Evolution of defects in titanium grade 2 under Ti2+ ion irradiation

The complexity and diversity of microstructure involved in titanium alloys make it rather difficult to quantitatively describe defect evolution due to irradiation. This paper focuses on defect evolutions of commercially pure titanium grade 2 under Ti²⁺ ion irradiation considering the effect of dose (0.6 and 3 dpa), temperature (300°C and 430°C) and flux (15:1 ratio). An irradiation damage profile was predicted using SRIM software to obtain a homogeneous damage on at least 500 nm depth for TEM observations and simulated using JANNUS‐Saclay facility. The details regarding the quantification methodologies of the defects from dark field images are provided, as are the origins of the associated uncertainties. In addition to a tangled dislocation network, presence of the <a>‐type and <c>‐component loops is observed. The latter was scarcely reported in the literature in the case of titanium alloys. At low temperature, the size distribution of the <a>‐type dislocation loops remained similar regardless of the dose and flux whereas these parameters have highly influence at 430°C. A widening of the size distribution and an increase of the threshold incubation dose (TID) was noted with the temperature. In the case of the <c>‐component loops, it was shown that the nucleation occurred in spite of the 0.6 dpa low dose.     

Investigation on the properties of gamma irradiated of polytetrafluoroethylene fibers

The physical, thermal, and chemical properties of gamma‐irradiated polytetrafluoroethylene (PTFE) fibers were investigated using X‐ray diffraction (XRD), differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy. Scanning electron microscopy (SEM) was also used to analyze the surface morphology of irradiated fiber samples. PTFE fiber samples were irradiated by gamma radiation doses ranging from 3 kGy to 40 kGy. The XRD analyses and DSC measurements showed the improvement of crystallinity by gamma irradiation with dose up to 25 kGy reflecting the induced crosslinking with irradiation for PTFE fibers. The crystallinity was found to decrease with higher dose of 40 kGy, reflecting induced amorphization of the polymer sample at the high radiation dose. The calculated crystallite size and XRD parameters showed obvious variations with sample irradiation. The FTIR results showed the liberation of CF₂ groups and the formation of some new chemical bonding with crosslinking‐induced irradiation. The SEM micrographs revealed no variation in the surface morphology of the irradiated fiber samples than the pristine fiber.     

Characterisation of lattice damage formation in tantalum irradiated at variable temperatures

The formation of radiation‐induced dislocation loops and voids in tantalum at 180(2), 345(3) and 590(5)°C was assessed by 3MeV proton irradiation experiments and subsequent damage characterisation using transmission electron microscopy. Voids formed at 345(3)°C and were arranged into a body centred cubic lattice at a damage level of 0.55 dpa. The low vacancy mobility at 180(2)°C impedes enough vacancy clustering and therefore the formation of voids visible by TEM. At 590(5)°C the Burgers vector of the interstitial‐type dislocation loops is a<100>, instead of the a/2 <111> Burgers vector characteristic of the loops at 180(2) and 345(3)°C. The lower mobility of a<100> loops hinders the formation of voids at 590(5)°C up to a damage level of 0.55 dpa.     

Effects of 10 MeV electron irradiation at high temperature of a Ni-Mo-based Hastelloy

A Hastelloy alloy was irradiated with 10 MeV electrons at 650 degrees C for 700 h to a total dose of 2 x 10(-3) displacements per atom (dpa). The microstructure of irradiated and non-irradiated specimens of this alloy were investigated by transmission electron microscopy (TEM). The non-irradiated specimens were analyzed by 3-D atom probe tomography (APT) in a local-electrode atom-probe (LEAP). TEM analysis before the irradiation detects small precipitates with a mean diameter of 22 nm, which are coherent with the FCC matrix. The number density of these precipitates is approximately 7 x 10(18) m(-3). Electron diffraction patterns from these precipitates exhibit superlattice reflections corresponding to the L1(2) ordered structure. The chemical composition of the precipitates, as measured by APT, is around 75 at% Ni with additions of Al, Ti and Mo. After electron irradiation, small precipitates with an irregular morphology are observed. The number density of these new precipitates about 10(20) m(-3) is greater than that of the L1(2) ordered precipitates before irradiation. The L1(2) superlattice reflections disappear completely, instead diffuse diffraction spots are observed at 1(1/2)0(FCC), which is attributed to compositional short-range order (SRO). The results are discussed with respect to the influence of the electron irradiation on the morphology and structure of the ordered precipitates.     

Effect of gamma irradiation on the physical and structural properties of basalt fiber

Digital holographic interferometry (DHI), X‐ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR) and scanning electron microscopy (SEM) were used to study the effects of gamma irradiation on the physical and structural properties of basalt fibers. For this purpose, set samples of basalt fibers were subjected to different doses of gamma irradiation (3, 10, 25, and 40 kGy). The Mach–Zehnder interferometer was used to capture holographic patterns which are used then to determine the unwrapped phase. From the unwrapped phase distributions, the optical path difference within the irradiated basalt samples was determined. Thus, refractive indices, and birefringence of irradiated basalt fibers were determined at different irradiation doses using DHI method. XRD technique was used to investigate the effect of irradiation doses on the crystalline behavior of fibers. FTIR was performed to each of the basalt samples to evaluate the changes in the surface chemical properties due to radiation exposure doses. The morphology of irradiated fibers was examined using SEM. The results indicate that basalt fiber has a resistance to gamma radiation. There are no significant effects on the physical, structural and chemical properties were demonstrated of basalt fibers in the doses range of irradiation.     

New developments in the characterization of dislocation loops from LACBED patterns

The characterization of the Burgers vector of dislocations from large‐angle convergent‐beam electron diffraction (LACBED) patterns is now a well‐established method. The method has already been applied to relatively large and isolated dislocation loops in semiconductors. Nevertheless, some severe experimental difficulties are encountered with small dislocation loops. By using a 2 µm selected‐area aperture and a carbon contamination point to mark the loop of interest, we were able to characterize both the plane and the Burgers vector of dislocation loops of a few tens of nanometres in size present in Al‐Cu‐Mg alloys.     

Assessing the corrosion–wear behaviours of Hastelloy C276 alloy in seawater

A systematic investigation has been carried out in the present work to study the electrochemical and corrosion–wear behaviours of Hastelloy C276 alloy sliding against Al₂O₃ pin in artificial seawater, using a pin‐on‐disc tribometer integrated with a potentiostat for electrochemical control. It can be observed that the cathodic shift of open circuit potential and three order of magnitude increase of current density formed due to sliding. The total corrosion–wear loss increases with increasing applied potential. Interestingly, the total material loss at the applied potential of 0.5 and 0.9 V is more than two times of that of pure mechanical wear, confirming the synergy between wear and corrosion. And, the contributions of wear‐induced corrosion (ΔK_c) and corrosion‐induced wear (ΔK_w) are dominant, especially at higher applied potentials. Copyright © 2015 John Wiley & Sons, Ltd.     

Observations of lattice defects using the weak-beam technique

The advantages of the weak-beam technique of electron microscopy for the study of small defects and dislocations are illustrated by micrographs taken of small loops in aluminium and Al–Ag alloys, GP zones and θ″ precipitates in Al + 4% Cu, and dislocation networks in Cu + 20% Zn. An estimate of 19·5 mJ m^?2 (erg cm^～2) is made for the stacking-fault energy of Cu–20% Zn from the size of extended nodes and the width of the dissociated dislocations imaged under weak-beam conditions.     

Synergistic effects of anisotropy and image force on TEM diffraction contrast of dislocation loops

Based on column approximation (CA) assumption, many-beam Schaeublin–Stadelmann diffraction equations are employed for simulating the transmission electron microscopy (TEM) diffraction image contrast of dislocation loops within thin TEM foil of finite thickness, and two beam and many beam diffraction conditions are compared. Moreover, the effects of materials anisotropy and free surface relaxation induced elastic fields distortion of dislocation loops on the black-white image contrast are specially focused. It is found that anisotropy has a remarkable impact on the TEM image contrast of dislocation loop, and free surface relaxation induced image forces can change the black-white contrast features when dislocation loops are near TEM foil free surfaces. Thus, in order to make reliable judgment on the nature of defects, effects of free surface and anisotropy should be included when analysing irradiation induced dislocation loops and other type of defects in in-situ electron, proton, heavy-ion irradiation experiments under TEM environments.     

Transmission Electron Microscope Investigations Of Defects Produced By Individual Displacement Cascades In Si And Ge

Monocrystalline {111} Si and Ge specimens have been irradiated with atomic and molecular heavy ions in order to study the influence of the cascade energy density and the interaction between displacement cascades on the defect production. Transmission electron microscope (TEM) studies were performed to investigate the defect parameters. After atomic irradiation of Si and Ge the defects analysed (typical size 3–5 nm) are of interstitial type. Both defects with three-dimensional strain centres and defects with a strongly asymmetric strain field were observed. An analysis of the yield and the defect size in Si as a function of ion dose suggests that the defects are formed within individual cascades rather than by a process involving overlapping cascades. Changes of the energy density locally deposited in the lattice do not affect yield and size significantly. Under otherwise similar experimental conditions, the average defect depth is significantly larger for Bi₂+ irradiations than for Bi+ irradiations.     

Effect of Ca addition on the microstructure and mechanical properties of as‐cast Mg–Sm alloys

This study investigated the effect of Ca addition on the microstructure and mechanical properties of as‐cast Mg–4Sm alloys. The addition of 1.0 wt% Ca led to a significant grain refinement of Mg–4.0Sm alloys owing to the formation of rod‐like Mg2Ca phases that acted as active nucleates for the Mg matrix. The as‐cast Mg–4.0Sm–1.0Ca alloy showed the smallest grain size at 45 μm. Furthermore, the Mg–4.0Sm–1.0Ca alloy exhibited greater hardness, higher tensile strength, and higher yield tensile strength and elongation than the other two alloys with different Ca contents. These results were attributed to the grain refinement and precipitation strengthening of the Mg2Ca and Mg41Sm5 phases. Microsc. Res. Tech. 79:707–711, 2016. © 2016 Wiley Periodicals, Inc.     

Effect of titanium carbonitride (Ti(C,N)) decomposition on failure mechanisms in inconel 617 alloy

Titanium Carbonitride (Ti(C,N)) decomposition in Inconel 617 alloy creep‐exposed at 650°C for 574 hours is reported using analytical electron microscopy techniques. Cr‐enriched M₂₃C₆‐type carbides enveloped in fine gamma prime particles thought to be precipitated from the decomposition reaction are observed in the alloy. The morphology of the M₂₃C₆ carbides is irregular and blocky and the particle size up to 5μm, whereas the morphology of gamma prime particles is mostly spherical and up to 30 nm in size. Intergranular carbides are mostly secondary precipitates of the M₂₃C_c type (M predominantly Cr) and these respond to solution heat treatment and precipitate on the grain boundaries as a result of ageing. The ability of intragranular MX to decompose is sensitive to the N content, high N resists decomposition. Decomposed intragranular MX provides an excess source of C which can react locally with Cr to form heat treatable intragranular fine Cr₂₃C₆ precipitates. M₆C can segregate in interdendritic locations during melting which may be the reason for high content of Mo in M₂₃C₆. These precipitates are generally very small and contribute to an additional hardening effect and are the reason for the onset of voiding and cracking along the grain boundaries that ultimately lead to a reduced creep rupture life. Microsc. Res. Tech. 78:336–342, 2015. © 2015 Wiley Periodicals, Inc.     

Weak-beam observation of dislocation loops in silicon

Weak-beam microscopy has been used to examine the dislocation loops formed when ion implanted silicon is annealed in the temperature range 900–1300 K. The extinction distances of about 10 nm, resulting from the use of large deviation parameters S' enable stacking fault fringes of 4nm spacing to be resolved in faulted loops. The projected shape of the dislocation loops and the variable contrast along the perimeter of the bounding partial dislocation enables the habit planes of the dislocation loops to be determined from inspection. These together with the width of the dislocation image, which is about 3 nm enables the type of loop to be characterized completely from a single micrograph.     

Mouse calvarial defect Model: An approach for the micro‐tomographic evaluation of polymer scaffolds

The ability of bone repair scaffolds to form bone is traditionally evaluated using cell culture and animal experiments. Mouse calvarial organ culture maintains the natural cell‐to‐cell and cell‐to‐matrix relationships as well as the anatomical order, and this model has been used to study the biological behavior of intramembranous bones. The aim of this study was to evaluate the potential of mouse calvarial organ culture to be used as an in vitro model to study the bone regenerative ability of bone repair polymer scaffolds. Critical size defects (CSD) were created in the parietal bones. Electrospun poly(ε‐caprolactone) scaffolds were placed into one group of defects. The remaining defects served as a control. The bones were cultured for 38 days and analyzed with μCT, phase‐contrast microscopy, dissecting microscopy, scanning electron microscopy, and energy‐dispersive X‐ray analyses. This organ culture technique is easily available and could permit researchers to quickly establish a valuable database of candidate bone repair scaffolds. Microsc. Res. Tech. 77:1037–1043, 2014. © 2014 Wiley Periodicals, Inc.     

Morphology of Co–Cr–Mo dental alloy surfaces polished by three different mechanical procedures

The present study aims at characterizing the three‐dimensional (3‐D) morphology of a Co–Cr–Mo dental alloy surface as a result of three different procedures used for polishing it. The sample surface morphology of the sampled surface was examined employing atomic force microscopy (AFM), statistical surface roughness parameters, and fractal analysis. An extra‐hard dental alloy of cobalt–chromium–molybdenum (Co–Cr–Mo) (Wironit^®, from BEGO, Bremen, Germany) was prepared and moulded. Different polishing treatments were carried out on three groups of six samples each—a total of 18 samples. The first group contained six electropolished (EP) samples. The second group containing six samples went through a mechanical polishing process employing green rubber discs and a high shine polishing paste applied by a rotating black brush (BB). The third group comprising six samples as well went through a mechanical polishing process by means of green rubber discs, high shine polishing paste, and a rotating deer leather brush (DL). Fractal analysis on the basis of a computational algorithm applied to the AFM data was employed for the 3‐D quantitative characterization of the morphology of the sampled surfaces. The fractal dimension D (average ± standard deviation) of 3‐D surfaces for BB samples (2.19 ± 0.07) is lower than that of the DL samples (2.24 ± 0.08), which is still lower than that of the EP samples (2.27 ± 0.09). The results indicated the BB samples as presenting the lowest values of statistical surface roughness parameters, thus the best surface finish, while the EP samples yielded the highest values. Microsc. Res. Tech. 78:831–839, 2015. © 2015 Wiley Periodicals, Inc.     

On‐axis versus off‐axis Transmission Kikuchi Diffraction technique: application to the characterisation of severe plastic deformation‐induced ultrafine‐grained microstructures

A new configuration for Transmission Kikuchi Diffraction (TKD) in a scanning electron microscope is presented; called ‘on‐axis TKD’. Compared to the usual off‐axis configuration, the scintillator is placed perpendicular to the incident beam under the electron‐transparent sample, not in vertical position. In this way, the setup benefits from intense forward scattered electrons enabling short acquisition times. At equivalent diffraction pattern quality, the electron dose needed on the sample is estimated to be 20 times lower in comparison to the off‐axis configuration. The technique is particularly suited to the characterisation of severe plastic deformation induced ultrafine grained microstructures. The evolution of the microstructure of an Al–Mg alloy deformed by high pressure tube twisting was analysed. It is shown that the grain refinement was in the steady state stage for a shear strain of 24 with a mean grain size of 120 nm.     

Formation and elimination of surface ion milling defects in cadmium telluride,zinc sulphide and zinc selenide

The nature of damage produced by low energy Ar⁺ ion and Ar atom milling in the II–VI semiconductors CdTe, ZnS and ZnSe is studied in detail by conventional and high resolution transmission electron microscopy. It is demonstrated that the damage consists of dense arrays of small dislocation loops near to each milled surface. When ion or atom milling of this type is used for thin specimen preparation prior to microscopy the loop arrays can seriously obscure images and so complicate their interpretation. This problem concerning the presence of artifactual defects can be greatly reduced by the use of reactive I⁺ ion milling for specimen thinning and, in the case of CdTe, spurious dislocation loop formation can be completely suppressed.     

Finite element analysis of the head–neck taper interface of modular hip prostheses

The purpose of this paper was to identify which parameters influence the micromotion at the head–neck taper interface of modular hip prostheses. Finite element analysis was performed where 3D models of the head–neck taper interface were subjected to an assembly force, 3300 N of compression, and 100 N of tension. The micromotion increased as the head size, assembly force, and taper size increased. The micromotion also increased when a mixed alloy material combination (CoCr head and Ti6Al4V neck) was used instead of all CoCr alloy prosthesis and when the center of the femoral head was in a more superior position relative to the center of the neck taper.     

Multiple-Shockley unfaulting of single-layer faulted defects

The general principles laid down by Swart & Kritzinger (1974a) in a paper dealing with the unfaulting of Frank dislocation loops by the simultaneous action of two shearing Shockley dislocations are applied to explain the structure and electron diffraction contrast behaviour of certain complex single-layer dislocation configurations observed in quenched aluminium and dilute Al-Mg alloys. In these cases the simultaneous operation of three Shockley dislocations is employed. It is also demonstrated that adequate stresses, such as those encountered during annealing at temperatures ～150°C, serve to transform butterfly hexagons to normal hexagonal prismatic dislocation loops, confirming the expectation that the butterfly defects are in a metastable state.     

Atomic structure of extended defects in boron-implanted silicon layers

The structure of extended defects introduced into Si by means of boron implantation followed by thermal annealing at T = 900 °C is studied by the method of high-resolution transmission electron microscopy and computer modeling for different values of the implantation dosage (D) and concentration of boron atoms in substitutional positions B₀ \((C_{B_0 } )\) injected into the Si lattice before implantation. It is shown that the Frank dislocation loops of both interstitial (I) and vacancy (V) type at a ratio of 4: 1 are observed in Si samples with D = 10¹⁶ cm^?2 up to \(C_{B_0 } \) = 0.8·10²⁰ cm^?3. The atomic structure of the I-type Frank dislocation loops is heavily deformed, which suggests segregation of finely dispersed boron in the defect plane. At the same time, the structure of the V-type Frank dislocation loops tends to be reconstructed due to interaction with self-interstitials. At \(C_{B_0 } \) = 2.5·10²⁰ cm^?3, the I-type Frank dislocation loops are found to transform to perfect dislocation loops, and boron precipitates with a high density appear in Si. Based on the results obtained, probable reasons for vacancy deficit formation in boron-implanted Si are discussed.