Microscopic Analysis of Welded Dental Alloys
— Microplasma welding is a less expensive alternative to laser welding in dental technology. The aim of the study was to highlight discontinuities present in the microplasma welded joints of dental base metal alloys by visual analysis. Five base metal alloys designated for fixed prostheses manufacture were selected for the experiments. Using these plates, preliminary tests were conducted by microplasma welding in butt joint configuration, without filler material, bilaterally and with filler material, proper for each base metal. Macroscopic visual inspection was performed to assess carefully the irregularities in the welds. Electron microscopy allowed detection of discontinuities that are not visible to the eye and revealing details regarding location, trajectory, morphology and size of discontinuities. Supplementing visual control with microscopic analysis allows to detect small discontinuities, which escapes the macroscopic control and to make a detailed study of the weld.
Penetration depth into dental casting alloys by Nd:YAG laser.
This study investigated the effect of laser-beam welding conditions [voltage (V) and spot diameter (mm)] on the penetration depth into dental casting alloys. Castings (3.0 mm x 8.0 mm x 50 mm) were prepared from the metals used in this study: commercially pure titanium (CP Ti), Ti-6Al-4V, Ti-6Al-7Nb, cobalt-chromium alloy (Co-Cr) and Type IV gold alloy. Two cast blocks of each metal were butted against one another at the 8.0 x 50-mm surfaces. They were then welded at their interface under the following conditions: voltage of 160-340 V, spot diameter of 0.4-1.6 mm, and pulse duration of 10 ms. After laser welding, the blocks were separated, and the penetration depth into each alloy was measured. The data were analyzed with the use of ANOVA at the p < 0.05 level of significance. The penetration depths were as follows: CP Ti (0.29-6.45 mm), Ti-6Al-4V (0.32-5.24 mm), Ti-6Al-7Nb (0.34-5.65 mm), Co-Cr (0.24-6.15 mm), and Type IV gold alloy (0.12-5.22 mm). The voltage and spot diameter affected the penetration depth into the metals tested. When the voltage increased and the spot diameter decreased, the penetration depth increased for each metal. Selecting suitable conditions for laser welding to obtain sufficient penetration depth for the optimal thickness of the metal is important when welding prostheses.
Composite monolayer fabrication by an arc-spray process
A single layer (monotape) technique for fabricating complex high-temperature tungsten-fiber-reinforced superalloy composites is proposed. The fabrication of sheets of arc-sprayed monotape 38 cm wide and 122 cm long has been demonstrated. Composites fabricated using the method are shown to have equal tensile strength and a cleaner matrix than composites fabricated from powder metal cloth monotapes, and the present technique is less expensive than the powder metal fabrication techniques.