TEM characterization of a nitrogen implanted austenitic stainless steel

Pure austenitic stainless-steel samples (18% Cr, 10% Ni) were implanted at room temperature with nitrogen ions at an energy of 40 keV with fluences from 10¹⁷ to 6X10¹⁷ ions cm^-2. Microstructures obtained after implantation were studied by transmission electron microscopy and selected-area diffraction. The observations show the formation of ε martensite (hexagonal), of α' martensite (tetragonal) and the appearance of nitrides (Fe, Cr, Ni)₂N_1-x hexagonal or orthorhombic.     

Damage annealing behavior of Se implanted GaAs

High resolution Rutherford backscattering-channeling (RBS-C) and transmission electron microscopy (TEM) have been used to investigate the annealing behavior of Se implanted Cr-doped GaAs layers. Two distinct annealing stages were observed; one at 250°C which is associated with amorphous zone annihilation and/or onset of solid phase epitaxial growth and the other at about 400–500°C, depending on the dose, that can be related to the dissociation of microtwins. Above 500°C, the residual defects are primarily dislocation loops and precipitates. The calculated number of atoms associated with the precipitates has been found to correspond closely to the number of implanted atoms, implying 100% precipitation for the cases studied in this work. This could explain the poor or nonexistent electrical activation of Se after low temperature annealing (6̃00°C), even though good regrowth of the amorphous layer has taken place. Experiments with high purity GaAs produced the same result, as far as the observed residual damage was concerned, thus eliminating speculation about the involvement of Cr in the nucleation of microtwins. Transmission electron microscopy investigations of the amorphous-crystalline interface in the as-implanted samples failed to reveal any extended defects. In the present paper, we discuss various mechanisms that could be responsible for the formation of twins in low temperature annealed GaAs.     

铒离子注入碳化硅的射程和退火行为研究

用300—500 keV能量的铒(Er)离子注入碳化硅(6H-SiC)晶体中,利用卢瑟福背散射技术研究了剂量为5×10¹⁵ cm^-2 的Er离子注入6H-SiC晶体的平均投影射程R_p和射程离散ΔR_p,将测出的实验值和TRIM软件得到的理论模拟值进行了比较,发现R_p的实验值与理论值符合较好,ΔR_p的实验值和理论值差别大一些 关键词： 离子注入 投影射程和射程离散 退火行为 卢瑟福背散射技术     

Effect of thermal annealing on nitrogen implanted epitaxial Fe films

Nitridated iron is a promising material for potential applications in permanent magnets. Recent work on stabilization of nitridated iron in a foil form through nitrogen ion implantation and annealing motivates to study effect of thermal annealing on the surface of nitrogen-implanted iron. In this work, we show effect of annealing on chemical state and magnetism of nitrogen implanted epitaxial iron films. It is observed that nitrogen in the lattices only stays at the lower temperatures than 450 °C. In addition, significant reduction and lattice modification are taken placed, when the film is annealed at 450 °C. The increases of saturation magnetization and coercivity, where it is annealed at 450 °C, are likely to be triggered by reduction of oxygen contents at the surface and thinning of Fe₂O₃.     

Corrosion behavior of low energy,high temperature nitrogen ion-implanted AISI 304 stainless steel

This work presents the results of a low-energy nitrogen ion implantation of AISI 304 type stainless steel (SS) at a moderate temperature of about 500°C. The nitrogen ions are extracted from a Kauffman-type ion source at an energy of 30 keV, and ion current density of 100 μA cm⁻². Nitrogen ion concentration of 6 × 10¹⁷, 8 × 10¹⁷ and 10¹⁸ ions cm⁻², were selected for our study. The X-ray diffraction results show the formation of CrN polycrystalline phase after nitrogen bombardment and a change of crystallinity due to the change in nitrogen ion concentration. The secondary ion mass spectrometry (SIMS) results show the formation of CrN phases too. Corrosion test has shown that corrosion resistance is enhanced by increasing nitrogen ion concentration.      

CEMS study of a nitrogen implanted CrNi 18.9 steel

Conversion electron Mössbauer spectroscopy (CEMS) has been used to study a commercial X10CrNiTi 18.9 steel implanted with varying nitrogen doses and at varying implantation temperatures. At low nitrogen doses the fcc γ-phase transformed to the bcc structure. With increasing implantation dosages we have observed the precipitation of Fe-nitrides and a reverse (α→γ) transformation. High implantation temperatures lowered the nitrogen content of the Fe-nitrides and favoured the formation of Cr-nitrides.     

The influence of implanted yttrium on the cyclic oxidation behaviour of 304 stainless steel

High-temperature alloys are frequently used in power plants, gasification systems, petrochemical industry, combustion processes and in aerospace applications. Depending on the application, materials are subjected to corrosive atmospheres and thermal cycling. In the present work, thermal cycling was carried out in order to study the influence of implanted yttrium on the oxide scale adherence on 304 steel specimens oxidised in air at 1273 K. In situ X-ray diffraction indicates that the oxides formed at 1273 K are different on blank specimens compared to implanted specimens. Glancing angle XRD allows to analyse the oxide scale composition after cooling to room temperature.Experimental results show that yttrium implantation at a nominal dose of 10¹⁷ ions cm⁻² does not improve significantly the cyclic oxidation behaviour of the austenitic AISI 304 steel. However, it appears that yttrium implantation remarkably enhance the oxidation resistance during isothermal oxidation. It reduces the transient oxidation stage and the parabolic oxidation rate constant by one order of magnitude.     

The annealing of damage in ion implanted gallium arsenide

Photoluminescence measurements at 77°K and Rutherford scattering of 450 keV protons were used to study radiation damage and annealing in ion implanted GaAs. The characteristic band edge luminescence (8225 Å) in GaAs is completely quenched by ion implantation. Photoluminescence measurements on samples which were isochronally annealed show a single annealing stage at 600°C. A luminescence peak at 9140 Å is introduced into the spectra of all implanted and annealed samples. This peak is attributed to an acceptor level created by As vacancies. The intensity of the peak is greatly reduced by protecting the surface of implanted layers with SiO₂ during annealing. Rutherford scattering measurements on isochronally annealed samples reveal two annealing stages. A 300°C annealing stage is observed on samples which have an initial aligned yield less than random while a 650°C stage is observed on samples which have an initial aligned yield equal to random.     

Dynamic behavior of implanted nitrogen in zirconium at various stages of implantations

Abstract

Depth profiles of nitrogen implanted into Zr with an energy of 50 keV were calculated by dynamic SASAMAL code with three different assumptions for the diffusion of excess atoms over stoichiometry, i.e., ‘no diffusion', ‘both-sides-diffusion’ and ‘upward-diffusion'. To distinguish nitrogens implanted certain stage of implantations, alternate implantations of ¹⁵N and ¹⁴N were used. The results were compared with the experimental results by the resonance nuclear reaction analysis, NRA. For ¹⁵N implantation with fluences from 1 × 10¹⁷ to 1 × 10¹⁸ ions/cm², the calculated results with ‘upward-diffusion’ agreed very well with the NRA results for all fluences. For the depth profile of pre-implanted ¹⁵N (1 × 10¹⁷ ions/cm²), which was changed by the subsequent ¹⁴N implantation with fluences of 1 ～ 10 × 10¹⁷ ions/cm², the agreement with the NRA results was satisfactory until the ¹⁴N fluence did not exceed 5 × 10¹⁷ ions/cm², but for higher fluences, the retained probabilities of ¹⁵N obtained by the ‘upward-diffusion’ code were too low compared with the experimental value obtained by NRA. For the depth profiles of ¹⁵N (1 × 10¹⁷ ions/cm²) implanted following after implantations of ¹⁴N with fluences of 1 ～ 10 × 10¹⁷ ions/cm², the agreement with the NRA results was quite good for all ¹⁴N fluences. It is concluded that the approximation of ‘upward-diffution’ is proper satisfactorily for the treatment of atoms implanted at the final stage of implantations, but a problem is left for the treatment of atoms implanted at the early stage of implantations.     

Use of grazing incidence X-ray diffraction for the study of nitrogen implanted stainless steels

The identification of Fe, Ni and Cr nitrides formed by nitrogen-ion implantation (4×10¹⁷ N⁺ cm^-2, 50 keV) in austenitic steels is performed by X-ray diffraction under very low glancing angles (0.00 ⩽ i ⩽ 1.5°). Spectra obtained with increasing angles i permit the investigation of layers with depths varying from 20 to more than 1000 Å. This non-destructive technique allows the surface to be controlled at each step of the treatments. Spectra were recorded on polished steel prior to and after implantation, with or without electrochemical attack. A 100 Å martensitic layer formed during the mechanical polishing is observed on the austenitic substrate. This layer is destroyed by an anodic attack before implantation of the samples. After implantation a CrN or carbonitride overlayer of a few tens of Å in thickness, may be observed. In the subjacent layers several iron and nickel nitrides are present, mainly ϵ-Fe₂N-Fe₃N, ς-Fe₂N and Ni₃N.     

Phase analysis of a nitrogen implanted CrNi 18.9 steel: A cems-study

Conversion Electron Mössbauer Spectroscopy (CEMS) has been used to study the modified structure of the near surface region of a nitrogen implanted austenitic X10CrNiTi18.9 steel. The implantation dose was varied from 2 to 8*10¹⁷N⁺/cm² using an implantation temperature of 200°C and an ion energy of 100 keV. The (γ/a′)-ratio in the near surface region of the untreated material was changed by electropolishing and mechanical polishing of the surface. The results of the spectra are discussed in terms of nitrogen solid solution in the case of low nitrogen doses and precipitation of Fe-nitrides (ε-Fe₂N, ε-Fe_2+xN) with increasing implantation dose. Phase transformations referring to the Fe-nitrides and the (γ/a′)-ratio are observed with increasing nitrogen content.     

316L不锈钢在静态液态锂中的腐蚀行为研究

利用脉冲激光诱导击穿光谱仪(LIBS)结合SEM、EDX和维氏硬度(HV)等分析手段,分析了316L不锈钢在350℃的液态锂中静态腐蚀500h后的腐蚀特性。微观形貌分析表明：样品存在较明显的晶间腐蚀,其腐蚀层厚度约为2.7μm。硬度分析表明：腐蚀后表面硬度值约HV234.72,约是腐蚀前硬度值的0.78倍。LIBS组分分析表明：经液态锂腐蚀后的样品表面Ni、Cr等元素含量相对减少;在被腐蚀区域Li元素含量随激光击打深度的增加而减少,而Ni、Cr等元素含量与之近似呈成正比递增;母材区Li元素的渗透深度约3.5μm,约是焊缝区的0.6倍。     

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利用脉冲激光诱导击穿光谱仪(LIBS)结合SEM、EDX和维氏硬度(HV)等分析手段,分析了316L不锈钢在350℃的液态锂中静态腐蚀500h后的腐蚀特性.微观形貌分析表明:样品存在较明显的晶间腐蚀,其腐蚀层厚度约为2.7μm.硬度分析表明:腐蚀后表面硬度值约HV234.72,约是腐蚀前硬度值的0.78倍.LIBS组分分析表明:经液态锂腐蚀后的样品表面Ni、Cr等元素含量相对减少;在被腐蚀区域Li元素含量随激光击打深度的增加而减少,而Ni、Cr等元素含量与之近似呈成正比递增;母材区Li元素的渗透深度约3.5μm,约是焊缝区的0.6倍.     

Influence of nitrogen on the mechanism of austenitic stainless steel hardening

On the example of a C18N12M2 austenitic stainless steel, the influence of nitrogen (whose content varied from 0 to 0.45 wt.%) on the grain boundary hardening coefficient k _h entering into the Hall-Patch equation is analyzed. High values of k _h in steels with and without nitrogen are found. The data of the Auger analysis show that the hardening coefficient in the steel without nitrogen is determined by the grain-boundary segregation of carbon and oxygen. The grain-boundary hardening in the steel with nitrogen is not connected with the predominant segregation of nitrogen at grain boundaries. It is completely governed by intragranular processes—interaction of nitrogen atoms with dislocations. Omsk State Pedagogical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 47–52, July, 1999.     

Effects of cold rolling deformation on microstructure,hardness, and creep behavior of high nitrogen austenitic stainless steel

Effects of cold rolling deformation on the microstructure, hardness, and creep behavior of high nitrogen austenitic stainless steel （HNASS） are investigated. Microstructure characterization shows that 70% cold rolling deformation results in significant refinement of the microstructure of this steel, with its average twin thickness reducing from 6.4 μm to 14 nm. Nanoindentation tests at different strain rates demonstrate that the hardness of the steel with nano-scale twins （nt-HNASS） is about 2 times as high as that of steel with micro-scale twins （mt-HNASS）. The hardness of nt-HNASS exhibits a pronounced strain rate dependence with a strain rate sensitivity （m value） of 0.0319, which is far higher than that of mt-HNASS （m = 0.0029）. nt-HNASS shows more significant load plateaus and a higher creep rate than mt-HNASS. Analysis reveals that higher hardness and larger m value of nt-HNASS arise from stronger strain hardening role, which is caused by the higher storage rate of dislocations and the interactions between dislocations and high density twins. The more significant load plateaus and higher creep rates of nt-HNASS are due to the rapid relaxation of the dislocation structures generated during loading.     

Flash-lamp annealing of boron implanted silicon

Structure and impurity behaviour of silicon doped by B⁺ ion implantation up to dose of 2 × 10¹⁵ ion/cm² have been investigated after lamp pulse annealing. It has been demonstrated that the implanted layer structure strongly depends on the implantation dose, light energy density, as well as the crystallographic orientation. The optimal annealing result in the structure, which is equivalent to that obtained in the thermal treatment, The impurity diffusive redistribution proved to be rather weaker then in the case of thermal treatment.     

Studies of structure and morphology of sputter-deposited stainless steel–nitrogen films

Stainless steel films doped with nitrogen were deposited on heated and unheated (100) silicon substrates by radio-frequency magnetron sputtering of an austenitic stainless steel target in argon and nitrogen gas mixtures, containing a range of nitrogen compositions. The evolution of phases, morphologies and grain structures in the resultant films was studied by X-ray diffraction and field emission scanning electron microscopy. It was found that, with increasing nitrogen composition in the gas mixture, the crystalline structure of the films deposited on the heated substrates changed from bcc ferrite (α), to nitrogen-stabilized fcc austenite (γ), then to distorted expanded austenite phase (γ_N) with nitrogen supersaturation, and finally to the newly discovered fcc ‘MN’ phase with ideal cubic symmetry and further enlarged lattice. On the unheated substrates, the phase-evolution trend was found to be different for % N₂ above 10. For the 25% N₂ film, amorphous phase formed along with the crystalline austenite and ferrite phases, while the percentage of amorphous content decreased when % N₂ was increased to 50. This different trend was understood to be due to the role of increase in % N₂ in decreasing the energy loss of sputtered species through collisions. The dependence of crystalline phase formation on the energy of sputtered species is less severe on the heated substrates. Although all the films deposited experienced three-dimensional fibrous growths, they exhibited different surface morphology and grain structure. There exists a correlation between film morphology and phase constituents, while grain size was influenced by the nucleation density and the energy and mobility of adatoms that are reduced due to nitrogen incorporation. PACS 68.55.-a; 81.15.Cd     

The surface alloying behavior of martensitic stainless steel cut with wire electrical discharge machine

The surface alloying behavior of tempered martensitic stainless steel multi-cut with wire electrical discharge machine (WEDM) is studied in this paper. Before machined with WEDM, the steel specimens were quenched at 1050 °C and then tempered at 200 °C, 400 °C, and 600 °C, respectively. The microstructure and surface morphology of the multi-cut surfaces were examined with scanning and transmission electron microscopes integrated with an energy-dispersive X-ray spectrometer for chemical composition analysis. Experimental results show that the cut surfaces of the steel specimens were alloyed with wire-electrode material in various extent. Especially the cut surface was much more alloyed when the steel was cut with the first rough cutting pass by using negatively biased potential and final fine cutting using positively biased potential. Alloying degree of cut surfaces can be distinguished with their anodic polarization curves in 0.5 M HClO₄ + 0.2 wt% NaCl at 27 °C. Higher passive current density induces deeper alloyed surface. On the severely alloyed surface, a secondary anodic peak in the potential of 120 mV (versus Ag/AgCl_sat.) of its anodic polarization curve was observed. The presence of the secondary anodic peak was attributed to dissolution of copper, which was the major element of wire-electrode material from the alloyed surface.