氩气和氮气被广泛用作增材制造中的保护气体, 但局部高温及材料中的氧逸出等因素会导致熔融区附近的氧含量与保护气体中的氧含量存在差异, 提出采用激光诱导击穿光谱技术检测熔融区附近的痕量氧含量。通过实验测量氧气/氩气和氧气/氮气的击穿光谱, 结合氧原子谱线强度与连续背景强度的比值, 获得了氩气和氮气中痕量氧含量的检测定标曲线, 得到氩气和氮气中氧体积分数的检测限分别为31×10-6和41×10-6; 通过分析等离子体的形成和衰退过程发现, 氩气等离子体的电子温度比氮气等离子体的高, 其衰减比氮气等离子体缓慢, 因此在相同的实验条件下, 氩气等离子体中的氧原子谱线强度和信噪比均比氮气等离子体的高, 从而使得氩气中氧含量的检测限低于氮气中氧含量的检测限。

Argon and nitrogen are widely used as shielding gas in additive manufacturing. However, the high temperature in localized melting area and the release of oxygen in the row materials can cause the difference of oxygen content between melting zone and shielding environment. Laser-induced breakdown spectroscopy is proposed to measure the trace oxygen content in argon and nitrogen near the melting zone. The experimental calibration curves are obtained from laser-induced spectra of oxygen/argon or oxygen/nitrogen mixture gas with different oxygen contents combined with the ratio of oxygen spectral line intensity to continuous background strength. Detection limits of oxygen concentration are determined to be 31×10-6 in argon and 41×10-6 in nitrogen. By analyzing the formation and decay characteristics of the plasma, we find that the electron temperature of argon plasma is higher than that of nitrogen plasma and the decay of argon plasma is slower than that of nitrogen plasma. Therefore, under the same experimental conditions, spectral line intensity and signal-noise ratio of argon plasma are stronger than that of nitrogen plasma, which lead to lower detection limit of the content of oxygen in argon.