Surface modification of Al-12.6Si alloy by high current pulsed electron beam

The paper investigates the microstructure and property modifications of Al-12.6Si alloy induced by high current pulsed electron beam (HCPEB) treatment. The scanning electron microscope (SEM) results show a fine and equiaxed grain structure of several micrometers is obtained on the top surface of the melted layer. Underneath the top surface, a remelted layer with about 10 μm thickness is obtained and a supersaturated solid solution of Al is formed in the remelted layer. XRD analysis shows that the relative strength of diffraction peaks of Al (1 1 1) and Si (1 1 1) crystal planes is increased after HCPEB treatment. As a result, relative wear resistance of HCPEB-treated sample is significantly improved by a factor of 2.5 due to fine grain strengthening and solid solution strengthening. Therefore, the HCPEB treatment has a good application future in treating Al-Si alloys.     

Surface modification of Al-20Si alloy by high current pulsed electron beam

Hypereutectic Al-20Si (Si 20 wt.%, Al balance)alloy surface was treated with high current pulsed electron beam (HCPEB) under different pulse numbers. The results indicate that HCPEB irradiation induces the formation of metastable structures on the treated surface. The coarse primary Si particle melts, producing a “halo” microstructure with primary Si as the center on the melted surface. A supersaturated solid solution of Al is formed in the melted layer caused by Si atoms dissolving into the Al matrix. Cross-section structure analysis shows that a 4 μm remelted layer is formed underneath the top surface of the HCEPB-treated sample. Compared with the matrix, the Al and Si elements in the remelted layer are distributed uniformly. In addition, the grains of the Al-20Si alloy surface are refined after HCPEB treatment, as shown by TEM observation. Nano-silicon particles are dispersed on the surface of remelted layer. Polygonal subgrains, approximately 50-100 nm in size, are formed in the Al matrix. The hardness test results show that the microhardness of the α(Al) and eutectic structure is increased with increasing pulse number. The hardness of the “halo” microstructure presents a gradient change after 15 pulse treatment due to the diffusion of Si atoms. Furthermore, hardness tests of the cross-section at different depths show that the microhardness of the remelted layer is higher than that of the matrix. Therefore, HCPEB technology is a good surface modification method for enhancing the surface hardness of hypereutectic Al-20Si alloy.     

强流脉冲电子束辐照诱发纯钼表面的损伤效应及结构缺陷

利用强流脉冲电子束（HCPEB）装置对纯钼表面进行辐照处理,并利用X射线衍射仪,扫描电子显微镜（SEM）、透射电子显微镜（TEM）详细分析了辐照表面的微观结构和损伤效应. 1次HCPEB辐照后,纯钼表层积聚了极大的残余应力,多次辐照后表面未融化区域出现大量绝热剪切带,且局部区域发生开裂. 微观结构分析显示,辐照后材料表面形成发散状的位错组态和大量空位簇缺陷;绝热剪切带内部是尺寸为1 μm 左右等轴状的再结晶晶粒. 剪切带造成的材料表面局部软化以及间隙原子偏聚于晶界是材料发生开裂的主要原因. 另外,表面熔化区域可形成尺寸为20 nm左右的纳米晶. 关键词： 强流脉冲电子束 纯钼 绝热剪切带 空位簇缺陷     

强流脉冲电子束作用下金属锆的微观结构与应力状态

利用强流脉冲电子束 (HCPEB) 技术对金属纯锆进行表面处理, 采用X射线衍射, 扫描电子显微镜及透射电子显微镜详细分析了辐照诱发的表层微观结构和缺陷. X射线分析结果表明, HCPEB辐照后在材料表层诱发幅值为GPa量级的压应力, 并形成{0002}, {1012}, {1120}及{1013}织构. 表层微观结构观察表明, 与其他金属材料不同, HCPEB辐照在材料表层诱发的熔坑数量极少, 多次轰击甚至几乎没有表面熔坑的形成. 此外, 在快速的加热和冷却状态下, 在表面熔化层形成大量的超细晶粒结构, 同时诱发马氏体相变和强烈的塑性变形. 1次HCPEB辐照后表层内形成的变形微结构以位错为主, 孪晶数量较少; 5 次辐照样品的位错密度迅速增高, 孪晶数量也显著增加; 10次辐照后样品中的变形微结构以变形孪晶为主, 且出现二次孪晶现象. 表层晶粒内部变形的晶体学特征不仅决定了表层的织构演化行为, 而且还起到细化晶粒的作用, 为纯锆及锆合金表面强化提供了一条有效的途径. 关键词： 强流脉冲电子束 纯锆 微观结构 应力状态     

强流脉冲电子束诱发纯镍表层纳米结构的形成机制

利用强流脉冲电子束（HCPEB）技术对多晶纯镍进行了表面处理,并采用扫描电镜和透射电镜对强流脉冲电子束诱发的表面及亚表面的微观组织结构进行了分析.实验结果表明,HCPEB辐照后表面熔化,形成了深度约为2 μm的重熔层,快速的凝固使重熔层中形成晶粒尺寸约为80 nm的纳米结构.位于轰击表面下方5—15 μm深度范围内强烈塑性变形引起的位错墙和其内部的亚位错墙结构是该区域的主要结构特征.这些缺陷结构通过互相交割细化晶粒,最终导致尺寸约为10 nm的纳米晶粒的形成. 关键词： 强流脉冲电子束 纳米结构 多晶纯镍 位错墙     

AISI 304L奥氏体不锈钢表面微孔结构的强流脉冲电子束快速制备与表征

 利用强流脉冲（HCPEB）电子束技术,对AISI 304L奥氏体不锈钢进行了辐照处理,并利用透射电子显微镜对HCPEB诱发的空位簇缺陷进行了表征。实验结果表明,HCPEB辐照金属可在辐照表层诱发大量的过饱和空位,并形成空位型位错圈和堆垛层错四面体（SFT）。利用金相显微镜、扫描电子显微镜和非接触式光学轮廓仪,对其表面形貌进行了详细的表征,发现电子束处理后的样品表面形成了高密度、弥散分布和尺寸细小的微孔,表面微孔是由于HCPEB轰击诱发的大量空位(簇)缺陷,以线或面等结构缺陷为路径,向表层迁移导致空位的累积而形成的。采用HCPEB技术,选择合适的材料和辐照工艺参数,可以成功地制备出表面多孔金属材料。     

Laser melting of GaAs covered with thin metal layers

GaAs melting simulations with a pulsed ruby laser are reported. The presence of a thin metal layer deposited on the GaAs surface gives rise to a reduction in the melting threshold and to an increase of melted depths when compared with nude GaAs surfaces. Melting thresholds around 0.3 J/cm² for nude GaAs surface and slightly below 0.25 J/cm² for GaAs covered with a 120 Å tin layer are predicted in reasonable agreement with experimental results.     

强流脉冲电子束作用下金属纯Cu的微观结构状态——空位簇缺陷及表面微孔结构

利用强流脉冲(HCPEB)电子束技术对多晶纯Cu进行了辐照处理,并利用透射电镜对HCPEB诱发的空位簇缺陷进行了表征.实验结果表明,HCPEP辐照金属可在纯Cu表层诱发大量的过饱和空位,并形成四方形空位胞及空位型位错圈和堆垛层错四面体(SFT),HCPEB瞬间的加热和冷却诱发的幅值极大的应力和极高的应变导致的整个原子平面的位移是空位簇缺陷形成的主要原因.此外,扫描电镜分析表明HCPEB辐照可以在纯Cu表面形成高密度、弥散分布和尺寸细小的微孔.过饱和空位或空位团簇沿晶体缺陷向表面扩散、凝聚是表面微孔形成的根     

强流脉冲电子束诱发纯钛表面的微观结构及应力状态

利用强流脉冲电子束(HCPEB)装置对金属纯钛进行轰击,采用X射线衍射,扫描电子显微镜及透射电子显微镜技术详细分析了轰击样品表层的结构和缺陷. X射线衍射分析表明, HCPEB能够在材料表层诱发幅值为 GPa量级的压应力,并在(100), (102)和(103)晶面出现择优取向.表层微观结构的观察表明: HCPEB轰击后材料表层发生了马氏体相变,形成了大量的片状马氏体组织; 此外, HCPEB轰击还在辐照表面诱发了强烈的塑性变形,一次轰击后,晶粒内部的塑性变形以(100)晶面的位错滑移为主,位错密度显著提高;多次轰击后,样品变形结构发生变化,变形孪晶的数量明显增多. 这些变形微结构不仅影响表层的织构演化行为,而且还能细化晶粒,进而提高材料表面硬度, 为HCPEB技术进行纯钛表面强化提供了一条有效的途径.     

强流脉冲电子束作用下纯镍表面的应力特征

 利用强流脉冲电子束（HCPEB）装置对多晶纯镍进行轰击,采用X射线衍射及扫描电子显微镜等技术,详细分析了受轰击样品的变形组织与结构。通过分析建立了强流脉冲电子束诱发的应力特征与变形结构之间的关系,并对目前现有的几种应力波数值模拟结果进行了讨论。实验结果表明：强流脉冲电子束能够在材料表层诱发约5GPa的应力,造成纯镍表面发生孪生塑性变形。除了热膨胀引起的表层横向准静态热应力外,强流脉冲电子束产生的等离子体脉冲爆炸可以直接诱发幅值很高的冲击应力波,二者的共同作用是引起表层微观结构变化的直接原因。     

强流脉冲电子束辐照诱发金属纯镍中的空位簇缺陷

利用强流脉冲电子束(high-current pulsed electron beam,HCPEB)技术对多晶纯Ni进行了辐照处理,采用透射电子显微镜详细分析了辐照诱发的缺陷结构.HCPEB辐照后,纯镍表层积聚了幅值极大的残余应力,沿{111}晶面形成了稠密的位错墙及孪晶结构,另外还形成了大量的包括位错圈、堆垛层错四面体(SFT)及孔洞在内的空位簇缺陷.SFT缺陷的数量远高于其他空位簇缺陷,其周围区域位错密度很低.孔洞缺陷主要出现在SFT密集区域.HCPEB瞬间的加热和冷却诱发的幅值极大的应力和极高的应变 关键词： 强流脉冲电子束 多晶纯Ni 空位簇缺陷 堆垛层错四面体     

强流脉冲电子束作用下纯镍表层中织构及结构缺陷的演化行为

利用强流脉冲电子束(HCPEB)装置对金属纯Ni进行轰击,采用X射线衍射及透射电子显微镜(TEM)技术详细分析了受轰击样品的变形结构和缺陷。X射线衍射分析表明,经强流脉冲电子束处理后,在{111}和{200}晶面出现了择优取向。TEM表层微观结构分析表明:强流脉冲电子束轰击1次和5次后,晶粒内部形成了大量的(111)[112]型波状条带结构,在波状条带内部包含大量平行的(200)[110]型微条带;10次轰击后,样品变形结构发生变化,除大量的条带状结构外,变形孪晶的数量明显增多。这些变形微结构不仅影响表层的织构演化行为,而且还能细化晶粒,强流脉冲电子束技术为制备表面纳米材料提供了一条有效的途径。     

表面状态对强流脉冲电子束辐照诱发金属表面熔坑的影响

 为了考察材料晶体学特性对表面熔坑形成机制的影响,利用强流脉冲电子束（HCPEB）对喷丸前、后的304奥氏体不锈钢进行表面辐照处理,对HCPEB诱发的表面熔坑形貌进行了详细的表征。实验结果表明,HCPEB辐照后样品表面形成了大量的火山状熔坑,熔坑数密度和熔坑尺寸随电子束能量的增加而减小,材料表面的杂质或夹杂物容易成为熔坑的核心,并在熔坑形成的喷发过程中被清除,起到净化表面的作用。此外,喷丸前、后样品表面熔坑数密度遵循相似的分布规律,喷丸处理使熔坑数密度显著增大,表明材料的晶体学特性对表面熔坑形成有重要的影响,晶界、位错等结构缺陷是熔坑形核的择优位置。     

Microstructure analysis of magnesium alloy melted by laser irradiation

The effects of laser surface melting (LSM) on microstructure of magnesium alloy containing Al8.57%, Zn 0.68%, Mn0.15%, Ce0.52% were investigated. In the present work, a pulsed Nd:YAG laser was used to melt and rapidly solidify the surface of the magnesium alloy with the objective of changing microstructure and improving the corrosion resistance. The results indicate that laser-melted layer contains the finer dendrites and behaviors good resistance corrosion compared with the untreated layer. Furthermore, the absorption coefficient of the magnesium alloy has been estimated according to the numeral simulation of the thermal conditions. The formation process of fine microstructure in melted layers was investigated based on the experimental observation and the theoretical analysis. Some simulation results such as the re-solidification velocities are obtained. The phase constitutions of the melted layers determined by X-ray diffraction were β-Mg₁₇Al₁₂ and α-Mg as well as some phases unidentified.     

Manifestation of the heterogeneous mechanism upon melting of low-dimensional systems

A melting process that is always heterogeneous in semi-infinite systems having a surface has been analyzed. It has been shown in terms of the classical thermodynamics that, in real one-component systems, a liquid layer on the solid-phase surface is formed at temperatures lower than the reference melting temperature of the bulk material at which the system is completely melted. Depending on the temperature, a liquid layer of particular thickness on the surface is in equilibrium with the other crystalline phase. The heterogeneous melting is shown to influence a number of processes and mechanisms, such as the dispersion of a thin film into droplets, the mechanism of vapor-liquid-solid epitaxy, the mechanism of layer-by-layer crystal growth, and the mechanism of growth of carbon nanotubes.     

强流脉冲电子束表面改性CuFe10合金的显微组织和性能研究

研究了不同脉冲次数强流脉冲电子束表面改性对CuFe10合金组织及性能的影响。强流脉冲电子束处理CuFe10合金的重熔表面出现了火山坑和直径为100 nm到1 m的富铁球,表明了强流脉冲电子束处理CuFe10合金表面发生了液相分离。强流脉冲电子束脉冲轰击30次后,CuFe10合金表面的显微硬度与耐蚀性能均得到显著改善,主要是由于强流脉冲电子束轰击处理CuFe10合金表层引发的快速熔凝过程中表面发生了液相分离及晶粒细化的缘故。     

Excessive hydrogen and deuterium Balmer lines broadening in a hollow cathode glow discharges

Results of a Doppler spectroscopy study of hydrogen and deuterium Balmer lines in the stainless steel and copper hollow cathode glow discharge, operated in pure hydrogen, deuterium and mixtures of inert gases with hydrogen, are reported. For all gases and gas mixtures plasma observations perpendicular to electric field revealed the excessively large Doppler broadening. By changing mode of glow discharge operation, the Doppler broadened line profiles in helium-hydrogen mixture are recorded parallel to the discharge electric field as well. The excessively broadened part of the H line profile is shifted towards blue or red wavelength by changing the direction of electric field vector. The presence of large excessive Balmer lines broadening in pure hydrogen and in its gas mixture with neon as well as shifting of the excessively broadened part of line profile by means of electric field is in contradiction with the resonance transfer model proposed by Mills et al. in several publications, see e.g. [IEEE Trans. Plasma Sci. 31, 338 (2003)].     

强流脉冲电子束作用下20钢的微观结构状态

 为了研究金属材料的超快变形行为,利用强流脉冲电子束（HCPEB）装置对20钢进行轰击,采用X射线衍射、光学显微镜及透射电镜等技术分析了受轰击样品的变形组织与结构。实验结果表明,强流脉冲电子束能够在材料表层诱发幅值为1 GPa量级的应力,快速的加热和冷却过程在近表层诱发了强烈的塑性变形,并在材料表层内形成了复杂的位错缠结结构和位错胞结构,同时还伴随位错圈等空位簇缺陷的形成,多次轰击导致局部区域形成纳米和非晶结构。HCPBE轰击诱发的幅值极大的应力和极高的应变速率而导致的整个原子平面的位移可能是非晶结构形成的关键原因。     

Microstructural analysis of TiC reinforced ferrous surface composites processed by accelerated electron beam irradiation

The present study aims to analyze microstructures of TiC reinforced ferrous surface composites processed by accelerated electron beam irradiation. Two kinds of powder/flux mixtures, i.e., TiC and (Ti + C) powders with 40 wt% of CaF₂ flux, were deposited evenly on an AISI 304 stainless steel substrate, which was then irradiated with electron beam. TiC agglomerates and pores were found in the surface composite specimen processed by irradiation of TiC powders because of insufficient melting of TiC powders. In the specimen processed by irradiation of Ti and C powders having lower melting points than TiC powders, a lot of large TiC carbides were precipitated in the melted region, together with a few TiC agglomerates or pores. This indicated the more effective TiC precipitation obtained from the melting of Ti and C powders, instead of TiC powders. The hardness of the surface composite layer was about two times higher than that of the AISI 304 substrate mainly due to the precipitation of TiC carbides.     

Microstructure evolution occurring in the modified surface of 316L stainless steel under high current pulsed electron beam treatment

High current pulsed electron beam (HCPEB) surface treatment of 316L stainless steel (SS) was carried out with a wide spectrum of treating parameters. Microstructure changes occurring in the modified surface were characterized with microscopy, X-ray diffractometry and electron backscatter diffractometry (EBSD) techniques. The evolution regularities of surface craters and microstructure refinement, as well as preferred orientation of (1 1 1) crystal planes were discussed on considering the coupled temperature-stress fields formed in surface layers after an absorption of HCPEB energy.