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.