Nitriding and Denitriding of Nanocrystalline Iron System with Bimodal Crystallite Size Distribution

An artificially prepared nanocrystalline iron sample with bimodal crystallite size distribution was nitrided and denitrided in the NH3/H2 atmosphere at 350 °C and 400 °C. The sample was a 1:1 mass ratio mixture of two iron samples with mean crystallite sizes of 48 nm and 21 nm. Phase transformations between α-Fe, γ’-Fe4N and ε-Fe3-2N were observed by the in situ X-ray powder diffraction method. At selected steps of nitriding or denitriding, phase transformations paused at 50% of mass conversion and resumed after prominent variation of the nitriding atmosphere. This effect was attributed to the separation of phase transformations occurring between sets of iron crystallites of 48 nm and 21 nm, respectively. This was due to the Gibbs–Thomson effect, which establishes the dependence of phase transformation conditions on crystallite sizes.

INFLUENCE OF THE POURING DIRECTION ON THE QUALITY OF THE MELT ENTERING THE MOLD AND OBTAINING A GOOD STANDARD CAST IRON SAMPLE

The paper presents the results of computer simulation (on the example of grey cast iron of SCH 20 grade) of the influence of melt pouring direction on the degree of defects of shrinkage origin in the axial zone of the neck of a tensile sample when filling the mold cavity with a standard cast sample for optimal values of melt mass flow rate.

Impediment of Iron Corrosion by N,N′-bis[2-hydroxynaphthylidene]amino]oxamide in 3.5% NaCl Solution

Hydrazone [N,N′-bis[2-hydroxynaphthylidene]amino]oxamide] derived from the condensation of ethanedihydrazide with 2-hydroxynaphthalene-1-carbaldehyde was synthesized and assessed on the basis of elemental analysis (CHN) and spectral (IR, mass, 13C/1H NMR and UV-Vis) measurements. The influence of N,N-bis([2-hydroxynaphthylidene]amino)oxamide (HAO) in terms of the inhibition of iron corrosion in concentrated sodium chloride solution (3.5 wt.% NaCl) after various exposure periods was assessed. Numerous electrochemical and spectroscopic assessment techniques were performed. Cyclic potentiodynamic polarization experiments indicated that the presence of HAO and its increased concentration decreased the corrosion of iron in NaCl solution by decreasing the corrosion values, anodic and cathodic currents, and corrosion rate. The electrochemical impedance spectroscopy results showed that HAO molecules greatly increased the corrosion resistance. The chronoamperometric experiments performed at −475 mV (Ag/AgCl) revealed that the HAO molecules decreased the absolute currents and reduced the probability of the occurrence of pitting corrosion. The effect of HAO on the inhibition of iron corrosion was also confirmed through scanning electron microscopy micrographs and energy-dispersive X-ray profile analyses, which proved that the surface of the iron sample exposed to chloride solution alone was pitted, while the presence of HAO molecules reduced the severity of the pitting corrosion. The results confirmed that the presence of HAO molecules inhibits the corrosion of iron and this impact increased when the exposure time was increased to 48 h.

Improved grain mapping by laboratory X-ray diffraction contrast tomography

Laboratory diffraction contrast tomography (LabDCT) is a novel technique for non-destructive imaging of the grain structure within polycrystalline samples. To further broaden the use of this technique to a wider range of materials, both the spatial resolution and detection limit achieved in the commonly used Laue focusing geometry have to be improved. In this work, the possibility of improving both grain indexing and shape reconstruction was investigated by increasing the sample-to-detector distance to facilitate geometrical magnification of diffraction spots in the LabDCT projections. LabDCT grain reconstructions of a fully recrystallized iron sample, obtained in the conventional Laue focusing geometry and in a magnified geometry, are compared to one characterized by synchrotron X-ray diffraction contrast tomography, with the latter serving as the ground truth. It is shown that grain indexing can be significantly improved in the magnified geometry. It is also found that the magnified geometry improves the spatial resolution and the accuracy of the reconstructed grain shapes. The improvement is shown to be more evident for grains smaller than 40 µm than for larger grains. The underlying reasons are clarified by comparing spot features for different LabDCT datasets using a forward simulation tool.

Synergistic Behavior of Graphene and Ionic Liquid as Bio-Based Lubricant Additive

The constant utilization of petroleum-based products has prompted concerns about the environment, hence a replacement for these products must be explored. Biolubricants are a suitable replacement for petroleum-based lubricants as they provide better lubricity. Biolubricant performance can be improved by the addition of graphene. However, there are reports that graphene is unable to form a stable suspension for a long period. This study used a graphene-ionic liquid additive combination to stabilize the dispersion in a biolubricant. Graphene and ionic liquid were dispersed into the biolubricant via a magnetic stirrer. The samples were tested using a high frequency reciprocating rig. The cast iron sample was then further observed using various techniques to determine the lubricating mechanism of the lubricant. Different dispersion stability of graphene was observed for different biolubricants, which can be improved with ionic liquids. All ionic liquid samples maintained an absorbance value of three for one month. The utilization of ionic liquid was also able to decrease the frictional performance by 33%. Further study showed that by using the ionic liquid alone, the frictional could only reduce the friction coefficient by 13% and graphene could only reduce the friction by 7%. A smooth worn surface scar can be seen on the graphene-IL sample compared to the prominent corrosive spot on the IL samples and abrasive scars on graphene samples. This indicates synergistic behavior between the two additives. It was found that the ionic liquid does not only improve the dispersion stability, but also plays a role in forming the tribolayer.

Optimizing laboratory X-ray diffraction contrast tomography for grain structure characterization of pure iron

Laboratory diffraction contrast tomography (LabDCT) is a recently developed technique for 3D nondestructive grain mapping using a conical polychromatic beam from a laboratory-based X-ray source. The effects of experimental parameters, including accelerating voltage, exposure time and number of projections used for reconstruction, on the characterization of the 3D grain structure in an iron sample are quantified. The experiments were conducted using a commercial X-ray tomography system, ZEISS Xradia 520 Versa, equipped with a LabDCT module; and the data analysis was performed using the software package GrainMapper3D, which produces a 3D reconstruction from binarized 2D diffraction patterns. It is found that the exposure time directly affects the background noise level and thus the ability to distinguish weak spots of small grains from the background. With the assistance of forward simulations, it is found that spots from the first three strongest {hkl} families of a large grain can be seen with as few as 30–40 projections, which is sufficient for indexing the crystallographic orientation and resolving the grain shape with a reasonably high accuracy. It is also shown that the electron current is a more important factor than the accelerating voltage to be considered for optimizing the photon numbers with energies in the range of 20–60 keV. This energy range is the most important one for diffraction of common metals, e.g. iron and aluminium. Several suggestions for optimizing LabDCT experiments and 3D volume reconstruction are finally provided.

Intrinsic Mechanisms of Self-Healing in Metallic Structures

Self-healing is the ability of a material to repair damages automatically. Approaches to self-healing are separated into two major categories, those are: 1) autonomous healing methods that depend on intrinsic mechanisms, and 2) assisted healing methods that need an external intervention. Recently, computational methods have gained a wide application to study self-healing in metals using molecular dynamics (MD) and finite element (FE) methods. These methods can be used to demonstrate and optimize different metallic alloys potential to self-heal, and to further tailor these metallic structures toward improving their mechanical and fracture properties through self-healing. Computational studies of self-healing phenomenon in metals have been small in number and scope till recently. Therefore, the current paper starts with a general introduction of different mechanisms of intrinsic self-healing in metallic structures. The paper highlights previous studies using different experimental and computational approaches to explore self-healing in metallic systems, while focusing on Iron/Steel alloys. Furthermore, the paper present authors work to study self-healing and its impact on mechanical properties of Iron. Simulations are carried on bi-crystalline iron sample to investigate the effect of alloying elements diffusion on the fracture / healing properties of iron alloys and their impact on its mechanical properties. Then the effect of the alloying elements diffusion on healing is studied upon stress application after annealing. Different samples been compared to healthy samples and cracked samples without self-healing to demonstrate the effectiveness of self-healing in Iron alloys.

Validation Tests of Prediction Modules of Shrinkage Defects in Cast Iron Sample

The paper presents the results of experimental-simulation tests of expansion-shrinkage phenomena occurring in cast iron castings. The tests were based on the standard test for inspecting the tendency of steel-carbon alloys to create compacted discontinuities of the pipe shrinkage type. The cast alloy was a high-silicone ductile iron of GJS - 600 - 10 grade. The validation regarding correctness of prognoses of the shrinkage defects was applied mostly to the simulation code (system) NovaFlow & Solid CV (NFS CV). The obtained results were referred to the results obtained using the Procast system (macro- and micromodel). The analysis of sensitivity of the modules responsible for predicting the shrinkage discontinuities on selected pre-processing parameters was performed, focusing mostly on critical fractions concerning the feeding flows (mass and capillary) and variation of initial temperature of the alloy in the mould and heat transfer coefficient (HTC) on the casting - chill interface.

Ultrasonic Nanocrystal Surface Modification Assisted Nitriding: An Experimental Study

A powerful surface severe plastic deformation (SSPD) technique, ultrasonic nanocrystal surface modification (UNSM) has been used to treat pure iron to induce surface nanocrystallization. Transmission electron microscopy and surface profiler were used to study the microstructure and surface roughness after UNSM. Results indicate that the surface nanocrystallization with the controllable surface roughness was obtained. After that, gas nitriding of the nanocrystalline and microcrystalline iron was carried out and compared. X-ray diffraction, micro hardness testing and energy dispersive spectroscopy were applied to investigate the phase, micro hardness and distribution of nitrogen atoms in the iron sample after nitriding. It has been found that nitriding efficiency has been significantly improved in UNSM-processed samples than that in the non-processed samples as manifested by higher hardness and higher volume fraction of the nitride phase. With appropriate nanocrystallization, nitriding can occur efficiently at temperature as low as 300 °C.

The Influence of the Cooler Material on the Structure and Hardeness Gradient of a Grey Pearlitic Cast Iron

The structure and properties of grey cast iron castings are considerably influenced by the cooling rate during solidification. In order to obtain grey cast iron parts with a hard superficial layer (wear resistant), external metallic coolers are placed on those surfaces during casting. This is the case of cam pushers, camshafts, driving shafts, metalworking rolls, etc. Cast iron coolers or steel coolers are mostly used in practice. The cooling rate during solidification is influenced by the thermo-physical characteristics of the coolers. This paper presents the results obtained by simulation and experimental research on coolers material influence on the structure and hardness of the surface layer of a pearlitic cast iron sample. It was studied the solidification of samples with dimensions 20 x 20 x 60 mm, cast of pearlitic cast iron in six variants: without a cooler and in the presence of some metallic coolers of different thermo-physical characteristics (iron, steel, copper, titanium and aluminum coated with a thin layer of steel). It was studied the influence of cooler material on structure of the superficial layer, on thickness of the hardened layer, on superficial hardness, on the temperature field and cooling rates. Conclusions are drawn regarding these influences and the possibility of using external coolers in industrial practice.