The effect of ion implantation on cyclic stress-strain response of polycrystalline copper

The effect of aluminum and boron ion implantation on strain-controlled (low cycle) and stress-controlled (high cycle) fatigue behavior of polycrystalline copper was investigated. The cyclic stress-strain, strain-life and stress-life relations, cyclic slip and crack nucleation behavior of implanted copper are compared with those of unimplanted copper.Under strain control, ion-implanted samples show a lower degree of cyclic hardening and longer fatigue lives than their non-implanted counterparts. Aluminum implantation has a larger effect than boron implantation. Under stress control the fatigue life and the fatigue limit are observed to increase for the aluminum-implanted samples compared with their non-implanted counterparts. These changes in fatigue behavior are associated with changes in deformation behavior in the surface region and surface residual stresses created by ion implantation.     

Low-cycle fatigue of polycrystalline α-iron modified by mutually immiscible silver-ion implantation

Cyclic deformations of annealed pure polycrystalline -iron with and without further mutually immiscible silver-ion implantation (90 keV, 6×10¹⁶ ions cm^–2) were studied in a plastic strain-controlled tension-compression fatigue test (triangular loading waveform, frequency 0.02–0.3 Hz, and plastic strain range 3×10^–3–1.2×10^–2). The obtained plastic strain-life (_p-N _f) curves showed that the iron specimens could survive for a greater number of cycles before failure when implanted. Comparison of the cyclic stress-strain curves suggested that the implanted specimens had maintained a relatively more stable microstructural change than those unimplanted ones which had undergone a violent cyclic hardening during cyclic deformation. This is proposed to be a strong indication that the fatigue ductility has been improved and the cross slip of screw dislocations, which leads to the evolution of the persistent slip bands for fatigue damage, was hindered to some extent after ion implantation.     

Surface physical and chemical changes of pure iron after molybdenum ion implantation and their effects on the tribological behaviour II: Tribological behaviour

The components of tribological systems are all quite sensitive to the surface chemistry and microstructure of the tribological material which may be dramatically changed by ion implantation. This paper is aimed at studying the effect of surface physical and chemical changes caused by molybdenum ion implantation on the friction and wear behaviours of pure iron. For this purpose, the wear tests of unimplanted and implanted specimens were conducted on an SRV fretting wear machine in air, at room temperature and with or without lubrication. The surface morphology, composition and chemical state of the wear tracks were also examined using electron probe microanalysis, Auger electron spectroscopy and X-ray photoelectron spectroscopy. The experimental results indicate that the wear resistance of pure iron is largely improved by molybdenum ion implantation. Under dry friction conditions, the wear resistance of the specimen implanted with a dose of 3 × 10¹⁷ is increased to 2.8 times that of unimplanated pure iron since the anti-adhesion, anti-abrasion and anti-deformation abilities are improved as a result of the increase in microhardness. When liquid paraffin is used as a lubricant, the wear resistance of the implanted specimen is 4.8 times as high as that of the unimplanted one. This further increase in wear resistance compared with that for dry friction is mainly due to the boundary lubricating film provided by liquid paraffin, which reduces the adhesion between the wear counterpart and molybdenum atoms in the implanted specimen. When liquid paraffin plus sulphurized olefin is used as a lubricant, the wear resistance of the implanted specimen is 2.8 times as high as that of the unimplanted one. It can be seen that the increasing value of the wear resistance is lower than that of the sample lubricated with liquid paraffin. The reason is that the compounds FeS and FeSO₄ formed between the element of the wear specimen and the active elements of the lubricant in the wear process play an anti-wear role. However, the presence of a molybdenum element in the implanted specimen decreases the atomic ratio of iron, and thus decreases the amount of FeS and FeSO₄ and the wear resistance.     

Causes of reduced fatigue strength of steel specimens previously strained in tension

Fatigue tests were carried out on specimens of 30CrNi3A steel (tempered at high temperatures and then strained in tension) from which surface layers of various thickness had been removed. It was concluded that the main part in reducing the fatigue strength of previously deformed specimens is played by very thin surface layers and that the cause of this reduction is the fact that fatigue cracks along the slip bands are more readily nucleated in deformed than in undeformed specimens.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 5, No. 5, pp. 548–551. September–October, 1969.     

Influence of ion implantation on the microstructure of oxide scales formed on a 20Cr/25Ni/Nb-stabilized stainless steel in carbon dioxide at 825° C

Specimens of a stainless steel (20%Cr, 25%Ni stabilized with niobium and also containing 0.9% Mn and 0.6% Si) implanted with lanthanum to a dose of 10¹⁷ ion cm^–2 , together with unimplanted specimens, have been oxidized in carbon dioxide at 825° C for times up to 9735 h. Transverse sections through the oxide scales formed on the respective specimens have been studied by analytical electron microscopy. After this exposure the scale on the unimplanted 20/25/Nb stainless steel consists of an outer, large-grained, spinel layer, a middle fine-grained Cr₂O₃ layer and an inner, discontinuous silicon rich, niobium and chromium bearing, amorphous layer. The main effects of the lanthanum implantation are to improve oxidation resistance and maintain scale adherence during thermal cycling. The microstructural changes in the scale formed on the lanthanum implanted 20/25/Nb steel include finer Cr₂O₃ oxide grains and an intermediate region between the outer spinel and inner Cr₂O₃ layers comprised of both oxides. The lanthanum concentrates in this region and appears to act as a marker due to its low diffusivity. Mechanisms of scale development on the 20/25/Nb stainless Red and the influence of lanthanum implantation are discussed.     

How surface damage removal affects fatigue life

The effect of the removal of work hardened surface layers from specimens of 2024-T4 aluminum alloy and AISI-4130 steel on their fatigue lives has been investigated. Specimens were fatigued at selected stress levels for a given number of cycles and the surface layer was removed followed by subsequent fatigue cycling. Results confirm that when a material is subjected to fatigue loading, damage accumulates in the surface layers in the form of work hardening. Removal of the surface layer brings the specimen back to its pre-fatigued condition.     

Investigation into relative slip during fretting fatigue under partial slip contact condition

A finite element analysis based methodology was developed to compute local relative slip on contact surface from the measured global relative slip away from contact surface. A set of springs was included in finite element model to simulate fretting fatigue test system. Compliance of springs was calibrated by comparing experimental and computed global relative slips. This methodology was then used to investigate local relative slip during fretting fatigue in cylinder‐on‐flat contact configuration under partial slip contact condition for unpeened and shot‐peened titanium alloy, Ti–6Al–4V. Relative slip on contact surface is significantly smaller (about one order) than the measured global relative slip by using a conventional extensometer near the contact surface. Effects of coefficient of friction, rigidity of fretting fatigue system and applied stress to specimen on the global and local relative slips were characterized. Coefficient of friction and contact load have considerable effect on local relative slip, and practically no effect on global relative slip. Gross slip condition can develop at some locations on contact surface in spite of overall partial slip condition. Increase in rigidity of fretting fatigue system increases local relative slip but decreases global relative slip. Finally, fatigue life diagrams based on relative slip on contact surface are established for both unpeened and shot‐peened titanium alloy. These show the same characteristics as of the conventional S–N diagram where fatigue life decreases with increase of relative slip.     

Microstructure and thermomechanical pretreatment effects on creep behaviour of helium-implanted DIN 1·4970 austenitic stainless steel

Microstructure investigations were carried out on unimplanted and 150 at.ppm helium implanted foil specimens of DIN 1·4970 austenitic stainless steel after various thermomechanical pretreatments. Creep tests were also carried out for both helium-implanted and unimplanted specimens at 700°C and 800°C. The strength, ductility and rupture time are correlated with the dislocation and precipitate distributions. Helium embrittlement can be reduced in these experiments when dispersive TiC precipitate distributions are produced by proper pretreatments or allowed to form during creep test.     

Effect of small scale notches on the very high cycle fatigue of AISI 310 stainless steel

Fatigue behaviour of AISI 310 stainless steel has been investigated up to very high cycles. The fatigue crack initiation sites were found at the surface of the material. Persistent slip bands developed at the surface of the specimens led to the crack initiation. At lower stress levels, shallow persistent slip bands were found at the surface of the specimens, and the fatigue limit was obtained. Notched specimens showed lower fatigue lives. Notched specimens with higher stress concentration factor (K_t) showed higher fatigue strength reduction factor (K_f). It was found that shallow notches of depth ~100 µm may reduce the fatigue life substantially.     

Effects of ion implantation on the microstructure and residual stress of filter arc CrN films

Chromium nitride coatings were deposited using a hybrid physical vapor deposition (PVD) system containing a filter arc deposition (FAD) and a metal plasma ion implantation source (MPII). Exactly how surface residual stress affects film characteristics is investigated using glancing incident X-ray diffraction (GIXRD) and pole figure analyses. Compared with unimplanted CrN, implanted carbon typically increases compressive residual stress and hardness. Wear resistance was also improved by implanted carbon.     

Demonstration of an in situ microscale fatigue testing technique on a titanium alloy

Under high cycle and very high cycle fatigue (HCF and VHCF) conditions, scatter in fatigue lifetimes is substantial; often 2–3 orders of magnitude. Characterization of fatigue crack initiation sites in laboratory scale fatigue specimens has led to the identification of characteristic initiation sites and microstructural arrangements. Despite these observations, in some cases, it is still unclear how apparently similar initiation sites exhibit such different total fatigue lifetimes. Differences in crack-initiation mechanisms can be further revealed if specific microstructural arrangements are isolated within a micro-specimen. Towards this end, an in situ microscale tension testing technique was adapted to enable microscale fatigue testing on tensile dog-bone specimens. Microscale tensile fatigue specimens with approximate gage diameters of 20 μm were prepared with a focused ion beam (FIB) microscope. Initial tensile experiments were conducted to characterize the mechanical behavior of microscale specimens for this microstructure. The microscale tensile specimens were observed to exhibit reduced yield and flow stresses in comparison to bulk tensile specimens. However, in this feasibility demonstration of in situ microscale fatigue testing, microscale specimens exhibit enhanced fatigue properties relative to conventional specimens, which may result from the differences in strain rate and, potentially, the method of test control (load vs. displacement) between these two testing methods. Both tensile and fatigue specimens have been characterized with electron backscatter diffraction to identify the neighborhood and the specific slip systems that were activated under local deformation conditions within the microstructure. Both basal and prism slip were observed, although prism slip was more prevalent. Results of the tension and fatigue experiments are discussed in the context of the growing body of literature on microscale testing, and avenues for future work are highlighted.     

Profiles of persistent slip markings and internal structure of underlying persistent slip bands

Focused ion beam sections and lamellae for transmission electron microscopy were prepared from fatigued specimens of polycrystalline copper and austenitic Sanicro 25 steel. The profiles of persistent slip markings developed on the surface were observed and documented simultaneously with the underlying dislocation structure. In copper fatigued at room temperature and close to liquid nitrogen temperature, persistent slip markings consisting of pronounced extrusions and parallel intrusions appeared at locations where persistent slip bands having the ladder‐like dislocation structure egress on the surface. Stage I cracks initiated from the tip of the intrusions. In Sanicro 25 steel, more planar character of the dislocation structure led to thin extrusions and intrusions and several stage I cracks running parallel to the primary slip plane. Exceptionally, ladder‐like structure and generally alternating dislocation‐rich and dislocation‐poor volumes were observed in the PSBs. Dislocations bands of secondary slip systems in the matrix disappeared on intersections with PSBs. Experimental findings were compared with predictions of recent physically based models of fatigue crack initiation.     

Cu注入PTC BaTiO3陶瓷的复阻抗谱研究

对传统工艺汉制备的ＢａＴｉＯ３陶瓷进行了Ｃｕ元素的离子注入。在较宽的频率范围内和不同温度下对样品进行了阻抗测量，确定了样品的等效电路。根据阻抗谱分析了Ｃｕ注入ＢａＴｉＯ３多晶陶瓷晶粒、晶界电阻与温度的关系。     

A finite element model of persistent slip band interaction with strengthened surface films during low cycle fatigue

Hardened surface layers such as those produced by ion implantation can inhibit the emergence of persistent slip bands (PSBs) at the free surface during low cycle fatigue, thereby extending crack initiation life. They have little effect, however, on bulk PSB formation. PSBs nucleated in the interior eventually impinge on the underside of the surface layer, producing localized cyclic shear strains in the film which lead to film rupture and rapid crack initiation. As a result, increases in fatigue life are modest. The present finite element model analysis shows that PSBs carrying plastic strains characteristic of fatigued f.c.c. metals produce stresses in an elastic surface layer which may exceed 1% of the surface film shear modulus. The detailed results are consistent with phenomenological data on surface damage accumulation during low cycle fatigue of ion-beam-modified nickel. Implications for the design of surface microalloys for inhibition of fatigue crack initiation are discussed.     

Infrared emission from selected areas in ion-beam-irradiated diamond

The infrared emission properties of an electrically heated single resistive element produced by ion implantation of diamond is reported. It is found that good contrast can be obtained between the implanted and unimplanted regions of the diamond mainly because of the increased emissivity following implantation. The infrared output is stronger if the diamond is viewed with the implanted surface facing away from the detector. The possible utilization of diamond-based pixels in infrared scene generation is discussed.     

Microstructural evaluation of fatigue damage in SA533-B1 and type 316L stainless steels

Transmission electron microscopy (TEM) examinations were made on fatigued SA533-B1 low alloy steel and Type 316L stainless steel specimens with the intention to investigate the mis-orientation changes among dislocation cells and the evolution of dislocation structures. Contrary to what might be expected for the cell structures, no clear relationship between fatigue damage and the mis-orientation changes of cell walls (or subgrain boundaries) was found in the fatigued samples of SA533-B1 steel (a bcc structure); however, significant changes of dislocation structures were observed in the fatigued samples of Type 316L stainless steel (an fcc structure). This could be accounted for by their different structures as well as complicated defect structures such as subgrain boundaries, small carbides, and dislocations inhomogeneously distributed in the SA533-B1 steel. It is interesting to note that at room temperature dislocations of fatigued SS316L specimens were observed to arrange themselves on {111} slip planes, in contrast, at 300°C the dislocations tend to move from their slip planes into subgrain boundaries in the surface layers rather than in the cross sectional layers.     

Relative Slip on Contact Surface under Partial Slip Fretting Fatigue Condition

Abstract:  A combined experimental–numerical approach was utilized to characterize the relative slip along the contact surface and its features under the partial slip fretting fatigue condition. Relative displacements at two locations on the substrate (specimen) and fretting pad were measured in fretting fatigue tests. These measurements were then utilized to validate finite element analysis. Effects of the coefficient of friction on the relative slip and contact condition were investigated. The stress state along the contact surface was also investigated. Two contact geometries were analysed: cylinder-on-flat and flat-on-flat. There was no change in relative displacement between locations away from the contact surface because of the change in the coefficient of friction, while relative slip on the contact surface was affected by coefficient of friction. In addition, stick/slip sizes were affected by the change in coefficient of friction. Comparison between present and previous finite element models showed that stress state, as well as a critical plane-based crack-initiation parameter, was not much different between these approaches, while relative slip on the contact surface changed considerably.     

Observation of fatigue damage in structural steel by scanning atomic force microscopy

Fatigue slip bands and plastic deformation around fatigue microcracks were observed by scanning atomic force microscopy. In fatigue slip bands, extrusions were observed but intrusions were not detected. Large extrusions were found in slip bands whose traces at specimen surface were almost perpendicular to the loading axis. Microcracks propagated under mixed mode condition of Mode I, Mode II, and Mode III.     

Effect of cutting speed and tool rake angle on the fatigue life of 2024-T351 aluminium alloy

Ring-shaped specimens of 2054-T351 aluminium alloy were machined orthogonally on a lathe equipped with a quick-stop device at cutting speeds of 0.5–1.5 m s^?1 with tools having positive rake angles in the range 10–30°. The machined specimens were then fatigued at a selected stress and the resulting fatigue lives were compared with that of the virgin material. The surfaces of the specimens were examined using optical and scanning electron microscopy.The fatigue life of the machined specimens was found to increase with increasing cutting speed or tool rake angle. The fatigue life of the specimens machined at higher cutting speeds was higher than that of the virgin material, due to the presence of compressive residual stresses in the surface layers. At lower cutting speeds the surface damage was so severe that, in spite of the presence of compressive residual stresses in the surface layers, the fatigue life of the machined specimens was lower than that of the virgin material.     

A microstructural and mechanical study on the effects of carbon ion implantation on zirconia-toughened-alumina

Biomedical grade (>99.97% purity) alumina, zirconia and zirconia-toughened-alumina (ZTA) have been implanted with carbon ions at a dose of 5 × 10¹⁷ C ions/cm² using an ion energy of 75 keV. The near-surface hardness of these bioceramics was examined using a load partial-unload indentation technique, both before and after implantation. The surfaces of the bioceramics have also been examined in cross-section using transmission electron microscopy (TEM) both before and after implantation and the implantation data correlated with a computer based simulation, TRIM (Transport and Range of Ions in Matter). The grinding and polishing treatment used prior to the implantation treatment has been found to have a strong influence on the surface microstructures for all three ceramics, although more significant modifications are brought about by carbon ion implantation. A comparison was made between the near-surface hardness of the unimplanted and carbon ion implanted surfaces of these bioceramics with relation to the modified microstructure. TEM examination of the implanted surfaces has demonstrated the formation of a sub-surface amorphous layer in all three materials as well as other microstructural modifications, such as microcracking and an increase in the near-surface dislocation density, that are characteristic of ion damage. The hardness data reveals that carbon ion implantation tends to decrease the surface hardness of alumina and zirconia with increasing ion dose, with a significant decrease occurring at the immediate near surface for both materials.