Non-destructive three-dimensional evaluation of pores at different welded joints and their effects on joints strength.
OBJECTIVE
The purpose of this study was to measure the porosity in different laser welded cast alloys non-destructively using X-ray micro-focus computerized tomography (micro-CT) and to evaluate the effect of porosity on the tensile strength of the welded joints.


METHODS
The welding procedure was conducted in rectangular cast metals, CoCr, Ti and platinum added gold alloy (AuPt). The metal plates were butted CoCr to CoCr (CoCr/CoCr) or Ti to Ti (Ti/Ti) for welding of similar metals and Ti to AuPt (Ti/AuPt) for welding of dissimilar metals. Specimens were welded under several laser-welding conditions; with groove (normal), without groove (no groove), spatter, crack, or no overlapped welding (no overlap) (n=5). Porosity in the welded area was evaluated using a micro-CT. Tensile strength of the welded specimens was measured at a crosshead speed of 1mm/min. Multiple comparisons of the group means were performed using ANOVA and Fisher's multiple comparisons test (α=.05). The relationship between the porosity and the tensile strength was investigated with a regression analysis.


RESULTS
Three-dimensional images of Ti/AuPt could not be obtained due to metal artifacts and the tensile specimens of Ti/AuPt were debonded prior to the tensile test. All other welded specimens had porosity in the welded area and the porosities ranged from 0.01% to 0.17%. The fractures of most of the CoCr/CoCr and Ti/Ti specimens occurred in the parent metals. Joint strength had no relationship with the porosity in the welded area (R(2)=0.148 for CoCr/CoCr, R(2)=0.088 for Ti/Ti, respectively).


CONCLUSIONS
The small amount of porosity caused by the laser-welding procedures did not affect the joint strength. The joint strength of Ti/AuPt was too weak to be used clinically.
Nomoto
Rie
R
Department of Dental Engineering, Tsurumi University School of Dental Medicine, 2-1-3 Tsurumi, Tsurumi-ku, Yokohama 230-8501, Japan. nomoto-r@tsurumi-u.ac.jp
Takayama
Yasuko
Y
Tsuchida
Fujio
F
Nakajima
Hiroyuki
H
D002858:Chromium Alloys / Q000737:chemistry; D003035:Cobalt / Q000737:chemistry; D003722:Dental Alloys / Q000737:chemistry*; D003734:Dental Casting Investment; D003735:Dental Casting Technique; D012994:Dental Soldering / Q000379:methods; D003799:Dental Stress Analysis; D006047:Gold Alloys / Q000737:chemistry; D021621:Imaging, Three-Dimensional; D053844:Lasers, Solid-State; D008422:Materials Testing; D010984:Platinum / Q000737:chemistry; D016062:Porosity; D013718:Tensile Strength; D014025:Titanium / Q000737:chemistry; D014896:Welding / Q000379:methods; D055114:X-Ray Microtomography
D002858:Chromium Alloys; D003722:Dental Alloys; D003734:Dental Casting Investment; D006047:Gold Alloys; C416206:gold-titanium alloy; D003035:Cobalt; D010984:Platinum; D014025:Titanium