Microstructural Investigations Research Articles

Critical role of slags in pitting corrosion of additively manufactured stainless steel in simulated seawater

Pitting corrosion in seawater is one of the most difficult forms of corrosion to identify and control. A workhorse material for marine applications, 316L stainless steel (316L SS) is known to balance resistance to pitting with good mechanical properties. The advent of additive manufacturing (AM), particularly laser powder bed fusion (LPBF), has prompted numerous microstructural and mechanical investigations of LPBF 316L SS; however, the origins of pitting corrosion on as-built surfaces is unknown, despite their utmost importance for certification of LPBF 316L SS prior to fielding. Here, we show that Mn-rich silicate slags are responsible for pitting of the as-built LPBF material in sodium chloride due to their introduction of deleterious defects such as cracks or surface oxide heterogeneities. In addition, we explain how slags are formed in the liquid metal and deposited at the as-built surfaces using high-fidelity melt pool simulations. Our work uncovers how LPBF changes surface oxides due to rapid solidification and high-temperature oxidation, leading to fundamentally different pitting corrosion mechanisms.

Sustainable Treatment Approach to Dumped Construction Waste with Acids and CO2 for its Effective Re-utilization in Concrete

<p>Dumping of construction wastes has become one of the serious concerns in the construction industries subsequent to the scarcity of construction materials, specifically aggregates. Extensive research works have been performed to utilize the dumped waste as aggregates, yet its substandard properties affect the concrete. Furthermore, several treatments were proposed to improve the quality of aggregates such as microbial, slurry etc, but the brittleness of concrete remains unavoidable. This research discusses the effect of acid treatment and carbonation treatment on recycled concrete aggregates (RCA) and the impact of hybrid fibres on concrete properties. The steel fibres (SF) and polypropylene fibres (PF) were optimized to 1.5% and 1.0% with 100% treated RCA to assess the concrete's hardened properties and water absorption. The study reports that the carbonation treatment to RCA performs better compared to acid treatment and the mix with the use of hybrid fibres shows enhanced properties than single fibres. The strength of the mix with 100% carbonated RCA 1.5% SF and 1.0% PF was 57% higher than that of recycled aggregate concrete (RAC) and the water absorption of similar mix was found to be lower than other mixes. Microstructural investigations through SEM and XRD were also performed to support the research findings.</p>

Microstructure investigation, Electrical properties, and γ-rays’ protection capacity for ZnO doped clay ceramic

A series of ceramic samples fabricated based on ZnO doped different concentrations of natural clay according to the relation (1-x) ZnO – (x) clay; 5 wt% ≤ x ≤ 20 wt%. The samples were pressed and sintered at 1200 °C. The experimental techniques were used to characterize and measure the chemical composition, density, and current-voltage measurements for the fabricated ceramics samples. The measurements depict an increase in the I–V nonlinearity with raising the clay concentration, where the increase in clay by up to 20 wt% shifts breakdown voltage to a higher value of up to 390 V/cm and decreases leakage current to 55 mA/cm2. The examinations for the gamma-ray shielding capacity for the fabricated composites (utilizing Monte Carlo simulation) demonstrate enrichment of clay concentration between 5 wt% and 20 wt% reduced the linear attenuation coefficient for the fabricated ceramics by 23.15% and 8.66% at γ photon energy of 0.059 MeV and 1.252 MeV, respectively. The half-value thickness and lead's equivalent thickness increased along with a drop in the linear attenuation coefficient, but the radiation protection effectiveness of the fabricated ceramics increased.

Development and directed energy deposition of high strength Hf5Mo15Nb35Ta25Ti20 refractory high entropy alloys

In this study, a novel HfMoNbTaTi refractory high entropy alloy was designed by empirical calculations and CALculation of PHAse Diagram (CALPHAD) method by using ThermoCalc software. Directed energy deposition (DED) based additive manufacturing process was used to produce the alloy. After the process parameter determination studies using single-track productions, cuboids were produced. The microstructural investigations showed that while the central region of cuboids has large grains, the outer region has a dendritic structure with some unmolten Mo powders. Although columnar grain formation, which is the general characteristic of directional solidification, was observed at some points, irregularly shaped grains were dominant in the structure. Moreover, there were micron to nano-sized Hf-Ti-O particles inside the grains and especially around the grain boundaries. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses confirmed the formation of disordered body-centered cubic (BCC) Hf5Mo15Nb35Ta25Ti20 alloy with ∼6 vol% of Hf-Ti-O particles. Electron backscatter diffraction (EBSD) analyses indicated that there is a slight texture in the building direction along 〈111〉. In order to determine the stability of these alloys, ex-situ heat treatments coupled with XRD studies were conducted. As opposed to CALPHAD calculations it was not observed any HCP phase formation. Compression test results showed that Hf5Mo15Nb35Ta25Ti20 alloys have high strength (σy = ∼1300 MPa) and high compressive ductility with good strain-hardening ability. Theoretical calculations revealed that the strength of the alloy mainly originated from solid solution strengthening.

Effects of Al3Ni compound on localized plastic deformation and creep strain of Al/Si hypoeutectic material

The mechanical resistance of AS10/xNi hypoeutectic alloy with (x = 0.05% and 0.1%) has been investigated. Vickers hardness (HV) was determined for the samples before and after sintering. All samples were subjected to a compressive creep test at a constant temperature of 298 K and a constant load of 45 MPa. Creep parameters, such as creep rate, sensitivity (m), time exponent (n), β, and ɣ have been calculated and related to the Ni content. Microstructure investigation was conducted using the scanning electron microscope technique (SEMT). After sintering, the results showed that there was a significant improvement in the hardness with the addition of nickel. There is an increase in creep resistance as a result of the distribution of Al3Ni chemical compound across grain boundaries, which stops additional dislocation movement and hence reduces the creep rate.

Multi-scale investigation of microstructure and texture evolution during equal channel angular pressing of silver

A multi-scale investigation was carried out on pure silver subjected to equal channel angular pressing up to 3 passes. Microstructure and texture were examined using scanning and transmission electron microscopy as well as diffraction of neutron and high-energy synchrotron radiation. The evolution of the deformation substructure in the material is in accordance with its low stacking fault energy followed by restoration mechanisms leading to overall microstructural refinement. The restoration mechanism sets in as early as after 3 passes. Twinning involved in the deformation process supports grain refinement through mechanisms of dynamic recrystallization involving strain-induced boundary migration contributing to a steady-state grain size. The global texture, as measured by neutron diffraction, forms through a twin-assisted deformation mechanism. The texture is found heterogeneous through thickness.Graphical abstract

Investigation of Microstructure, Microhardness and Thermal Properties of Ag-In Intermetallic Alloys Prepared by Vacuum Arc Meltings

Investigation of Microstructure, Microhardness and Thermal Properties of Ag-In Intermetallic Alloys Prepared by Vacuum Arc Meltings

Enhancing formability of Ti-6Al-4V cylindrical cups by pulsating hydroforming process: Experimental, numerical and microstructural investigations

Ti-6Al-4V alloy sheet is an engineering material that is widely used due to its superior properties such as high strength-to-density ratio besides high temperature and corrosion resistance. However, its low formability at room temperature limits its wider applications. In this study, a cylindrical cup was hydroformed using a female die to examine how the pulsating effect would result under frictional conditions. Initially, finite element simulations were performed to design a proper die geometry. Next, forming tests were run on Ti-6Al-4V blanks under pressure increased monotonically and with pulsation, and microstructural analyses were performed on the formed specimens. The effects of pulsation frequency, amplitude, and base pressure on the formability were investigated. The nose radius/thickness ratio, maximum thinning, bursting pressure, and die-filling ratio measured on the specimens formed under monotonic and pulsating loadings were compared, and the improvement in the formability was demonstrated. An increase of 38.5 % in bursting pressure occurred and the nose radius of the part was decreased up to 30 % with pulsating loading. The die-filling ratio was improved from 87.9 % to 95.3 % with optimized pulsation parameters. The underlying microstructural reasons for the improved formability were elaborated using XRD, SEM, and TEM analyses.

Microstructural investigation of concretes with recycled aggregates using X-ray microtomography

Recycled aggregates (RA) derive from reprocessed materials from construction and demolition activities. Although the use of RA has been growing worldwide, material standardization and new mix design protocols still need to be developed to enable its use on larger scales. For this, an investigation of the properties of this material is necessary. The present study used microcomputed tomography (microCT) to observe the material's porous structure in cylindrical concrete samples of reference concrete (RC) with natural aggregates and sustainable concrete (SC) with the addition of RA. Through a computational routine, the images obtained were evaluated qualitatively and quantitatively. The pore volume and shape in concretes with and without recycled aggregates were analyzed and correlated with their respective compressive strengths. Even though the SC samples' resistance was lower than the RC samples, the values found followed the required standards. Porosity, pore volume, and shape were similar for the two kinds of concrete. The Pore Network Modeling (PNM) approach was applied to characterize further the pores' spatial distribution and connectivity. The analysis showed that 98.20 % and 97.26 % of the pores were disconnected for the RC and SC samples, respectively. The results indicate that the addition of RA is not detrimental to the properties of concrete. Further PNM-based analysis can help evaluate both samples' absolute and relative permeability to various fluids.

Structure, Phase Composition, and Mechanical Properties of ZK51A Alloy with AlN Nanoparticles after Heat Treatment

The paper studies the influence of the content of aluminum nitride nanoparticles on the structure and mechanical properties of the ZK51A magnesium alloy. The microstructure investigations with optical and electron microscopy show that 1 wt.% AlN promotes the best grain refinement and size distribution. According to tensile strength testing of the ZK51A alloy, grain refinement is not a dominating mechanism in the property improvement of the alloy after heat treatment. The maximum values of mechanical parameters are achieved at the lowest (0.1 wt.%) content of aluminum nitride. The main mechanism of mechanical characteristics increase with the addition of AlN nanoparticles is dispersion hardening.

Microstructural characterisation of grain size effect on creep properties of 304HCu SS

The influence of grain size, in the range of 10 to 180 μm, on creep properties of 304HCu stainless steel (SS) was evaluated at 180 MPa and 923 K. A 30 μm grain size showed a peak in creep life and minimum in steady-state creep rate with low damage potential. Detailed microstructural investigations revealed an increase in the tendency to intergranular fracture at grain sizes above 30 μm, whereas ‘transgranular fracture coupled with isolated intergranular cracks/cavities’ have been observed with decreasing grain size from 30 to 10 μm.

Triple structuration and enhanced corrosion performance of 316L in laser powder bed fusion

This work focuses on the influence of the feedstock powders on the microstructural properties and corrosion behavior of 316 L stainless steel (SS) produced by laser powder bed fusion (L-PBF) from two different suppliers. Microstructural investigations conducted after additive manufacturing reveal many particularities depending on the powders. These microstructural differences lead to a different corrosion behavior in boiling nitric acid containing oxidizing ions. The presence of the triple structuration (grains, large cells, small internal cells) shows a positive effect on intergranular and cellular corrosion resistance. In both cases, L-PBF 316 L SS provides better resistance to intergranular corrosion than wrought 316L SS.

Structural, microstructure, spectroscopic, and magnetic investigation of vanadium‐doped SrTiO3 perovskite ceramics

AbstractIn this study, we provide the synthesis and analysis of the structure, microstructure, and spectroscopic properties of V‐doped SrTiO3. The monophasic samples were made using the usual ceramic method, which involved calcination at temperatures of 1000°C and 1300°C. The X‐ray diffraction analysis, combined with the Rietveld refinement, conclusively demonstrates that they have crystallized in a cubic structure, namely under the space group . The inclusion of vanadium (V) at the titanium (Ti) site has been investigated by evaluating the size of the crystallite and grain. The investigation of dielectric and dissipation factors at different frequencies indicates the existence of interfacial and orientational polarization. Two distinct conduction and relaxation processes were identified within the temperature range examined based on the spectroscopic plot. The presence of a paramagnetic phase in the samples, caused by the presence of V and its magnetic interaction with oxygen vacancies, indicates that it can be classified as a soft magnetic material. The electrode's consistent dielectric constant and dissipation factor make it well‐suited for use in supercapacitor dielectric capacitors. Additionally, its mixed‐type conduction, involving both ionic and electronic conduction, makes it excellent for use as electrode materials in intermediate‐temperature solid oxide fuel cells’ applications.

Composite Materials of Epoxy Resin–W System for Radiation Shielding Against Gamma Radiation

Сomposite materials based on the epoxy resin–W system with varying W content (0–80 %) were obtained using the method of chemical curing. Microstructural investigations of the samples showed that with increasing W content there is a more uniform distribution of grains in the epoxy resin matrix could be observed. Agglomeration of W grains is noted for samples with filler content up to 40 %. Statistical analysis of the grain size of the initial W powder revealed that the probable diameter of W grains is 475 nm. The values of effective and relative densities of the experimental samples were obtained using the Archimedes method. The effective density varied from 1.16 to 4.36 g/cm3 with W powder content rising. The relative density values received ranged from 91 to 94 %, indica ting that there were no significant defects in the samples. X-ray diffraction analysis showed the presence of vcc-W and WO2 phases, indicating the oxidation of W in the thin surface layer of the powder. Calculation in Phy-X/PSD software allowed to evaluate the gamma radiation shielding efficiency for the epoxy resin–W system composite materials in 0.8–2.5 MeV energy range. It was observed that samples with filler content of 60 and 80 % were the most suitable for radiation shielding. It was found that the addition of W powder to the epoxy matrix contributed to the reduction of half attenuation layer values by 3.5 times from 9.448 to 2.672 cm for samples with 0 and 80 % W content, respectively, for 1.25 MeV radiation energy. The obtained results demonstrate the high efficiency of the proposed composite materials for shielding gamma radiation, which makes them a perspective candidate for manufacturing radiation shields.

Study on mechanical and micro structural properties of spin arc welding in Hastelloy C-2000

Nickel-based Hastelloy C-2000 is widely used in the aerospace, chemical, and medicinal sectors. Investigating the potential efficacy of the spin arc welding process on Hastelloy C-2000 was the main focus of this study. In spin arc welding the centrifugal force has been obtained in the fusion zone, thus the weldbead quality increases. Weld current, rotating speed, and spin diameter are all separate parameters used in the welding procedure. The microstructural investigation was carried out using optical microscopy, X-Ray Diffraction (XRD), and field emission scanning electron microscopy (FESEM). The mechanical characteristics of the welded specimens were examined closely. Spin Arc Welding ultimate tensile strength (UTS), hardness value (HV), and impact experiments were compared to those of the Multi-pass Pulsed Current Gas Tungsten Arc welding method (MPCGTAW). In 27 tests, increasing the current and rotating speed resulted in greater penetration depth and weld height. The width of the weld was found to be a little high, with a spinning diameter of 2 mm. In comparison, samples 5 and 15 were found to have better hardness, tensile strength, and toughness, especially with suitable welding parameters such as current (120 I and 140 I), speed (1800 rpm), and spin diameter (2 mm and 3 mm). A microstructural study showed no grain segregation, contributing to the material’s increased hardness and tensile strength. The novel findings of the present study suggest that spin arc welding might be superior for various Hastelloy C-2000 connections that might have great applications in industries.

Structural patterns and ages of Permian-Triassic multistage strike-slip faulting in the Chifeng area, southeastern Inner Mongolia, China: Implications for the final closure of the Paleo-Asian Ocean

The closure of the Paleo-Asian Ocean (PAO) to the north of the North China Craton (NCC) holds significance in comprehending the Phanerozoic continental evolution of East Asia. However, the timing of the final closure of the PAO, tectono-magmatic records of this process in the northern margin of the NCC, and related geodynamics remain to be resolved. Here we undertaken detailed macro- and micro-structural investigations on the E-W-striking and NNE-striking fault system in the Chifeng area, northern edge of the NCC. Combined with new zircon U-Pb and muscovite 40Ar/39Ar dating, we delineated three phases of strike-slip faulting in the research region during the Permian-Triassic, including WNW-ESE-striking and NE-SW-striking ductile sinistral shearing at ∼ 270–258 Ma and 258–246 Ma, respectively, and subsequent ∼ E-W-oriented ductile–brittle dextral shearing at ∼ 230–209 Ma. Based on analysis of paleotectonic stress fields, we propose that the first two-stage deformation shared a regional unified N-NNE contractional setting, while the late ∼ E-W-striking dextral shearing reflected a distinct regional NNW-SSE shortening event. The regional magmatism reveals three age peaks of ∼ 270 Ma, ∼250 Ma and ∼ 230 Ma, corresponding well to the above three-phase deformation. Further, zircon Hf isotopic data imply that the composition of juvenile material in regional deep-seated crust gradually increased from Permian to Triassic. The N-NNE contraction may be controlled by the eastward scissor-like final closure of the PAO during the Middle Permian-Early Triassic. The middle-late Late Triassic NNW-SSE contraction is likely influenced by the remote effect of the low-angle southward subduction of the Mongol-Okhotsk oceanic plate.

Comparative Analysis of Tribological Behavior in Aluminum Matrix Composites Incorporating Fe75Si15Zr5B5 Metallic Glass and SiC Particles

In this study, a comparative investigation was conducted to assess the impact of Fe-based metallic glass (FMG) and silicon carbide (SiC) reinforcing particles on the tribological properties of aluminum matrix composites. The composites were synthesized using the powder metallurgy method, and subsequent dry sliding wear tests were performed by a pin-on-disc machine at ambient temperature. Thorough examinations of the microstructure, mechanical properties, and densification behavior were carried out for the developed composites, and these findings were then correlated with their wear performance. To gain insights into the wear mechanisms, comprehensive characterizations of the worn surfaces and debris were conducted utilizing field-emission scanning electron microscopy (FESEM) and energy-dispersive spectroscopy (EDS) analysis. The outcomes of the dry sliding tests revealed that, in contrast to SiC, the addition of FMG reinforcing particles significantly decreased the friction coefficient while concurrently enhancing the wear resistance of the aluminum matrix. The microstructural investigations divulged that the pure aluminum sample experienced severe abrasive and adhesive wear mechanisms, which were effectively mitigated through the incorporation of FMG particles, due to the formation of an oxide tribolayer in the composite during the wear test. Conversely, the SiC-reinforced composites exhibited a dominant wear mechanism characterized by severe delamination, which consequently contributed to their elevated wear rate. These findings shed light on the distinct effects of FMG and SiC particles on the tribological properties of aluminum matrix composites, providing valuable insights for potential applications in engineering and industrial sectors, particularly in scenarios involving metal-to-metal contact.

Investigation of production conditions of interstitial-free steels in electric arc furnace

The iron and steel industry has had a strategic importance throughout history. In recent years, with the development of technology and sectoral competition, new investments have been investigated. One of them is Interstitial-Free (IF) steels. Interstitial-Free Steel, containing very small amounts of carbon and nitrogen, is used in the production of automotive interior and exterior panels. IF steel structures have high formability. This feature has been obtained by removing interstitial atoms such as C and N in vacuum degassing method. In addition, remaining of these elements can be stabilized in steel by adding Ti and/or Nb. After the steel production process is completed, the slab is heated to a certain temperature in the heating furnace. The finishing and coiling temperatures are also important factors in determining the deep-drawing capability. These parameters help in obtaining the coarse TiC and NbC precipitates and the high r value, which is an important indicator of fine-grained structure, high ductility and formability. In this study, the effect of process parameters on IF steels in electric arc furnace steel production, secondary metallurgy processes and hot rolling are explained. Also, the effect of microstructures of steel samples with different chemical compositions and thicknesses on mechanical properties was investigated. In addition, the samples taken from the hot rolled coil were examined under scanning electron microscope (SEM), and texture analysis was performed with electron backscatter diffraction (EBSD) technique. Particularly, the microstructure investigations have shown that Ti and/or Nb is the critical element in terms of ensuring the formability, so interstitial atoms are not formed

Permissible domain walls in monoclinic MAB ferroelectric phases.

The concept of monoclinic ferroelectric phases has been extensively used over recent decades for the understanding of crystallographic structures of ferroelectric materials. Monoclinic phases have been actively invoked to describe the phase boundaries such as the so-called morphotropic phase boundary in functional perovskite oxides. These phases are believed to play a major role in the enhancement of such functional properties as dielectricity and electromechanical coupling through rotation of spontaneous polarization and/or modification of the rich domain microstructures. Unfortunately, such microstructures remain poorly understood due to the complexity of the subject. The goal of this work is to formulate the geometrical laws behind the monoclinic domain microstructures. Specifically, the result of previous work [Gorfman et al. (2022). Acta Cryst. A78, 158-171] is implemented to catalog and outline some properties of permissible domain walls that connect `strain' domains with monoclinic (MA/MB type) symmetry, occurring in ferroelectric perovskite oxides. The term `permissible' [Fousek & Janovec (1969). J. Appl. Phys. 40, 135-142] pertains to the domain walls connecting a pair of `strain' domains without a lattice mismatch. It was found that 12 monoclinic domains may form pairs connected along 84 types of permissible domain walls. These contain 48 domain walls with fixed Miller indices (known as W-walls) and 36 domain walls whose Miller indices may change when free lattice parameters change as well (known as S-walls). Simple and intuitive analytical expressions are provided that describe the orientation of these domain walls, the matrices of transformation between crystallographic basis vectors and, most importantly, the separation between Bragg peaks, diffracted from each of the 84 pairs of domains, connected along a permissible domain wall. It is shown that the orientation of a domain wall may be described by the specific combination of the monoclinic distortion parameters r = [2/(γ - α)][(c/a) - 1], f = (π - 2γ)/(π - 2α) and p = [2/(π - α - γ)] [(c/a) - 1]. The results of this work will enhance understanding and facilitate investigation (e.g. using single-crystal X-ray diffraction) of complex monoclinic domain microstructures in both crystals and thin films.

Investigation of weld bead geometry and microstructures of 316L stainless steel in Activating flux TIG Welding using ultrasonic vibrations

Investigation of weld bead geometry and microstructures of 316L stainless steel in Activating flux TIG Welding using ultrasonic vibrations