激光诱导击穿光谱技术对钢中缺陷的快速表征

Rapid defect characterization of steel by laser induced breakdown spectroscopy

激光诱导击穿光谱技术(LIBS)作为一种快速而简单地检查钢表面缺陷的技术,可直接观测到激光脉冲被聚焦于样品之上而感生的等离子体发射物。一个平凸透镜把斑直径大约为1 mm的光量开关Nd:YAG激光器(脉宽:12 ns;重复频率:10 Hz)辐照聚焦于样品表面,用来烧蚀样品的一部分,形成一个微等离子体。等离子体的发射由光纤传送至帕邢-龙校格装置多色仪(焦距:500 mm)。在已被流入和流出的氩气排空的空间里,样品被安装在一个二维移动台上进行两点分析——常规分析和缺陷分析。通过比较两个分析结果,可检测到缺陷部分有显著信号强度的元素。由不同类型的夹杂物可以检测出典型的元素,由氧化铝可检测出铝,由保护渣可检测出铝、钙、镁、硅和钠,由矿渣可检测出铝、钙和镁。经证实,由LIBS分析得到的结果与EPMA(电子探针)研究得到的结果一致。因此,导致缺陷的夹杂物的类型都能通过LIBS技术确定属性。当涂层被激光烧蚀去掉后,镀锌钢也可以被直接分析出来。包括制样,该项技术评定时间不到半小时,因此在炼钢过程中,可以迅速采取合适措施。

A rapid and simple technique has been developed for inspection of defects on steel surface using laser induced breakdown spectroscopy （LIBS）, in which emission from the plasma induced by focusing a laser pulse onto the sample is observed directly. Irradiation from a Q-switched Nd：YAG laser （pulse duration. 12 ns, repetition rate. 10 Hz） was focused onto the sample surface by a piano-convex lens with a spot diameter of about 1 mm to ablate a portion of sample and generate a micro plasma. Emission from the plasma was transmitted by a fiber optics to a Paschen-Runge mounting polychrometer （focal length. 500 mm）. Sample was mounted on a XY translation stage in a chamber, which was purged by Ar gas flowing in and out of it. Each sample was analyzed at two points, normal and defect parts. Elements detected with significant intensity at the defect part were found by comparing these two analytical results. Typical elements could be detected for different types of inclusionn; A1 for alumina, A1, Ca, Mg, Si, Na for mold flux and A1, Ca, Mg for slag. These results by LIBS were consistent with those by EPMA. Therefore, type of inclusion causing the defect could be attributed by LIBS. Zinc-coated steel could also be analyzed directly as the coating was removed by laser ablation. The proposed method would make it possible to take a suitable action quickly in steel making process because evaluation time is within 30 minutes including sample preparation.