YAG激光毛化技术进展

二十世纪八十年代，当比利时冶金研究中心(CRM)开发出CO_2激光毛化冷轧辊技术后，尝试用YAG激光进行轧辊毛化一直吸引着众多的研究者，这是因为YAG(1.06μm)激光波长比CO_2(10.6μm)激光波长短一个量级，材料对YAG激光有更高的吸收率，并用YAG激光可以聚焦到更小的光斑尺寸，同时使用电信号驱动的声光开关技术便于对毛化分布进行可设定控制。但是用传统声光调制的YAG激光虽然可以碇以很高的脉冲频率(>30kHz)，但单脉冲有量仅为10mJ左右，难以达到辊面毛化粗糙度的要求，因此人们认为YAG激光用于毛化的主要困难是脉冲能量太小。

<span style="color: rgb(0, 0, 0); font-family: 'Microsoft Yahei', 宋体, Arial, '​ Helvetica', '​ sans-serif'; font-size: 13px; line-height: 22px;">Calculations showed that 5 mJ energy was enough to vaporate materials in a pit of 100μm diameter and 10μm depth. When a laser pulse with duration 600ns and energy 10mJ shoot on the surface of metal, the power density is 10~8W/cm~2 if it was focused on a region of 100μm diameter. This energy was well enough to evaporate iron within 6.37ns, while plasma plumb was produced. So it was clear that most of laser energy was absorbed by plasma. It was found that major loss of laser energy was inverse bremsstrahlung absorption by plasma. To lower the electron density of plasma, an unique technique was developed to modified laser waveform. When high repetition frequency pulse laser beam radiated on the roller surface, a number of micro-pits were formed, in which metal was melt and solidified. We say the roller was textured. Experiments showed that the tensile strength σb of laser-textured steel sheet increased 4-7% than that of shoot-peening steel sheet, and the yield strength σ0.2 of laser-textured steel sheet decreased 6-7% than that of shoot-peening steel sheet, the stretchability δ10 increased 6-105. Another advantage of laser-texturing sheet was its good lubricity comparing with shot-peening steel sheet.</span>