【作者】 董志宏；

【导师】 雷明凯；

【作者基本信息】 大连理工大学 ， 材料表面工程， 2007， 博士

【摘要】 为了满足HIPIB辐照材料表面改性需求，开展了磁绝缘离子二极管阳极特性的系统研究，确定了优化的辐照工艺参数。通过HIPIB辐照不同材料的力学效应研究，揭示了辐照表面反冲应力波的形成和传播机制，以及HIPIB辐照材料表面强化机制，为彻底弄清HIPIB与材料表面的相互作用提供了实验依据。通过对TEMP-6型和ETIGO-2型两种HIPIB装置阳极聚乙烯膜的寿命研究发现，TEMP-6型装置的绝缘磁场为“闭环”结构，二极管间隙放电稳定，在420 kV放电电压下阳极聚乙烯膜可使用500-700次。ETIGO-2型装置的绝缘磁场为“开环”结构，二极管间隙放电不稳定，在1100 kV放电电压下阳极聚乙烯膜仅可使用2-4次。外磁绝缘离子二极管阳极等离子体的形成基于阳极聚乙烯膜的表面脉冲击穿放电过程，聚乙烯膜表面发生电子崩，并形成导电通道，载能电子和离子的多次轰击导致聚乙烯膜表面粗糙化，聚乙烯分子链断裂形成低分子量物质，引起HIPIB束流密度降低，稳定性变差。通过改变阳极聚合物材料种类，优化二极管结构及放电回路的阻抗匹配，聚合物阳极的稳定放电次数可提高到1000次以上。采用束流密度30-1500A／cm²，辐照次数1次的HIPIB辐照纯金属Ti和Al，被辐照表面的粗糙度R_a随束流密度增加而增大，200A／cm²辐照条件下，两种金属的R_a分别从原始的0.181μm和0.164μm增加到0.693μm和0.372μm。通过辐照和沉积实验证明了表面微凸被优先加热而发生选择性烧蚀，产生液滴喷射现象，导致形成具有烧蚀坑和波纹状扰动的烧蚀表面形貌。随束流密度增加液滴喷射现象加剧，造成被辐照表面显著的粗糙化。采用10MHz的压电陶瓷—锆钛酸铅（PZT）压电晶体传感器，对束流密度30-400A／cm²的HIPIB在纯金属Al，Ti，Cu，以及耐热钢基体上等离子体喷涂的ZrO₂热障涂层（TBC）等材料中诱导的应力波进行了实时动态测量，随束流密度从100 A／cm²增加到400 A／cm²，金属Al中的应力波强度从2 MPa增加到约80 MPa。350 A／cm²、1-10次辐照条件下，金属Al、Ti和TBC中的应力波强度分别为70-90 MPa、27-40 MPa和15-20MPa。应力波的HIPIB诱导机制包括热弹性机制和反冲机制，分别形成热弹性波和反冲应力波。形成的应力波波形具有双峰结构，其中仅反冲应力波的强度随束流密度的增加显著增大。相同辐照条件下，低熔点材料因烧蚀剧烈而形成较强应力波，高熔点材料则应力波强度减弱，TBC的组织结构和界面特性造成应力波衰减和宽化。采用束流密度100-350 A／cm²，辐照次数1-10次的HIPIB辐照纯金属Cu，随束流密度和辐照次数增加，被辐照表面的粗糙度R_a先减小后增大，100 A／cm²、1次辐照条件下R_a从原始的0.12μm减小到0.09μm，350a／cm²、10次辐照条件下达到最大，约0.51μm。被辐照表面的显微硬度则呈现递增趋势，350A／cm²、10次辐照条件下表面显微硬度增加幅度最大，约70％。辐照形成的硬化层深度在100A／cm²、10次条件下约为100μm，350A／cm²、10次条件下增大到300μm。HIPIB辐照金属Cu造成表面位错、孪晶等缺陷增加和晶粒细化的强烈冲击硬化效应，归结为表面应力及反冲应力波的形变强化作用机制。HIPIB辐照金属Cu的球-盘式摩擦磨损实验表明，磨合阶段持续时间受被辐照表面粗糙度和硬度的影响，稳定磨损阶段的摩擦系数则受硬化层硬度和深度的影响。350A／cm²、10次辐照条件下，金属Cu表面的摩擦系数从原始试样的0.9减小到0.45，磨痕深度则从20μm减小到0.8μm，耐磨性显著提高。采用束流密度100-350A／cm²，辐照次数1-10次的HIPIB辐照Al-Cu合金，随束流密度和辐照次数增加被辐照表面粗糙化，350A／cm²、10次辐照条件下R_a达到最大，约0.5μm。Al-Cu合金表面形成界面平直的熔融层，厚5-6.5μm，熔融层硬度随束流密度增加而增大，随辐照次数的变化不显著，350A／cm²、1次辐照条件下熔融层硬度增加幅度最大，约50％。辐照形成的硬化层深度在100A／cm²、10次条件下约为50μm，350A／cm²、10次条件下增大到150μm。HIPIB辐照Al-Cu合金造成熔融层中Cu原子过饱和固溶于Al基体，以及位错等缺陷增加的冲击硬化效应，归结为固溶强化和反冲应力波形变强化的综合作用机制。HIPIB辐照Al-Cu合金的球一盘式摩擦磨损实验表明，Al-Cu合金耐磨性主要取决于硬化层的硬度和深度。200A／cm²、10次条件下，Al-Cu表面的磨痕深度从原始试样的10μm减小到4μm，耐磨性改善。更多还原

【Abstract】 High-intensity pulsed ion beam（HIPIB） technique has been progressively developed as a unique approach for surface modification of materials in the recent years. Generation of high-stability HIPIB for practical application necessitates fully understanding the characteristics of the magnetically insulated ion diode（MID）. In this work, effect of the lifetime of anode polyethylene sheet on HIPIB generation from the MID with an external-magnetic field has been studied systematically to obtain the optimized ion beam parameters. Based on the achievement of high-stability HIPIB generation, the dynamic behavior of HIPIB-irradiated materials has been subsequently investigated to clarify the mass transfer mechanism on the different ablated surfaces of metallic materials, the formation and propagation of the induced stress wave in the irradiated materials, and the hardening mechanism of the irradiated materials, providing an experimental evidence with a further understanding of exploring the interaction mechanism between HIPIB and materials.Study of lifetime of anode polyethylene in the MIDs with an external-magnetic field operated in unipolar pulse mode has been carried out in parallel on TEMP-6 and ETIGO-2 HIPIB apparatuses. The discharge times of anode polyethylene sheet in the TEMP-6 HIPIB apparatus can reach to 500-700 pulses at a peak diode voltage of 420 kV, where the cathode with improved structure works as a "close" magnetic coil that effectively increases the continuity and uniformity of magnetic field. As for the MID in ETIGO-2 HIPIB apparatus, the distribution of the magnetic field is not so uniform due to the presence of an opening in the cathode, resulting in a much shorter lifetime of anode polyethylene with 2-4 pulses during discharging at a higher peak diode voltage of 1100 kV. The anode plasma is produced during the surface discharging process on polyethylene sheet under the electrical and magnetic fields in MID, i. e. high-voltage surface breakdown. The electron avalanche under the discharging process causes formation of discharge channels on the anode polyethylene surface. The bombardments of energetic electrons and ions lead to the surface roughening of the anode polyethylene, and the polyethylene in the surface layer degrades into low-molecular-weight polymer, resulting in the decrease of ion current density and the poor stability of HIPIB extraction. The stabilized discharge of anode polyethylene can exceed 1000 pulses through changing the anode polymer, and optimizing the structure and impedance of MID.HIPIB irradiation of pure Ti and Al was performed at the ion current density of 30-1500 A/cm² with 1 shot. Surface roughness （R_a） of the irradiated surfaces increased with increasing the ion current density for both the metals. The values of R_a increased from 0.227μm and 0.185μm for the non-irradiated Ti and Al to 0.639μm and 0.372μm for the irradiated Ti and Al at 200 A/cm², respectively. The selective ablation originated from surface irregularities with a preferential heating effect was confirmed by the irradiation and deposition experiments where the droplet ejection was detected on the irradiated Ti and Al surfaces. And the droplet ejection caused the disturbance features of crater and waviness on the ablated surface. As increasing the ion current density, droplet ejection became severer on the irradiated surface and resulted in the significantly roughening of the irradiated surface.The stress waves induced in the irradiated materials, i. e. pure Al, Ti, Cu and plasma sprayed ZrO₂ thermal barrier coating（TBC） on heat-resistant steel, have been measured in situ by using lead-zirconte-titanate（PZT） piezoelectric sensor with central frequency of 10 MHz during HIPIB irradiation at the ion current density of 30-350 A/cm² with shot nurnber of 1-10. With increasing the ion current density from 100 to 350 A/cm², the magnitude of stress wave for pure Al increased from 2 to 80 MPa. At 350 A/cm², the peak intensity of stress wave was 70-90 MPa and 27-40 MPa for the irradiated Al and Ti with 1-10 shots, respectively. And for TBC, the value decreased to 15-20 MPa. Two mechanisms account for the generation of Stress wave, i. e. thermoelastic and recoil, which resulted in the fomation of thermoelastic stress wave and recoil stress wave, respectivly. The intensity of recoil stress wave increased apparently with the increase of ion current density. Under the same HIPIB irradiation parameters, the intensity of induced stress wave on the materials with low melting temperature was higher than that of the materials with high melting temperature, due to the different melting and evaporation behavior on the irradiated surface. The structue of TBC with microcracks and cavities weakened the induced stress wave and changed the propagation process.Pure Cu was irradiated by HIPIB with the ion current density of 100-350 A/cm² and shot number of 1-10. The surface roughness of pure Cu firstly decreases and then increases as increasing the ion current density and the shot number. R_a decreased from 0.12μm for the non-irradiated surface to 0.09μm for the irradiated Cu at 100 A/cm² with 1 shot. The maximum roughness of 0.51μm was found at 350 A/cm² with 10 shots. The microhardness of the irradiated Cu increased with increasing the ion current density and the shot number, where the value increased nearly 70％at 350 A/cm² with 10 shots with the respect to the non-irradiated one. The hardened layer of the irradiated Cu at 100 A/cm² with 10 shots reached to 100μm, and the maximum thickness was 300μm under the irradiation condition of 350 A/cm² with 10 shots. HIPIB irradiation caused the grain refinement and increased the density of defects in the hardened layer, such as dislocations and twins etc. This shock-hardening effect is attributed to the strengthening resulted from the stress on the irradiated Cu surface and induced recoil stress wave. Based on the ball-on-disk wear tests, the duration of running-in stage depends on the roughness and the hardness of irradiated Cu surface. While the steady-state friction coefficient was mainly influenced by the hardness and the depth of hardened layer. For the irradiated Cu at 350 A/cm² with 10 shots, the friction coefficient decreased to a value of 0.45 from 0.9 for the non-irradiated Cu. Correspondingly, the depth of worn track significantly decreased from 20μm to 0.8μm.HIPIB irradiation into Al-Cu alloy was performed at the ion current density from 100 to 350 A/cm² with shot number of 1-10. It was found that the surface roughness increased with increasing the ion current density and the shot number. The maximum R_a of 0.5μm was obtained at 350 A/cm² with 10 shots. A melted layer of 5-6.5μm thick induced by HIPIB was formed on the Al-Cu alloy, with a straight interface between the melted layer and Al-Cu matrix. The microhardness of remelted layer increased as increasing the ion currednt density, and showed little change with increasing the shot number. The maximum value of microhardness was detected for the irradiated Al-Cu alloy with 350 A/cm² at 1 shot, with an increase up to 50％as compared to that of the non-irradiated Al-Cu alloy. The depth of hardened layer was about 50μm for the irradiated Al-Cu alloy, at 100 A/cm² with 10 shots, and increased to 150μm at 350 A/cm² with 10 shots. HIPIB irradiation resulted in the Cu supersaturated solution in Al lattice and the increase of defects density in the melted layer. This shock-hardening effect of Al-Cu alloy under HIPIB irradiation is attributed to the solution strengthening and the hardening by the induced recoil stress wave. The ball-on-disk wear tests demonstrated that the wear-resistance of irradiated Al-Cu alloy was influenced by the hardness and the depth of hardened layer. At 200 A/cm² with 10 shots, the depth of worn track on the irradiated Al-Cu alloy decreased to 6μm compared with that of 10μm for the non-irradiated one.更多还原