Atom probe tomography analysis of the white etching layer in a rail track surface

Atomic scale characterization of the white etching layer (WEL) in a rail track surface made of pearlitic steel was performed with respect to elemental distribution using atom probe tomography. The atomic distributions of the alloying elements at various depths below the surface were analyzed inside and outside the WEL. Manganese-enriched and silicon-depleted zones corresponding to pre-existing cementite lamellae were observed in the WEL, although the cementite lamellae of the matrix pearlite had completely decomposed. The manganese-enriched and silicon-depleted zones were more distinct in the bottom region than in the topmost surface region of the WEL. The width and spacing of the zones indicated that the WEL region did not undergo heavy deformation. A temperature rise in the rail-to-wheel contact areas was predicted by friction calculation, which was confirmed through shape analysis of the manganese-enriched zones. These results support the hypothesis that martensitic transformation after rapid austenization was the origin of the WEL.     

Atom probe tomography study of the decomposition of a bulk metallic glass

The microstructural evolution of a Pd₄₀Ni₄₀P₂₀ bulk metallic glass that was isothermally annealed at 260 °C for 14 h, and then aged at 340 °C for times up to 1280 min has been studied. Differential scanning calorimetry (DSC) curves of the aged samples show an endothermic peak at approximately 370 °C in addition to the ubiquitous glass transition. The endothermic peak appears after 20 min aging and disappears after 320 min aging. The corresponding X-ray diffraction (XRD) data show no Bragg peaks that could indicate the formation of a crystalline phase. Near-atomic-resolution atom probe tomography (APT) was used to study changes in the atomic spatial distributions as a function of aging time. The chemical environment around each of the atomic species, and the tendencies for solute clustering and chemical short range ordering, were determined from statistical analysis of the APT data. Clustering and possible phase separation are identified by APT after only 20 min aging at 340 °C, which correlates with the appearance of the peak in the DSC signal. Crystallization is apparent in the APT and XRD data after aging for 320 min. The study suggests that the amorphous Pd₄₀Ni₄₀P₂₀ annealed at a temperature 40 °C above T_g phase separates into two or more amorphous phases. The endothermic peak in the DSC trace is produced by the dissolution of the phase separation.     

Atom probe tomography of nanoscaled features of oxide-dispersion-strengthened ODS Eurofer steel in the initial state and after neutron irradiation

Atom probe tomography has been used to investigate nanoscale features in the yttrium oxide dispersion strengthened steel ODS Eurofer, which is a perspective structural material for the reactor cores. In the initial material, a large number (∼2 × 10²⁴ m⁻³) of ultrafine (∼2.5 nm in diameter) clusters enriched in yttrium, oxygen, nitrogen, and vanadium have been revealed. The investigation of the ODS Eurofer steel irradiated at 330°C to 32 dpa in the BOR-60 fast reactor has also revealed a large number of ultrafine (1–3 nm in diameter) nanoclusters significantly enriched in yttrium, oxygen, manganese, and chromium. In the irradiated material, an increase in the concentration of clusters and changes in the chemical composition of the clusters and matrix have been noted. The irradiation by fast neutrons leads to a partial transition of vanadium from the clusters into the surrounding matrix and to a general increase in the concentrations of yttrium and oxygen in the volumes under investigation.     

Analysis of strengthening in AA6111 during the early stages of aging: Atom probe tomography and yield stress modelling

In this work, a series of aging treatments has been conducted on AA6111 alloy samples for various times at ambient temperature (so-called natural aging) and at temperatures between 60 and 180 °C (artificially aged). The time at artificial ageing was chosen such that samples with approximately the same yield stress were produced. The microstructures of these alloy samples have been carefully characterized using atom probe tomography together with advanced cluster-finding techniques in order to obtain quantitative information about the changes in distribution of both the solute clusters and early-stage precipitates that are formed. The size distribution of clusters has been mapped onto the glide plane and then the stress necessary for a dislocation to pass through the range of obstacles has been estimated using an areal glide model where the dislocation–obstacle interaction strength has been assumed to be related to the obstacle size on the glide plane. It is demonstrated that the contribution of cluster strengthening during artificial aging at higher temperatures is dominated by the high number density of small clusters (Guinier radius <1 nm), whereas the situation during room temperature natural aging is more complex.     

Atom probe study of sodium distribution in polycrystalline Cu(In,Ga)Se2 thin film

This article reports the first investigations of CuIn_1?xGa_xSe₂ (CIGSe) polycrystalline thin films by means of atom probe tomography. Attention is focused on the distribution of Na atoms within the films. Both Na-containing and Na-free CIGSe thin films have been investigated. When Na is available during the CIGSe coevaporation, it is observed to be mainly segregated at the grain boundaries of the films; however, it is also detected within the grains of CIGSe at very low concentration.     

Measurement of the saturated dislocation pinning force in hydrogenated nickel and nickel base alloys

Static strain ageing experiments are used to measure the saturated dislocation pinning force as a function of the hydrogen concentration in hydrogenated nickel and binary nickel—16 wt% chromium. The role of hydrogen transport by mobile dislocations on hydrogen embrittlement is demonstrated.     

Chromaluminizing of nickel and its alloys

Chromaluminide diffusion coatings on nickel and nickel-base superalloys, EI 867 and IN 100, have been formed by a two-step pack cementation technique. The effect of pack composition on coating formation and structure has been discussed. It has been stated that the appropriate choice of coating parameters enables the enrichment of aluminide coating in chromium either near its surface or near the coating/substrate interface.     

Oxidation of hafnium alloys with nickel

Conclusions Alloying of hafnium with 2–8% Ni substantially increases its scale resistance, evidently due to formation of HfNi at the scale-alloy interface, which along with the intermetallic phases substantially reduces the solution of oxygen in the alloys.Institute of Problems of Material Sciences, Academy of Sciences of the Ukrainian SSR. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 23–26, March, 1975.