Bulk Microstructure Research Articles

Study of the effects of drinking water treatment sludge on the properties of Class F fly ash-based geopolymer.

Drinking water treatment sludge (DWTS) generated from water treatment plants is a global issue because of the environmental risks it imposes. Managing the abundance of DWTS in landfills remains an important issue. The reuse of these sludges as a construction material could contribute to the development of a geopolymer and mitigate the harmful effects of the excessive production of these sludges on the environment. This study aims to evaluate the effect of DWTS on the properties of Class F fly ash (FFA) geopolymers. Seven geopolymer blends were made with the addition of DWTS in the total fly ash weight of 0%, 5%, 10%, 15%, 20%, 30%, and 40%, and with an alkaline solution composed of 12M sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) solution; the liquid/solid and (Na2SiO3)/NaOH weight ratios were set to 0.75 and 2.5 respectively. The polymerization temperature was set at 60°C and different polymerization times such as 3, 7, 14, and 28days were considered. The bulk density, apparent porosity, compressive strength, and microstructure of the geopolymer samples were tested. The experimental results revealed that the optimum percentage of DWTS incorporation is 20 wt%, which generates a dense and homogeneous microstructure. The addition of more than 20% DWTS decreased the compressive strength from 40.87 to 35.3MPa and bulk density from 2.134 to 2.087g/cm3 due to the retention of air bubbles and evaporation of water during the polymerization process forming voids in the matrix, which results in increased apparent porosity from 19 to 22%. This investigation confirmed the feasibility of incorporating DWTS into FFA-based geopolymers.

Enhancing the thermoelectric properties through hierarchical structured materials fabricated through successive arrangement of different microstructure

The importance of ZT in thermoelectric (TE) materials is critical for green power generation and cooling applications. Therefore, tremendous efforts were underway to improve ZT, in which we proposed a layer structured approach by successively arranging of coarse Bi0.5Sb1.5Te3 (BST) and fine BST/0.07Cu microstructure materials and investigated their transportation mechanism. The dual bulk microstructure was well-bonded and confirmed by analyzing the microstructure through scanning electron microscope (SEM), electron backscatter diffraction analysis (EBSD) and simulated the electrical potential and temperature distribution during spark plasma sintering with COMSOL software. The results indicate that the highest power factor of 3.8 mW/m-K2 was attained in the layer structured sample, which is significantly higher than other samples due to its synergistically optimized electrical conductivity and Seebeck coefficient. Through the varied microstructure, the κ was decreased at 400 K and consequently the ZT was improved to 1.25 at 400 K for the layer structure samples. Therefore, it is suggested that layered arrangement of different microstructure material could improve the thermoelectric properties of materials.

Sintering behaviors and thermal properties of Li2SiO3-based ceramics for LTCC applications

A series of new Li2SiO3+4 wt% Al2O3-xK2O–B2O3–SiO2 (x = 1–4 wt%) LTCC materials were prepared by standard traditional solid-state method and their bulk density, microstructure and crystalline phase composition were shown in detail. The sintering behavior, heat conduction and thermal expansion of the samples were all thoroughly studied. And their microwave dielectric properties were also demonstrated. The bulk density of the samples was enhanced with the addition of 3 wt% KBS glass, and the sintering temperature was reduced from 1020 °C to 900 °C. Meanwhile, the thermal diffusivity of the samples was determined using the LFA447 laser flash apparatus and the specific heat was calculated, according to the results of thermal diffusivity and specific heat, all samples possessed high thermal conductivity ranging from 5.5 ± 0.02 W/mK to 8.6 ± 0.08 W/mK. Furthermore, the attractive flexural strength and average coefficient of thermal expansion reach to 270 MPa and 15.7 × 10−6/K (at 100 °C), respectively. The reduction of the sintering temperature is attributed to the addition of KBS glass which reduces the crystallization activation energy of the samples. Besides, increasing bulk density can substantially reduce pores in the grain boundary, which has great effects on phonon scattering, improving the thermal conductivity.

Resourceful utilization of quarry tailings in the preparation of non-sintered high-strength lightweight aggregates

Quarry tailings are usually stockpiled due to stable crystalline structures below 100 °C and abundant sources, which lead to a serious environmental impacts and high ecological risks. This paper presents a study of transforming the fly ash and quarry tailings as the main raw materials into lightweight aggregates (LWAs) for using in civil engineering. A novel curing regime (autoclave technology) has been proposed to obtain higher compressive strength of LWAs. The effects of curing parameters (including temperature and steam pressure) on the properties (compressive strength, water absorption, loose bulk density, phase composition, pore structure and microstructure) of LWAs were systematically evaluated. On the other hand, this research also studies the effect of cement content on the basic properties of LWAs, which was decreased from 30 to 10 wt% for declining the CO2 emission. Results show that the strength sharply increases from 2.48 to 11.95 MPa and the water absorption decreases from 11.2 to 2.09% with increasing the elevated curing temperature from 25 to 190 °C. The LWA prepared with 70 wt% solid wastes (fly ash and quarry tailings) at 190 °C achieved the highest strength (11.95 MPa) and the lower loose bulk density (1160 kg/m3), which could meet the requirement of Chinese LWAs standard (GB/T 17431.1-2010). The water absorption of LWAs is below 5% except sample T25. The total porosity of LWAs decreases from 39.65% to 26.32% at 150 °C and from 42.54% to 27.24% at 190 °C while the cement content increases form 10 wt% to 30 wt%. At the same time, the percentage of pores (>50 nm) also gradually decreases. While the curing temperature, pressure and cement usage are above 150 °C, 1.00 MPa and 10 wt% respectively, will promote the formation of new phase composition (analcime). That also further increases the strength and percentage of harmless pores and few harmful pores. Therefore, this research offers a new curing method for producing LWAs from 70 to 90 wt% solid waste and is a rapid and sustainable solution for the large-scale recycling of quarry tailings.

The effect of Sr addition on the microstructure and corrosion behaviour of a Mg-Zn-Ca alloy

The application of magnesium alloys is rather limited due to their poor corrosion resistance despite of their promising mechanical properties. Alloying is considered one of the most efficient methods to influence the corrosion susceptibility of Mg alloys either by altering the bulk microstructures or by changing the surface chemistries. In the present study, the effects of Sr addition on the microstructure and corrosion properties of a Mg-Zn-Ca alloy were studied. The microstructure characteristics of the alloys were investigated using optical microscopy, scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy, while the corrosion properties were evaluated by hydrogen collection method and electrochemical techniques including potentiodynamic polarization and electrochemical impedance spectroscopy. The results indicate that Sr addition significantly deteriorates the corrosion performance of the Mg-Zn-Ca alloy mainly by forming more micro-galvanic couples due to the precipitation of the more populous secondary phase particles. The corrosion product film accumulated on the sample surface marginally affects the corrosion resistance, as their compactness is rather compromised as the immersion time is prolonged.

Effect of processing parameters on formability, microstructure, and micro-hardness of a novel laser additive manufactured Ti-6.38Al-3.87V-2.43Mo alloy

A novel Ti-6.38Al-3.87V-2.43Mo alloy was designed with a cluster formula of 12[Al-Ti12] (V0.75Mo0.25Ti2)+4[Al-Ti12](Al3) by replacing Ti with Mo/V on the basis of the Ti-Al congruent alloy. The effects of laser power and scanning speed on the molten pool size, surface roughness, relative density, microstructure, and micro-hardness of single-track and bulk Ti-6.38Al-3.87V-2.43Mo samples prepared via laser additive manufacturing (LAM) were investigated. The results show that processing parameters significantly affect the formability, microstructure, and micro-hardness of the alloy. With decreasing laser power from 1,900 W to 1,000 W, the relative density is decreased from 99.86% to 90.91% due to the increase of lack-of-fusion; however, with increasing scanning speed, the relative density does not change significantly, but exceeds 99%. In particular, Ti-6.38Al-3.87V-2.43Mo samples of single-track and bulk exhibit a good formability under an input laser power of 1,900 W and a scanning speed of 8 mm·s-1, and display the lowest surface roughness (Ra=13.33 µm) and the highest relative density (99.86%). Besides, the microstructure of LAM Ti-6.38Al-3.87V-2.43Mo alloy coarsens with increasing laser power or decreasing scanning speed due to the greater input energy reducing the cooling rate. The coarsening of the microstructure decreases the microhardness of the alloy.

Mechanical and microstructural characterisation of bulk Inconel 625 produced by direct laser deposition

Direct laser deposition (DLD) is an advanced additive manufacturing (AM) technology with growing industrial importance. In the present study, the mechanical and microstructural characterisation of a bulk produced by DLD depositing a nickel superalloy (type Inconel 625) on 42CrMo4 structural steel was performed. Optimized processing parameters (laser power, scanning speed and feed rate) were used for deposition and remained constant during bulk production. The bulk showed structural integrity, with no cracking or unmelted particles. Successive layers were deposited on a pre-heated substrate to reduce the cooling rate and minimize both the formation of metastable phases in the heat-affected zone and the dimensions of the deleterious phases in bulk. The bulk microstructure mainly consists of a coarse columnar/dendritic structure, and the longitudinal section microstructure revealed the layer-by-layer deposition pattern. Microstructural and mechanical characterisation demonstrated that a sound bulk was formed, with mechanical properties similar to wrought Inconel 625. These results contribute to the recognition of DLD as a suitable technique for the repair and remanufacturing of industrial components.

Properties of Sn-3 wt%Ag-5 wt%Cu alloys with Cu6Sn5 intermetallics grain refined by Mg

This paper investigates the influence of Mg additions on the microstructure, thermal properties, electrical properties, and joint strength of bulk and ball grid array (BGA) reflowed Sn-3 wt%Ag-5 wt%Cu solder alloy and the joint intermetallics (IMCs). The cross-sectional microstructure analysis revealed that the addition of Mg effectively triggered the grain refinement of primary Cu6Sn5 IMCs in the bulk solder alloys. In addition, the thickness of the interfacial Cu6Sn5 IMCs layer was suppressed. The optimal addition for refinement is in the vicinity of 0.10 wt%Mg. Furthermore, synchrotron tomography three-dimensional reconstructed imaging reveals that the grain refinement of primary Cu6Sn5 IMCs is also effective even in BGA scale solder joint at normal reflow conditions. These primary Cu6Sn5 IMCs showed a non-faceted morphology. 0.10 wt%Mg addition reduced the number and size of the Cu6Sn5 IMCs. The grain refinement of primary Cu6Sn5 IMCs could be attributed to the presence of Mg, Mg2Sn, and MgO phases that potentially serve as heterogenous nucleation sites. The thermal analysis showed that the degree of undercooling values was significantly reduced to the minimum with 0.10 wt%Mg addition, which increased when the amount of Mg increased to 0.15 wt%. The mechanical properties showed that the ductility of the solder joint at high shear speed was improved.

Grain boundary segregation in Si-doped B-based ceramics and its effect on grain boundary cohesion

Boron carbide and boron suboxide are attractive for their low densities and ultrahigh hardness values, yet they exhibit poor fracture resistance. Strategies to improve mechanical performance aim to control bulk microstructures and properties by incorporating Si-based additives. A related approach to toughen boron carbide is tailoring the phase-like states of grain boundaries by applying the concept of grain boundary complexion engineering. This work directly investigates the potential of grain boundary complexion engineering to improve fracture resistance by systematically evaluating grain boundary segregation behavior of a polycrystalline silicon hexaboride / boron carbide diffusion couple using aberration-corrected scanning transmission electron microscopy and ζ-factor microanalysis. A main result was that all grain boundaries in the diffusion couple exhibited Si segregation that, depending on the bulk Si concentration, approached up to 3 monolayers of coverage, thereby resulting in nanolayer complexions (oftentimes known as intergranular films). Furthermore, upon analyzing 110 distinct grain boundaries throughout the diffusion zone and an impurity boron suboxide region, free energies of Si segregation in boron carbide and boron suboxide were experimentally determined using the Brunauer, Emmett and Teller (BET) multilayer grain boundary segregation theory. Subsequently, changes in grain boundary energy due to Si segregation were quantified and a maximum energy reduction of 51% and 81% were observed in boron carbide and boron suboxide, respectively, which led to decreases in works of adhesion of 18% and 17%, respectively. In summary, this work uncovers grain boundary processing-structure-property relationships that can be used to improve the fracture resistance in icosahedral boron-based ceramics.

The influence of the plasma-nitriding temperature on the microstructure evolution and surface properties of additive-manufactured 18Ni300 maraging steel

Maraging steel grade18Ni300 produced by powder bed fusion (PBF) in its as built condition was plasma nitrided at three different temperatures. The aim of the work was to investigate the impact of the nitriding temperature on the microstructural changes as well as on the surface properties such as hardness, wear and corrosion resistance. The microstructural features in the bulk as well as in the nitride layer were investigated using electron-backscatter diffraction (EBSD), transmission electron microscopy (TEM) and X-Ray diffraction (XRD) analysis. The bulk microstructure consists of martensite with a small amount of retained austenite, the amount of which increases with a higher nitriding temperature. The nitriding process also causes the formation of precipitates and can therefore also act as an aging treatment. A specific lamellar structure occurs on the surface during the nitriding process, which in the majority of cases consists of the Fe4N phase. The retained austenite also transforms during nitriding to the nitride phase Fe4N. It was found that nitriding at higher temperatures leads to the formation of cracks in the nitride layer. The crack formation is related to nano and micro segregation during the LPBF. These segregations lead to austenite formation, which also takes place along the grain boundaries and transforms during nitriding to Fe4N. Higher nitriding temperatures lead to a thicker nitride compound layer and to better wear resistance. The impact of the cracks on the static mechanical properties is negligible. However, the corrosion resistance is governed by the formation of cracks at higher nitriding temperatures.

Influence of Fly Ash Geopolymer Ceramic Powder Addition on Sn-3.0Ag-0.5Cu Solder Joints

This paper reports the effect of 1.0 wt.% fly ash (FA) geopolymer ceramic powder addition in Sn-3.0Ag-0.5Cu (SAC305, in wt.%) solder joint. Powder metallurgy route was used to fabricate the new composite solder. Solder balls were formed from the new composite solder and reflowed on Cu substrate. The effect of FA as ceramic reinforcement on the bulk microstructure and the interfacial intermetallic compound layer formation of solder joints were investigated under optical microscope. Microstructure observation showed that the β-Sn dendrite size was refined in SAC305-1.0FA/Cu bulk solder joint sample than that in the non-reinforced sample. The addition of FA geopolymer ceramic powder into the solder matrix also produced a thinner intermetallic compound layer.

Impact of Two-Step Calcination on Microstructure, Phase, Electronic, and Dielectric Properties of Kca2nb3o10 Bulk Layered Perovskite

Impact of Two-Step Calcination on Microstructure, Phase, Electronic, and Dielectric Properties of Kca2nb3o10 Bulk Layered Perovskite

Effects of Cu substitution on microstructures and microwave dielectric properties of Li2ZnSiO4 ceramics

Herein, the influence of Cu2+ substitution on the phase composition, bulk density, microstructures, and microwave dielectric properties of Li2CuxZn1−xSiO4 (0 ≤ x ≤ 0.06) ceramics prepared by a solid-state reaction were investigated. The results of XRD and mapping showed that Cu2+ substitution can avoid the influence of secondary phase on the properties of samples. According to the analysis of bulk density, microstructure and microwave dielectric properties, a proper amount of Cu substitution not only improved the sintering characteristics of Li2CuxZn1−xSiO4 ceramics, reduced the densification temperature from 1250 °C to 950 °C, but also increased the Q×f value. Furthermore, Cu2+ substitution also improved the temperature stability of the samples. Particularly, the Li2Cu0.04Zn0.96SiO4 ceramics sintered at 950 °C for 5 h possessed excellent microwave dielectric properties: εr = 5.624, Q×f = 12,764 GHz, and τf = −77 ppm/°C, exhibiting a potential for the low temperature co-fired ceramic applications.

Preparation of high-strength Si3N4 antenna window using selective laser sintering

In this study, a high-strength silicon nitride (Si 3 N 4 ) antenna window was successfully developed via selective laser sintering (SLS) with cold isostatic pressing (CIP) after debinding before final sintering. The effects of CIP after debinding and sintering additives on the bulk density, total porosity, bending strength and microstructure of Si 3 N 4 ceramics were examined. The results show that the bending strength of SLS Si 3 N 4 ceramics can be greatly improved by adding sintering aids between Si 3 N 4 granules and by CIP after debinding. Optimal performance of ceramics is obtained by CIP after debinding and the use of inter-granule sintering additives. The porosity, bulk density, and bending strength are 18.7%, 3.11 g/cm 3 , and 685 MPa, respectively. Eliminating the pores by the CIP after debinding and by inter-granule sintering additives promotes the growth of rod-like β-Si 3 N 4 , which lock with each other contribute to the strengthening of Si 3 N 4 ceramics.

Effect of Zn and in to microstructure of aged SAC305/Cu joint

In this project, Sn-3.0Ag-0.5Cu (SAC305) solder was alloyed with Indium (In) and Zinc (Zn) at 0.5–1.5 wt%, and the aim was to reduce growth rate of IMC layer at interface of solder joint during thermal exposure. Five samples were prepared via casting; SAC305, SAC/1In, SAC/1In-0.5Zn, SAC/1In-1Zn and SAC/1In-1.5Zn. Solders were characterized via SEM equipped with EDX for the bulk microstructure, and the IMC layer after reflow and aging at 150 °C for 100 h. Reflow was done on bare copper (Cu) substrate at 270 °C for 10 s. Among the percentages evaluated, microstructural analysis revealed that addition of 1.0% Zn not only refined the Ag3Sn and Cu6Sn5 particles, but also increased the eutectic area and promoted the formation of small (Cu,Ag)5Zn8 intermetallic compound (IMC). This would potentially increase the strength of solder, and at the same time, provide blocking mechanism for atomic diffusion during thermal aging and could lead to lower IMC growth. With increasing Zn content up to 1.0 wt%, the reaction phase (Cu,Ag)5Zn8 becomes larger and its morphology changed from a strip-like shape into flower-like or dendritic shape. Highest addition of Zn at 1.5 wt% gave slowest growth indicating that addition of Zn did suppress growth of IMC in SAC305. This could be because Cu was being used to form (Cu,Ag)5Zn8 which was observed at vicinity of the Cu6Sn5 layer. The results showed great potential of Zn alloying to suppress growth of IMC layer during thermal aging of solder joint, and this could lead to higher reliability of solder joint in electronic packaging.

Microstructure Study of Mix Assembly Lead-free Sn-Ag-Cu Ball Grid Array and Sn-10Cu Solder Paste

In recent years, electronic technologies have been striving to minimize the use of lead in their manufacturing and production. As a result, the electronic packaging industry is slowly transitioning from lead solder to lead-free solder. Though environmentally lead-free solders are advantageous, there are still needs some work in meeting current technological demand and requirements. In this study, the microstructure analysis on lead-free Sn-Ag-Cu Ball Grid Array (BGA) and Sn10Cu solder paste was done. The main aim of this study is to investigate the effect of isothermal aging on the microstructure of the solder paste joint and evaluate the intermetallic compound (IMC) thickness on the solder joint reliability. Optical Microscope (OM) and ImageJ software have been utilized to study the bulk solder microstructure. The results show that the bulk microstructure consists of β-Sn and Cu6Sn5 / β-Sn eutectic phases. The IMC layer has undergone rapid growth with increasing aging temperature and time. The two main IMC layers (Cu3Sn and Cu6Sn5) grew thicker due to high temperature. The growth kinetic of Sn10Cu resulted in 16.70 kJ/mol activation level. Therefore, the significance of the findings from this study might provide a potential answer for future development for highly reliable solder joint applications.

Can We Enhance Passivity with a Surface Finish? Spectroscopic and Electrochemical Analysis on 316L Stainless Steel

The effects of surface finish by mechanical polishing, vibratory polishing, and high-temperature annealing were studied on 316L stainless steel by combining microscopic and spectroscopic analysis of the surface morphology and composition and electrochemical analysis of the corrosion resistance. Compared to mechanical polishing, vibratory finishing promotes passivity at the active-passive transition in acid solution and enhances resistance to chloride-induced passivity breakdown. Cr and Mo enrichments in the native oxide film increase owing to preferential iron etching. The bilayer structure develops a thicker Cr(III) oxide inner barrier layer and an outer exchange layer further enriched in Cr(III) hydroxide and Mo(IV/VI) oxides. The Fe-rich weak sites of passivity are reinforced. High-temperature annealing in reducing hydrogen environment enables us to fully reconstruct the cold-worked layers left by mechanical or vibratory finishing, thus allowing us to expose the bulk microstructure at the topmost surface. The benefits brought by vibratory finishing are lost upon reducing the initial native oxide. The re-formed native oxide develops a bilayer structure with similar Cr and Mo enrichments as that obtained from mechanical polishing and no beneficial effects on passivity. The results provide comprehensive insight into how the passivity of stainless steel can be enhanced by surface enrichment engineering.

Microstructure evolution of 316L stainless steel during solid-state additive friction stir deposition

ABSTRACT Solid-state additive friction stir deposition was employed to three dimensionally print a 316L stainless steel. The microstructure, texture and grain boundary distribution were characterised using five-parameter boundary analysis. The bulk microstructure was exceptionally fine (∼0.7 µm) throughout the thickness of the deposited layers, consisting of equiaxed grains along with sub-grains delineated by high and low angle boundary segments. The misorientation angle distribution of the deposited layers was considerably different from the as-received microstructure, exhibiting a significant reduction in the relative areas of ∑3 annealing twin boundaries due to their distortion by severe plastic deformation. The overall texture also exhibited strong shear components associated with FCC metals, suggesting that the microstructure refinement largely took place through progressive subgrain rotation, known as continuous dynamic recrystallisation. The grain boundary plane distribution revealed significantly lower anisotropy compared with the as-received material, showing two moderate peaks at the (111) and (110) orientations. The migration of high-angle mobile boundaries, which may have been induced by thermal cycle upon subsequent deposition along with the dislocation gradients between adjacent grains, slightly enhanced the intensity of low energy (111) orientations at the expense of (110) high-energy boundaries.

Direct ink writing of aluminium oxynitride (AlON) transparent ceramics from water-based slurries

In this study, transparent AlON ceramics were fabricated via the direct ink writing (DIW) method from the water-based ceramic slurry. The solids loading of the ceramic slurry was optimised by changing the dispersant content, and the printability and water content were then adjusted by adding hydroxyethyl cellulose (HEC). The structure of the green body was complete and no impurity phases were detected. The effects of sintering temperature and dwell time on the bulk density, phase evolution, microstructure, in-line transmittance, and mechanical properties of the ceramics were studied systematically. High optical and mechanical properties of 10 × 10 × 0.9 mm3 single-phase AlON ceramic tiles were obtained by sintering at 1960 °C for 10 h in a nitrogen atmosphere: in-line transmittance of 81.90% at a wavelength of 780 nm, fracture toughness of 1.74 MPa·m1/2 (2.94 N), and Vickers hardness of 18.56 GPa (2.94 N). This study provides a novel method for synthesising AlON transparent ceramics from water-based ceramic slurries.

Microstructural and Mechanical Properties of a Solid-State Additive Manufactured Magnesium Alloy

Abstract In recent years, additive manufacturing (AM) has gained prominence in rapid prototyping and production of structural components with complex geometries. Magnesium alloys, which have a strength-to-weight ratio that is superior compared with steel and aluminum alloys, have shown potential in lightweighting applications. However, commercial beam-based AM technologies have limited success with magnesium alloys due to vaporization and hot cracking. Therefore, as an alternative approach, we propose the use of a near net-shape solid-state additive manufacturing process, additive friction stir deposition (AFSD), to fabricate magnesium alloys in bulk. In this study, a parametric investigation was performed to quantify the effect of process parameters on AFSD build quality including volumetric defects and surface quality in magnesium alloy AZ31B. In order to understand the effect of the AFSD process on structural integrity in the magnesium alloy AZ31B, in-depth microstructure and mechanical property characterization was conducted on a bulk AFSD build fabricated with a set of acceptable process parameters. Results of the microstructure analysis of the as-deposited AFSD build revealed bulk microstructure similar to wrought magnesium alloy AZ31 plate. Additionally, similar hardness measurements were found in AFSD build compared with control wrought specimens. While tensile test results of the as-deposited AFSD build exhibited a 20% drop in yield strength (YS), nearly identical ultimate strength was observed compared with the wrought control. The experimental results of this study illustrate the potential of using the AFSD process to additively manufacture Mg alloys for load bearing structural components with achieving wrought-like microstructure and mechanical properties.