| The submitted study is about the comparison of the mechanical
solidity of soldered and differently laser welded test specimens
from a Palladium based alloy before and after six months of chemical
stress. By vacuum-pressure-technique 80 DIN meeting test specimens
have been produced from the Palladium alloy BegoPal® 300. 3 of
the 10 series originated from five times cast reused metal, the
remaining from pure new metal. After visual check of the test
specimens, separating and linking took place for the respective
method of fusion to tested. Series 3 and 4, both from metal, was
soldered with the help of the flame and solder. Series 5 and 6 from
new metal were welded together (butt joint) under application of a
laser with in pilot tests found laser-parameter-combination of 0,6
mm diameters, tension of 310 V, and impulse-duration of 11,5 ms.
The series 7 and 8 were equally treated like the 5 and 6 series,
but consisted of reused metal however. The series 9 and 10 from new
metal were cut symmetrical too, but also roof-ridge like, and a
gauge was used as well as additional material for welding. The
laser parameter were not changed for this fusion. All series were
tested in the zone of fusion through an EDX-analysis, determined
with micro-temper-stress-marks after Vickers with 10 measuring
points. After the series 4, 6, 8, and 10 were stored for 6 month in
artificial saliva, these series were again tested through
EDX-analysis after this chemical stress. Altogether 100 EDX test
results were established. First of all, a tension test after DIN EN
10002: 1991 was applied to the genuine series 1 (new metal) and 2
(reused metal) to establish a standard of comparison. The
tension-resistance-factor for the series 1 and 2 reached an average
of 829 MPa and 838 MPa. The soldered series achieved 42 % of these
results (349 ± 64 MPa), respectively after treatment with
artificial saliva 40 % of the results of the genuine series1. All
soldered test specimens broke in the soldered seam. The series 5
and 6 (new metal) achieved not only before, but also after the
treatment with artificial saliva very good tension-test results of
77 % - 82 %, as well as the additional material laser welded test
specimens, which achieved 77 % before and 69% after chemical stress
(artificial saliva). The light-microscopic examinations of the
fracture-surface after the tests showed surfaces with shrinkholes
on the soldered series, but no corrosion. The laser-welded series
showed gas-shrinkholes and zones of incomplete welding. However,
homogeneous surface could be found too. The resistance was not
essentially lowered despite gas-shrinkholes in comparison to
homogenous surfaces. All by laser welded test specimens broke,
however, in the seam also. The applied EDX-analysis showed on the
laser-welded specimens after the chemical treatment (artificial
saliva) basically no change of the adhesive oxides on the surface.
The element-distribution on the soldered surface showed
considerably differences in comparison to the genuine test
specimens already before the chemical treatment with artificial
saliva. With reference to the tensile strength, the laser welding,
and here above all the butt joint method, has to be preferred to
soldering, under consideration that even the untrained use of laser
welding results in higher and not only with standards complying
tensile strength.
|
