–Au–Cu alloy of the dental applicationM.L. Santos*, H.A. Acciari, L.C.O. Vercik, A.C. GuastaldiInstituto de Qu? ´mica de Araraquara-UNESP, C.P. 355, 14800-900 A

2、raraquara, Sa ?o Paulo, BrazilReceived 10 June 2002; accepted 20 June 2002AbstractThe laser welding process was introduced into dentistry by the end of the 1980s, resulting on a great impulse to that area with the develo

3、pment of cheaper and smaller equipment, using simpler technique. This allowed greater use of that process on the confection of prostheses compared to the brazing process since the heat source for that process is a concen

4、trated light beam of high power, which minimizes distortion problems on the prosthetic pieces. Ag–Pd–Au–Cu alloy used on the confection of dental implant prostheses was observed before and after subjection to the laser w

5、elding process. The microstructure was analyzed with the use of optic microscopy and the corrosion resistance was studied by the traditional electrochemical techniques and by electrochemical impedance, under environmenta

6、l conditions simulating the aggressiveness found in the mouth cavity. A structural change was detected on the weld area, which presented a refined microstructure deriving from the high-speed cooling. The base metal out o

7、f the weld area presented a fusion coarse microstructure. The electrochemical essays showed differences on the potentiodynamic polarization behavior in both weld and metal base areas, indicating superior corrosion resist

8、ance in the weld area. The impedance spectra were characterized by capacitive distorted components, presenting linear impedance in the low frequencies area. D 2002 Elsevier Science B.V. All rights reserved.Keywords: Ag–P

9、d–Au–Cu; Laser; Corrosion; Dental alloys1. IntroductionIn search for alternative metal alloys for odonto- logical purposes, some researchers have applied the AgPd alloy to substitute the gold alloys, trying to reduce cos

10、ts and to improve mechanical properties and corrosion resistance [1–4]. Due to some difficulty in obtaining adaptation in prosthetic pieces, mainly the larger ones such as metallic structures molten intoone piece, called

11、 cast monoblocks, the use of welding is necessary since this technique accepts the work with segments of the prosthesis, which makes pos- sible a balanced force distribution and the best suit- able adaptation, occurring

12、in an accurate passive way [4,5]. The process of laser welding produces a coherent, monochromatic, concentrated light beam of high power, and it has been applied to substitute the brazing in odontological prostheses weld

13、ing. The laser welding process was introduced into dentistry by the end of the 1980s, resulting on a0167-577X/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0167-577X(02)01095-9* C

14、orresponding author.www.elsevier.com/locate/matlet Materials Letters 57 (2003) 1888–1893The polarization curves on Fig. 4 present differ- ences on the anodic behavior, with the occurrence of an area corresponding to the

15、first transpassive region close to + 0.07 V (SCE) on the laser weld. The numbers obtained for the corrosion potentials, Ecor, indicate that the laser weld area presents higher corrosion resistance. The impedance response

16、s originated in the open circuit potential, obtained in the steady state for the base metal area, present the occurrence of one distorted semicircle at high frequencies (Fig. 5). The equivalent electrical circuit model b

17、etter adjust- able to the characteristics of the resulting spectrum is composed of a parallel association of RTC and CPE, which represents the electrochemical behavior of the interface in the high frequencies area, inclu

18、d-ing only one charge transfer process. In the low frequencies areas, the spectrum is controlled by the occurrence of a straight line, and a new Rp and CPEp composition was used to represent the for- mation of a permeabl

19、e nature interface since this dispersion, observed during the frequency variation, may have been originated from the formation of pits on the surface, thus confirmed by the optic micro- scopy analysis after the corrosion

20、 essays (not showed) and by the significant decrease on the polarization resistance number from around 10 kV cm2 to 100 V cm2 (Table 2). According to the correspondent impedance diagrams obtained with the Bode format, fa

21、ir concordance between the experimental and calculated numbers is observed.Fig. 1. Micrograph of the Ag–Pd–Au–Cu alloy base metal.Fig. 2. Micrograph of the Ag–Pd–Au–Cu alloy weld cord.Fig. 3. Open circuit potential versu

22、s time curves to Ag–Pd–Au– Cu alloy, in 0.9% NaCl airy solution: (a) base metal; (b) laser.Fig. 4. Potentiodynamic polarization curves to the Ag–Pd–Au–Cu alloy, in 0.9% NaCl airy solution: (a) base metal; (b) laser.M.L.