Microstructure, tribological performances, and wear mechanisms of laser-cladded TiC-reinforced NiMo coatings under grease-lubrication condition

NiMo-5%TiC, NiMo-15%TiC, and NiMo-25%TiC coatings were prepared on GCr15 steel by laser cladding (LC). The microstructure and the phases of the obtained coatings were analyzed using ultra-depth-of-field microscopy (UDFM) and X-ray diffraction (XRD), respectively. A ball-on-disk wear test was used to analyze the friction-wear performance of the substrate and the NiMo-TiC coatings under grease-lubrication condition. The results show that the grain shape of NiMo-TiC coatings is dendritic. The wear resistance of NiMo-TiC coatings is improved by the addition of TiC, and the depths of the worn tracks on the substrate and on the NiMo-5%TiC, NiMo-15%TiC, and NiMo-25%TiC coatings are 4.183 μm, 2.164 μm, 1.882 μm, and 1.246 μm, respectively, and the corresponding wear rates are 72.25 μm3/s/N, 32.00 μm3/s/N, 18.10 μm3/s/N, and 7.99 μm3/s/N, respectively; this shows that the NiMo-25%TiC coating has the highest wear resistance among the three kinds of coatings. The wear mechanism of NiMo-TiC coatings is abrasive wear, and the addition of TiC plays a role in resisting wear during the friction process.

Solidification microstructure in a supercooled binary alloy

The maximum undercooling that has been achieved for Ni-Cu alloy, by using molten glass purification and cyclic super-heating technology, is 270 K. With the help of high-speed photography, the solidification front images of Ni-Cu alloy at various typical undercooling were obtained. Two grain refinements occurred in the range of 60 K< ΔT < 100 K and ΔT > 170 K, the solidification front became smoother, and the solidification position appeared randomly. With the increase of undercooling, the transition from solute diffusion to thermal diffusion leads to the transition from coarse dendrite to directional fine dendrite. At large undercooling, considerable stress is accumulated and some dislocations exist in the microstructure. However, the proportion of high-angle grain boundaries is as high as 89%, with twin boundaries of 13.6% and most strain-free structures, and the microhardness decreases sharply. This indicates that the accumulated stress at large undercooling causes the plastic strains in the microstructure, and in the later stage of recalescence, part of the plastic strains is dissipated by the system and acts as the driving force to promote the recrystallization of the microstructure.

Effect of graphite nanoplatelets on spark plasma sintered and conventionally sintered aluminum-based nanocomposites developed by powder metallurgy

In this work, aluminum (Al)-based nanocomposites reinforced with graphite nanoplatelets (GnPs) have been fabricated by conventional sintering as well as spark plasma sintering (SPS) techniques, and their microstructure and mechanical properties have been studied. The powder metallurgy (PM) route has been adopted to fabricate the various Al–GnP nanocomposites. Characterization of the powder mixtures and the nanocomposites has been carried out through different characterization techniques, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy. Compressive strength, Young's modulus, density, and Vickers microhardness of the various nanocomposites have also been determined. The HRTEM results show the formation of nonstoichiometric Al4C3 nanoparticles – during both conventional sintering and SPS – at the interface of the Al grains and GnP, which worsen the mechanical properties of the nanocomposites. SPSed nanocomposites show superior mechanical properties due to higher densification, finer grain size, and homogeneous nanofiller dispersion in the Al matrix, compared to the conventionally sintered Al–GnP nanocomposites.

The bandgap energy of the dilute bismuth GaBi x Sb1−x alloy depending on temperature

The bandgap energy of the dilute bismuth GaBi x Sb1−x alloy vs. temperature is investigated in this study. Its reduced temperature-sensitiveness is because of the localized character of the valence band states (VBS). In order to describe the reduced temperature-sensitiveness of the bandgap energy, a new term including localized energy is added to Varshni's equation. It is found that the localized energy exhibits an increasing trend as the bismuth fraction increases, which indicates that the localized character of the VBS becomes strong with the increasing bismuth fraction. It is also found that the influence of the bismuth fraction on the temperature dependence of the bandgap energy of GaBi x Sb1−x is smaller than that of GaBi x As1−x . In addition, the element indium is undoubtedly a good candidate to lessen the bismuth fraction to realize that the spin-orbit-splitting (SOP) energy surpasses the bandgap energy in GaBi x Sb1−x .

Stable aqueous dispersions of bare and double layer functionalized superparamagnetic iron oxide nanoparticles for biomedical applications

Superparamagnetic iron oxide nanoparticles (SPIONs) have attracted the particular interest of scientists from various disciplines since their obtaining to the present day. The physicochemical and pharmacokinetic properties of SPIONs-containing magnetic nanofluids, and their applicability in biomedicine, largely depend on the stability of the colloidal system, particle size, size distribution, net magnetic moment, phase composition, and type and properties of stabilizers. Also, in some cases, when using magnetic nanoparticles for biomedical purposes, it is necessary that the stabilizing ligands of nanoparticles should not significantly change the magnetic properties. From this point of view, the preparation of stable colloidal systems containing bare iron oxide nanoparticles (BIONs) in water at physiological pH attracts particular attention and becomes increasingly popular in scientific circles. This study is focused on the development of the synthesis of aqueous suspensions of SPIONs stabilized with various organic molecules (oleic acid [OA] and poly(ethylene glycol) monooleate - with molecular weights 460 and 860) using a modified controlled chemical coprecipitation reaction, as well as stable nanofluids containing BIONs in an aqueous medium at neutral pH (near-physiological). The obtained samples were characterized using X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy, small-angle x-ray scattering (SAXS), dynamic light scattering (DLS), electrophoretic light scattering (ELS), and Vibrating Sample Magnetometry.

Synthesis of a novel UV-curable prepolymer 1,3-bis[(3-ethyl-3-methoxyoxetane)propyl]tetramethyldisiloxane and study on its UV-curing properties

Precursor 3-ethyl-3-hydroxymethyloxetane was synthesized with trihydroxypropane and diethyl carbonate as the main raw materials. Intermediate 3-ethyl-3-allylmethoxyoxetane was synthesized with 3-ethyl-3-hydroxymethyloxetane and allyl bromide. Prepolymer 1,3-bis[(3-ethyl-3-methoxyoxetane)propyl]tetramethyldisiloxane was synthesized with 3-ethyl-3-allylmethoxyoxetane and 1,1,3,3-tetramethyldisiloxane. Cationic photoinitiator triarylsulfonium hexafluoroantimonate of 3 wt% was added to the prepolymer, and a novel kind of photosensitive resin was prepared. Structures of the compounds obtained at individual stages of the synthesis were analyzed and characterized by FTIR and 1H-NMR. Photo-DSC analysis showed that the prepolymer had excellent photosensitivity. Thermogravimetric analysis (TG) revealed that the ultraviolet (UV)-cured samples owned excellent thermal stabilities of up to 405°C. And the mechanical properties of the UV-cured samples were tested by the universal material testing machine, giving 25.95 MPa of tensile strength, 2,935.15 MPa of elastic modulus, and 4.09% of elongation at break.

Study of load bearing capacity of an infinite sheet weakened by multiple collinear straight cracks with coalesced yield zones

This paper is concerned with the analytical solution of a multi-side damage problem. The objective is to investigate the load-bearing capacity of an infinite elastic-plastic plate weakened by three pairs of collinear straight cracks with coalesced yield zones. Stress intensity factors (SIFs) are obtained when yield zones are subjected to three different patterns of yield stress distribution, i. e., constant, linearly, and quadratically varying. Muskhelisvili's complex variable approach is applied for uncovering the solution to this problem. The problem is solved and analyzed rigorously based on Dugdale's hypothesis. The numerical results are deduced for the load-bearing capacity of the plate and yield zone lengths. These results are analyzed and demonstrated graphically for various mechanical loading conditions and different crack lengths.

Microstructure refinement mechanism of undercooled Cu55Ni45alloys

Different undercooling degrees of Cu55Ni45 alloy were obtained by the combination of molten glass purification and cyclic superheating, and the maximum undercooling degree reached 284 K. The microstructure of the alloy was observed by metallographic microscope, and the evolution of microstructure was studied systematically. There are two occasions of grain refinement in the solidification structure of the alloy: one occurs in the case of low undercooling, and the other occurs in the case of high undercooling. Electron backscatter diffraction (EBSD) technology was used to analyze the rapid solidification structure under high undercooling. The features of flat polygonal grain boundary, high proportion of twin boundary, and large proportion of large angle grain boundary indicate recrystallization. The change in microhardness of the alloy under different undercooling degrees was studied by microhardness tester. It was found that the average microhardness decreased sharply at high undercooling degrees, which further confirmed the recrystallization of the solidified structure at high undercooling degrees.

2D and 3D numerical simulation of fatigue crack growth path and life predictions of a linear elastic

This paper describes implementation of the finite element method (FEM) to investigate crack growth problems in linear elastic fracture mechanics and the correlation of results with experimental and numerical data. The approach involved using two different software to compute stress intensity factors (SIFs), the crack propagation trajectory, and fatigue life estimation in two and three dimensions. According to the software, crack modeling might be run in various ways. The first is a developed source code program written in the Visual Fortran language, while the second is the widely used ANSYS Mechanical APDL 19.2 software. The fatigue crack propagation trajectory and the corresponding SIFs were predicted using these two software programs. The crack direction was investigated using the maximum circumferential stress theory, and the finite element (FE) analysis for fatigue crack growth was done for both software based on Paris's law. The predicted results in both software demonstrated the influence of holes on the crack growth trajectory and all associated stresses and strains. The study's findings agree with other experimental and numerical crack propagation studies presented in the literature that reveal similar crack propagation trajectory observations.

Cyclic behavior of precast concrete beam-column connection using steel fiber reinforced cast-in-place concrete

Three equivalent exterior precast concrete beam-column (PCBC) connections have been investigated in this study in orderto analyze the effect of steel fiber reinforced concrete (SFRC) as cast-in-place (CIP) on the seismic performance of the PCBC connection. The connection was designed as a ductile connection for a moment-resisting frame and consists of a precast U-beam, precast column with corbel, interlocking bars, and CIP-concrete to connect the precast beam to precast column. The volume fractions of steel fiber incorporated within the CIP-concrete were 0%, 0.5% and 1%. A quasi-static load was applied vertically to the beam tip of the PCBC specimen. The results showed that the steel fibers contained within the CIP-concrete provided 2% increase of the maximum load, 17.7% increase of the energy dissipation, and increase in the joint stiffness of the PCBC connection. The steel fibers delayed the onset of cracking and slowed down the crack propagation, resulting in shorter cracks in the joint core of PCBC specimen, which correlates well with the deflection-hardening characteristic found from the modulus of rupture test.