Electron Beam Surface Treatment. Part I: Surface Hardening of AISI D3 Tool Steel

The effects of electron beam surface hardening treatment on the microstructure and hardness of AISI D3 tool steel have been investigated in this paper. The results showed that the microstructure of the hardened layer consisted of martensite, a dispersion

Electron Beam Surface Remelting of AISI D2 Cold-Worked Die Steel

Electron beam surface remelting has been carried out on AISI D2 cold-worked die steel. The microstructure and hardening behavior of the electron beam surface remelted AISI D2 cold-worked die steel have been studied by means of optical microscopy and Vickers hardness testing. It was found that AISI D2 steel can be successfully surface hardened by electron beam surface remelting. This surface hardening effect can be attributed to microstructural refinement following electron beam surface remelting. (C) 2002 Elsevier Science B.V. All rights reserved.

Mixed-mode fracture mechanisms near the fatigue threshold of aisi-316 stainless-steel

Near threshold, mixed mode (I and II), fatigue crack growth occurs mainly by two mechanisms, coplanar (or shear) mode and branch (or tensile) mode. For a constant ratio of ΔK_I/ΔK_II the shear mode growth shows a self-arrest character and it would only start again when ΔK_I and ΔK_II are increased. Both shear crack growth and the early stages of tensile crack growth, are of a crystallographic nature; the fatigue crack proceeds along slip planes or grain boundaries. The appearance of the fracture surfaces suggest that the mechanism of crack extension is by developing slip band microcracks which join up to form a macrocrack. This process is thought to be assisted by the nature of the plastic deformation within the reversed plastic zone where high back stresses are set up by dislocation pile-ups against grain boundaries. The interaction of the crack tip stress field with that of the dislocation pile-ups leads to the formation of slip band microcracks and subsequent crack extension. The change from shear mode to tensile mode growth probably occurs when the maximum tensile stress and the microcrack density in the maximum tensile plane direction attain critical values.

3.02MeV离子辐射316L不锈钢引起的内部氦泡显微结构分析

本文以TEM为测量手段，研究了室温下3.02MeV的He离子辐照固溶处理和固溶冷轧处理的两种316L不狙钢中的内部氦泡空间排列及分布与深度的关系，辐照剂量分别为5.46 * 10~(17)He/cm~2和5.14 * 10~(17)He/cm~2。TEM试样是采用了一种特殊的横截面技术制成的。这种方法可以方便地从一个样品中获得整个投影射程上的全部信息。对TEM照片的测量得到了He泡直径数密度及体积肿胀随粒子λ射深度的分布。TEM研究表明：He主要以He泡形式存在于基体中。He泡直径分布在1到4nm间，He泡数密度高达10~(17)-10~(18)no./cm~3，He泡肿胀约为0.4%；He泡直径数密度及He泡肿胀随深度的变化而变化。也就是说，He泡直径数密度及He泡肿胀随剂量的增加而增大；TEM照片中观察到了He泡连通；固溶冷轧样中的He泡直径数密度及He泡肿胀比固溶处理样中的要小； He泡数密度及肿胀分布与用TRIM-86程序计算得到的注He浓度及位移损伤分布基本相一致。另外，用SEM观察辐照样品表面形貌时，表面未见有任何发泡产生

高温下碳离子在316L不锈钢中辐照损伤电子显微镜分析

用51.4 MeV的碳离子，在500 ℃的温度下辐照了两个316L不锈钢样品，峰剂量分别达到34dpa(3.15 * 10~(17) ions/cm~2)和124dpa(1.14 * 10~(18) ions/cm~2)。通过扫描电子显微镜（SEM）和透射电子显微镜（TEM）观察了离子入射面的形貌和横截面试样中的空洞肿胀。提出了用SEM观测空洞肿胀的新方法并在原理上论证了通过SEM观测来推测空洞肿胀及空洞大小分布的可行性。得出了空洞面积肿胀在数值上等于体积肿胀的结论，并推导了由SEM观测的空洞切口大小分布计算空洞大小分布的公式。通过横截面试样的扫描电镜照片，测量了横截面空洞切口直径和面积肿胀随离子注入深度的变化关系；通过横截面试样的透射电镜照片，测量了样品内部的空洞大小分布。用TRIM计算机程序计算了位移损伤分布，并将它与空洞面积肿胀在深度方向上的分布进行了比较

不同温度下氦离子辐照316L不锈钢氦泡形成的研究

本工作用2.5MeV的~4He~+分别在室温、500 ℃和600 ℃对经过固溶和冷扎处理的316L不锈钢进行了辐照，辐照剂量为2.7 × 10~(17)ions／cm~2，剂量率在3.6 × 10~(11) - 2.6 × 10~(12)ions／cm~2·s之间。用扫描电镜（SEM）观察样品表面形貌的变化，发现600 ℃时，辐照样品的表面出现许多形状不规则的小坑和类似颗粒的东西。用透射电镜（TEM）结合横截面制样技术观察样品内部氦泡的特征，发现室温和500 ℃下氦泡呈圆形，在600 ℃下氦泡呈多面体形状。温度由室温上升到500 ℃，氦泡的大小、数密度的变化比较小，当温度上升到600 ℃，氦泡直径迅速增大、数密度减小，估计在500 ℃和600 ℃之间存在一个氦泡演变转折点。对室温和600 ℃辐照样品中氦泡大小、数密度随深度的变化做定量测量，发现室温下氦泡的形核、长大主要依赖于氦原子的沉积浓度，而600 ℃下氦泡的形核、长大主要依赖于氦引进过程中产生的离位损伤（dpa）。另外，不同晶界处氦泡的特征也不同，大角晶界处氦泡优先生长；小角晶界处不存在氦泡的优先生长。在同一温度下，CW样品中氦泡的数密度比SA样品中氦泡的数密度大、直径小，对应氦泡产生的肿胀比SA样品的小

不同温度下离子注入研究316L不锈钢中氦泡的形核与生长

鉴于在较低温区（<600 ℃）金属中氦泡形核生长的实验数据尚缺乏，我们安排了在400 ℃、500 ℃ 下用2.5MeV He~+离子注入316L 不锈钢（固溶样和冷轧样）的实验，剂量2.5 * 10~(21)ions·m~(-2)，剂量率3.4-3.6 * 10~(16)ions·m~(-2)·s~(-1)。由于在透射电镜（TEM）观测中采用横断面制样技术，得到了各样品中He泡深度分布的信息。分析表明实验结果与He泡的双原子形核模型的预言一致；He泡的迁移合并机制不显著，这与实验测得He泡中存在极高的原子密度相对应。固溶样品的离位损伤峰区发生了大量空位向He泡的凝聚从而加速了He泡生长。位错的存在显著增强了He泡的形核并抑制了空位的凝聚，并且这种作用在较低温度下更加显著

Effect of Cl- on the corrosive wear of AISI 321 stainless steel in H2SO4 solution

The effect of Cl- on the corrosive wear behaviour of AISI 321 stainless steel in H2SO4 solution was studied via the corrosive wear rate, the load bearing capacity of passive film and the relationship between pitting and corrosive wear. There is a critical load at natural potential, below which the corrosive wear rate is slightly lowered by Cl-, while above which is increased. At natural potential there are more pits at low load than that at a higher one in the wear tracks and the pits are also deeper. The load bearing capacity is lowered by Cl- at passive region and then the corrosive wear rate increased.

Stress corrosion cracking of AISI 321 stainless steel in acidic chloride solution

The stress corrosion cracking (SCC) of LambdaISI 321 stainless steel in acidic chloride solution was studied by slow strain rate (SSR) technique and fracture mechanics method. The fractured surface was characterized by cleavage fracture. In order to clarify the SCC mechanism, the effects of inhibitor KI on SCC behaviour were also included in this paper. A study showed that the inhibition effects of KI on SCC were mainly attributed to the anodic reaction of the corrosion process. The results of strain distribution in front of the crack tip of the fatigue pre-cracked plate specimens in air, in the blank solution (acidic chloride solution without inhibitor KI) and in the solution added with KI measured by speckle interferometry (SPI) support the unified mechanism of SCC and corrosion fatigue cracking (CFC).

Characteristics of sulfide corrosion products on 316L stainless steel surfaces in the presence of sulfate-reducing bacteria

It has been found that microbial communities play a significant role in the corrosion process of steels exposed in aquatic and soil environments. Biomineralization influenced by microorganisms is believed to be responsible for the formation of corrosion products via complicated pathways of electron transfer between microbial cells and the metal. In this study, sulfide corrosion products were investigated for 316L stainless steel exposed to media with sulfate-reducing bacteria media for 7 weeks. The species of inorganic and organic sulfides in the passive film on the stainless steel were observed by epifluorescence microscope, environmental scanning electron microscope combined with energy dispersive spectroscopy and X-ray photoelectron spectroscopy. The transformation from metal oxides to metal sulfides influenced by sulfate-reducing bacteria is emphasized in this paper. (c) 2005 Elsevier B.V. All rights reserved.

Electron Beam Surface Treatment. Part II: Microstructure Evolution of Stainless Steel and Aluminum Alloy During Electron Beam Rapid Solidification

Surface rapid solidification microstructures of AISI 321 austenitic stainless steel and 2024 aluminum alloy have been investigated by electron beam remelting process and optical microscopy observation. It is indicated that the morphologies of the melted layer of both stainless steel and aluminum alloy change dramatically compared to the original materials. Also, the microstructures were greatly refined after the electron beam irradiation.

具有梯度结构表层301不锈钢的压缩性能

利用表面机械研磨处理技术,在301奥氏体不锈钢中得到晶粒尺度呈梯度分布的变形表层,进行了压缩试验和微观组织观察。结果表明,变形表层中晶粒可细化至100nm。相比原始态的屈服强度236MPa,具有变形梯度表层后屈服强度增加到436MPa,变形后的加工硬化指数为0.31,经400和700℃的退火后分别增加到0.32和0.35。另外,随着应变速率的增加,流变应力增大而加工硬化能力降低.

同轴送粉激光成形中粉末与激光的相互作用

详细介绍了同轴送粉激光成形过程中,金属粉末与激光束相互作用时间的计算方法。在ANSYS软件平台上,建立了金属粉末穿越激光束过程中粉末温度场的计算模型。系统计算了不同颗粒大小316L不锈钢粉末与不同功率激光束相互作用后的温度。在此基础上,计算了金属粉末与激光束的能量交换及金属粉末落入激光熔池后与激光熔池的能量交换。计算结果表明,在激光束直径为3 mm条件下,316L不锈钢粉末穿过功率大于1000 W的激光束后,所有尺寸金属粉末均被熔化,即金属粉末以液态进入激光熔池。通过金属粉末与激光束及激光熔池的能量交换计算,可知在激光成形中,约有5%的激光能量用于加热和熔化粉末,而大约95%的激光能量用于激光熔池的形成及由于热传导造成的热量损失。