等离子体电解氧化(Plasma Electrolytic Oxidation, PEO)是一项在阀金属及其合金表面制备氧化物陶瓷膜的表面处理技术。PEO 过程中会产生光、声、振动等物理现象，并伴随大量气体的释放。通过监测这些现象的变化有助于理解 PEO 放电过程。本论文提出通过光、声、振动无损诊断方法，分析 ZL101Al-Si 合金和 60% SiCp/Al 复合材料 PEO 过程中这些信号的演变，来探索 PEO 放电和氧化膜生长的关系，并阐明声学和振动信号产生机制。
  ZL101 铝合金 PEO 过程中，在 0~20 kHz 范围内水声和空气噪声信号的声压级，以及0~10 kHz 范围内样品振动信号强度，均随着正电压、正脉冲宽度及脉冲频率的增加而增加；此时频率范围在 50~400 kHz 的高频声发射(Acoustic Emission, AE)信号幅值也随之增加。但负电压和负脉冲宽度的增加，则使这些信号强度降低。电参数对低频声学和振动信号，以及高频 AE 信号的影响规律也适用于 60% SiCp/Al 复合材料 PEO 过程。
  其它电参数固定，ZL101 铝合金 PEO 过程中，负电压从 0 V 增加到 200 V 时，软火花现象出现的时间随之提前，且伴随光、声、振动及 AE 信号强度的降低。该现象的出现促进膜层生长和致密化。负电压增加到 200 V 时，氧化后期膜层出现局部剥落，此时空气噪声信号的声压级和样品振动强度局部增强，表明声学和振动信号的变化可以反映 PEO 膜生长过程。根据声学、振动信号和膜层微观结构结果，ZL101 铝合金在 10 g/L Na2SiO3·9H2O + 1 g/L KOH 电解液中进行 PEO 处理时，负电压的最佳范围是 100~150 V。+480 V/-100 V电压下，光、声、振动结果表明 ZL101 铝合金 PEO 过程可以分为 6 个阶段。另一方面该电压下，一个脉冲周期内 AE 波形和参数随氧化时间的演变结果表明，放电火花的密度和强度决定了样品表面 AE 信号幅值，而水下 AE 信号幅值主要受较强放电火花的影响。AE参数中幅值和持续时间的关联图可以区分一个脉冲周期内正、负脉冲及脉冲暂停时间内产生的 AE 信号。此外，持续时间和振铃计数之间的皮尔逊相关系数接近 1，存在很强的线性相关性。
  60% SiCp/Al 复合材料 PEO 过程中，SiCp 表面沉积一层 Al-Si-O 化合物，该化合物膜中微孔和微裂纹为表面放电电流的传导提供了路径。单极性脉冲 PEO 模式下，在正电压360~520 V 区间，15% SiCp/Al 和 60% SiCp/Al 复合材料阳极析出的气体都由 H2、O2 及微量CO组成，且它们的H2浓度均随正电压升高而增加。但正电压达到440 V (15% SiCp/Al MMC)或 480 V (60% SiCp/Al MMC)后，H2 浓度基本稳定在 80 vol.%左右，不再随正电压变化。负电压的引入仅使复合材料析出的 H2 浓度提高 1 vol.%~4 vol.%。阳极析出气体中 H2 和 O2主要来自于电解液的溶剂水而不是电解质，而 CO 全部来自于 SiCp 的氧化。CO 气体的析出和 NaF 溶液中溶解的 Si 元素表明，铝合金基体中 SiCp 增强体确实在 5500 K 高温等离子体放电通道中被氧化。此外，由于 H2 的还原作用，阳极析出气体中几乎检测不到 CO2。
  ZL101 铝合金和 SiCp/Al 复合材料 PEO 过程中，水声、空气噪声、样品振动及 AE 信号的产生均同等离子体放电火花演变有关。正脉冲时间内样品 AE 信号主要来自以下四个过程中产生的弹性波：等离子体放电通道外气泡膨胀-收缩过程、等离子体气泡坍塌时产生微射流的过程、放电通道中熔体喷出时与其内表面的摩擦过程，以及放电微区熔体快速凝固时微裂纹扩展过程。等离子体气泡膨胀-收缩过程中产生的弹性波是水下 AE 信号和水声信号的主要来源；水声信号通过液面向空气中传播，形成空气噪声信号；等离子体气泡坍塌过程中产生的微射流是样品振动信号的主要来源。
  发射光谱、声学和振动，以及声发射这些无损检测方法是分析 PEO 过程中放电火花状态和膜层生长演变的有效手段，有望将其运用到 PEO 生产工艺的监测中。

 Plasma electrolytic oxidation (PEO) is a promising surface treatment technology to fabricate the ceramic coatings on valve metals and their alloys. During PEO process, the optics, acoustics, vibration and other physical phenomena related to plasma discharges take place, accompanied by an intensive gas release. Hence, monitoring the evolution of these physical signals can evaluate the characteristics of plasma discharges, which is beneficial to understand the PEO discharge process. In order to explore the relationship between PEO discharge and coating growth. The evolution of these physical signals during PEO process of ZL101 Al-Si alloy and 60% SiCp/Al composite was analyzed based on the optics, acoustics and vibration nondestructive diagnostic methods. Moreover, the generation mechanism of acoustics and vibration signals was analyzed.
  During ZL101 Al-Si alloy PEO process, with the increase of positive voltage, positive pulse width and pulse frequency, the sound pressure level (SPL) of underwater sound and airborne sound signals within 0 - 20 kHz, and the intensity of sample vibration signal within 0 - 10 kHz, all increased. Meanwhile, the amplitude of high-frequency acoustic emission (AE) signal with a frequency range of 50 kHz to 400 kHz also increased. However, the increase of negative voltage and negative pulse width reduced the intensities of these signal. The effect of electrical parameters on low frequency acoustics and vibration signals, and high frequency AE signals was also applicable to the PEO process of 60% SiCp/Al composite.
  Other electrical parameters were fixed. When the negative voltage increased from 0 V to 200 V, the soft sparking phenomenon appeared earlier during the ZL101 Al-Si alloy PEO process, accompanied by the intensity decrease of optics, acoustics, vibration and AE signals. The appearance of soft sparking phenomenon promoted the PEO coating growth and densification. When the negative voltage increased to 200 V, the local spalling of coating appeared in the late oxidation stage, which led to the SPL of airborne sound signal and the intensity of sample vibration signal were locally enhanced. This indicates that the variation of sound and vibration signals could reflect the growth process of PEO coating. The optimal negative voltage was in range of 100 V to 150 V, when the PEO treatment was operated in the 10 g/L Na2SiO3·9H2O + 1 g/L KOH electrolyte, according to the evolution of sound and vibration signals, and coating microstructure. At +480 V/-100 V, the evolution of optics, acoustics and vibration signals showed that the ZL101 Al-Si alloy PEO process can be divided into 6 stages. On the other hand, the evolution of AE waveform and its parameters showed that the amplitude of AE signals on the ZL101 Al-Si alloy sample surface was depended on the density and intensity of discharge sparks, while the underwater AE signal amplitude was mainly related to the relatively strong discharge sparks. The AE correlation diagram of amplitude and duration can distinguish AE signals generated from positive pulse time, negative pulse time, and pulse pause time within a pulse period. Moreover, the Pearson correlation coefficient between duration and count was close to 1, showing a strong linear correlation.
  During the PEO process of 60% SiCp/Al composite, micro-pores and micro-cracks in the Al-Si-O compounds deposited on the surface of SiCp provide the path for the conduction of surface discharge current. During the unipolar pulse PEO process of 15% SiCp/Al and 60% SiCp/Al composites, the anode gas was composed of H2, O2 and trace CO in the range of +360 V to +520 V. H2 concentration first increased with the increasing positive voltage. However, when the positive voltage reached 440 V for 15% SiCp/Al composite or 480 V for 60% SiCp/Al composite, it was basically stable around 80 vol.%, even if the positive voltage further increased. The introduction of negative voltage only increased the H2 concentration by 1 vol.% - 4 vol.%. The H2 and O2 in the anode gas mainly result from the water rather than electrolyte, but the CO completely comes from the oxidation of SiC reinforcement phase. The appearance of CO and the dissolved Si element in NaF solution illustrate that the SiC reinforcement phase in the Al alloy matrix are indeed oxidized in the plasma discharge channels with the high temperature of about 5500 K. The CO2 was hardly detected because it might be reduced by H2 in discharge channels.
  During the PEO process of ZL101 Al-Si alloy and SiCp/Al composite, the generation ofunderwater sound signal, airborne sound signal, sample vibration signal, and AE signal is related to the evolution of plasma discharge. The AE signal on the sample surface during the positive pulse time mainly comes from the elastic waves generated in the following four processes: the expansion-shrinkage process of plasma bubbles, the process of microjet generation when plasma bubbles collapse, friction process between molten oxides and the inner surface of discharge channel, and micro-crack propagation during rapid solidification of molten oxides. However, the expansion-shrinkage process of plasma bubbles plays a key role on the generation of underwater AE signal and underwater sound signal. The underwater sound signal is transmitted to the air through the electrolyte/air interface to form the airborne sound signal. The microjet generated from plasma bubble collapse process is the main source of sample vibration signal.
  These nondestructive testing methods, including optical emission spectrum (OES), sound and vibration testing technique, and acoustic emission technique, are effective ways to analyze the plasma discharge state and coating evolution during PEO process, which are expected to be applied to the monitoring of the PEO production process.