Dense Product Research Articles

Effect of Al content on mechanical properties and corrosion performance of novel Fe-Cr-Al alloy steels in a CO2-O2 coexistence environment

The present study involved preparing five novel Fe-Cr-Al alloy steels with varying Al content based on commercially available 3Cr steel. The effect of Al content on the mechanical properties and corrosion performance in a CO2-O2 coexistence environment was investigated in novel Fe-3Cr-(0–2.5)Al alloy steels, and the microhardness, impact, and tensile properties were measured and compared. The corrosion rate, corrosion product film, and corrosion mechanism were studied using a weight-loss method, microscopic characterization, and electrochemical tests. The results showed that the tensile and impact properties of Fe-Cr-Al alloy steels exhibited a decreasing trend with increasing Al content. No localized corrosion was observed at an Al content of 2 wt%, attributed to the formation of a dense amorphous corrosion product film on the material surface and pre-passivation. Among the alloy steels examined in this study, the 3Cr2Al alloy steel exhibited the most optimal balance between mechanical properties and corrosion resistance.

Mixed‐alkali effect in the thermal collapse and melting kinetics of Zeolite X

AbstractThe thermal stability of zeolites underlies their many applications. Structural collapse usually occurs through a series of reactions, involving an initial low‐density amorphous state (LDA), a high‐density melt (HDA), and, eventually, a dense recrystallization product. The LDA–HDA transition resembles a glass melting process; the HDA phase can sometimes be quenched into a glass. Using isothermal as well as nonisothermal in situ observation methodology on the faujasitic zeolite X and its potassium‐for‐sodium ion‐exchanged derivatives, we find a pronounced mixed‐alkali effect in the characteristic nonisothermal transition temperatures as well as in the isothermal reaction timescale of the LDA–HDA transition. The latter is taken as being directly related to the viscosity of the liquid into which the zeolite framework is melting; the apparent viscosity associated with this melting process was found to reach as high as 1015 Pa.s at 740°C. The observed mixed‐alkali effect is similar to the one observed in the dynamics of common oxide glasses and their corresponding melts.

Investigating the mechanical properties and corrosion resistance of extruded Mg-1Zn-xCaO (x=0, 0.5, 1.0 wt%) materials

The effect of nano-CaO content on the microstructure, mechanical properties, and in vitro degradation performance of extruded Mg-1Zn alloys was investigated to enhance the strength and corrosion resistance of biodegradable materials for medical implants. The results showed that the addition of CaO nanoparticles effectively refined the size of dynamic recrystallization grains in the extruded composites. During the extrusion process, Ca2Mg6Zn3 and Mg2Ca phases precipitated in the Mg-1Zn-0.5CaO and Mg-1Zn-1CaO composites, respectively. As the CaO content increased, the basal texture strength was elevated from 3.97 for the Mg-1Zn alloy to 12.05 for the Mg-1Zn-1CaO composite. Benefiting from the combined mechanisms of grain refinement, dislocation strengthening, and precipitation strengthening, the yield strength of the materials was fortified with an increase in CaO content. During the short immersion time, the matrix of the extruded Mg-1Zn-0.5CaO composite was preferentially corroded, resulting in the formation of a dense corrosion product layer that impeded the transport of ions in the electrolyte solution, thereby exhibiting the lowest annual corrosion rate. With an increase in the immersion time, galvanic corrosion destroyed the protective film, leading to a slightly higher corrosion rate in the extruded Mg-1Zn-0.5CaO composite compared to the Mg-1Zn alloy. The substantial nano-Mg2Ca phase particles were preferentially degraded, causing severe pitting corrosion in the extruded Mg-1Zn-1CaO composite, which exhibited the highest degradation rate. The extruded Mg-1Zn-0.5CaO composite exhibited superior overall properties; its yield strength, elongation, and annual corrosion rate after immersion (21 d) were 334.9 MPa, 8.9 %, and 1.06 mm/y, respectively.

Hydrogen permeation behavior of X80 pipeline steel under alternating wet-dry environment in the South China Sea

The riser sections of offshore pipelines are subject to cathodic potentials, alternating wet-dry (AWD) cycles and stresses in the service environment. The hydrogen permeation of X80 offshore pipeline with different cathodic potentials, dry/wet ratios, and constant tensile stress in AWD environment were investigated by the self made experimental equipment, which includes the three modules, i.e., the constant stress loading, the two-component cell hydrogen permeation, and AWD environment. Results showed that hydrogen permeation current fluctuates with the AWD, which is different from that in the bulk solution. In one AWD cycle, the permeation increases in the wetting stage and decreases in the dry stage. The smaller the dry/wet ratio, the longer the hydrogen permeation current keeps high level which is caused by the dense corrosion product layer. The hydrogen permeation currents in the elastic stress are greater than those in the plastic deformation, and unstressed conditions is the smallest.

Dense Water Production in Storfjorden, Svalbard, From a 1‐Year Time Series of Observations and a Simple Model: Are Polynyas in a Warming Arctic Exporting Heat to the Deep Ocean?

AbstractThe formation of dense Brine‐enriched Shelf Water (BSW) in Storfjorden is analyzed during Winter 2016–2017 from mooring observations, a polynya model nudged to satellite observations, and an original BSW production model. The ice season was two months shorter than average, yet 44.2 of sea ice were formed, in line with estimates for the period preceding the atlantification of the Barents Sea in the mid‐2000s: A thinner, more fragile ice may favor polynya openings and frazil ice production. A saline specimen of BSW was produced in large volumes, corresponding to an annual mean transport of 0.042 Sv, larger than previous estimates. The important production is due to the preconditioning of the polynya with a more saline source water, exceeding the pre‐2005 values by 0.37. The BSW overflow was observed on the West Spitsbergen shelf slope from hydrographic sections down to 750 m, thus entering the Norwegian Sea Deep Water layer. Its core temperature was about C warmer than the pre‐2005 values owing to the entrainment of a warmer water in Storfjordrenna, suggesting that a part of the excess surface heat of the Barents Sea could be exported into the deep ocean. Overall our results suggest that dense water formation in the Storfjorden polynya may not, at least for now, be hampered by the atlantification of the Barents Sea, and perhaps even temporarily favored by the more saline source water. Anomalous atmospheric warming during the Winter‐Spring may however disrupt the production, as was observed 1 year before.

Processing and characterization of Ultra High Temperature High‐Entropy (Ti0.2Zr0.2Hf0.2Mo0.2W0.2)B2-based Ceramics: Effect of W granulometry, graphite, and SiC addition

A highly dense and single phase (Ti0.2Zr0.2Hf0.2Mo0.2W0.2)B2 ceramic product is obtained in this work at 1950°C (20 min, 20 MPa) by Spark Plasma Sintering (SPS) from powders prepared by Self-propagating High-temperature Synthesis (SHS). The formation of the (W,Mo)B2 secondary phase is avoided using fine W precursors and adding 1 wt% graphite to the SHS powders before SPS. Kinetic limitations responsible for hindering the synthesis of the high entropy boride are correspondingly eliminated. The resulting 98.5 % dense sample exhibits a homogeneous microstructure, with Vickers hardness of 26.8 GPa. The introduction of 20 vol% SiC produces an increase of the KIC values from 2.32 to 5.11 MPa m1/2. Very relevant is that the volatilization of Mo- and W-oxides occurring during sample oxidation at high temperature, which leads to its rapid degradation with the formation of a very porous oxide scale, can be strongly inhibited by the silicate phases generated in the composite ceramic.

Wet carbonation of recycled cement paste powder using a CO2-loaded monoethanolamine solvent as an internal CO2 source

To address the challenge posed by the carbonation product layer formed on recycled cement paste powder (RCPP) on the efficiency and degree of carbonation, CO2-loaded monoethanolamine (MEA) “microcapsules” were used. The CO2 within MEA was released by heating after the formation of the dense carbonation products layer on RCPP to provide an additional internal CO2 source to penetrate into the uncarbonated layer. Results showed that using CO2 dissolved in 15 %, 30 %, and 45 % MEA aqueous solution increased the carbonation degree of RCPP by 10.8 %, 11.2 %, and 13.8 %, respectively, compared to RCPP wet carbonated in water. In addition to calcite, vaterite and aragonite were observed in the CO2-loaded MEA carbonated RCPP. The long-term compressive strength of cement pastes with 30 % CO2-loaded MEA carbonated RCPP increased, and the porosity decreased compared to cement paste with RCPP wet carbonated in water. However, MEA negatively affected the early compressive strength of the cement paste.

Investigating the process parameter window for laser powder bed fusion of copper chrome zirconium

ABSTRACT Copper-based alloy UNS C18150 has become an attractive material for laser powder bed fusion (LPBF) processing. However, the complexity of LPBF mandates that unique process parameters be devised for each alloy as these are highly sensitive to material chemistry. This work aims to clarify the general boundaries of the process window for the most influential parameters alongside an exploration into the effects of scan strategy on the density. A series of statistical design of experiments were utilised to model density as a response and predict process parameters that would result in minimised residual porosity. Using optimised parameters, specimen with up to 99.1% of theoretical density were produced, and a window of process parameters was established that yielded similarly dense products. Post-build aging of the LPBF parts was also explored. Here, direct aging of the as-built product at 390°C for 100 h resulted in a peak hardness of 83.3 ± 0.6 HRB.

Mechanical, freeze-thaw resistance and heavy metals leaching properties of alkali-activated recycled concrete powder solidified sludge

Solidified sludge was an efficient method to consume the large amount of sludge, which can be used as the subgrade filler in road engineering. However, the traditional solidified materials, such as cement and lime, consumed a large amount of natural resources and increased carbon emissions. This study used the alkali-activated recycled concrete powder (ARCP) to solidify sludge, which could be used as a potential subgrade stabilization filler. The optimal factors of ARCP were firstly determined by orthogonal test according to the compressive strength. Then the influences of different ARCP dosage, sludge moisture content and curing method on the mechanical properties, freeze-thaw resistance and heavy metals immobilization of the ARCP solidified sludge (ARCPS) were investigated. At last, microstructures of ARCPS were analyzed by SEM, XRD and TG-DTG tests. The experimental results demonstrated that the optimal mixture for ARCP: the silicate modulus of 1, liquid-solid ratio of 0.48 and calcium hydroxide content of 3 %. The solidified process by ARCP improved the mechanical properties and freeze-thaw resistance of ARCPS greatly. The 7 d unconfined compressive strength of ARCPS could reach 1305–2033 kPa when the sludge moisture content was 15 %, which meet the requirement of 500 kPa from the Chinese standard. The frost heaving rates of ARCPS were between non-frost heaving and mild frost heaving. The sludge moisture content was the most important factor affecting the freeze-thaw resistance of ARCPS. The properties of ARCPS were further improved after carbonation curing. The leaching mass concentration of heavy metals decreased significantly after the solidification of sludge. After 5 freeze-thaw cycles, the heavy metal leaching concentration increased but was still met the requirement of standards. SEM results showed that the surface of carbonated ARCPS was covered by dense scale-like carbonation products, which further enhanced the strength and freeze-thaw resistance of ARCPS. The results can be used to guide the application of sludge and ARCP in construction.

Influence of anionic silica forms in clear sodium silicate precursors on metakaolin geopolymerisation via 29Si and 27Al MAS-NMR and microstructural studies

A number of synthesis parameters directly influence the degree of reticulation/geopolymerisation of metakaolin exposed to alkaline solutions of sodium hydroxide and/or sodium silicate. In the latter case, a sodium silicate solution can be depolymerised by the introduction of an appropriate amount of NaOH. The effects of the ageing of the activator solution on the reticulation of metakaolin-based geopolymers are quantified for the first time in this work. We studied the anionic species of the sodium silicate solution with the addition of NaOH made just before the preparation of the paste, 24 h or 7 days before. These three ageing periods cause a significant difference in the Si-bearing species in solution, as demonstrated by nuclear magnetic resonance on 29Si. The effect of these anionic species on the reticulation/polymerisation of metakaolin at room temperature was demonstrated by solid-state 27Al and 29Si MAS-NMR, the chemical stability in various solutions (deionised water, HCl, HNO3, H2SO4), and X-ray diffraction on geopolymer powders before and after immersion in acids. Compressive strength before and after the immersion in acidic media was an additional measurement to assess the overall structural stability of the 3D polymerised network of the final dense ceramic-like product. Ageing of the activator solution affected the chemical stability of the hardened geopolymers accompanied by a slight to severe reduction in strength after leaching in HNO3 or HCl and in H2SO4, respectively. The quantitative MAS-NMR description of the Si and Al coordination in the geopolymers was correlated with the chemical stability where the formulations with the higher number of Q4(0Al) and Q4(1Al) for the silicon species were more resistant (lower number of Na+ compensating for Al+3 to be exchanged with H+). The formulations with higher Al content in the structure, i.e. higher number of Q4(3Al) silicon species showed higher mechanical stability. These results show that the timing of the preparation of the alkaline activator is essential for a correct mix design.

Selective adsorption and corrosion mechanism of SO2 and its hydrates on X65 welded joints steel in CO2-saturated aqueous solution

In this study, the corrosion mechanism in different regions of the welded joints in CO2/SO2 saturated aqueous solution was investigated by electrochemistry and morphological analysis. The results demonstrated that SO2 and its hydrolysis have some adsorption properties and tend to adsorb in the region of the base metal and generated FeS product. A dense corrosion product film could form on this region, effectively reducing the corrosion rate. Due to the selective adsorption which increases the potential difference between different regions of the welded joint, further intensifying the galvanic corrosion and ultimately leading to the failure of the welded joint.

Study on the workability and early mechanical properties of carbon nanotube-coated fly ash modified cement-based grouting materials

Carbon nanotube (CNTs) reinforced cementitious composites have obvious advantages over traditional building materials in strength and impermeable durability. However, the material in question has not been widely employed in grouting engineering due to the limitations posed by dispersion issues. This study introduces a novel method of using amino functional groups to coat carbon nanotubes on the surface of fly ash to improve dispersion. The objective is to produce high-quality industrial-grade slurry and facilitate the transition of carbon nanotubes from small-scale research to large-scale engineering applications. The results show that mixing 14.3 wt% fly ash and 0.023 wt% CNTs in cementitious composites can replace an equivalent proportion of cement. Compared to traditional cement-based grouting material, the modified composites exhibit a 21.6 % increase in fluidity, a 7.9 % increase in the 7-day consolidation strength, and an 11.9 % reduction in the porosity of the slurry consolidation. The CNTs with large specific surface area on the fly ash surface provide sites for cement hydration reaction, accelerate cement hydration, and form dense hydration products. Additionally, the interaction between hydration products and CNTs within the microcracks of the cement matrix forms a 'bridging role' that enhances mechanical properties. The effectiveness of incorporating CNTs in reducing micro-damage during the loading process of slurry consolidation, enhancing integrity, and improving the grouting material's resistance to loading was further proved by acoustic emission, scanning electron microscopy, and fractal analysis of the fracture surface.

Pressure-less melt infiltration characteristics of Mg melt into Ti powder preforms with various pore structures: Toward the application to the binder jetting additive manufacturing

Binder jetting (BJT) additive manufacturing enables the fabrication of complex-shaped metallic parts but requires sintering as post-processing to obtain dense parts. The sintering inevitably causes the shrinkage from green body to dense products, resulting in low dimensional accuracy. In contrast, pressure-less melt infiltration (PMI) fills pores in the green body with a liquid metal driven by capillary pressure and fabricates a dense metal matrix composite without severe shrinkage. To consider the applicability of pressure-less melt infiltration to the post-processing of binder jetting additive manufacturing, it is required to clarify the relationship between pressure-less melt infiltration process conditions and the relative density of the composites. In this study, the liquid Mg/solid Ti system was selected because of good wettability and absence of Mg-Ti intermetallic, and the conditions of Ti powder preforms (corresponding to the green body) were focused on. Ti powder preforms with various powder sizes (2300, 410, 140, and 20 μm) and different shapes (irregular and spherical) were cold-pressed at 76, 102, 127, 153, and 178 MPa to fabricate preforms with various relative densities, pore sizes, and pore morphologies to response the similar characteristics in BJT preforms. Mg melt infiltrated into the preforms under constant conditions to fabricate Mg/Ti composites. The structures of the preforms and composites were characterized by sample size measurement, optical and scanning electron microscopy, and X-ray computed tomography. It was revealed that the relative density of the composite increased with decreasing Ti powder size and using spherical Ti powder, whereas the compact pressure exhibited a slight effect. Furthermore, defect volume increased with increasing infiltration height but decreased around the top surface of the sample. Minute observations around defects in the composites revealed that defects were formed at larger pores, and Mg melt was infiltrated into pores above the defects. These results indicated that infiltration velocity varied depending on the flow channel structure, and gas was trapped at larger pores (far from the outside of the sample) where infiltration velocity was low. Using smaller Ti powder decreased the variation in pore size in the preform, resulting in improving the relative density of the composites by suppressing the gas trapping. This study provides a new insight into the pressure-less melt infiltration process as a post-processing of binder jetting additive manufacturing.

Enhancement of the tensile properties of cement mortar composites with nanoadditives produced by chemical vapor deposition

While graphene effectively enhances the performance of cement-based materials, its current production methods are characterized by environmental unfriendliness and high energy consumption. To investigate a large-scale and eco-friendly graphene preparation approach, Carbon Nano Sheets (CNS) were synthesized via chemical vapor deposition (CVD). The influence of CNS content on the tensile strength of cement mortar was assessed through the Brazilian splitting test. Concurrently, the mechanism of CNS was examined using acoustic emission monitoring and scanning electron microscope. The experimental results revealed that methane can be effectively decomposed into high-quality CNS at 1080 ℃ when using fly ash, silica fume, and sand as substrates. The Brazilian splitting test revealed that CNS effectively enhances the tensile strength of cement mortar, with improvements ranging from 9 % to 58.7 %. Acoustic emission results indicated that the inclusion of CNS reduces the occurrence of micro-fractures during the failure of cement mortar specimens. Furthermore, nano-mechanical testing and microstructural characterization demonstrate that CNS can reduce micro-cracks and pores in the interface transition zone and hydration products, playing a role in dense hydration products. Furthermore, it can decrease the width of the interface transition zone and enhance the micro-mechanical properties of cement pastes. This study offers a novel approach for the eco-friendly production of cement nano additives.

Different effects of TiB2 particles on corrosion behaviors of in-situ TiB2/7075 composites in active and passive environments

The different effects of TiB2 on intergranular corrosion (IGC) and exfoliation corrosion (EXCO) in TiB2/7075 composites were investigated. Lower particle content accelerated IGC due to the first dissolution of large TiB2/Al interface precipitates, causing TiB2 deposition in corrosion channels. Conversely, higher particle content reduced the maximum IGC depth to 47 % with dense corrosion products inhibiting penetration of corrosive solution. EXCO weight loss increased by 271 % and 388 % with 3.5 wt% and 7 wt% particles, respectively. Micro-galvanic corrosion and recrystallization caused by particles reduced EXCO resistance. The passive IGC environment and active EXCO environment lead to different corrosion resistances of composites.

Material Extrusion Additive Manufacturing of Ceramics: A Review on Filament-Based Process.

Additive manufacturing is very important due to its potential to build components and products using high-performance materials. The filament-based 3D printing of ceramics is investigated, revealing significant developments and advancements in ceramic material extrusion technology in recent years. Researchers employ several typologies of ceramics and binders to achieve fully dense products. The design of the filament and the necessary technological adaptations for 3D printing are fully investigated. From a material perspective, this paper reviews and analyzes the recent developments in additive manufacturing of material-extruded ceramics products, pointing out the performance and properties achieved with different material-binder combinations. The main gaps to be filled and recommendations for future developments in this field are reported.

Development of highly corrosion-resistant Mg-Al-Y extruded alloy via regulating the Mg17Al12 phase

A highly corrosion-resistant AW90 extruded alloy (Mg-9Al-0.2Y wt %) was developed via alloying and solution-aging treatment (PW = 0.14 mm/y). The solution-treated AW90 alloy exhibits the most severe localized corrosion due to the strong micro-galvanic acceleration effects. The finely dispersed Mg17Al12 phase promotes the strong quasi-passive behavior and uniform corrosion of the aged AW90 alloy due to the formation of a dense and uniform corrosion product film. The high corrosion resistance of the aged AW90 alloy is attributed to the formation of a Mg-Al layered double hydroxide film, which has stronger resistance to chloride ions.

Surface microstructure and corrosion characterization of AZ31 magnesium alloys fabricated by laser surface-modification

This study aimed to improve the corrosion resistance of Mg alloys, and to this end, AZ31 Mg alloy was subjected to laser surface re-melting using a fiber laser. Subsequently, a comparative analysis was conducted on the microstructures of the re-melted surfaces under various laser power settings, and the influence of laser surface re-melting on corrosion characteristics was investigated through a potentiodynamic polarization test. The test results show that laser surface re-melting produced a distinct reduction in the crystallite size of magnesium, ranging from 11.23–15.80 μm within the laser-melted layers. The maximum melted layer thickness of 820 μm was achieved with a laser power of 2100 W. The process of laser surface re-melting notably heightened the hardness, particularly as the power increased, which was attributed to swift solidification. The most noteworthy hardness measurement of 92.1 HV0.02 was recorded at 2100 W. Thus, the study shows that laser surface re-melting significantly enhances the corrosion resistance of Mg alloys, primarily owing to the formation of a corrosion product. The smaller grain size on the surface contributes to the formation of a dense product film.

Microstructure of corrosion product film formed on aged WE43 alloy

A dense three-layer corrosion product film was formed on aged WE43 alloy in 3.5 wt.% NaCl solution. The microstructure of the film was analyzed in detail by TEM. The three-layer corrosion product film is composed of RE2O3, MgO layer doped with RE2O3 and Mg(OH)2 layer doped with RE2O3 from the inside to the outside. A large amount of rare earth oxide particles formed both by the outward oxidation of rare earth precipitates and rare earth elements, are the main reason for the formation of the corrosion film. The RE2O3 has the preferential orientation with ( 2-11) plane and [231] direction parallel to (002) plane and [ 1-1-0] direction of MgO, respectively. Thus, the rare earth oxide particles can fill the gap of porous MgO layer, and improve the compactness of the film. The inner RE2O3 layer and mixed layer of MgO and RE2O3 play an important role in the formation of the film. The compact inner film can prevent the corrosion medium from reacting with the Mg matrix.

Effect of hydrostatic pressure on the anodic dissolution process of X80 steel

Based on the fact that hydrostatic pressure affects chemical potentials of reaction species and the structure evolution of electric double layer (EDL), the authors propose a generalized-BV equation to analyze the anodic dissolution process of X80 steel in deep-sea environment. Combined with the results of potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests, the following conclusions can be drawn: hydrostatic pressure can compress the electric double layer non-uniformly. The CHCD (CD: capacitance of diffused layer; CH: capacitance of compact layer) value increases first and then decreases with increasing hydrostatic pressure and reaches its maximum at 15 MPa, which is sure to influence the difference in electrical potential that drives chemical reaction at interface. Ultimately, the anodic dissolution current increases and then decreases with rising hydrostatic pressure at the same anodic polarized potential. Besides, low hydrostatic pressure may contribute to forming a dense corrosion product film and inducing a good inhibiting effect on further dissolution of X80 steel; However, when the hydrostatic pressure exceeds the critical value of 20Mpa, too high anodic dissolution rate along with promoted Cl− adsorption will deteriorate the protection performance of corrosion product film, and exacerbate local corrosion process.