Mechanism of and method to avoid discoloration of stainless steel surfaces in laser cleaning

2 O₃. Based on Auger Electron Spectroscopy analyses and optical microscopic observations, γ-Fe₂O₃ and Fe₃O₄ are formed on the stainless steel surface in laser cleaning in the air. Since laser can induce high temperature rise in stainless steel surfaces, the above phenomenon can be explained by a thermochemical reaction between oxygen in the air and the stainless steel. With increasing laser fluences, the temperature rise in the irradiated area of stainless steel surface increases, which enhances oxygen diffusion into the surface and oxidation reaction within the irradiated area. In order to avoid discoloration of stainless steel surfaces, a vacuum system was used to reduce the oxidation reaction between oxygen and stainless steel. Received: 7 June 1996/Accepted: 30 September 1996     

Fiber laser welding of austenitic steel and commercially pure copper butt joint

The fiber laser welding of austenitic stainless steel and commercially pure copper in butt joint configuration without filler or intermediate material is presented. In order to melt stainless steel directly and melt copper via heat conduction a defocused laser beam was used with an offset to stainless steel. During mechanical tests the weld seam was more durable than heat affected zone of copper so samples without defects could be obtained. Three process variants of offset of the laser beam were applied. The following tests were conducted: tensile test of weldment, intermediate layer microhardness, optical metallography, study of the chemical composition of the intermediate layer, fractography. Measurements of electrical resistivity coefficients of stainless steel, copper and copper–stainless steel weldment were made, which can be interpreted or recalculated as the thermal conductivity coefficient. It shows that electrical resistivity coefficient of cooper–stainless steel weldment higher than that of stainless steel. The width of intermediate layer between stainless steel and commercially pure copper was 41–53 µm, microhardness was 128–170 HV_0.01.     

激光扫描阵列结构增强不锈钢与塑料的连接强度

本文采用光纤激光器在不锈钢表面上制备圆形阵列结构来增强不锈钢与塑料的连接强度。研究了激光制备的圆形阵列结构参数以及连接参数对不锈钢与塑料连接强度的影响。结果表明,不锈钢表面经过激光扫描构形处理后能显著提高不锈钢与塑料的连接强度,在压力作用下,熔融塑料渗入激光构造微孔形成的机械互锁是增强不锈钢与塑料连接强度的主要机制。激光构形后不锈钢表面上的毛刺高度、数量以及覆盖率对连接接头的连接强度有重要影响。毛刺高度为10~20μm,毛刺数量占比Tm小于14.82%时,不锈钢与塑料在连接面处断裂,剪切力随着Tm的增加而增加;当Tm值高于14.82%时,在塑料处断裂,且剪切力数值在塑料的平均拉伸断裂力(950 N)上下浮动。不锈钢与塑料连接接头断裂于塑料处时所对应的最小覆盖率为38.5%,此时剪切力为900 N。此外,激光扫描处理过程中不锈钢与塑料连接的温度与压力对连接强度有重要影响,在加热温度为400℃时,不锈钢与塑料连接接头的剪切力最强;当压力为75 kN时,不锈钢与塑料连接接头的剪切力最强。     

不锈钢网/铝板多冲击防护屏高速撞击防护性能实验研究

 通过对铝Whipple防护结构进行扩展变形,设计出不锈钢网/铝板组合多冲击防护屏,并利用二级轻气炮对其进行高速撞击实验,撞击速度为3.93~4.25 km/s,弹丸直径为6.35 mm。分析了不同规格不锈钢网、不同间距组合以及网格间结膜对不锈钢网/铝板多冲击防护屏高速撞击防护性能的影响。结果表明：不锈钢网位于防护屏的最后层有利于碎片云的扩散;不锈钢网位于防护屏最前层不利于撞击粒子的初次破碎;丝网几何参数、防护层间距组合是提高不锈钢网/铝板多冲击防护屏高速撞击防护性能的重要参数;网格间结膜有助于弹丸撞击动能的吸收。     

Development and evaluation of electroless Ag-PTFE composite coatings with anti-microbial and anti-corrosion properties

Electroless Ag-polytetrafluoroethylene (PTFE) composite coatings were prepared on stainless steel sheets. The existence and distribution of PTFE in the coatings were analysed with an energy dispersive X-ray microanalysis (EDX). The contact angle values and surface energies of the Ag-PTFE coatings, silver coating, stainless steel, titanium and E. coli Rosetta were measured. The experimental results showed that stainless steel surfaces coated with Ag-PTFE reduced E. coli attachment by 94-98%, compared with silver coating, stainless steel or titanium surfaces. The anti-bacterial mechanism of the Ag-PTFE composite coatings was explained with the extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The anticorrosion properties of the Ag-PTFE composite coatings in 0.9% NaCl solution were studied. The results showed that the corrosion resistance of the Ag-PTFE composite coatings was superior to that of stainless steel 316L.     

The crack control during laser cladding by adding the stainless steel net in the coating

The generation of crack is one of the key problems which restrict the development of laser cladding technique. The purpose of this study is to control the cracks during laser cladding by adding a plastic phase—an austenitic stainless steel net in the coatings. With Ni-, Co- and Fe-based alloy powders, laser cladding experiments were carried out. The microstructure of the coatings and the stainless steel net was investigated. Experimental results show that the stainless steel net is partly melted and strongly bonded to the cladding powder materials and the substrate. Thus the crack density is significantly reduced. The amount of the reduction increases as the diameter of the stainless steel net increases. Without preheating the substrate, large area coatings which remain free of cracks can be achieved when adding the stainless steel net with appropriate diameter. The characteristics of the coatings were investigated and the results indicate that the hardness fluctuations of the coatings become larger and the wear resistance decreases when adding 316 stainless steel net.     

Electrochemical recycling of cell phone Li-ion batteries: application as corrosion protector of AISI 430 stainless steel in artificial seawater

This article aims to present a new alternative to waste management of spent Li-ion batteries from cell phones. In this sense, the proposed is recycling the cobalt from Li-ion cathode by electrodeposition and apply it as corrosion protector of AISI 430 stainless steel. Thus, two greatest environmental problems can be solved, producing a low-cost and high-corrosion-resistant stainless steel. The cobalt electrodeposition bath came from acid dissolution of spent Li-ion cathode with chemical formula LiCoO₂. The charge efficiency for cobalt electrodeposition in ?1.0 V and pH = 3 reaches 95 %. A protective layer of Co₃O₄ was successfully obtained by treatment of AISI 430 stainless steel with cobalt electrodeposited at 800 °C for 200 h in air atmosphere. The corrosion current of AISI 430 stainless steel in artificial seawater was reduced from 30 to 0.76 μA cm^?2. The treatment proposed produces a AISI 430 stainless steel with double of corrosion resistance and half of cost if compared with AISI 304 stainless steel.     

低温下不锈钢导热系数的测量

在低温条件下利用稳态纵向热流法测量了制造低温阀门常用的316L不锈钢和17-4PH不锈钢的导热系数,通过实验表明两者的导热系数与316不锈钢的导热系数十分接近。     

Mo nanocrystallite effects on nanostructural properties of stainless steel

Mechanical properties of stainless steel can be improved by grain size refinement down to nanocrystalline structures. In the present work, the effects of Mo nanoparticles on stainless steel powders synthesized using the sol-gel method have been studied. The results show that decreasing of the size of Mo crystallites in stainless steel is accompanied by phase transformations as well as the mesoporous surface area and narrow pore size distribution. The structure of the synthesized sample was investigated by XRD (X-ray diffraction), AFM (atomic force microscopy) and SEM (scanning electron microscopy) technologies. As revealed in AFM, SEM images and XRD patterns, worm-like pores were formed and ordered to some extent. The influence of various conditions on the structure of ordered mesoporous stainless steel is also discussed.     

LTD模块气体开关电极材料烧蚀性能实验

针对直线变压器驱动源(LTD)对开关的长寿命需求,基于前期研制的200kV低抖动多间隙气体开关电极几何参数以及开关通流水平,详细开展了不同电极材料(钼、黄铜、铜钨合金、高密度石墨、304和321不锈钢)的烧蚀性能实验。实验结果表明,在单次电荷转移量15.4mC,脉冲电流20kA条件下,体积烧蚀速率从大到小依次为:石墨、黄铜、铜钨合金、钼、不锈钢。电极烧蚀微观形貌分析表明,不锈钢是用于LTD开关相对较好的电极材料。根据不锈钢电极的体积烧蚀速率,可知理论上LTD开关的运行寿命可以超过1×106次,但前提是开关外壳需保持足够的绝缘强度。     

Mössbauer study of martensitic transformation in Xe ion-irradiated type 304 austenitic stainless steel

Foil specimens of type 304 stainless steel have been irradiated with Xe⁺ ions in the range of 100–400 keV and 1×10²⁰–1×10²¹ ions/m² to elucidate the dynamics of the ion-induced martensitic phase transformation in stainless steel. It has been clearly shown by depth selective conversion electron Mössbauer spectroscopy (DCEMS) that the ion-induced martensitic phase in type 304 stainless steel has grown from the surface to a depth dependent both on the ion energy and the fluence of the Xe⁺ ions. Especially, we observed by means of DCEMS that the extension of the martensitic phase into the interior of stainless steel has been induced with increasing ion energy. It is concluded from these results that the depth distribution of the ion-induced martensitic phase is stress-induced by the formation of the highly pressurized Xe⁺ inclusion in type 304 stainless steel.     

Colorizing stainless steel surface by femtosecond laser induced micro/nano-structures

We demonstrate colorizing of stainless steel surfaces by femtosecond laser induced periodic microholes and micro/nano-gratings on sample surfaces. Suitable adjustment of laser induced features on stainless steel surfaces offer a variety of colors, including multi-color, gold, and black. We also report that multi-color metal surfaces exhibit diverse colors when they are exposed to the incident light of different incident and azimuthal angles. Finally, we briefly explain how the femtosecond laser induced micro/nano scale features introduce different colors on stainless steel surfaces.     

不锈钢管道低温溅射镀TiN薄膜技术

 设计了一套适用于加速器细长管道真空室的低温溅射镀TiN薄膜装置。利用该装置，对86 mm×2 000 mm的不锈钢管道真空室进行溅射镀TiN膜实验，并对镀膜实验结果进行分析，得到了适用于加速器管道真空室内壁溅射镀TiN膜的表面处理参数。样品测试结果表明：在压强为80～90 Pa、基体温度为160~180 ℃的镀膜参数下，不锈钢管道内壁获得的TiN薄膜最佳，薄膜沉积速率为0.145 nm/s。镀膜后真空室的二次电子产额明显降低。     

Electromagnetic and Thermal Properties of a Conductively Loaded Epoxy

We discuss the mechanical, thermal, and electromagnetic properties of a castable microwave absorber consisting of a mixture of stainless steel powder suspended in a commercially available epoxy. The resulting mixture is well suited for cryogenic applications. Its coefficient of thermal expansion closely matches most metals to reduce mechanical strain during cool down. The absorption can be tuned by varying the volume filling fraction of the stainless steel powder in the mixture and exhibits little change from room temperature to 4 K. We provide simple expressions for the real and imaginary parts of the dielectric permittivity as a function of frequency and the stainless steel filling fraction.     

Determination of the spatial distribution of trace elements in stainless steel by imaging microprobe secondary ion mass spectrometry

Imaging microprobe secondary ion mass spectrometry (SIMS) using a liquid metal ion source (LMIS) has been used to determine the spatial distribution of metal ions in stainless steel. This scanning ion microprobe is used to achieve high resolution chemical maps of the surface of a sample. For conductive samples such as stainless steel, the practical spatial resolution approaches 0.2 μm and the sensitivity varies with the ion of interest. We have obtained important information relating to the distribution of surface contaminants, segregation, and corrosion phenomena of the elements in these alloys. In this report we hope to demonstrate the usefulness of this important new technique by describing its capabilities and by reviewing data obtained from two separate studies involving stainless steel.

Significant findings obtained in these mapping experiments were:

• . Stainless steel 316 tubing, which had been found previously to be catalytically active, showed remarkable differences between the used and unused samples. Sodium, potassium, and hydrocarbons were found to exist in agglomerations (islands) in the unused tubing, but were very well distributed in the used tubing.

• . A used stainless steel impeller was found to be inhomogeneous with respect to iron and chromium. The surface was entirely covered by chlorine, which is believed to be responsible for the corrosion. Water and elevated levels of chloride ion were found inside numerous scratches or fissures covering the surface. The unused stainless steel showed no signs of streaks or segregated metal regions, and was free from fissures.

     

Characterization of oxide layers and interface layers of ferrite stainless steel (SUS430) by57Fe CEMS

The oxide layers on stainless steel formed by heating at various high temperatures and by dipping in LiF + BeF₂ molten (Flibe) bath at 600 °C were characterized by CEMS. Hematite was a major iron product at 600 °C and fine oxides with paramagnetic Fe(III) species were produced at the higher temperatures than 700 °C. The interface of stainless steel beneath oxide films was characterized as the hyperfine field distributions. Paramagnetic Fe(III) species were produced on Cr depleted layers in the Flibe bath. CEMS is effective for simultaneous characterization of both oxide surface and interface layers of the ferritic stainless steel.     

Effect of substrate bias voltage on corrosion of TiN/Ti multilayers deposited by magnetron sputtering

Austenitic stainless steel can be attack by localized corrosion in saline environments, such as seawater. TiN/Ti multilayers can improve the corrosion resistance of the stainless steel better than TiN monolayers, because the titanium layers improve the impermeability of TiN/Ti multilayers. In this work, 1.75-4.55 μm thick layers were deposited on to grounded or −100 V biased substrates of 304 stainless steel substrates by reactive magnetron sputtering. The corrosion resistance of the layers was studied by means of potentiodynamic polarization in 0.5 M NaCl solutions. It was found that the pitting corrosion resistance was dependent on the bias and period number of the multilayers.     

Investigation of defect structures in deuteron irradiated and deformed stainless steel 316 by positron annihilation

Abstract

Deuteron-irradiated and deformed stainless steel specimens were investigated by positron lifetime and Doppler broadening measurements. The evolution of the defect structures was studied as a function of the isochronal annealing temperature and for various degrees of deformation. A different behaviour was observed for deformed and irradiated stainless steel specimens. Evidence for vacancy clusters was found in the deuteron-irradiated steel. These clusters disappear after annealing around 900 K.     

Ultrasonic inspection of stainless steel butt welds using horizontally polarized shear waves

Inspection of austenitic stainless steel weldments by conventional ultrasonic means is fundamentally limited by the textured, columnar grain structure of the weld metal. It is shown that, for selected angles of incidence, shear waves normally polarized with respect to the columnar grains can pass through the weld metal-base metal interface without partial reflection. As a consequence, the inspectability of stainless steel weldments can be improved. The operation of a low frequency, ultrasonic system for stainless steel butt weldments is demonstrated.     

Mild corrosion behavior on sulphurized steel surface during friction

After treatment by low temperature ion sulphuration, the solid lubrication sulphuration layers (FeS films) were produced on the AISI 1045 and stainless steel. A mass of corrosion peeling pits occurred on the worn scars of 1045 steel sulphuration layer after wear test, whereas none of them on the stainless steel one. AFM was used to observe the morphology of sulphuration layer, SEM equipped EDS was utilized to analyze the morphologies and compositions of worn scars. XPS and XRD were employed to detect the valence states of sulphuration layer and its worn scars, as well as the phase structures. The results showed that during friction, under the frictional heat, the sulfate radical with mild corrosion was produced, so that the 1045 steel without any anti-corrosion was corroded in some certain, meanwhile the stainless steel was not corroded depending on its excellent corrosion resistance.