Sample Surface Research Articles

High Temperature Oxidation Behavior of ODS Ferritic Stainless Steel Fe-16Cr-4Al-1Ni-0.4Y<sub>2</sub>O<sub>3</sub>

This study investigates the isothermic oxidation behavior of the new ODS alloy Fe-16Cr-4Al-1Ni-0.4Y2O3 (% by weight) at 700, 800 and 900 °C, with exposure times of 5, 20, 50, and 100 h at each temperature. The purpose is to obtain new data on its high-temperature parabolic oxidation constant for assessing oxidation resistance. The methods used include isothermal oxidation testing, XRD, SEM-EDS characterization, and analysis of oxidation kinetics by monitoring changes in oxide thickness using microscopy and SEM-EDS. The oxide products formed on the sample surface are Fe2O3, Fe3O4, AlFe2O4, and (Fe,Cr)2O3. Al and Cr oxides are located under the dominant Fe oxide layer on the surface of the sample. The oxidation test results showed that the most protective sample was obtained at a temperature of 700 °C for 100 h with an oxide thickness of 263.99 μm. The kinetics analysis correlates strongly with the parabolic equation (R2 ≈ 1). The oxidation rate constants at temperatures of 700, 800, and 900 °C were 681.76, 2957.5, and 12300 μm2 h−1, respectively. The activation energy required by the oxidation reaction in this alloy is 136.5 kJ mol−1. This research enhances understanding and potential applications of the Fe-16Cr-4Al-1Ni-0.4Y2O3 alloy in high-temperature environments.

In-plane thermal conductivity measurements of Si μ-cantilevers using the suspended thermo-reflectance (STR) technique.

The Suspended Thermoreflectance (STR) technique is described in this paper. This optoelectronic measurement tool performs thermal characterization of freestanding micro-/nanoscale materials. STR performs thermal mapping at the submicron level and produces unconstrained thermal conductivity unlike other optical measurement techniques where independent conductivity measurement is not possible due to their reliance on heat capacity. STR works by changing the temperature of a material and collecting the associated change in light reflection from multiple points on the sample surface. Reflection is a function of the material being tested, the wavelength of the probe light, geometry, and the composition of the specimen for transparent and quasi-transparent materials. In this article, Si μ-cantilevers are studied. In addition, a thermal analytical model is developed and incorporated with optical equations to characterize the conductivity of the Si μ-cantilevers. The analytical model is compared with a finite element model to check its applicability in the STR experiment and data analysis. To validate the technique, the thermal conductivity of 2 and 3 µm thick Si μ-cantilevers was determined using STR at a temperature range of 20-350K and compared to simulations using the equation of phonon radiative transfer and literature values.

Establishment of Multi-Physics coupling model and analysis on thermal stress and crack risk in directional growth of TiAl alloys under electromagnetic confinement

The electromagnetic confinement directional solidification (EMCDS) technique is an optimal method for preparing large-size and non-contamination directional TiAl alloy crystals. Despite its advantages, the high temperature gradient inherent to this process induces thermal stress within the ingot, which increases the risk of cracking. To address this challenge, an innovative Integrated Multi-Physics Coupling Model was established to map and study the thermal stress field during EMCDS in this study. It synchronized the computation of the electromagnetic field, temperature field, solute field, flow field, and stress field during the crystal growth of TiAl alloy, and its high accuracy was proved by the micro-indentation experiment. Our analysis reveals that transverse temperature differences are crucial in inducing thermal stresses, and identifies that hot cracks and cold cracks are prone to occur respectively at the area of radial 23R along the sample (X = 23R) and on the sample surface, which aligns with experimental observations impressively. This model can more accurately and efficiently optimize the process parameters of the EMCDS process to avoid cracks and promote its industrial application.

Properties of Thin Film Composites of rGO–SnO2 and Modeling of Ultraviolet Laser‐Induced Conductivity Decay

AbstractReduced graphene oxide (rGO) and tin dioxide (SnO2) form composites in a wide range of SnO2/rGO proportions, which are deposited as thin films on borosilicate glass and silica substrates. The rGO proportion affects the SnO2 optical properties and the sample surface, as observed by optical transmittance and confocal and scanning electron microscopies images, mainly for high proportion of rGO. For low proportion, the presence of small surface islands may contribute to optical confinement. The evaluated bandgap is basically from the SnO2 matrix unless the presence of rGO affects the optical absorption edge. Monochromatic ultraviolet light from a He–Cd laser (325 nm) irradiating on the composite film increases the conductivity, giving rise to the phenomenon of persistent photoconductivity (PPC), even very close to room temperature. Modeling by considering mainly the SnO2/rGO interface barrier for electron transport, yield an interface energy barrier of 250 meV. The strong response to ultraviolet light and the phenomenon of PPC indicates potential application in amplifiers, which could be adjusted by doping with rare‐earth ions, such as Er3+ in the SnO2 matrix.

Isolating microbes from the surface of an introductory laboratory halite hand sample

Isolating microbes from the surface of an introductory laboratory halite hand sample

Shear mechanical behavior and fracturing path of red sandstone treated by joninted effect of water-fractures

Water content and primary fractures can change the mechanical characteristics of rock, making it easy to induce geological disasters. Therefore, direct shear tests of red sandstone under the action of water-fracture were carried out in this paper. The results show that shear strength of rock samples with fractures is less than that of intact rock samples. With the increase of primary fracture dip angle, shear strength and macroscopic crushing area of the rock sample increases first and then decreases with 20° as the boundary. It shows that the primary fractures weaken the shear mechanical properties and change the macroscopic failure mode. The shear performance of water-bearing rock samples is weaker than that of intact rock samples, and the weakening degree of water-saturated on shear performance of rock samples is lower than that of unsaturated water state. The fracture surfaces of rock samples are divided into 'shortest path single through type', 'longest path single through type' and 'cross path through type'. The failured rock samples are divided into 'single through type' and 'cross through type'. The research results can provide reference for geological disaster management under relevant conditions.

Study on A New Type of High Temperature Resistant Adsorption Type Retarded Acid System

Abstract Deep carbonate reservoirs present significant hurdles for reservoir stimulation due to extreme temperatures and rapid acid-rock reactions. The dense adsorption layer has the ability to postpone the interaction between rock and hydrogen ions, which is crucial for lowering the acid rock reaction rate. Based on the surfactant and film-forming agent’s synergistic impact, the retarding agent SH-1—which has the ability to generate a dense adsorption film on the surface of rock samples—was chosen for this study. After adding synergist and corrosion inhibitor, a new type of high temperature resistant adsorption type retarding acid system ’ 0.9% SH-1 + 20% HCl + 0.1% synergist + 1.5% corrosion inhibitor ’ was developed. The retarding performance of the retarding acid system at high temperature and various parameters of acid rock reaction kinetics were studied. The results show that the new adsorption-type retarded acid system can achieve good retarding effect at high temperature and ultra-high temperature, and the retarding rate is 90 % at 180 °C. In comparison to traditional hydrochloric acid, the new adsorption-type retarded acid exhibits a lower hydrogen ion mass transfer rate and a higher acid-rock reaction activation energy. These differences can effectively lower the acid-rock reaction rate. Additionally, an examination of the etching morphology reveals that the retarded acid is more easily etched along the cracks leading to the deep core. The novel adsorption-delayed acid offers excellent retarding power, high temperature resistance, and minimal damage. Consequently, it has certain reference value for the study of acidification transformation of ultra-high temperature deep carbonate reservoirs.

Study of the mechanisms of change in hydride phases in zirconium beryllide during its linear heating

Abstract Beryllides have a number of unique properties that make them promising for use in various fields of industry and energy. Since some of the beryllides have the potential to dissolve large amounts of hydrogen (in some cases forming hydride phases), there is some interest in evaluating their possible applications in hydrogen technologies. This paper presents the results of studies of changes in the phase composition of the zirconium beryllide deuteride compound during its linear heating. The studies were carried out using a complex method including thermal gravimetrical analysis (TGA), differential scanning calorimetry (DSC) and mass spectrometry. Based on the results of the experiments, a number of parameters were obtained characterizing the transitions of deuteride from the phase of the Orthorhombic I mma crystal structure of deuteride ZrBe2D into the Orthorhombic C mcm crystal structure of deuteride ZrBe2D0.67, as well as the decomposition parameters of Orthorhombic C mcm crystal structure of ZrBe2D0.67. The energies of endothermic reactions of the corresponding transitions and decompositions of deuteride phases were estimated, and the activation energy of the interaction of water vapor with the surface of zirconium beryllide samples was also estimated.

Cermet coatings obtained by electric spark alloying to increase service life of dental instruments

The article presents the results of our study of protective cermet coatings obtained by the method of electric spark alloying on a dental instrument (excavator) using SHS (self-propagating high-temperature synthesis) electrodes based on TiC-NiCr. The influence of discharge energy during electric spark alloying on the roughness, thickness, and proportion of the TiC carbide phase in the cermet coating has been established. It has been shown that during electric spark alloying, the material of the used SHS electrode and the surface of the substrate melt, their convective mixing occurs, and during crystallization, coatings are formed that consist of a strengthening phase TiC and iron-based solid solutions: Fe9.64Ti0.36, F1.88C0.12, and Cr-Ni-Fe-C. It has been found that the maximum size of TiC grains is formed on the surface of the cermet coating, and as they approach the substrate, their size decreases to less than 10 nm. It has been found that the microhardness of the surface of the resulting cermet coatings increased to 6.2 times compared to the microhardness of the original metal base, which was 2 GPa. The results of scanning electron microscopy and energy dispersive analysis of the surface of samples with and without cermet coating before and after corrosion tests are presented. The influence of disinfectants (2 and 100 % Trilox, Wendelin, MegaDes-ortho) on the corrosion resistance of samples with and without developed protective cermet coatings at room and elevated temperatures up to 50 °C and their exposure for 120 h has been established.

Mass finishing of additively manufactured AISI 316L using pecan nutshells as sustainable abrasive media

Abrasive processes represent the main methods for obtaining high-quality surface finish in metal parts. As one main characteristic, these processes have a relatively high consumption of energy per material volume removed, as well as many inputs, such as abrasive tools and equipment, and, consequently, a high associated environmental impact. Additive manufacturing is becoming a competitive method to produce customized parts, but the surface finish is often not good enough for the application, and post-processing is needed. In this work, a mass finishing process using a planetary mill with abrasive media made of sustainable materials (pecan nutshells) was used on AISI 316L stainless steel samples manufactured by selective laser melting (SLM). The main goal was to perform a multicriteria analysis of the sample surface before and after post-processing. Through the analysis, it could be observed that the nutshell abrasive media has results close to those of traditional ceramic media. The increase in the rotation speed of the planetary mill, increase of finishing time, and use of abrasive pastes can further increase the effectiveness of the process.

Microstructure and surface properties of Co-based brazed alloys coatings

Abstract The paper investigates the characteristics of two different manufactured high temperature brazed coatings using a cobalt based powder applied onto the surface of a stainless-steel substrate (AISI 904L). The coatings are intended to shield components exposed to high temperatures in an atmosphere where wear is expected. Energy dispersive analysis (EDX) together with scanning electron microscopy (SEM) was used to characterise the coating microstructure and morphology, and X-ray diffraction was used to identify the phase composition. Properties evaluations were carried out on the coatings’ surface characteristics, including hardness, erosion behaviour and hot corrosion resistance. The hot corrosion test was conducted at 650°C in a salt mixture that contained 75 wt. % sodium sulphate (Na2SO4) and 25 wt.% sodium chloride (NaCl). Alumina particles were used in the erosion tests, which hit the samples surface with an impact angle of 90°.The degree of corrosion attack, erosion behavior and hardness depended on the microstructure of the manufactured vacuum brazed coatings.

Friction and wear characteristics of DLC-terminated coatings deposited on AlSi10Mg alloy produced by Additive Manufacturing

Al–Si alloys are attractive materials for the fabrication of mechanical components, mainly because of their high strength-to-density ratio. Though the advent of Selective Laser Melting (SLM) has potentially expanded the range of their applicability, their poor tribological performances limit their effective use. Identifying post-processing protocols and coating strategies enhancing these properties and compatible with large-scale production is fundamental to the industrial uptake of SLM-fabricated Al–Si parts. This work tests the possibility of depositing self-lubricating Diamond-Like Carbon (DLC)-terminated films on AlSi10Mg built by SLM and subjected to different surface finishing processes. The applied coating architectures consist of an electroless nickel‐phosphorus buffer layer deposited on the AlSi10Mg surface, plus a series of interlayers and a DLC top film grown by Plasma Assisted – Chemical Vapor Deposition. The wear resistance and frictional behavior of the samples are evaluated for different substrate pre-treatments and coating assemblies under two applied loads. Cast substrates, processed and coated in a similar way, are also studied for comparison. The DLC film lends good tribological performances to all the coating-substrate combinations explored, being mechanically assisted by the underlying Ni–P layer. The friction coefficients stabilize around 0.20 at the lowest load, independently of the sample surface roughness (Sq), which spans the range 0.47–4.6 μm. Conversely, the counterpart wear rates increase with roughness up to 10−5 mm3/(N⋅m). Both tribological parameters decrease by nearly 20 % and 70 %, respectively, after a tenfold increase in load. These results indicate that DLC-terminated multilayers are extremely efficient on AlSi10Mg even in the presence of significant roughness. Their application requires a limited number of well-established processing steps also in the case of SLM grown parts.

Fracture resistance of pottery laminates with intentionally introduced defects

AbstractLaminated ceramics containing layers of pottery materials with high and low Young's moduli were developed to mimic the nacre structure of abalone shells with high resistances against dynamic fractures. The layers with the low Young's modulus moderated crack deflection and impact, thereby exhibiting a high fracture resistance. The ceramic pores were formed by the CO2 gas generated through the oxidation of SiC during firing. The dynamic fracture resistance was enhanced by elastic wave scattering owing to the difference between the Young's moduli of the dense and porous layers. The effect of lamination on the dynamic fracture resistance was observed because the elastic waves were scattered owing to the difference in the elastic modulus between the porous and dense layers, and their propagation to the back sample surface was suppressed. The fracture energy of the 5‐layer laminate was determined to be about four times larger than that of the dense monolayer, which indicates that the introduction of intentional defects is effective in improving the dynamic fracture resistance of the pottery ceramics.

Reprecipitation-mediated regulation on the surface architecture of uniform spray dried lactose microspheres

Lactose microspheres (LMs) are commonly used in the pharmaceutical field. Although the surface architecture of LMs directly correlates with the performance of the final products, surface manipulation remains challenging. In this study, uniform LMs were fabricated using template-assisted spray drying with polyethylene glycol 200 as the template. The influence of the solvent composition (methanol, ethanol, 1-butanol, and acetone, with and without added water) and post-treatment parameters (time and temperature) on the moisture content, particle morphology, surface architecture, and crystal polymorphism were investigated. The sample surfaces post-treated using methanol were covered with particulate crystals with a crystallinity of ∼88.3 %, whereas those treated using acetone were covered by coral-like crystals with a crystallinity of ∼80.6 %. This is attributed to the higher solubility of lactose in methanol than in acetone. Adding a small amount of water to the post-treatment solvent facilitated amorphous lactose reprecipitation, achieving a block-like crystal stacking surface with a more stable Lα∙H2O content (∼40.4 % w/w). Lα∙H2O enriched on the LM surfaces prevents water absorption during storage, thus maintaining their high dispersity, uniformity, and surface architecture. This study provides a promising strategy for tailoring the surface architecture of spherical crystalline lactose microspheres.

Local heating at the running crack tip in bcc iron according to molecular dynamics

Abstract This study presents estimates of a possible temperature rise at the crack tip from three dimensional (3D) atomistic simulations of fracture via molecular dynamics (MD) technique. Simulations start from an initial temperature of 0 K. The pre-existing edge crack was loaded in tension mode I. Crack initiation in MD is accompanied by surface dislocation emissions and later by a cross slip of the emitted dislocations into other slip systems. This leads both to stress waves radiation and to local heating in the plastic zone created by these dislocations. The local heating at the crack tip in the surface layers reaches a level of 480–500 K at some atoms, but an average temperature in the plastic zone is lower and depends on a chosen crack tip zone size. In the bulk crystal, where no dislocation emission (i.e. no plastic zone) has been realized, no significant heating is observed at the crack tip. MD results at the free sample surface comply with experimental data for ferritic steels with a pre-existing notch, loaded (quasi-statically) in mode I, as well as with some continuum predictions.

Relationships between pollen assemblages and modern vegetation of the southern Gaoligong Mountains region, southwest China

Comprehensive understanding of the modern pollen–vegetation relationship is crucial for utilizing fossil pollen to reconstruct palaeovegetation, especially in mountainous areas of southwestern China. In this study, we present forty-five modern surface samples collected from five different vegetation communities of the southern Gaoligong Mountains region, and the vegetation composition was investigated at each sample site. The modern pollen assemblages were analyzed through multivariate analysis to evaluate the relationships between vegetation types and pollen assemblages, and to investigate the representation of major pollen types in different vegetation types. The results indicate that the surface pollen assemblages of different vegetation types reliably represent the modern vegetation. The median R-values of dominant pollen taxa in the Gaoligong Mountains region can be ordered as follows: Pinus > Alnus > Poaceae > evergreen Quercus. The over-representation of Pinus pollen, attributed to its high productivity and strong dispersal ability, makes it the dominant component of exotic pollen. Conversely, the under-representation of evergreen Quercus suggests that the presence of its pollen within a sample might indicate the growth of the local parent plant in the study area. The human activities in the region have a recognizable effect on the surface pollen spectra and also exert a significant negative impact on pollen diversity. Our study supplements the modern pollen database of the mountain regions in southwestern China, and provides representative modern pollen analogues to interpret fossil pollen records from southwestern China and similar regions.

Mechanism of Boron Carbide Oxidation in a Dry Environment

ABSTRACT We analyze in detail the published experimental data on the high-temperature oxidation of compact boron carbide in dry oxygen in the range of 600–1200°C. The results of the analysis show that the oxidation of boron carbide occurs with the accumulation of excess (compared to stoichiometry) boron. Using experimental data, the time dependences of the thickness of the boron oxide melt layer formed on the sample surface during its oxidation and the mass of boron oxide evaporated from the sample surface are determined. For different temperatures, the evaporation rates of boron oxide are determined. Based on the analysis, a model of the high-temperature oxidation of compact boron carbide in dry environment was developed. Using the developed model, calculations of the process of boron carbide oxidation at different temperatures were carried out. Based on the results of calculations, the time dependences of the mass of the sample, the mass of the resulting carbon dioxide, and the thickness of the boron oxide melt layer were determined. The calculation results are compared with the experimental data and with the theoretical temperature dependence of the boron oxide melt evaporation rate, calculated using the Hertz – Knudsen equation. Based on the simulation results, it is concluded that the rates of chemical reactions are finite, and the process of B4C oxidation cannot be reduced only to oxygen diffusion through the boron oxide layer.

(10–13)-oriented semipolar GaN growth on (10–10) m-plane ScAlMgO4 substrate

Abstract We report the growth of a GaN layer on (10–10) m-plane ScAlMgO4 (SAM) substrate. The GaN layer demonstrated (10–13) preference growth orientation. The anisotropy of the crystalline quality was distinctly observed through X-ray rocking curve taken across the sample surface over various azimuths across the orthogonal directions [0001] and [1–210] of the SAM substrate. Notably, the crystalline quality exhibited gradual degradation as the substrate is rotated around its surface normal away from the c-direction [0001] of the SAM substrate toward the a-direction [11–20]. Additionally, basal stacking faults in the (10–13)-oriented GaN were observed along [0001] direction using scanning transmission electron microscopy. Moreover, the selected area electron diffraction analysis was utilized to confirm the (10–13) growth orientation that was found to be consistent with the X-ray diffraction result. The (10–13) GaN layer exhibited a metal face through integrated differential phase contrast imaging.

Effect of isothermal cooling on solidification behaviour of peritectic steel under in situ observation

In order to improve the volume shrinkage of peritectic steel during solidification, the solidification path of peritectic steel was changed by adjusting the cooling mode in this article. The solidification behaviour of peritectic steel under isothermal cooling conditions was studied by in situ observation experiment. The transformation shrinkage degree was reflected by sample surface roughness. The results show that the solidification path under the isothermal cooling is L→L+δ-Fe→δ-Fe→δ-Fe+γ-Fe without peritectic reaction. Moreover, the sample surface morphology was flat under isothermal cooling, and no granular morphology was observed. The surface roughness was 2.55 μm under isothermal cooling, which is much lower than that under different continuous cooling conditions. The surface roughness decrease indicates the solidification volume shrinkage is reduced. Therefore, the risk of cracking can be decreased by adjusting the cooling mode to control the solidification pattern of peritectic steel.

Prevention of hot cracking in Ni-based superalloy via passivation layer formation during additive manufacturing

We investigated the prevention of hot cracking in a non-weldable Ni-based superalloy by utilizing a passivation layer formed through laser-based directed energy deposition. The addition of Hf to the Ni-based superalloy facilitated the formation of a passivation layer consisting of Hf oxide on the surface of the as-deposited sample. An increase in the amount (thickness) of the passivation layers with increasing Hf content resulted in a reduction in hot cracking occurrence. Specifically, the addition of 2.5 wt% Hf led to the formation of uniformly distributed fine oxides without inducing hot cracks. This passivation layer effectively inhibited the formation of coarsened Mo oxides, which typically occur during oxidation in the liquid state and contribute to the hot cracking of Ni-based superalloy. During oxidation in the liquid state, Hf diffuses out to the surface and forms a passivation layer, thereby suppressing the formation and growth of oxides to sizes large enough to induce hot cracking.