Multicyclic fatigue of stainless steel treated by a high-intensity electron beam: surface layer structure

It is shown that an electron-beam treatment of the 08X18H10T steel specimens under the condition of melting of the ~5 μm surface layer (electron beam energy density 25 J/cm²) increases their fatigue life by a factor of 3.5. The structural-phase states and defect substructure of this steel are studied by the methods of optical, scanning and transmission electron microscopy, and the factors responsible for its increased fatigue life are revealed.     

Electron-beam modification of a surface layer deposited on low-carbon steel by means of arc spraying

State-of-the-art means of physical materials science are used to study the structure, phase composition, defect substructure, and tribological properties of a coating formed on low-carbon Hardox 450 martensite steel via the electrocontact deposition of an Fe–C–Ni–B wire and modified through subsequent irradiation with high-intensity pulsed electron beams. It is shown that electron-beam treatment results in the formation of a modified 50-μm thick surface layer, the main phases of which are the α-phase, iron boride FeB, and boron carbide B₄C. In the layer modified by electron-beam treatment, the transverse size of batch martensite crystals is reduced by a factor of 3, relative to the initial Hardox 450 steel, and ranges from 50 to 70 nm. It is established that the wear resistance of the deposited layer after electron-beam treatment grows by more than 20 times with respect to the wear resistance of Hardox 450 steel, and the friction coefficient is reduced by a factor of 3.5. The microhardness of a deposited layer ~7 mm thick is more than double that of the base metal.     

On the fatigue strength of grade 20Cr13 hardened steel modified by an electron beam

The treatment of 20Cr13-grade hardened steel (0.2% C, 13% Cr) with an electron beam whose energy density is 10–30 J/cm² results in an increase in the fatigue life by a factor of 1.9. The irradiated surface is investigated by scanning electron microscopy; substantial refinement of the grain structure and a change in the Cr content in the surface layer are revealed.     

Features and mechanisms of the evolution of the structure-phase state of a quenched carbon steel under electrostimulated fatigue

Electron-microscopic examinations of the evolution of the defect substructure and phase composition have been carried out for quenched 60GS2 carbon steel subjected to multiple cycles of fatigue loading. The mechanisms by which the fatigue durability of the steel processed at an intermediate stage of loading by alternating electric current is increased have been investigated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 53–60, September, 2004.     

The effect of nanostructured surface layer on the fatigue behaviors of a carbon steel

A nanostructured surface layer was formed on a carbon steel by means of surface mechanical attrition treatment (SMAT). The microstructure of the surface layer of the SMATed sample was characterized by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Microhardness and residual stress distribution along the depth from the SMATed surface layer were measured at the same time. Fatigue behaviors of the carbon steel subjected to the SMAT process were investigated. A nanostructured layer with average grains size of ∼12.7 nm was formed, of which microhardness is more than twice as high as that in matrix and residual compressive stress can reach about −400 MPa with maximum depth of ∼600 μm. The fatigue strength of as-received sample is 267 MPa and that of SMATed sample is 302 MPa based on fatigue life 5 × 10⁶ cycles. The SMAT process has improved the fatigue strength by as much as 13.1% for the carbon steel. It is shown that the SMAT is an effective method to render the material with the features, such as a nanostructured and work-hardened surface layer as well as compressive residual stresses, which can pronouncedly improve the fatigue strength of the carbon steel.     

Nitriding of Stainless Steel in Electron-Beam Plasma in the Pulsed and DC Generation Modes

The influence of electron-beam parameters on the thickness and phase composition of a hardened layer formed upon the nitriding of austenitic stainless steel 12Cr18Ni10Ti in plasma produced by a beam in a low-pressure (3 Pa) nitrogen-argon mixture is studied. The results obtained in the DC and pulse-periodic modes of beam generation with the same mean current and electron energy are compared. In this case the negative bias voltage applied to the samples is 100 V. The nitriding temperature of 400°C is maintained at a mean beam current of 2.6 A and various combinations of frequency (100–500 Hz) and current pulse durations (0.1–0.3 ms) with an amplitude of 80 A. The mean ion-plasma current densities in the DC and pulsed modes are close in magnitude (2–3 mA/cm² at 400°C). The high pulsed ion-current density (35–70 mA/cm²) creates conditions under which the surface sputtering rate during the pulse exceeds the growth rate of the nitrided layer. The nitriding of steel in the pulsed and DC modes over four hours gives the same result. Hardened layers with a thickness of 7–8 μm and a microhardness of the surface component of 15 ± 1 GPa in which the main phase is a supersaturated nitrogen solid solution (expanded austenite) are formed. A possible explanation is that nitriding in an electron-beam plasma proceeds mainly under the action of long-lived active neutral nitrogen particles rather than as a result of ion bombardment.     

On the fatigue properties of high-strength steels

Summary The paper gives the results of an investigation of the optimal tensile strength level suitable for obtaining the maximum fatigue limit of a Mn-Cr-Ni-Mo steel produced by current technology with constant amount of alloying elements, but three different carbon contents, 0·21–0·41%, after conventional (CT) and thermomechanical treatment (TMT). The study was carried out in an effort to explain the considerable difference in the fatigue limit data of high strength steels published by different authors [1, 2, 3]. For a tensile strength of about 260 kp/mm² the fatigue limits were found from 38 up to 116 kp/mm².In addition to confirming the influence of the TMT on the tensile strength and ductility already known, it was found that the maximum of the fatigue properties for medium carbon content can be obtained in the tensile strength area of cca 220 kp/mm². When the tensile strength is raised beyond this limit the fatigue limit falls. The values of the fatigue limit after CT as well as after TMT, but in comparison to the same tensile strength range, are very similar. The fatigue limits of about 90 kp/mm² lie within the great range of other published data.Suggested causes for the decreased fatigue limit at high strength such as the method of testing, the shape of the test bar, the effect of ductility, the grain size and the level of internal stresses, are discussed and the idea is advanced that the main cause of the great differences is the increasing influence of the size of non-metallic inclusions as the strength increases.As a result, a preliminary hypothesis was made to explain the relation of the fatigue limit of steels to the size of non-metallic inclusions, referred to different limits of strength, based on the results of Stulen and co-workers [4]. By means of extrapolation the fatigue limit of a steel containing an inclusion of 0 m diameter was also determined as a function of the tensile strength. This can be considered as the theoretical fatigue limit of the metal matrix itself, where the mechanism of the fatigue fracture is controlled by the fatigue phenomena in the matrix itself. Below this limit, on the contrary, the mechanism of the fatigue fracture is controlled by the presence of nonmetallic inclusions.     

Structural and phase states in austenitic steel subjected to high-cycle fatigue

The destruction surface and defect substructure of the Fe-0.1C-1.71Mn-0.92Ti-18.2Cr-10.4Ni-0.71Si steel subjected to high-cycle fatigue tests is investigated by the methods of scanning and transmission electron microscopy. It is demonstrated that the fatigue tests, irrespective of the loading scheme (continuous or under conditions of intermediate stimulation by pulse current), result in the formation of a structural gradient in the material manifested through regular changes of the relief parameters of the destruction surface and defect substructure with increasing distance from the loading surface (face or back specimen side). It is revealed that scalar and excess dislocation density, volume fraction of grains that comprise deformation microtwins, and degree of dislocation substructure organization maximize near the free specimen surface. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 88–95, January, 2006.     

Excitation of the hydrogen subsystem in metals and alloys by ionizing radiation

The results of research on the nonequilibrium liberation of deuterium from niobium, palladium, and stainless steel under electron-beam bombardment are reported. The maximum on the deuterium gas liberation curve in the low-temperature region is shown to shift under linear heating with simultaneous electron-beam bombardment in comparison with linear heating without such bombardment. The shift reaches 130° in Nb, 100° in stainless steel, and 65° in Pd. The rate of radiation-stimulated gas liberation increases nonlinearly with the concentration of deuterium introduced and the electron-beam current. Tomsk Polytechnical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, p. 41–46. July, 1998.     

Structural phase states and properties of the layer surfaced on low-carbon steel with Fe‒C‒Cr‒Nb‒W powder-core wire followed by electron-beam processing

Structural phase states and tribological properties of the coating surfaced onto Hardox 450 martensite low-carbon steel with powder wire Fe?C?Cr?Nb?W and modified by subsequent electron-beam processing are studied by methods of modern physical material science. It is shown that irradiation of ~5 thick surfaced layer with high intensity pulsed electron beams results in the formation of ~20 μm thick surface layer with the master phases of α-Fe and NbC, Fe₃C and M₆C(Fe₃W₃C) carbides. The main difference of the surface layer modified with electron-beam processing from the unmodified volume of the surfacing is the morphology and dimensions of the second phase inclusions. In the modified layer of the surfacing the inclusions have smaller dimensions and are located in the form of interlayers along the grain boundaries. In unmodified surfacing the particles of the faceted shape located chaotically in the grain volume are the basic morphological type of the inclusions. It is noted that the small value of crystal lattice Nb parameter observed in the experiment may be caused by the high level of vacant interstitial sites having the smaller size in comparison with the occupied interstitial sites. It is established that wear resistance of the surfaced layer after electron-beam processing increases more than 70-fold relative to wear resistance of Hardox 450 steel and friction coefficient decreases significantly (~3-fold).     

Evolution of the phase composition and defect substructure of rail steel subjected to high-intensity electron-beam treatment

The morphology, structure-phase states, and defect substructure of annealed rail steel subjected to electron-beam treatment in the surface-layer melting mode are studied by scanning and transmission electron microscopy methods. The formation of the lath martensite structure, as well as cellular and dendritelike structures, containing nanoscale martensite crystals, is revealed.     

A fractographic study of fatigue failure in two high strength steels

Results are given of a detailed fractographic study of a commercial 1 1/2 Ni-Cr-Mo steel (S95 Specification) and a high purity laboratory-made steel of similar alloy content tested in uniaxial alternating and pulsating loading. The specimens were hardened by oil quenching and tempering to strength levels of 1544 and 1930 MN/m² (100 and 125 tonf/sq. in.). tested at room temperature and the fractures examined by scanning-electron and optical microscopes and by the electron microscope employing a two stage replication technique.All fractures consisted essentially of a fatigue region and a region of tensile failure; the former appeared, in all instances, to be nucleated at non-metallic inclusions. The fatigue regions were composed of smooth featureless areas (probably resulting from micro-cleavage in the tempered martensite), areas of intergranular separation along prior austenite grain boundaries (although very seldom observed in the high purity alloy) and areas exhibiting characteristic striation. The nature of the regions of tensile failure was markedly dependent on steel purity; the primary mode of fracture in the commercial steel was along prior austenite grain boundaries while in the high purity alloy final separation occurred predominantly by ductile shearing. Estimates of fatigue crack growth rates derived from striation spacing data are given.The authors are indebted to Mr. B. E. Hopkins for his advice and encouragement throughout the programme. They would like to thank Mrs. Daphne Thomas for her painstaking work with the scanning electron microscope. The assistance of Mr. K. B. Armstrong, Mr. N. B. Owen and Mr. J. M. Jennings with the fatigue testing phase of the investigation is gratefully appreciated.The work described above has been carried out as part of the General Research Programme of the National Physical Laboratory.     

Hardening and softening during fatigue fracture

Summary The comparison of the change of hardness and plastic deformation amplitude at a constant stress loading or stress amplitude at a constant deformation loading during the fatigue process shows some singularity of the hardening and softening effects. These effects were investigated on mean carbon and low-alloyed steel and on globular cast iron.The fatigue fractures at cycle numbers 10⁴÷10⁶ under stresses below the yield strength predominate in the softening process, which arises after an inconsiderable hardness increase extends in the region to 0·2 from the fracturing cycle number. Under the stresses above the yield strength, which in some cases for annealed and coarse-grained states are below the fatigue limit, the hardening process predominates, followed by a hardness increase in the field up to 0·25 and above the fracturing cycle number.At low cycle fatigue fractures with cycle numbers < 10⁴ depending on the cyclic plastic properties of steels the fatigue process can be followed by a continuous hardening or softening till fracture. This process is characterized by the change of the deformation amplitude and a one-sided accumulation of plastic deformations at a constant amplitude of active stresses. The one-sided accumulation of deformations commonly ends in a quasistatic failure. Under loading with a constant deformation amplitude during softening a fatigue fracture takes place as a result of damage accumulation under the alternating stresses with amplitudes decreasing with cycle number.     

Healing fatigue damage in steel with electric current pulses

A 15–30% enhancement of steel resource upon low-cycle fatigue tests is achieved by steel treatment with power electric current pulses at the instant when a sharp decrease in the ultrasound velocity occurs. Possible mechanisms of the effect are discussed.     

Principles of the alloying of steel in a beam of relativistic electrons

It is shown that it is possible to significantly strengthen steel by alloying a surface layer melted by the energy from a beam of relativistic electrons. A study was made of the effect of different treatment parameters (accelerating voltage, beam current, specimen velocity and temperature, etc.) on the structure, depth, hardness, and wear resistance of the alloyed layer. Several types of alloying mixtures were developed based on carbides of tungsten, chromium, and boron, and including special additions and modifiers. The proportions of the components was optimized. The technology of alloying in a beam of relativistic electrons is compared with vacuum electron-beam alloying. Heat treatment is used to additionally improve the structure of the layers.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 115–125, March, 1996.     

A study of time-of-flight spectra of excited krypton molecular ions in an electron gun

Investigation of time-of-flight spectra of excited krypton molecular ions observed under electron-beam bombardment of excitation tube electrodes is continued. Particular attention is focused on a study of the profile of the light signal produced in the dissociation of the molecular ions. An analysis of the light signal profile provides information on the processes involved in the formation and destruction of molecular ions. A model developed for these processes permitted calculation of the light signal profile. A comparison is made with experimental data on the spectral lines of krypton atoms and ions, whose excitation is caused by the destruction of the molecular ions.     

Tribological properties of chemically bonded polyimide films on silicon with polyglycidyl methacrylate brush as adhesive layer

Polyimide thin films, which possess good stability and film uniformity, are successfully fabricated on single crystal silicon wafers coated with a thin polymer brush by suface-initiated polymerization (SIP) as an adhesive layer. The growth kinetic of polyglycidyl methacrylate (PGMA) brush was studied by the means of ellipsometry. The nano-scale morphology and chemical composition of PGMA brush and polyimide film were studied with atomic force microscopy (AFM), Fourier transform infrared spectrum (FT-IR), and X-ray photoelectron spectroscopy (XPS). The tribological behaviors of the thin films sliding against AISI-52100 steel ball were examined on a static-dynamic friction precision measurement apparatus and UMT-2MT tribometer. The worn surface of the polyimide thin films was investigated with scanning electron microscopy (SEM). The results indicated that the chemically bonded polyimide films exhibited better friction reduction and antiwear behavior compared to the polymide films on bare silicon surface. At a load of 0.5 N and sliding speed of 20 mm s⁻¹, the durability life of the polyimide thin films is over 25,000 sliding cycles and the friction coefficient is about 0.08.     

Peculiarities of Structure Formation in Copper/Steel Bimetal Fabricated by Electron-Beam Additive Technology

Russian Physics Journal - In the present paper, the microstructure of heterogeneous material bimetal compound fabricated by wire-feed electron-beam additive technology from CrNiTi stainless steel...     

Ionic Synthesis of Ga1–x In x As Solid Solution Films

The Ga_1–x In _x As compound obtained by In-ion implantation (100 keV and (0.45–6)·10¹⁷ cm^–2) followed by thermal (800 °C and 15') or high-energy electron-beam (1 MeV, 0.6 mA·cm^–2, 660 °C, and 16 s) annealing is investigated by Rutherford backscattering, optical absorption, and capacitor photoelectromotive force. It is shown that x increases from 0.07 up to 0.21, and the band gap decreases from 1.34 down to 1.21 eV as the implantation dose increases. The surface potential decreases from 0.79 down to 0.58 V. A high efficiency of electron-beam annealing is pointed out.     

Preparation of large area sub-50 nm polymer nanoring arrays

We have prepared large area (4 mm²) periodic arrays of polymer nanorings on GaAs and Si by means of an electron-beam lithography process based on dose-dependent negative PMMA. The rings have identical outer diameters which can be precisely chosen between 40 and 95 nm. The width of the inner diameter can be adjusted between 20 and 60 nm, resulting in line widths between 10 and 20 nm. The periodicity of the rings can be arbitrarily chosen down to 500 nm. The nanorings have been characterized by using several high resolution microscopy techniques including high resolution scanning electron microscopy (HR-SEM) and atomic force microscopy (AFM). First experiments to prepare lattices of metal nanorings have been performed by using the nanorings as a negative resist.