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实验上采用磁控溅射在铀、不锈钢、铝基底上分别沉积钼、铌、铝等薄膜后采用纳秒激光熔覆,薄膜发生飞溅,未能形成熔覆层。针对这一问题,采用有限元方法分析了脉冲激光作用的温度场,并对瞬时热膨胀造成薄膜垂直于表面的运动进行了分析。计算以及分析结果表明:由于界面热阻,纳秒激光熔覆薄膜与基底存在较大的温度差,在本例计算铝薄膜与基底温差超过450℃。瞬时热膨胀导致薄膜具有向外的速度以及动能。当薄膜动能大于拉伸断裂所需要克服的弹性以及塑性变形能量,薄膜将发生飞溅。理论分析还表明存在一个临界的光束尺寸,当光束小于该尺寸,薄膜不会发生飞溅,熔覆能够发生,对于准分子激光,光束尺寸达微米量级薄膜不会飞溅。
Experimentally, magnetron sputtering was used to deposit molybdenum, niobium, aluminum and other films on uranium, stainless steel and aluminum substrates, respectively, and the films were spattered by nanosecond laser and the coating did not form a cladding layer. In response to this problem, the finite element method is used to analyze the temperature field of the pulsed laser and the movement of the film perpendicular to the surface caused by the instantaneous thermal expansion is analyzed. The results of calculation and analysis show that there is a large temperature difference between the nanosecond laser cladding film and the substrate due to the thermal interface resistance. In this case, the temperature difference between the aluminum film and the substrate exceeds 450 ° C. Instantaneous thermal expansion causes the film to have an outward velocity as well as kinetic energy. When the film kinetic energy is greater than the elastic and plastic deformation energy to be overcome by the tensile fracture, the film will splash. Theoretical analysis also shows that there is a critical beam size. When the beam is smaller than this size, the film will not splatter and the cladding will occur. For the excimer laser, the film will not spatter on the order of microns.