外文翻译激光焊AGPDAUCU合金显微结构和腐蚀状态的研究在牙科领域的应用英文版精品.docx

1、外文翻译激光焊AGPDAUCU合金显微结构和腐蚀状态的研究在牙科领域的应用英文版精品Laser weld: microstructure and corrosion study of AgPdAuCu alloy of the dental applicationM.L. Santos*, H.A. Acciari, L.C.O. Vercik, A.C. Guastaldi Instituto de Qumica de Araraquara-UNESP, C.P. 355, 14800-900 Araraquara, Sao Paulo, Brazil Received 10 June 20

2、02; 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 development of cheaper and smaller equipment, using simpler technique. This allowed greater use of that process on the confection of pr

3、ostheses compared to the brazing process since the heat source for that process is a concentrated light beam of high power, which minimizes distortion problems on the prosthetic pieces. AgPdAuCu alloy used on the confection of dental implant prostheses was observed before and after subjection to the

4、 laser welding 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 environmental conditions simulating the aggressiveness found in the mouth cavity. A

5、structural change was detected on the weld area, which presented a refined microstructure deriving from the high-speed cooling.The base metal out of the weld area presented a fusion coarse microstructure. The electrochemical essays showed differences on the potentiodynamic polarization behavior in b

6、oth weld and metal base areas, indicating superior corrosion resistance in theweld 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: AgPdAuCu; Laser; C

7、orrosion; Dental alloys1. IntroductionIn search for alternative metal alloys for odontological purposes, some researchers have applied the AgPd alloy to substitute the gold alloys, trying to reduce costs and to improve mechanical properties and corrosion resistance 14. Due to some difficulty in obta

8、ining adaptation in prosthetic pieces, mainly the larger ones such as metallic structures molten into one piece, called cast monoblocks, the use of welding is necessary since this technique accepts the work with segments of the prosthesis, which makes possible a balanced force distribution and the b

9、est suitable adaptation, occurring in an accurate passive way4,5.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 welding. The laser welding process was introduced int

10、o dentistry by the end of the 1980s, resulting on agreat impulse to the area with the development of cheaper and smaller equipment due to its advantages and wide application, which made possible to use welding in a wide variety of metals and prostheticpieces 6. The use of electrochemical techniques

11、in the corrosion study is important for the understanding of its performance, biocompatibility and biofunctionality, when clinically applied, for these are constantly exposed to aggressive environments.This research observes AgPdAuCu alloy microstructure behavior and the materials resistance to corr

12、osion under environmental conditions simulating the aggressiveness found in the mouth cavity, when used on dental implant prostheses before and aftersubjected to the laser welding process.2. ExperimentalTable 1 presents the mineral composition of the studied material, using Wave Dispersive Spectrosc

13、opyWDS. The cylindrical test specimens, with 0.27-cm diameter and 1.0-cm length, have been subjected to the welding process on butt joints 7. The welding machine, Dentaurum DL 20002S, used for the laser welding, uses a crystal NdYAG as source of laser, and the beam power was approximately 6.08 kW in

14、 14 ms, originating a welding energy of approximately 85.12 J. The test specimens were manually placed in the chamber, with shield atmosphere of argon, and spots of lap welding, in approximately 2/3 of the surfaces, were applied in the whole section of the joint, with 60% of beam penetration. A prec

15、ise disc model 15 HC DIAMOND was used to obtain the test specimens of AgPdAuCu alloy with area comprehending only the welding area, and an ISOMET 1000-BUEHLER machine was used to separate the base metal from the welding area after the laser process. The exposed geometricareas of the welding cord and

16、 of the base metal were 0.057 cm2. The metallographic analysis of the exposed surface of the base metal and the welding area was done with optic microscopy, after polishwith emery cloth from 180 to 1000 mesh, alumina with granulation 1 and 0.3 Am and nitro-muriatic acid application 8. The work elect

17、rodes were prepared from the test specimens used on the metallographic analysis. Measures of open circuit potential versustime were used in the electrochemical essays, as well as potentiodynamic polarization and electrochemical impedance. An electrochemical cell containing NaCl 0.15 mol l _ 1 (0.9%)

18、 airy solution with three electrodes was also used, with the saturated calomel electrode (SCE) as reference system and a graffiti cylinder as auxiliary electrode. Electrochemical measures of corrosion were done with a potentiometer Solartron SI1287. Potentiodynamicpolarization curves were observed a

19、t 0.001 V s _ 1 immediately. Impedance measures were done with the analyzer of frequency response, Solartron 1255, connected to an electrochemical interface, Solartron 1287, and an amplitude of 10 mV was applied to a frequency channel that varied from 100 kHz to 6 MHz,obtaining five points for each

20、frequency decade, controlledby the software Zplot 9. The software Zveiw 10 was responsible for the adjustments3. Results and discussionFig. 1 presents a coarse biphasic fusion microstructure in the base metal area. Fig. 2 illustrates a refined dendritical microstructure in the laser weld area, deriv

21、ing from the high speedy cooling imposed by the laser weld because of a located fusion process, followed by a quick cooling during the welding, which does not allow the microstructure to return to its initial biphasic structure.Fig. 3 shows the open circuit potential versus time curves for the base

22、metal and laser weld areas of the AgPdAuCu alloy. The stabilization of the potential was observed 3 h after immersion for both areas, and the laser weld presented a stabilization potential 50 mV higher. Some AgPd alloy researchers have observed that, usually, an alloy open circuit potential increase

23、s with the increase of the noble metals concentration1.show minute details the observationShow minute details the observation to include to scan to give or get an electric shock the mirror and golds generally mutually analytical wait.Scanning to give or get an electric shock the mirror analysis is t

24、o will break the oral test piece to place in scan to give or get an electric shock the mirror observationIts crystal structure, split the characteristic,deep, pore, hot influence area Size etc.The gold is mutually analytical to try the piece to the welding to make into the gold first to whet mutuall

25、y Slice, through the sour eclipse, clean, blow the stem to postpose is mutually the microscope in the gold next,Observe its area organization structure, the is deep and melts the area and hot influence areasSize etc.Chai etc. the is in the gold of the piece of mutually analytically detection, Connec

26、t the set displays the brittleness open wound shape of split the , but matched control then is .The tenacity open wound of the cup form, the cone form phenomenon., this is from the tiny view last reflectionThe tenacity of the piece of lower:Discover the laser while study the laser weldingThe hot inf

27、luence area grain of the piece of is smaller, appearing only one horse surname body structure,But deal with contact for the welding of the 3 mms at the diameter all the not yet finished whole is deeplyThe polarization curves on Fig. 4 present differences on the anodic behavior, with the occurrence o

28、f an area corresponding to the first transpassive regionclose to + 0.07 V (SCE) on the laser weld. The numbers obtained for the corrosion potentials, Ecor, indicate that the laser weld area presents highercorrosion resistance.The impedance responses originated in the opencircuit potential, obtained

29、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 better adjustable to the characteristics of the resulting spectrum is composed of a parallel association of RTC andCPE, which represent

30、s the electrochemical behavior of the interface in the high frequencies area, include-including only one charge transfer process. In the low frequencies areas, the spectrum is controlled by theoccurrence of a straight line, and a new Rp and CPEp composition was used to represent the formation of a p

31、ermeable 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 microscopy analysis after the corrosion essays (not showed) and by the significant decrease on the polarization re

32、sistance number from around 10 kV cm2 to 100 V cm2 (Table 2). According to thecorrespondent impedance diagrams obtained with the Bode format, fair concordance between the experimental and calculated numbers is observed.The use of one CPE to substitute the double electrical layer is due to a correction of the distortions caused by the uniformity in the currentdistribution caused by the geometry of the electrodic surface 1113. A diffusion process representedby a straight line on the complex plane and by the distortion degree, ac0.5 (Table 2), is obs