No abstract

No abstract

RESEARCHprosthodontics have a laser in their laboratory. However, looking at the available literature, since 1970 many experiments have been conducted into non precious and precious alloys and have shown contradictory results, probably because the experimental procedures used were different. 15,16,17,18,19 Therefore no comparison could be made. In this study, the weldability of three non precious alloys was investigated. The procedure consisted of determining the appropriate welding parameters which could achieve a deep joining in depth without cracks or gas entrapments in the welding area. The quality of the joining was checked by metallographic observations on polished sections. Wires of different diameters were then laser-welded and tested in tension. In order to understand the different behaviours between the three alloys (2 Ni-Cr and 1 Co-Cr based alloys), the composition of the welded area was determined by a X-Ray microprobe. Particular attention was given to the role played by the impurities. Methods Chemical compositionsTwo Ni-Cr-Mo alloys and 1 Co-Cr-Mo alloy, manufactured by Dentaurum (Pforzheim, Germany) were chosen for their applications in the dental field (Table 1) : 1 G mou is a low cost alloy used for crowns and bridges. 2 Remanium Cs is used for ceramic fixed partial dentures. 3 GM 800 is a cobalt chrominium alloy used for removable and fixed partial dentures Laser parameters and welding conditionsIn order to determine the welding conditions against the metal thickness and the ability of the laser device, two series of cast wires (0.6 to 2 mm thick), and five specimen DIN 50125 (3mm thick) were prepared by investment casting. The samples were then cut, joined by hand, edge to edge and welded without fillers or fluxes, using a commercial Nd-Yag laser (DL 2002 manufactured by Dentaurum) whose technical characteristics are given in table 2. In order to avoid the laser beam reflection and to improve the weld penetration, all the wires were sand-blasted with alumina powders and welded under Argon shielding atmosphere to decrease the oxidation contamination. All the samples were welded using the same procedure. The Laser conditions depend on the thickness and the volume of material to be welded (Table 2).Each wire was first assembled by the 4-cardinal points and thenThe laser welding technique applied to the non precious dental alloys procedure and results Aim The laser welding technique was chosen for its versatility in the repair of dental metal prosthesis. The aim of this research is to assess the accuracy, quality and reproducibility of this technique as applied to Ni-Cr-Mo and Cr-Co-Mo alloys often used to make prosthesis Method The alloy's ability to weld was evaluated with a pulsed Nd-Yag Laser equipment. In order to evaluate the joining, various cast wires with different diameters were used. The efficiency of the joining was measured with tensile tests. In order to understand this difference, metallographic examinations and XRay microprobe analysis were performed through the welded area and c...

International audienceThe difficulty in using above 2000°C in an oxidizing atmosphere C/C composites as structural components is their poor life time. The solution proposed here consisted in combining two refractory carbides, hafnium and silicon carbides, in coating with a complex architecture, named a three dimensional coating, over a C/C substrate. Such a coating protects the C/C composite at 2050°C under air. The oxidation of the coating leads to the formation of a Si x O y Hf z hafnium-containing silicate liquid, combined with HfO 2(s). This liquid limits oxygen diffusion more than pure SiO 2 does, so it is a better protection against oxidation. Furthermore, HfO 2(s) acts as a grip holding Si x O y Hf z in place. From these results, an oxidation mechanism is proposed and discussed

Objective Interactions between lasers and materials are very complex phenomena. The success of laser welding procedures in dental metals depends on the operator's control of many parameters. The aims of this study were to evaluate factors relating to the operator's dexterity and the choice of the welding parameters (power, pulse duration and therefore energy), which are recognized determinants of weld quality. Design In vitro laboratory study. Materials and methods FeNiCr dental drawn wires were chosen for these experiments because their properties are well known. Different diameters of wires were laser welded, then tested in tension and compared to the control material as extruded, in order to evaluate the quality of the welding. Scanning electron microscopy of the fractured zone and micrograph observations perpendicular and parallel to the wire axis were also conducted in order to analyse the depth penetration and the quality of the microstructure. Additionally, the micro-hardness (Vickers type) was measured both in the welded and the heat-affected zones and then compared to the non-welded alloy. Results Adequate combination of energy and pulse duration with the power set in the range between 0.8 to 1 kW appears to improve penetration depth of the laser beam and success of the welding procedure. Operator skill is also an important variable. Conclusion The variation in laser weld quality in dental FeNiCr wires attributable to operator skill can be minimized by optimization of the physical welding parameters.

No abstract

No abstract

No abstract