Oxidation of AISI 304L stainless steel surface with atomic oxygen

Oxidation of stainless steel surface in oxygen atmosphere was investigated by Auger electron spectroscopy (AES) depth profiling. The samples made of AISI 304L stainless steel were exposed to highly non-equilibrium oxygen atmosphere at different temperatures between 300 and 800 K and for different periods between 5 and 600 s. The degree of dissociation of oxygen molecules was of the order of 10%. A thin oxide layer formed on the stainless steel surface consisted of the iron oxide. The thickness depended on the sample temperature. At room temperature it was 7 nm, and it remained the same up to 200 °C. With further increase of temperature, the thickness of the oxide layer increased and reached 40 nm at 450 °C. The thickness was independent of exposure time. The results were explained by two mechanisms of oxide growth. Up to 200 °C the oxidation was run by electro-migration, while at higher temperatures the thermal induced migration prevailed.     

Surface transformation of AISI 304 stainless steel by high power diode laser

A high power diode laser was used in continuous mode to irradiate milled AISI 304 substrates in order to modify their surface morphology. Milling of the steel substrates was operated at different feeds, thus allowing the achievement of a broad range of starting surface texture, characterized by average roughness of ∼0.65-1.5 μm. Laser finishing was then operated on them by varying laser power and scan speed.The effectiveness of the laser finishing was evaluated by 3D surface profilometry and SEM imaging. Laser was found to modify the surface morphology of the irradiated zones and achieve high quality surface textures. Further, consistent trends of the amplitude, spacing and hybrid roughness parameters according to laser operational settings can often be found. Finally, mapping of the experimental data can lead to the definition of a first approximation tool, which can be profitably used for simulation and process control.     

Ultrasonically enhanced corrosion of 304L stainless steel I: the effect of temperature and hydrostatic pressure

A systematic study of the effect exerted by various parameters on the corrosion of 304L stainless steel in an ultrasonic field has been carried out. Ultrasound increased the corrosion rate under all the investigated conditions. In this paper, attention is focused on the effect of temperature and hydrostatic pressure. At ambient pressure, increase in temperature, T, was found to increase the ultrasonically enhanced corrosion rate up to a maximum of 40 degrees C; at 50 degrees C a marked decrease in the effect of ultrasound was observed. At constant temperature, increase in hydrostatic pressure caused a strong increase in corrosion rate to values in excess of 2500 mm yr(-1) at 4 bar.     

Optical absorption in PECVD deposited thin hydrogenated silicon in light of ordering effects

We report results obtained from measurements of optical transmittance spectra carried out on a series of silicon thin films deposited by plasma-enhanced chemical vapour deposition (PECVD) from silane diluted with hydrogen. Hydrogen dilution of silane results in an inhomogeneous growth during which the material evolves from amorphous hydrogenated silicon (a-Si:H) to microcrystalline hydrogenated silicon (μc-Si:H). Spectral refractive indices and absorption coefficients were determined from transmittance spectra. The spectral absorption coefficients were used to determine the Tauc optical band gap energy, the B factor of the Tauc plots, E ₀₄ (energy at which the absorption coefficient is equal to 10⁴ cm⁻¹), and the Urbach energy as a function of the hydrogen dilution. The results were correlated with microstructure, namely volume fractions of the amorphous and crystalline phase with voids, and with the grain size.      

Corrosion monitoring of stainless steel 304L in lithium bromide aqueous solution using transmittance optical detection technique

We report a method based on the power ratio of transmittance for monitoring the corrosion rate in stainless steel 304L immersed in an aqueous solution of lithium bromide at 50 wt%, at 70 °C. The optical transmittance measured in the solution contaminated with corrosion oxides at different times of exposure is related to the physical degradation of the stainless steel samples. Lasers at 532 and 632 nm were utilized for monitoring the accumulation of corrosion oxides dissolved in the lithium bromide solution of the metallic samples for 480 h. The change in the optical power of transmittance was 13 μW/480 h measured at 532 nm and 3.6 μW/480 h at 632 nm. The variation of the power ratio for 532 nm was from 0.01 to 0.24, and for 632 nm, from 0.01×10⁻³ to 15.61×10⁻³; this is proportional to an accumulated corrosion rate of [0.0142×10⁻³–0.552×10⁻³ g/cm²] for an exposure time of 432 h.     

Localized modification of magnetic properties in 304 stainless steel foil by MeV ion beams

MeV ions were implanted in 304 stainless steel foils to investigate the localized modification of the magnetic susceptibility associated with the phase transformation. The magnetic susceptibility was found to be increased by Au⁺ or Si⁺ implantation because of the localized formation of a martensitic phase. The magnetic susceptibility of ferromagnetic substrates was enhanced much more than that of non-magnetic substrates. The enhancement in the magnetic susceptibility for Au⁺-implanted samples was a factor of 4–5 greater than that for Si⁺-implanted samples.On leave from GLORY Ltd., Simoteno, Himeji, Hyogo 670, Japan     

用变温霍尔效应估测锑化铟的禁带宽度

通过变温霍尔效应实验获得锑化铟的霍尔系数随温度变化的数据,根据半导体的霍尔系数随温度的变化规律,计算出禁带宽度,并且着重讨论禁带宽度的两种求法,比较了两种方法的计算精度.     

Microscopic analysis of surface state of SUS-304L stainless steel by low energy scanning electron microscopy in ultra high vacuum

The variation of surface state of SUS-304L stainless steel with heat treatment in a vacuum of 10^?9 Torr was observed by the ultra high vacuum low energy scanning electron microscope (UHVLESEM) by detecting the absorption electron current. The absorption electron current was very sensitive to the surface state and a large effect of the electron beam irradiation was observed. The variation of the absorption electron current with the surface segregation was measured within a microscopical dimension of 0.3 microm on a selected area of the scanning electron microscopic image. At the same time, the surface state was characterized by Auger electron spectroscopy and relations between surface states and the absorption electron current were discussed in relation to the secondary electron and backscattered electron yields.     

利用反射与透射光谱测量GaN外延层的光学参数

GaN是一种理想的紫外发光和探测材料,其光学特性参数是光学器件设计的重要依据。采用紫外反射与透射光谱相结合的方法对国产GaN外延层进行光学特性测量,利用反射率与折射率之间的关系和薄膜干涉效应,建立了GaN外延层厚度、表面反射率、光谱吸收系数的光谱测量公式。测量结果表明,GaN外延层在紫外波段存在三个吸收区,其中364nm以下波段为强吸收区,吸收系数接近10^5cm^-1,364～375nm为吸收过渡区,375nm以上波段为弱吸收区;GaN表面反射率在三个吸收区的变化不大,为0．2～0．25之间。     

Synthesis and optical characterization of nanocrystalline CdTe thin films

From several years the study of binary compounds has been intensified in order to find new materials for solar photocells. The development of thin film solar cells is an active area of research at this time. Much attention has been paid to the development of low cost, high efficiency thin film solar cells. CdTe is one of the suitable candidates for the production of thin film solar cells due to its ideal band gap, high absorption coefficient. The present work deals with thickness dependent study of CdTe thin films. Nanocrystalline CdTe bulk powder was synthesized by wet chemical route at pH≈11.2 using cadmium chloride and potassium telluride as starting materials. The product sample was characterized by transmission electron microscope, X-ray diffraction and scanning electron microscope. The structural characteristics studied by X-ray diffraction showed that the films are polycrystalline in nature. CdTe thin films with thickness 40, 60, 80 and 100 nm were prepared on glass substrates by using thermal evaporation onto glass substrate under a vacuum of 10⁻⁶ Torr. The optical constants (absorption coefficient, optical band gap, refractive index, extinction coefficient, real and imaginary part of dielectric constant) of CdTe thin films was studied as a function of photon energy in the wavelength region 400–2000 nm. Analysis of the optical absorption data shows that the rule of direct transitions predominates. It has been found that the absorption coefficient, refractive index (n) and extinction coefficient (k) decreases while the values of optical band gap increase with an increase in thickness from 40 to 100 nm, which can be explained qualitatively by a thickness dependence of the grain size through decrease in grain boundary barrier height with grain size.     

Ultrasonically enhanced corrosion of 304L stainless steel II: the effect of frequency, acoustic power and horn to specimen distance

The effects of frequency in the range 20 to 60 kHz, acoustic power and horn to specimen distance on the corrosion of 304L stainless steel in an ultrasonic field were investigated. At 40 and 60 kHz, the corrosion rate increased to a maximum and thereafter decreased with increasing transmitted power. At 20 kHz, the corrosion rate increased continuously with increasing power over the range investigated. At 18 W transmitted power, the corrosion rate increased continuously with frequency. However, at 40 W transmitted power a pronounced maximum in the corrosion rate occurred at 40 kHz. A significant effect of horn to specimen distance was found, the corrosion rate increasing with decreasing distance. High corrosion rates in excess of 800 mm yr(-1) were observed when the specimen was situated 0.1 mm from the radiating face of the ultrasonic probe. In addition, the area affected by sonication was found to increase with increasing distance.     

Effect of Er doping on optical band gap energy of TiO2 thin films prepared by spin coating

In order to evaluate the effect of Er doping in the range of 0–1.0 mol% on optical indirect band gap energy (E_g) of the film, the Er-doped TiO₂ (Er-TiO₂) thin films were spin-coated onto fluorine-doped SnO₂ coated (FTO) glasses. Glancing angle X-ray diffraction (GAXRD) results indicated that the films whose thickness was 550 nm consisted of pure anatase and FTO substrate. The anatase (101) TiO₂ peaks became broader and weaker with the rise in Er content. The apparent crystallite size decreased from 12 nm to 10 nm with increasing the amount of Er from 0 mol% to 1.0 mol%. UV–vis spectrophotometry showed that the values of E_g decreased from 3.25 eV to 2.81 eV with the increase of Er doping from 0 to 0.7 mol%, but changed to 2.89 eV when Er content was 1.0 mol%. The reduction in E_g might be attributed to electron and/or hole trapping at the donor and acceptor levels in the TiO₂ band structure.     

Deformation-induced martensite and nanotwins by cryogenic laser shock peening of AISI 304 stainless steel and the effects on mechanical properties

Laser shock peening (LSP) of stainless steel 304 was carried out at room and cryogenic temperature (liquid nitrogen temperature). It was found that the deformation-induced martensite was generated by LSP only when the laser-generated plasma pressure is sufficiently high. Compared to room temperature laser shock peening (RT-LSP), cryogenic laser shock peening (CLSP) generates a higher volume fraction of martensite at the same laser intensity. This is due to the increase in the density of potential embryos (deformation bands) for martensite nucleation by deformation at cryogenic temperature. In addition, CLSP generates a high density of deformation twins and stacking faults. After CLSP, an innovative microstructure, characterised by networks of deformation twins, stacking faults and composite structure (martensite and austenite phases), contributes to material strength and microstructure stability improvement. The combined effect of higher surface hardness and a more stabilised microstructure results in greater fatigue performance improvement of the CLSP samples compared to that of the RT-LSP samples.     

Tribological changes on SS304 stainless steel induced by nitrogen plasma immersion ion implantation with and without auxiliary heating

In order to achieve quite thick treated layers with reasonable thickness uniformity in SS304 steel, the plasma immersion ion implantation (PIII) process was run in high-temperature, up to 350 °C, to induce high thermal diffusion but avoid the white layer formation. In these experiments, we heated the sample-holder with a shielded resistive wire properly wound around it and subjected the SS samples to nitrogen glow discharge PIII with relatively low voltages (10 kV) in different temperatures. We also treated the SS samples by the traditional PIII method, slowly increasing the high voltage pulse intensities, until 14 kV at the end of processing, reaching temperatures of up to 350 °C. These modes of treatments were compared with respect to nitrogen implantation profiles, X-ray diffraction, tribology and mechanical properties. X-ray diffraction results indicated a much higher efficiency of auxiliary heated PIII mode compared to the ordinary PIII. Very prominent γ_N peaks were observed for the first mode, indicating large concentration of nitrogen in thick layers, confirmed by the nitrogen profiles measured by GDOS and AES. Improved mechanical and tribological properties were obtained for SS304 samples treated by the PIII with auxiliary heating, more than for ordinary PIII. Hardness was enhanced by up to 2.77 times, as seen by nanoindentation tests.     

First-principles study of the relaxation and energy of bcc-Fe, fcc-Fe and AISI-304 stainless steel surfaces

Relaxations and surface energies of bcc-Fe, fcc-Fe and AISI-304 stainless steel surfaces are investigated by using first-principles total energy calculations. The low-index surfaces (1 0 0), (1 1 0), and (1 1 1) are optimized with respect to the atomic coordinates. The calculations are performed within the density functional framework using the projector augmented plane wave (PAW) method. The structural property, surface relaxations and surface energies of bcc-Fe agree well with experimental data from previous computational studies. For bcc-Fe, the order of surface relaxations and surface energies is (1 1 0) < (1 0 0) < (1 1 1). The orders of surface relaxations and energies for fcc-Fe and AISI-304 stainless steel are (1 1 1) < (1 0 0) < (1 1 0) and (1 0 0) < (1 1 1) < (1 1 0), respectively. The surface energies of AISI-304 stainless steel achieved in this study provide a good basis for future experimental application.     

Influence of annealing treatment on the microstructure and mechanical performance of cold sprayed 304 stainless steel coating

In this study, 304 stainless steel coatings were deposited on interstitial-free steel substrate by cold spraying method. The effect of annealing treatment on microstructure, microhardness, ultimate tensile strength and fracture performance of the coatings were studied. The results showed that annealing treatment had made a dominant contribution to heal up the incomplete interfaces between the deposited particles. Both of the microstructure and the mechanical properties have been obviously optimized by annealing treatment. In addition, the coating microhardness decreased from 345 HV_0.2 for the as-sprayed coating to 201 HV_0.2 for the annealed coating. The coating ultimate tensile strength increased from 65 MPa for the as-sprayed coating to 357 MPa for the annealed coating, which resulted from the increase of the metallurgically bonded areas in the coating induced by annealing treatment. Fracture morphology of the coatings also revealed that annealing treatment changed the fracture character of the cold sprayed 304 stainless steel coating from brittle type to plastic type.     

光学性质对超快激光辐照下铜膜热响应的影响

在超快激光照射过程中,金属靶材的光学性质是动态变化的。采用双温模型与分子动力学结合法,考虑动态和常数光学性质两种情况,对不同脉宽的超快激光照射下铜薄膜的热响应进行了模拟研究。其中,常数光学性质包括由激光沉积能量相等计算得到的等效平均反射率和室温下的吸收系数。结果表明:两种情况下的电子温度和晶格温度均差别较小,尤其是脉宽远小于电子-晶格弛豫时间的飞秒激光; 而当激光脉宽相当于或大于电子-晶格弛豫时间时,如皮秒激光,光学性质的动态变化对材料的熔化和重凝的影响则比较明显。     

新型远红外Ge-Te-Se-Sn硫系玻璃的热学与光学性质研究

采用熔融淬冷法制备了新型远红外Te基硫系玻璃Ge20-xTe65 Se15 Snx(x=0,2,4).在Ge-Te-Se玻璃的基础上,通过引入重金属Sn,研究其对玻璃组成、结构和性能的影响.测试了样品的中红外热成像、X射线衍射(XRD)图谱、差热分析曲线(DSC)、可见/近红外吸收光谱、红外透射光谱.利用经典的Tauc...     

Optical Properties of the (CuInSe2) x ·(2ZnSe)1−x and (CuInTe2) x (·2ZnTe)1−x Solid Solutions

Crystals of the compounds CuInSe₂, CuInTe₂, ZnSe, and ZnTe, and the solid solutions (CuInSe₂) _x ·(2ZnSe)_1–x and (CuInTe₂) _x ·(2ZnTe)_1–x were grown by the Bridgman and chemical transport reactions methods. Their transmission and reflection spectra in the region of the main absorption line edge were studied. The forbidden band gap of the indicated materials was determined and its concentration dependences were built for the solid solutions. It is established that the forbidden band gap changes linearly with the x composition and is satisfactorily described by the square-law dependence.     

V高掺杂ZnO最小光学带隙和吸收光谱的第一性原理研究

对于V高掺杂ZnO,当摩尔分数为0.0417—0.0625时,随着掺杂量的增加,吸收光谱出现蓝移减弱和蓝移增强两种不同实验结果均有文献报道.采用密度泛函理论的第一性原理平面波超软赝势方法,构建未掺杂ZnO单胞模型、V高掺杂Zn1-xVxO(x=0.0417,0.0625)两种超胞模型,采用GGA+U方法计算掺杂前后体系的形成能、态密度、分波态密度、磁性和吸收光谱.结果表明,当V的掺杂量(原子含量)为2.083%—3.125%时,随着V掺杂量增加,掺杂体系磁矩增大,磁性增强,并且掺杂体系体积增加,总能量下降,形成能减小,掺杂体系更稳定,同时,掺杂ZnO体系的最小光学带隙增宽,吸收带边向低能级方向移动.上述计算结果与实验结果一致.