Microstructure Of Substrate Research Articles

Effects of Substrate Microstructure and Chemical Composition on Liquid Metal Embrittlement in Galvanized 3rd Generation AHSS

Extensive efforts have been undertaken worldwide to develop new high strength steels with substantial fractions of retained austenite, for lightweight automobile manufacturing and other applications requiring improved combinations of strength and formability. These “3rd Generation” Advanced High Strength Steels (AHSS) are being implemented, and spot-welding has been found to present new challenges for these steels when Zn-based corrosion resistant coatings are involved, wherein zinc liquid metal embrittlement (LME) can occur. Some recent work is highlighted here that was designed to examine the separate effects of prior microstructure and alloy composition on LME sensitivity. LME behavior was assessed by comparing hot-ductility of steels with and without a Zn coating tested under conditions simulating spot-weld thermal cycles. Effects of prior microstructure on LME susceptibility were assessed with a single AHSS alloy composition, using annealing modifications to produce martensitic, Q&P, TBF and dual-phase substrates. The dual-phase steel exhibited less sensitivity to LME, perhaps because the Zn penetration and cracking are unable to follow (prior) austenite boundaries in this microstructure. With respect to alloy composition, carbon and manganese variations did not lead to noticeable effects on LME sensitivity, while silicon clearly leads to increased LME sensitivity. Addition of 1.3 wt. pct. aluminum to a 0.5 wt. pct silicon-containing AHSS steel further increased LME sensitivity at some test temperatures. The effects of alloying are interpreted in terms of the propensity to form an intermetallic reaction layer that consumes liquid and physically separates the substrate and liquid zinc.

Effect of microstructure and texture of AZ31 magnesium alloy substrate on nucleation and growth of biomimetic calcium phosphate coating

Magnesium has a special place in biomedical applications due to its biocompatibility and biodegradability properties. The high corrosion rate of magnesium in the body environment requires the use of a biocompatible coating such as calcium phosphate. In this paper, the effect of microstructure and crystalline texture of AZ31 magnesium alloy substrate on the morphology of calcium phosphate coating and the corrosion behavior of the material was investigated. The results imply that apatite crystals can form and grow on the surfaces of the biomimetic coating after soaking in simulated body fluid (SBF). The corrosion behavior of the material was investigated using an electrochemical polarization test in SBF solution for 3 days. The results showed that changes in the microstructure and crystalline texture of the substrate changed the coating morphology so that the growth of calcium phosphate changed from a rod-shaped with a diameter of 100–150 nm to a blade-shaped with a thickness of 20–50 nm. An increase in the corrosion resistance of the coated specimens with the corrosion rate of 0.65 mm/year was obtained compared to the uncoated specimen with the corrosion rate of 2.62 mm/year.

Mechanical properties and quality of plasma sprayed, functionally graded tungsten/steel coatings after process upscaling

The First Wall of a fusion reactor needs to withstand high heat flux as well as particle bombardment. For this, a First Wall made of steel requires a protective coating with a material that may still transfer heat for conversion to energy, such as tungsten. Its thermal expansion mismatch towards steel is overcome by vacuum plasma spraying of a functionally graded material onto the steel wall, followed by a tungsten top coat. This process was recently transferred to industry for upscaling, to develop a coating technology that can cover the large dimensions of First Wall components without deteriorating the substrate steel's properties by overheating. This work represents an instrumented indentation study of the achieved coating quality and properties, combined with microstructural analysis. Hardness profiles within coating and substrate indicate successful establishment of a linearly functionally graded material and only minor substrate overheating. The latter observation is supported by electron backscatter diffraction showing no change in the substrate's microstructure. The substrate hardness was investigated on several positions of coated plates sizing up to 500 × 250 mm2. The results indicate faster cooldown in the plate corners. Cooling channel bores that were pre-fabricated in the plates had no effect on plate hardness after coating. The elastic modulus of the coating's interlayers, determined by instrumented indentation, was found lower than predicted from bulk properties. This is attributed to the heterogeneous microstructure of the thermally sprayed coating.

Hydrothermal Coating of the Biodegradable Mg-2Ag Alloy

Developing antibacterial biodegradable Mg alloys is of paramount importance to prevent infection and inflammation during the healing process. In this regard, the Mg-2Ag alloy is proposed as a suitable candidate with appropriate biocompatibility as well as antibacterial activity. However, its rapid degradation rate limits its clinical application. To tackle this problem, the hydrothermal coating technique was employed to synthesize a barrier coating to enhance the degradability of the Mg-2Ag alloy using distilled water as the reagent. Field emission scanning electron microscopy (FESEM) micrographs and X-ray diffraction (XRD) patterns showed that a hydroxide coating was formed on the studied samples. Furthermore, it was observed that the substrate microstructure plays an essential role in the obtained coating quality and hence, the degradation behavior. The dendritic microstructure with the nonuniform distribution of Ag-rich precipitates of the as-cast Mg-2Ag alloy lead to undesirable cracks and holes in the coating owing to Mg deficiency to form Mg(OH)2, whereas the solution-treated alloy with a homogenized microstructure resulted in the formation of a more compact, thick, and integrated coating, which remarkably improved the corrosion resistance of the alloy.

Silicon nitride assisted carbon nanotubes induced stacking faults and twins in aluminum alloy composite joint

The extensive heat input during welding can generally disrupt the meticulously crafted microstructure of the Al alloy substrate, leading to a marked decrease in the mechanical performance of the traditional joint. Here, we conducted a study of adding silicon nitride and CNTs to form Al composite joints, which not only compensated for the microstructural defects caused by welding, but also improved the tensile strength of the joints by 31%. Importantly, microstructural analysis reveals that there are twinning and SFs in both Al and Al4C3 phase. It was contributed to Al4C3 growth and the reduction in Al alloy SFs energy by CNTs. Moreover, the residual CNTs and Al4C3 phase in the composite joints refined the original precipitation phase network. This work is supposed to provide new insights into the strengthening of composite joints based on SFs and twins.

Corrosion-fatigue property of anodic oxidation coated 6082-T6 aluminium alloy: Effect of substrate residual stress and microstructure beneath coating-substrate interface

Plain (anodic oxidation) and composite (prior shot peening + anodic oxidation) coatings were prepared to investigate their effects on the corrosion-fatigue (CF) property of 6082-T6 aluminium alloy in a 3.5 wt% NaCl aqueous solution. The results indicate that plain coated specimens exhibited similar CF properties to as-machined specimens at low applied stresses. However, under high applied stresses, the plain coating led to a preferential fracture and was unable to effectively prevent corrosion medium. Hence, the CF property of plain coated specimens was found to be inferior to as-machined specimens at high applied stresses. The synergetic effect of substrate residual stress and microstructure beneath the coating-substrate interface reduced the crack propagating rate in the initial stage by deflecting the crack at the grain boundary. Therefore, the CF property of composite coated specimens improved as a whole when compared with as-machined and plain coated specimens. Besides, under low applied stresses, the near-interface substrate residual stress of composite coated specimens occurred the relaxation due to the substrate crack propagation, while under high applied stresses, this was due to the synergetic effect of materials' local cyclic yield and plastic flow, as well as the substrate crack propagation.

Effect of the Solder Powder Size of Sn-Bi-Ag-In Lead-Free Solder on the Wettability and Microstructure of Cu Substrate

Abstract In this study, tin-bismuth-silver-indium (Sn-Bi-Ag-In) lead-free solder powders are prepared by the consumable-electrode direct current arc (CDCA) method. Without agglomeration, the satellite-free solder powders show good sphericity. The effect of solder powder sizes on the wettability and microstructure of Sn-Bi-Ag-In solder alloy on copper substrate is systematically investigated. The solder joints prepared by solder powder in a size of 53–120 μm exhibit relatively small wetting angles. In addition, the microstructure of the solder joints is composed of bismuth-rich phases, tin-rich phases, and Ag3Sn phases. A continuous intermetallic compound (IMC) layer with a thickness in the range of 0.64–0.70 μm is formed at the interface between the solder and the copper substrate. The results show that the formation and morphology variety of the IMC layers for different solder joints are unobvious, reflecting the good wettability of the Sn-Bi-Ag-In lead-free solder powders on the copper substrate in a wide size range.

Study on microstructure of rare earth Mg-9%Gd-2%Y-3%Nd -0.7%Zr alloy and properties of micro-arc oxidation films

The micro-arc oxidation protective film has been prepared on the surface of Mg-9%Gd -2%Y-3%Nd-0.7%Zr alloy by using the microarc oxidation technique of “step by step depressurization”. The microstructure of magnesium alloy substrate and micro-arc oxidation film were measured by OM, SEM and XRD, and the properties of the film were evaluated by electrochemical test of film thickness and surface morphology. The results show that the discontinuous network multiple eutectic phases are distributed in the grain boundary and there are dispersed-granular precipitates in the alloy matrix. After the micro-arc oxidation treatment, the thickness and corrosion resistance of the micro-arc oxidation film increased with the increase of oxidation time, and the surface micropore size increased first and then decreased, and the surface morphology of the micro-arc oxidation film changed from no micro-crack to micro-crack, and finally the micro-crack disappeared.

Impact of Fireside Corrosion on the Creep Rupture Life and Oxide Scale Structure of a Super304H Boiler Tube

The creep rupture life of commercial Super304H in fireside corrosion (coal ash and flue gas) and static air environment at 650°C was investigated. Results showed that the creep rupture life under fireside corrosion conditions decreases by 26.5% to 83.3% at different stress levels, compared with that in air. The corrosion products, including their composition, morphology, and distribution, and the microstructure of substrate were characterized to research the impact of the fireside corrosion on the creep rupture life. The exfoliation of oxide scales and serious surface cracking resulted from fireside corrosion were detrimental for the creep properties of the alloy. The formation of internal sulfides promoted the initiation and propagation of intergranular cracks in the substrate during creep tests. These degradations of Super304H in fireside corrosion contributed to premature creep rupture.

Anti-coking performance of Al/Si/Cr/Ce ceramic coating during naphtha steam cracking applied on Cr25Ni35Nb alloy

To reduce the coke formation, a novel Al/Si/Cr/Ce composite ceramic coating was prepared on the surface of the Cr25Ni35Nb alloy substrate by pack cementation. The microstructure, phase composition, surface morphology and element distribution of substrate and coating were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The results reveal that the outer layer of the coating forms a protective layer with a high proportion of AlN and Cr3Si and trace amounts of Ce. The inter-diffusion layer is mainly aluminide coating (AlNi and AlFe) and transition layer contains a small amount of AlN. The anti-coking performance of the coating was assessed using naphtha steam cracking. To study coking behavior, the morphology and microstructure of the coke layer were analyzed and characterized by SEM and Laser Micro-Raman Spectrometer. The coke layer on uncoated sample has a higher focal density and is more likely to spall and peel off when subjected to coking experiment. A large number of filamentous and granular cokes appear on the surface of the uncoated sample, whereas only less granular cokes appear on the surface of the coated sample, and the coke on the uncoated sample has a more disordered and amorphous carbon structure. The coating significantly inhibited the growth of filamentous coke and reduced coke accumulation.

Application of Self-Assembled Polyarylether Substrate in Flexible Organic Light-Emitting Diodes.

The structure used in this study is as follows: substrate/PMMA/ZnS/Ag/MoO3/NPB/Alq3/LiF/Al. Here, PMMA serves as the surface flattening layer, ZnS/Ag/MoO3 as the anode, NPB as the hole injection layer, Alq3 as the emitting layer, LiF as the electron injection layer, and aluminum as the cathode. The properties of the devices with different substrates were investigated using P4 and glass, developed in the laboratory, as well as commercially available PET. After film formation, P4 creates holes on the surface. The light field distribution of the device was calculated at wavelengths of 480 nm, 550 nm, and 620 nm using optical simulation. It was found that this microstructure contributes to light extraction. The maximum brightness, external quantum efficiency, and current efficiency of the device at a P4 thickness of 2.6 μm were 72,500 cd/m2, 1.69%, and 5.68 cd/A, respectively. However, the maximum brightness of the same structure with PET (130 μm) was 9500 cd/m2. The microstructure of the P4 substrate was found to contribute to the excellent device performance through analysis of the AFM surface morphology, film resistance, and optical simulation results. The holes formed by the P4 substrate were created solely by spin-coating the material and then placing it on a heating plate to dry, without any special processing. To confirm the reproducibility of the naturally formed holes, devices were fabricated again with three different emitting layer thicknesses. The maximum brightness, external quantum efficiency, and current efficiency of the device at an Alq3 thickness of 55 nm were 93,400 cd/m2, 1.7%, and 5.6 cd/A, respectively.

Thermomechanical Responses of Microcracks in a Honeycomb Particulate Filter

Manufacturing honeycomb‐structured catalysts require a careful understanding of the microstructure of the solid substrate and its dependence on thermal‐processing conditions. Herein, it is the thermal responses of microcracks in an uncoated microcracked aluminum titanate honeycomb catalyst is investigated by analyzing the material's resonance frequency using the high‐temperature impulse excitation technique. The resonance frequencies are presented as Young's modulus values to avoid sample size effects. Dynamic Young's modulus measurements show closed‐loop hysteresis due to microcracks healing and reopening, causing a reversible response. The hysteresis is further used to understand microcracks’ dependence on critical thermal‐processing conditions used in a catalyst manufacturing plant, including peak operating temperature (800–1000 °C), dwell period (1–3 h), and heating rates (1–5 °C min−1). Microcracks are observed to have two healing responses: instantaneous and delayed healing. Both responses significantly influence the design of catalyst manufacturing. Complete reopening of microcracks from their healing temperature (1150 °C) is a very time‐consuming process (50–60 h). However, it is shown in the analysis that microcrack relaxation is a critical phenomenon that must be considered in quality‐controlled environments.

Aerosol deposition of alumina films on microstructured silicon substrates

Aerosol deposition (AD) is a room-temperature ceramic coating method, which has been used for many applications. Various substrates, such as metals and ceramics, have been used depending on the application, but it is not clear how the substrate microstructure affects the deposition processes and film quality. In this study, AD alumina films deposited on silicon substrates with microstructures consisting of line and space patterns were systematically investigated. The films were formed along the microstructure on the substrate when the linewidth was much larger than the grain size of the raw powder. Conversely, on narrow-linewidth substrates, the films were supported by the lines and the spaces were sealed. The effect of the substrate microstructure was analyzed in terms of the residual stress of the films.

Calibration of Cellular Automaton Model for Microstructure Prediction in Additive Manufacturing Using Dissimilarity Score

Abstract Additive manufacturing (AM) simulations offer an alternative to expensive AM experiments to study the effects of processing conditions on granular microstructures. Existing AM simulations lack support from reliable validation techniques. The stochastic nature and spatial heterogeneity of microstructures make it difficult to validate the simulated microstructures against experimentally obtained images through statistical measures such as average grain size. Another challenge is the lack of reliable and automated methods to calibrate the model parameters, which are unknown and difficult to measure directly from experiments. To overcome these two challenges, we first present a novel metric to quantify the difference between granular microstructures. Then, using this metric in conjunction with Bayesian optimization, we present a framework that can be used to reliably and efficiently calibrate the model parameters. We employ this framework to first calibrate the substrate microstructure simulation and then the laser scan microstructure simulation for Inconel 625. Results show that the framework allows successful calibration of the model parameters in just a small number of simulations.

Development of high-strength magnesium alloys with excellent ignition-proof performance based on the oxidation and ignition mechanisms: A review

High reactivity and ease of ignition are the major obstacles for the application of Mg alloys in aerospace. Thus, the ignition mechanisms of Mg alloys should be investigated systematically, which can guide the ignition-proof alloy design. This article concludes the factors influencing the ignition resistance of Mg alloys from oxide film and substrate microstructure, and also the mechanisms of alloying elements improving the ignition resistance. The low strength is another reason restricting the development of Mg alloys. Therefore, at the last section, Mg alloys with the combination of high strength and good ignition-proof performance are summarized, including Mg-Al-Ca based alloys, SEN (Mg-Al-Zn-Ca-Y) alloys as well as Mg-Y and Mg-Gd based alloys. Besides, the shortages and the future focus of theses alloys are also reviewed. The aim of this article is to promote the understanding of oxidation and ignition mechanisms of Mg alloys and to provide reference for the development of Mg alloys with high strength and excellent ignition-proof performance at the same time.

Enhancing C≥2 product selectivity in electrochemical CO2 reduction by controlling the microstructure of gas diffusion electrodes.

We fabricate polymer-based gas diffusion electrodes with controllable microstructure for the electrochemical reduction of CO2, by means of electrospinning and physical vapor deposition. We show that the microstructure of the electrospun substrate is affecting the selectivity of a Cu catalyst, steering it from H2 to C2H4 and other multicarbon products. Specifically, we demonstrate that gas diffusion electrodes with small pores (e.g. mean pore size 0.2 μm) and strong hydrophobicity (e.g. water entry pressure >1 bar) are necessary for achieving a remarkable faradaic efficiency of ∼50% for C2H4 and ∼75% for C≥2 products in neutral 1M KCl electrolyte at 200 mA cm-2. We observe a gradual shift from C2H4 to CH4 to H2 during long-term electrochemical reduction of CO2, which we ascribe to hygroscopic carbonate precipitation in the gas diffusion electrode resulting in flooding of the Cu catalyst by the electrolyte. We demonstrate that even with minimal electrolyte overpressure of 50 mbar, gas diffusion electrodes with large pores (mean pore size 1.1 μm) lose selectivity to carbon products completely, suddenly, and irreversibly in favor of H2. In contrast, we find that gas diffusion electrodes with small pore size (mean pore size 0.2 μm) and strong hydrophobicity (water entry pressure ∼5 bar) are capable of resisting up to 1 bar of electrolyte overpressure during CO2RR without loss of selectivity. We rationalize these experimental results in the context of a double phase boundary reactivity, where an electrolyte layer covers the Cu catalyst and thus governs local CO2 availability. Our results emphasize the pivotal role of microstructure and hydrophobicity in promoting high C≥2 product selectivity and long-term stability in CO2RR flow cells.

Influence of scanning strategies on laser-cladded AISI 420 steel

ABSTRACT In this study, the influence of different laser scanning strategies on substrate deformation, microstructure and properties of laser-cladded thin-walled 420 martensitic stainless steel (MSS) plate have been carefully investigated. The continuous offset-out scanning strategy (COSS) and continuous raster scanning strategy (CRSS) was compared with the subarea offset-out scanning strategies (SOSS) and subarea raster scanning strategy (SRSS) with different sequences. The results show that the minimum and maximum macroscopic deformation was generated using COSS and CRSS, respectively. The temperature distribution with characteristic of quasi-symmetry was generated by COSS, which can largely suppress the substrate deformation, in marked contrast to a long ellipse symmetry by CRSS. All the laser-cladded 420 MSS layers exhibit lath-martensite microstructure, while some cracks are distributed by using SOSS. The optimal comprehensive performance of the laser-cladded 420 MSS can be obtained using COSS, with smallest outermost deformation of 1.57 mm, superior hardness of 54.9 HRC and wear rate of 0.9626 × 10−5 mm3/N·m.

Effect of Substrate Microstructure and Hydrophobicity on Ag Gas Diffusion Electrodes for Electrochemical CO2 Reduction

Electrochemical CO2 reduction (CO2RR) is a very promising way to convert detrimental CO2 emissions into sustainable fuels and chemicals, and move us closer to a circular economy.1 To compete with traditional fuel/chemical production routes, we need to develop electrocatalysts that are highly active, selectivity towards a desired product, and stable. Thanks to the use of gas diffusion electrodes (GDEs) that provide gaseous CO2 close to the catalyst, high activities can be achieved.2,3 However, product selectivity and stability must still be improved before practical application. An emerging strategy in this regard is to control the local environment surrounding a catalyst, i.e. the concentration of the various products and reagents therein.4 In this work, we achieve such control by varying the microstructure of substrates later used to fabricate GDEs by Ag deposition. By systematically studying the CO2RR performance, we observe a clear correlation between the pore size of the GDEs and their product selectivity, stability, and even resilience to Cu impurities.5 We rationalize it with the different effective hydrophobicity of the GDEs, which control the extent of electrolyte penetration within the electrode and depends on both substrate chemistry and pore size. We show that a higher effective hydrophobicity correlates with higher Faradaic efficiency towards carbon monoxide production (FECO up to 95 % at 100 mA/cm2) and longer stability (~100 % retention after a 1 hour electrolysis at 100 mA/cm2). These results show the importance of the substrate's microstructural properties in GDE for CO2RR, and highlight a new strategy to achieve control over selectivity and stability of these electrodes.

Corrosive properties of CuNi2SiCr fabricated through directed energy deposition on a nickel-aluminum bronze substrate

In this study, CuNi2SiCr powders were deposited on nickel-aluminum bronze (NAB) substrates through directed energy deposition (DED) and the corrosive resistance properties of the deposited CuNi2SiCr were evaluated through comparisons to the substrate. Metallographic observations revealed that the microstructure of the deposited layers was α-Cu, which is characterized by low strength and hardness, and high toughness. The microstructure of the NAB substrate exhibited higher hardness and strength than the deposited CuNi2SiCr because the substrate was composed of a typical α + β solid solution and different intermetallic κ phases. The electrochemical corrosion test demonstrated that the corrosion stability of the CuNi2SiCr-deposited was slightly better than that of the NAB substrate. Furthermore, the corrosion current density of NAB is slightly greater than that of the deposited CuNi2SiCr based on the existence of multiple phases forming a corrosion galvanic cell. The results of the cavitation erosion test revealed that the wear rate of the deposited material under the mechanical impact of bubbles is significantly greater than that of the substrate. The results of immersion test demonstrated that the corrosive resistance of NAB is significantly greater than that of CuNi2SiCr because a dense Al2O3 oxide film is formed on its surface. This study provides new concepts for the application of DED technology and CuNi2SiCr alloy. However, experimental results also demonstrate that the corrosion resistance of CuNi2SiCr alloy is lower than that of NAB and its performance must be further improved for application it in a marine-like working environment.

B2O3‐modified geopolymer and its liquid‐phase sintered products for immobilization of strontium

AbstractSr‐containing ceramic products produced from geopolymer, (Na, Sr)‐GP, have been reported as excellent candidate materials for the immobilization of radionuclide 90Sr, despite sintering temperature at 1200°C. In this work, the product possessing the best immobilization performance (leaching rate of 1.29% for Sr2+) can be produced at 1000°C in the method of liquid‐phase sintering via the addition of fluxing agent B2O3 at 2.0 wt% in the geopolymer precursor. The mechanical properties of the geopolymer precursor (Na, Sr)‐GP were also enhanced via the promotion role of B2O3 to geopolymerization. It was revealed that the overall anti‐leaching ability of the Sr‐containing ceramic product not only depends on the microstructure of the loading substrate but also can be affected by the chemical state of radioactive strontium retention in the loading matrix.