[Stress-corrosion test of laser welded ceramic alloys]

The corrosion properties of dental material are very critical. This study is to investigate the corrosion properties of laser welded basemetalalloys.

The precise stainless rod molds had been made in size of phi 3 mm x 4 mm, with which 20 wax patterns were made. They were invested with inner investment (Bellavest) and outer investment (phosphate and gypsum). Then they were casted with CW-PA (Ni-Cr-Nb) alloys. All casted alloy rods were ultra-sonic washed in distilled water. Every two rods were contacted longitudinally by a special welding jig. Laser welding machine (DL-2002) was used to weld them at 305 V, 20 ms. The specimens were divided into 2 groups as following: 1. The group of stress-corrosion: 5 laser welded samples were subjected to the stress-corrosion test under 261.44 MPa in the 37 degrees C artificial saliva for 3 months in a special stress-corrosion test jig. After that, the ultimate tensile strength (UTS) was tested, the surface microcrack at the fusion zone (FZ), the heat affecting zone (HAZ) and the interface zone was observed with SEM (ARMY-1845, USA), the elements were also analyzed with EPMA (ARMY-1845, USA) at the fusion zone (FZ), the parent metal zone and the interface zone. 2. The other 5 laser welded samples were made as the controlled group. No special treatment were done to them, and the UTS was also tested, the surface of the micro crack and the elements at the FZ, the HAZ, parent metal zone and the interface zone were observed and analyzed with SEM, EPMA as well.

The study showed us that the UTS of the stress-corrosion group was 502.48 +/- 12.49 MPa, while that of the controlled group was 446.05 +/- 82.50 MPa, there was no significant difference (P > 0.05). There was no microcrack on any sample's surface at the FZ, the HAZ and the interface zone. The main elements of the FZ were Ni(56.63%), Cr(19.36%), Nb (6.57%), Si(6.01%), Al(0.32%) and Mo(11.11%), while the elements of the parent metal zone were Ni(60.77%), Cr (20.59%), Nb(5.03%), Si(3.95%), Al(0.37%) and Mo(9.29%) respectively.

The results suggest that the corrosion properties of laser welded alloys are excellent.