Mechanical and elemental characterization of solder joints and welds using a gold-palladium alloy,☆☆,,★★,

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Abstract

Purpose. This study was conducted to determine whether newer infrared or laser welding technologies created joints superior to traditional furnace or torch soldering methods of joining metals. It was designed to assess the mechanical resistance, the characteristics of the fractured surfaces, and the elemental diffusion of joints obtained by four different techniques: (1) preceramic soldering with a propane-oxygen torch, (2) postceramic soldering with a porcelain furnace, (3) preceramic and (4) postceramic soldering with an infrared heat source, and (5) laser welding.

Material and methods. Mechanical resistance was determined by measuring the ultimate tensile strength of the joint and by determining their resistance to fatigue loading. Elemental diffusion to and from the joint was assessed with microprobe tracings. Scanning electron microscopy micrographs of the fractured surface were also obtained and evaluated.

Results. Under monotonic tensile stress, three groups emerged: The laser welds were the strongest, the preceramic joints ranged second, and the postceramic joints were the weakest. Under fatigue stress, the order was as follows: first, the preceramic joints, and second, a group that comprised both postceramic joints and the laser welds. Inspection of the fractographs revealed several fracture modes but no consistent pattern emerged. Microprobe analyses demonstrated minor diffusion processes in the preceramic joints, whereas significant diffusion was observed in the postceramic joints.

Clinical Implications. The mechanical resistance data conflicted as to the strength that could be expected of laser welded joints. On the basis of fatigue resistance of the joints, neither infrared solder joints nor laser welds were stronger than torch or furnace soldered joints. (J Prosthet Dent 1997;77:607-16.)

Section snippets

MATERIAL AND METHODS

Five techniques were compared: two conventional techniques, propane-oxygen torch and furnace heating, and three novel approaches, preceramic and postceramic soldering with an infrared heat source and laser welding. Comparisons were based on mechanical tests by determining the ultimate tensile strength and the resistance to fatigue failure on diffusion analysis of metal elements to and from the solder and on the evaluation of fractographs (Fig. 1). The compositions of the parent metal and the

Ultimate tensile strength

The UTS values are illustrated in Figure 4. Three groups emerged: the parent metal with a mean UTS of 812 MPa, the laser welds (633 MPa), and the furnace, torch, and IR-soldered specimens with UTSs in the 357 to 490 MPa range.

. Ultimate tensile strength of joints tested. Gray shaded overlapping box indicates groups that were not statistically different.

Resistance to cyclic loading

The fatigue resistance of the six joints investigated is depicted in Figure 5.

. Fatigue resistance of joints tested. Gray shaded overlapping box

Preparation of the test specimens

Machining the Au-Pd rods instead of casting the specimens was at variance with normal laboratory procedures. Nevertheless, this approach was advisable when considering the following. First, the production cost of the rods was markedly reduced when they were industrially manufactured instead of being cast individually and, second, machining the specimens excludes significant variations in the parent metal, because what is being tested is the solder joint not the parent metal. Whether the heat

CONCLUSION

Although they were not included as variables in this investigation, two technical aspects should be mentioned. First, it was nearly impossible to maintain both rods in their original relationship during laser welding. The initial welding impact always distorted the coaxial arrangement, which could be somewhat reestablished by a second weld on the opposite side. A welding technique that ensures uniform stress distribution during joint formation is needed. Second, both the laser and the IR

Acknowledgements

The help of the following persons is gratefully acknowledged: Dr. C. Susz, for his technical advice and for supplying the alloys tested, Dr. R. Barraud for his helpful hints and suggestions, Messrs. G. Devenoge and D. Werner for their help in specimen preparation for SEM and microprobe analyses.

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  • Cited by (0)

    a Lecturer, Division of Fixed Prosthodontics.

    ☆☆

    b Research Associate, Institute of Mineralogy and Petrography, University of Lausanne.

    c Professor and Chairman, Division of Fixed Prosthodontics.

    ★★

    Reprint requests to: Dr. H. W. A. Wiskott Division of Fixed Prosthodontics School of Dentistry University of Geneva 19, Rue Barthelemey-Menn 1205 Geneva SWITZERLAND

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