Department of Prosthodontics, University Victor Segalen Bordeaux 2, France.
Dent Mater. 2011 Mar;27(3):e43-50. doi: 10.1016/j.dental.2010.10.012.
To describe the influence of pulse shaping on the behavior of a palladium-based dental alloy during laser welding and to show how its choice is effective to promote good weld quality.
Single spots, weld beads and welds with 80% overlapping were performed on Pd-Ag-Sn cast plates. A pulsed Nd:Yag laser was used with a specific welding procedure using all the possibilities for pulse-shaping: (1) the square pulse shape as the default setting, (2) a rising edge slope for gradual heating, (3) a falling edge slope to slow the cooling and (4) a combination of a rising and falling edges called bridge shape. The optimization of the pulse shape is supposed to enhance weldability and produce defect-free welds (cracks, pores…) Vickers microhardness measurements were made on cross sections of the welds.
A correlation between laser welding parameters and microstructure evolution was found. Hot cracking and internal porosities were systematically detected when using rapid cooling. The presence of these types of defects was significantly reduced with the slow cooling of the molten pool. The best weld quality was obtained with the use of the bridge shape.
The use of a slow cooling ramp is the only way to significantly reduce the presence of typical defects within the welds for this Pd-based alloy studied.
描述在激光焊接过程中，脉冲成形对钯基牙科合金行为的影响，并展示如何选择脉冲成形来促进良好的焊接质量。
在 Pd-Ag-Sn 铸造板上进行单点、焊缝和 80%重叠的焊缝。使用脉冲 Nd：Yag 激光，采用特定的焊接程序，利用所有可能的脉冲成形：（1）默认设置为方波形状，（2）逐渐加热的上升沿斜率，（3）缓慢冷却的下降沿斜率，以及（4）称为桥接形状的上升沿和下降沿的组合。脉冲形状的优化旨在提高可焊性并产生无缺陷的焊缝（裂纹、气孔等）。在焊缝的横截面进行维氏硬度测量。
发现激光焊接参数与微观结构演变之间存在相关性。当使用快速冷却时，系统地检测到热裂纹和内部孔隙。通过减缓熔池的冷却，可以显著减少这些类型缺陷的存在。使用桥接形状可以获得最佳的焊接质量。
对于研究的这种钯基合金，使用缓慢冷却斜坡是唯一可以显著减少焊缝中典型缺陷存在的方法。
