【作者】 韩晓光；

【导师】 雷明凯；

【作者基本信息】 大连理工大学 ， 材料表面工程， 2009， 博士

【摘要】 利用TEMP-6型和ETIGO-II型强流脉冲离子束（HIPIB）装置,分别产生加速电压300kV和1 MV,脉冲宽度50-80 ns,束流密度100-1500 A/cm²,能量密度1-90 J/cm²的C⁺和H⁺离子束。通过HIPIB辐照石墨和ZrO₂涂层烧蚀行为实验和理论研究,分析了烧蚀表面温度场和应力场,探明了HIPIB辐照材料的烧蚀作用机制;利用HIPIB辐照的烧蚀作用,实现了镁合金AZ31微弧氧化膜的表面改性,烧蚀改性的镁合金表面形成的连续、致密的氧化膜,耐腐蚀性能显著改善,进一步提高了镁合金微弧氧化膜保护作用。HIPIB辐照镁合金AZ31微弧氧化膜烧蚀改性,提供了一种新的、可靠的脉冲离子束表面改性技术。通过HIPIB辐照石墨和ZrO₂涂层,烧蚀表面的温度场和应力场的实验和理论研究表明,在高能量密度5-90 J/cm²条件下,表面升温速率为10¹²-10¹³K/s,温度梯度达到10³ K/μm,表面应力波呈压应力和拉应力交替的周期性传播,最大压应力达到500 MPa。石墨可发生向类金刚石的非平衡相转变,ZrO₂柱状晶则发生重熔和再结晶。辐照表面的熔化、汽化和烧蚀,导致表层材料转移去除和亚表层材料的均匀化和致密化;同时烧蚀表面在反冲应力和温度梯度作用下,形成非平衡的表面结构。HIPIB辐照的热-力学耦合作用是表面烧蚀改性的主要原因。采用束流密度100-350 A/cm²,辐照次数1-10次的HIPIB烧蚀改性镁合金AZ31微弧氧化膜。随束流密度和辐照次数的增加,具有内、外亚层双层结构的镁合金微弧氧化膜烧蚀表面熔化趋势加剧,200 A/cm²已经观察到清晰的表面重熔特征,但表面重熔层深度呈先增大后减小的变化过程,最大重熔深度在200 A/cm²,5次辐照下可达10μm,完全熔化的外亚层孔隙减少且内亚层更为致密。烧蚀表面粗糙度（Ra）则呈先减小后增加的过程,在200A/cm₂,1-10次辐照下,粗糙度由原始氧化膜表面的2.10μm减小到1.18μm,后增加到4.13μm。相应的烧蚀表面表面能增加,表面静态接触角由原始氧化膜表面的145.9°单调减小,最小值可达到49.7°。烧蚀表面具有混合的Mg₂SiO₄和MgO相结构,与原始微弧氧化膜相同。烧蚀改性显著增加了AZ31微弧氧化膜的连续性和致密性。采用动电位阳极极化和电化学阻抗谱,测试了HIPIB烧蚀改性镁合金AZ31微弧氧化膜在3.5%NaCl溶液中的腐蚀性能。烧蚀氧化膜表面发生的腐蚀过程由活化溶解向钝化-孔蚀击穿转变,孔蚀击穿电位随束流密度和辐照次数的增加呈先增加后减小的趋势,随束流密度由100A/cm²增加到350A/cm²,5次辐照下,孔蚀击穿电位由-1240 mV（SCE）增加到-800 mV（SCE）,后减小到-1240 mV（SCE）,钝化电流密度则由10^-8 A/cm²减小到4×10^-9 A/cm²,后增加到10^-7 A/cm²。束流密度200 A/cm²,辐照次数由1次增加到10次,孔蚀击穿电位由-1420 mV（SCE）增加到-800 mV（SCE）,阳极极化曲线的钝化电流由3×10^-7A/cm²减小到4x10^-9A/cm²。辐照后氧化膜的自腐蚀电位均有明显提高,由原始氧化膜的-1580 mV（SCE）增加到200 A/cm²,5次辐照时的最大值-1350 mV（SCE）。烧蚀氧化膜表面的阳极极化性能显著改善。为了表征HIPIB辐照AZ31微弧氧化膜连续性和致密性对腐蚀性能的影响,采用在3.5%NaCl溶液中不同浸泡时间测量电化学阻抗谱。烧蚀改性氧化膜的电化学阻抗谱Nyquist图呈典型的容抗弧和感抗弧特征,Bode图辐角-频率曲线则呈典型的高频容抗弧、中频容抗弧和低频感抗弧特征。随束流密度和辐照次数的增加,Nyquist图的容抗弧和感抗弧均呈先增大后减小的变化过程,最大容抗弧和感抗弧均在200 A/cm²,5次辐照下,浸泡时间5 h可达6x10⁷Ω和1.5x10⁵Ω。Bode图的两个容抗弧辐角和感抗弧辐角大小和宽度变化不显著,仅中频容抗弧宽度呈先增宽后变窄的过程。在不同浸泡时间的测试中,烧蚀改性氧化膜的Nyquist图容抗弧和感抗弧均随浸泡时间的增加而减小,Bode图的高频容抗弧辐角减小,中频容抗弧宽度变窄。在200A/cm²,5次辐照下,浸泡时间增加至48 h,容抗弧减小到4.5x10⁵Ω,相应的Bode图开始出现低频感抗弧,进一步增加到192 h,容抗弧继续减小,但低频感抗弧基本不变。采用Zsimpwin软件对烧蚀改性氧化膜电化学阻抗谱进行模拟。改性氧化膜内、外亚层阻抗较原始氧化膜显著提高。在200 A/cm²,5次辐照下,与原始微弧氧化膜相比较,浸泡时间5 h,内、外亚层电阻由1.52×10⁶Ω和5.3×10⁴Ω分别增加到7.31x10¹⁰Ω和3.5x10⁵Ω,HIPIB辐照微弧氧化膜有效改善的氧化膜的连续性和致密性,是提高腐蚀性能的主要原因。更多还原

【Abstract】 The experimental and theoretical investigation of ablation behavior on graphite and ZrO₂ coatings irradiated by high-intensity pulsed ion beam（HIPIB） is performed in TEMP-6 and ETIGO-II HIPIB apparatuses with the ion energy of 300 keV and 1 MV,the pulse width of 50-80 ns,the ion current density of 100-1500 A/cm² and the energy density of 1-90 J/cm².The temperature field and stress field of the ablated surface are confirmed to explore the ablation effects mechanism of HIPIB irradiation on materials.Based on ablation effects of HIPIB, modification of microarc oxidation film on AZ31 magnesium alloy is achieved by forming a continuous and compact remelted layer on the surface of magnesium alloy to enhance the protective effect of microarc oxidation film（MAO） and further improve the corrosion performance of magnesium alloy.The experimental and theoretical investigation on the temperature field and stress field of ablated surface of graphite and ZrO₂ coating irradiated by HIPIB shows that the elevated temperature rate and temperature gradient of the irradiated surface could reach to 10¹²-10₁₃ K/s and 10⁹ K/m under the high energy density,respectively.The stress wave transmits in the irradiated materials periodically with a compressive stress and tensive stress alternately and the maximal value of compressive stress is obtained to 300 MPa.The phase transformation form graphite to diamond like carbon（DLC） on ablated graphite surface and the remelting and recrystalization of ZrO₂ columnar crystal could happen under HIPIB ablation effects.The remelting,evaporation and ablation on the irradiated surface induced the removal of the surface layer and the uniformity and compaction of the sublayer on irradiated materials,as well as a nonequilibrium surface structure was formed on the ablated surface under impulse stress and temperature gradient.The surface ablation modification is mainly attributed to thermo-mechanical coupling effects of HIPIB irradiation.The MAO films on magnesium alloy irradiated by HIPIB were performed at 100-350 A/cm² up to 10 shots.Surface remelting of MAO films with double layer structure of inner and outer sublayer becomes intense with the increase of ion current density and irradiation shot number,the apparent remelting characteristic could be observed on the irradiated surface at 200 A/cm².The thickness of remelted layer increased and then decreased and the maximal value of 10μm was obtained at 200 A/cm² with 5 shots,the porosity of the completely remelted sublayer decreased and inner sublayer became more compact.Surface roughness of the ablated surface increased and then decreased with the increase of shot number at 200 A/cm².The surface roughness for the original MAO film is about 2.10μm,it decreased to 1.18μm with 1 shot irradiation and then increased to 4.13μm with irradiation shots up to 10. Correspondingly,the surface energy of the ablated surface augmented,resulting in the tedious decrease of static contact angle from 145.9 for original film to 49.7 for the film with 10 shots.The phase structure of the ablated surface still consisted of Mg₂SiO₄ and MgO,which are the same as that of the original ones.The ablation modification enhanced the continuity and compaction of the MAO films on AZ31 magnesium alloy.Potentiodynamic polarization measurements and electrochemical impedance spectrum （EIS） in 3.5%NaCl solution were performed to test the corrosion performance of MAO films on AZ31 magnesium alloy.The corrosion process of the ablated surface transformed from the active solution to passivation-pitting breakdown.The passivation-pitting breakdown voltage increased and then decreased with increasing ion current density and shot number.With the increase of ion current density from 100 A/cm² to 350 A/cm² at 5 shots,the breakdown voltage increased from-1240 mV（SCE） to-800 mV（SCE）,and then down to -1240 mV（SCE）. On the contrary,the passivation current density show a tendency of decrease followed by an increase,which is described by an decrease from 1x10^-8A/cm² to 4×10^-9 A/cm²,and then up to 1x10^-7A/cm².With the increase of shot number from 1 to 10 at the ion current density of 200 A/cm²,the breakdown voltage increased from -1420 mV（SCE） to -800 mV（SCE）. Correspondingly,the passivation current density decreased from 3×10^-7A/cm² to 4x10^-9 A/cm².The corrosion potentials of MAO films irradiated by HIPIB were all enhanced compared with those of original films.The corrosion potential was enhanced from -1580 mV（SCE） for original MAO films to maximal value of -1350 mV（SCE） for the irradiated films at 200 A/cm² with 5 shots.The anode polarization performance of the ablated MAO film was pronounced improved by HIPIB irradiation.The（EIS） in 3.5%NaCl solution was measured,in order to characterize the effect of modified continuity and compaction of the ablated MAO film on AZ31 magnesium alloy by HIPIB on its corrosion properties.The Nyquist plots for EIS shows typical capacitive arc and inductive loop,the phase-frequency curves show typical high-frequency（HF）and middle-frequency（MF）capacitive arcs and low-frequency（LF） inductive loop.The diameters for capacitive arc and inductive loop are both increased and then decreased with increasing the ion current density and irradiation shot number,the maximal value for diameters obtained at 200 A/cm² with 5 shots at immersion time of 5 h was achieved to 6x10⁷Ωand 1.5x10⁵Ω,respectively.No apparent changes were observed on the two capacitive arcs and inductive loop for Bode plots except for the width of MF capacitive arc.With immersion time augment, the diameters for capacitive arc and inductive loop of Nyquist plots both are decreased,and phase angle for HF capacitive arc and width for MF capacitive arc of Bode plots decreased, either.The diameter for the capacitive arc of Nyquist plots for ablated MAO films at 200 A/cm² with 5 shots decreased to 4.5x10⁵Ωwith immersion time up to 48 h,correspondingly, the LF inductive loop just appeared on Bode plots,the diameter for capacitive arc decreased continuously and no obvious changes observed on LF inductive loop with further increasing the immersion time.The EIS for ablated MAO films were fitted by Zsimpwin software,which indicated that the corrosion resistances for inner and outer sublayer are all improved by HIPIB irradiation. The corrosion resistance for inner and outer sublayer at 200 A/cm² with 5shots all increased from 1.52x10⁶Ωand 5.3x10⁴Ωto 7.31x10¹⁰Ωand 3.5x10⁵Ω,respectively,compared with the original ones at immersion time of 5 h.The enhancement in corrosion property of ablated MAO films is mainly caused by improvement of continuity and compaction of films irradiated by HIPIB.The ablation modification on MAO films on AZ31 magnesium alloy irradiated by HIPIB affords a new and reliable surface modification technique with pulse ion beam.更多还原