Elemental Vapor Research Articles

Characterization of TiC particle reinforced magnesium matrix composites (MMCs) prepared by laser cladding based on element evaporation

In this study, we report the preparation of AZ31/TiC composites by laser cladding based on elemental vaporization and supplementation and investigate the effects of laser process parameters and mixed powder ratio on the vaporization and spattering. It was found that the capillary pressure generated by using TiC could effectively suppress the molten pool sputtering during laser cladding. In addition, TiC particles promoted the recrystallisation behavior of the molten pool, and the grains were significantly refined from 61.58 μm to 6.46 μm. The random orientation of the recrystallized grains led to a weaker texture, decrease from 12.349 to 1.964. The microhardness of the composites higher than AZ31 from 46 to 86.2 HV0.2, and the average wear rate was reduced by 21.9%.

Directed energy deposition with a graded multi-material compatibility interface enables deposition of W on Cu

Multi-material Directed Energy Deposition of new high-performance components is limited by phase incompatibilities between metals and by the composition variations which complicate parameter optimization. In this work, a methodology of incorporation of a graded Multi-Material Compatibility Interface (MMCI) was employed to allow deposition of tungsten layers (melting at 3410 °C) on a much less refractory metal, copper (boiling at 2562 °C). The manufacturing of parts combining tungsten and copper is of interest for components designed to dissipate heat in extreme environments, such as the divertor for tokamak fusion reactors. A succession of miscible filler metals rationally selected from thermodynamics were printed by laser and powder injection, with optimization of energy and material inputs for each layer, supported by material characterization and physical numerical analysis of the process phenomenology. 90 %wt. tungsten layer deposition on a copper initial substrate is achieved using an MMCI with 6 intermediate layers and 1.6 mm total thickness. The results reveal the importance of controlling the dilution ratio to achieve stable depositions of multi-material with compositional gradients, with a progressive increase in melt pool temperatures. The numerical analysis highlighted the important role of the dissolution and mixing of partially melted refractory powders, and the selective vaporization of volatile elements.

Rapid and simultaneous detection of cadmium and mercury in foods based on solid sampling integrated electrothermal vaporization technique

This work presents an innovative solid sampling (SS) integrated electrothermal vaporization (ETV) approach for simultaneous determination of Cd and Hg based on differentiated elemental vaporization and transportation behavior characteristics. A miniature N2/H2 generator, only consuming electricity and H2O, was utilized to yield reducing atmosphere for Cd vaporization; MgO filler was modified to absorb matrix interferent and keep Hg and Cd transportation via 1st catalytic pyrolysis furnace (CPF); and a gearing was employed to move 2nd CPF to receive and trap (amalgamation) the vaporized Hg from ETV and then thermo-release them for simultaneous detection. Under optimized conditions, the limits of detection of Cd and Hg reached 0.02–0.04 ng/g using 0.4 g sample size. The linearities (R2) exceeded 0.998 and recoveries were 85.0–111.9%, indicating favorable analysis precision and accuracy within ∼3 min without sample digestion process. The proposed HgCd analyzer is suitable for rapid monitoring food with simplicity, green and safety.

Effect of primary air and coal properties on the formation of fine mode particles during low NOx gasification-combustion of coal in a self-sustaining furnace

Gasification-combustion technology can reduce NOx while the formation characteristics of fine mode PM is unclear. This research studied the impact of the excess air coefficient (αg) of the gasifier and the properties of coal on the formation and evolution of fine mode PM. The experiment was conducted on a self-sustaining furnace consisting of a gasifier where pyrolysis/gasification occurs and a combustion chamber where burnout of gasification gas and char occurs. The results showed that fine mode PM and NOx can be synergistically reduced by optimizing αg during gasification-combustion. A low or high αg can lead to a high furnace temperature in the gasifier or combustion chamber, respectively. Elimination of high temperature is crucial to reduce element vaporization which promotes the formation of fine mode PM. Additionally, an optimized combination of furnace temperature and reducing atmosphere in the gasifier can decrease NOx. The optimal αg was 0.32 for bituminous coal (BC). Fine mode PM generated from gasification-combustion of BC, lean coal (LC), and semi-char (SC) mainly consists of Ca, Si, Fe, and S. The vaporization of element from LC and BC primarily occurs during char combustion in the combustion chamber, while the vaporization of element from SC occurs almost equally in the gasifier and combustion chamber.

Chemical Vapor Deposition of Elemental Crystallogen Thin Films

A consolidation of the fundamentals of elemental crystallogen chemical vapor deposition (CVD) is a necessity in view of the extensive evidence accumulated over the last few decades. An in-depth understanding of deposition mechanisms via hydrides asks for a discerning understanding of molecular hydrogen dissociative adsorption, precursor thermal decomposition, and CVD growth rates. With those, a groundbreaking paradigm shift comes to light. GR activation energy E(GR) fingerprints the surface energy. SE ≈ 2 × E(GR)/(a×a), where SE is surface energy, E(GR) activation energy, a lattice parameter. Hydride precursor thermal decomposition consistency with the corresponding solid growth kinetics is demonstrated. Heterogeneous TD kinetics captures a solid deposition and not a gas phase molecular reaction. Thermodynamic equilibrium is achieved during the heterogeneous thermal decomposition of silicon precursors. The popular split between mass-transfer and kinetic regimes is not supported by evidence. Three mechanisms are apparent. The first is controlled by a Si–H bond dissociation energy. The second is controlled by an H–H bond dissociation energy. The last is controlled by a Si–Si bond dissociation energy as lattice sites are sealed off with Si–H bonds.

Experimental study on the formation characteristics of PM0.4 from preheating combustion of sewage sludge

Municipal sewage sludge (SS) is gaining increasing attention as a carbon–neutral fuel. Preheating combustion has been applied in coal combustion to reduce both PM0.4 and NOx. It is a promising technology for SS disposal while PM formation from preheating combustion of SS is still unknown. This study investigated the formation characteristics of PM0.4 from preheating combustion of SS. The effects of preheating temperature (Tp) and combustion temperature (Tc) on PM0.4 were analyzed. The experimental results showed that simultaneous reduction of PM0.4 and NOx from preheating combustion of SS can be achieved with Tp ≤ 1300 °C and Tc ≤ 1200 °C. The reduction of PM0.4 in preheating combustion compared to conventional combustion is mainly attributed to reduction in vaporization of Ca. Tc has more significant effect on PM0.4 while Tp can affect NOx more effectively. Because SS has a low content of fixed carbon, vaporization of refractory elements (Ca, Mg, Fe, Si and Al) through reduction reaction of refractory oxides mainly occurs under reductive atmosphere in preheating furnace. Increasing Tc will significantly increase vaporization of alkali metals (Na and K), S and Cl, while has no significant effect on vaporization of refractory elements. These are different with the results from high-alkali coal in our previous research (Reference [28]). Fe-precipitation agent used in waste water treatment results in uniform distribution of Fe in SS particles, which enhanced interaction between Fe and Si-Al containing minerals. This decreases reaction between Si-Al containing minerals and Na containing compounds. Therefore, even SS contains less Na and more Si-Al than high alkali coal, Na is easier to transfer to PM0.4 in preheating combustion of SS than high alkali coal.

Efficiency Boost of (Ag0.5,Cu0.5)(In1‐x,Gax)Se2 Thin Film Solar Cells by Using a Sequential Process: Effects of Ag‐Front Grading and Surface Phase Engineering

AbstractPost‐selenization‐fabricated (using elemental Se vapor) Cu(In,Ga)Se2 solar cell efficiency is limited by a low open‐circuit voltage, which is attributable to the Ga‐deficient surface and insufficient grain growth. In this study, a band‐grading structure is demonstrated by combining Ag‐front and Ga‐back grading in selenized (Ag,Cu)(In,Ga)Se2 (ACIGSe) absorbers with a properly designed precursor structure (Mo/CuGa/In/AgGa) and high Ag content ([Ag]/([Ag]+[Cu]) = 0.5). The phase evolution during post‐selenization reveals that the precursor structure suppresses Ag2Se formation and promotes the ACIGSe phase formed at a low temperature with enhanced grain growth. A widened surface bandgap by Ag‐front grading substantially increases the open‐circuit voltage. Furthermore, Ag addition promotes ordered vacancy compound (OVC) formation on the front surface to enlarge the valence band offset, which in turn reduces interface recombination. Furthermore, the OVC phase also assists interface passivation. Promoting surface OVC phase by Ag addition is also validated by first‐principles calculations. Furthermore, the K‐doped CuGa precursor is used for a ACIGSe absorber to address the significantly reduced carrier density by the Ag addition. With a band‐grading structure and surface OVC phase, the superior device achieves an efficiency of > 19%, the highest efficiency by post‐selenization with an elemental Se source.

Inhibiting the formation of PM0.4 by optimizing the distribution of excess air coefficient in preheating combustion of lignite

Preheating combustion can effectively reduce NOx concentration, but the formation characteristics of PM0.4 in preheating combustion is unclear. In this study, the emission of PM0.4 in preheating combustion was reduced by optimizing the distribution of excess air coefficient. The mass-based particle size distribution (MPSD) of PM10, mass yield of PM0.4, elemental compositions and morphologies of PM, and the number-based particle size distribution (NPSD) were analyzed to discuss the effect of αp on PM formation. The results showed that in preheating combustion, with an increase of αp, the mass yield of PM0.4 first decreased and then increased. The mass yield of PM0.4 is minimum when αp is 0.6. Preheating combustion can simultaneously reduce PM0.4 mass yield and NOx concentration. The relationship between NOx concentration and αp is similar to the relationship between the mass yield of PM0.4 and αp. The MPSD of PM0.4 is multimodal and unimodal when αp is less than 1 and larger than 1, respectively. Particle volume concentration of PM0.4 indicates that the multimodal and unimodal of PM0.4 is a result of evolution of particles with different characteristics of gas-to-particle transformation. The effect of αp on the transformation of inorganic element from coal particles to PM0.4 is S > Fe ≈ Ca ≈ Mg > Na > Si. αp affects the mass yield of PM0.4 by affecting the combustion intensity of coal/char particles in preheating furnace and combustion furnace. When αp is 0.6, the combustion intensity of coal particles in preheating furnace and combustion furnace minimize the vaporization of inorganic elements.

The effect of preheating temperature and combustion temperature on the formation characteristics of PM0.4 from preheating combustion of high-alkali lignite

Preheating combustion is getting popular because it can reduce NOx formation, but its effect on particulate matter (PM) formation is still unclear. This study focuses on the effect of preheating temperature (Tp) and combustion temperature (Tc) on the formation characteristics of fine mode particles (PM0.4) in preheating combustion. The mass-based particle size distribution, elemental compositions and morphologies of PM and number-based particle size distribution were analyzed to reveal the mechanisms of reducing PM0.4 formation during preheating combustion. The results showed that compared with conventional combustion, preheating combustion with optimized Tp and Tc can effectively decrease the mass yield of PM0.4 and NOx concentration by 77.9% − 82.2% and 70.9% − 77.8%, respectively. In preheating combustion, the mass yield of PM0.4 basically didn’t change with Tp. When Tc was lower than Tp, the mass yield of PM0.4 was basically unchanged with Tc. The precursors of PM0.4 mainly vaporized in the preheating furnace. The vaporization of inorganic elements, gas-to-particle transformation, and coagulation occurring in the combustion furnace had a negligible effect on the mass yield of PM0.4. When Tc was higher than Tp, increasing Tc can significantly increase the vaporization of inorganic elements from unburned char/coal particles in the combustion furnace. As a result, the mass yield of PM0.4 increased. To effectively reduce the formation of PM0.4 and NOx, a higher Tp and a lower Tc is suggested. The volatility of inorganic elements in preheating combustion has an order as S > Na > Mg > Fe≈Ca > Si. Refractory elements including Fe, Mg, and Ca contributed the most to decrease of PM0.4 in preheating combustion compared with conventional combustion. Preheating combustion has a stronger reductive atmosphere and a lower particle temperature. The vaporization of inorganic elements from coal particles in preheating combustion is probably determined by particle temperature rather than reductive atmosphere.

VapoRock: Thermodynamics of Vaporized Silicate Melts for Modeling Volcanic Outgassing and Magma Ocean Atmospheres

Silicate vapors play a key role in planetary evolution, especially dominating early stages of rocky planet formation through outgassed magma ocean atmospheres. Our open-source thermodynamic modeling software “VapoRock” combines the MELTS liquid model with gas-species properties from multiple thermochemistry tables. VapoRock calculates the partial pressures of 34 gaseous species in equilibrium with magmatic liquid in the system Si–Mg–Fe–Al–Ca–Na–K–Ti–Cr–O at desired temperatures and oxygen fugacities (fO2, or partial pressure of O2). Comparison with experiments shows that pressures and melt-oxide activities (which vary over many orders of magnitude) are reproduced to within a factor of ∼3, consistent with measurement uncertainties. We also benchmark the model against a wide selection of igneous rock compositions including bulk silicate Earth, predicting elemental vapor abundances that are comparable to (Na, Ca, and Al) or more realistic than (K, Si, Mg, Fe, and Ti) those of the closed-source MAGMA code (with maximum deviations by factors of 10–300 for K and Si). Vapor abundances depend critically on the activities of liquid components. The MELTS model underpinning VapoRock was calibrated and extensively tested on natural igneous liquids. In contrast, MAGMA’s liquid model assumes ideal mixtures of a limited set of chemically simplified pseudospecies, which only roughly approximates the nonideal compositional interactions typical of many-component natural silicate melts. Finally, we explore how relative abundances of SiO and SiO2 provide a spectroscopically measurable proxy for oxygen fugacity in devolatilized exoplanetary atmospheres, potentially constraining fO2 in outgassed exoplanetary mantles.

The Resistance to Wear and Thermal Cracking of Laser Surface Engineered P20 Steel

This study reports the microstructure and surface properties of P20 steel processed by laser surface engineering (involving surface hardening and melting), which are carried out using a fiber laser with the maximum power of 2 kW. Ultrafine martensite laths with high boundary density are formed both in the laser surface hardened layer and in the melted layer. This dramatically improves the surface hardness of the P20 steel. However, the laser surface melted layer exhibits a relatively lower hardness than the laser surface hardened layer. It can be attributed to the remarkable autotempering effect and the vaporization of alloy elements in the melted layer. The wear resistance and thermal cracking resistance of the samples treated by laser surface engineering show a significant improvement compared with the as received material. The surface hardened layer exhibits superior wear and thermal cracking resistance due to its relatively high surface hardness and plastic deformation resistance, which can effectively suppress the formation of cracks during wear and thermal cracking tests.

Effects of torrefaction on ash-related issues during biomass combustion and co-combustion with coal. Part 1: Elemental partitioning and particulate matter emission

Torrefaction is a promising technology to scale up the utilization of biomass for power purposes. The ash-related issues during biomass combustion and co-combustion are essential to be addressed, however, on which the effects of torrefaction are seldom concerned and need in-depth and comprehensive investigation. To provide useful information related, the authors conducted a series of studies. In the present work, the particulate matter (PM) emission during combustion is focused on. Three biomasses were torrefied at a fixed-bed reactor, and the elemental release and transformation during torrefaction were characterized through chemical fractionation analysis. The combustion tests of the raw and torrefied biomass and their blends with two typical coals were conducted on a drop-tube furnace at 1300℃ in air. The PM10 (particulate matter with an aerodynamic particle size below 10 μm) collected by a Dekati low-pressure impactor and PM10+ (particulate matter with an aerodynamic particle size above 10 μm) collected by a Dekati cyclone were characterized by a scanning electron microscope equipped with energy dispersive spectrometer (SEM-EDS). The results indicate that torrefaction effectively reduces S and Cl in biomass while slightly reducing the alkalis. The contents of refractory elements (Mg, Ca, and Fe) are hardly influenced. Torrefaction promotes the transformation of AAEMs (alkaline and alkaline earth metals) into less-reactive forms (HCl-soluble and insoluble). The vaporization of alkalis, S, and Cl during biomass combustion is reduced and the retention of AAEMs into aluminosilicates is promoted after torrefaction. This reduces the emission of PM1 (particulate matter with an aerodynamic particle size below 1 μm) from biomass combustion. During co-combustion, the PM emission largely depends on the combined effects of elemental vaporization, competing reactions (alkalis against Mg, Ca, and Fe), retention of metals into aluminosilicates, and sulfation of chlorides. The inhibited effect of torrefaction on mineral vaporization reduces the formation of PM1 by condensation. The emission of PM1-10 (particulate matter with an aerodynamic particle size between 1 and 10 μm) either increases due to the promoted retention of the metals in coarse particles or decreases by agglomerating into PM10+. Torrefaction shows a preferable performance concerning its effects on PM emission during biomass combustion and co-combustion with coal.

Investigation of the process of sulfiding of gold-arsenic containing ores and concentrates

Purpose. Research of the removal of arsenic by sulfiding from gold-arsenic containing concentrates of the Bakyrchik deposit. Methodology. To determine the composition of the samples, chemical and electron probe analysis were carried out; to determine the phase composition of materials, X-ray analysis was conducted. In order to predict the process of sulfidation of arsenic and its compounds in the range of 2982000 K, a thermodynamic analysis was performed. To establish the optimal conditions for the process of sulfiding arsenic and its compounds, studies were carried out to determine the effect of temperature and the consumption of elemental sulfur on the degree of sublimation of arsenic from gold-arsenic concentrate. The sulfiding roasting of the concentrate was carried out with elemental sulfur vapor coming from a new design evaporator with a mixture of gaseous nitrogen. Findings. The main minerals of the original concentrate are pyrite, marcasite, arsenopyrite, native gold and silver. Significant elements in the concentrate are, %: arsenic 2.93.1, iron 707.3, gold 40. It has been calculated by thermodynamic analysis that when the main minerals of gold-arsenic containing refractory ores and concentrates interact with sulfur in a neutral environment and in the range of 5001000 C, reactions of formation and removal of arsenic in the form of sulfides As2S3 and As4S4 occur. When a new design evaporator supplies elemental sulfur in a mixture with neutral gas and with an increase in firing temperature from 700 to 850 C at S : As = 0.35 : 1, the degree of sublimation of arsenic increases from 94.7 to 98.2%, with FeS2 : As = 1.3:1 from 94.0 to 99.5%. With an increase in the consumption of elemental sulfur vapor (with an increase in the S : As ratio from 0.35:1 to 0.6 : 1 and a temperature from 700 to 800 C), the degree of sublimation of arsenic from the gold-arsenic product reaches up to 99%. The condensed sublimes contained up to 98.599% As4S4 and As2S3, the dust caught in cyclones is close in its composition to the composition of cinder. Originality. A new technology for the removal of arsenic from gold-arsenic containing concentrates in an oxygen-free atmosphere in the temperature range of 700850 C with the removal and capture of arsenic sulfides up to 100% is proposed. The regularity of the degree of sulfidation of arsenic and its oxidized compounds by elemental sulfur vapors in a mixture with a neutral gas to As4S4 and As2S3 has been established. Practical value. The use of the new technology makes it possible to completely convert arsenic into sulfide forms which are environmentally friendly, convenient for storage, burial, or for use as antiseptics. The development can be used for processing arsenic-containing polymetallic ore materials.

Microstructure and mechanical properties of WMoTaNbTi refractory high-entropy alloys fabricated by selective electron beam melting

WMoTaNbTi RHEAs formed by SEBM with negative defocus distance were investigated. Four scanning speeds were applied, an electron beam with scanning speed at 2.5 m/s completely fused the premixed WMoTaNb alloyed powder and pure Ti powder. Significant vaporization of Nb and Ti elements happened during the formation of WMoTaNbTi RHEAs, however, the single BCC phase remains stable. Weakened solid-solute strengthening caused by elemental vaporization, dropping percentage of Nb and Ti solutes in the matrix as well as improved ductilizing effects with decreasing scanning speeds leads to falling microhardness and better local ductility. Microhardness of scanning speed at 4.0 m/s, 3.5 m/s, 3.0 m/s and 2.5 m/s is 578 ± 17 HV, 576 ± 12 HV, 573 ± 10 HV and 511 ± 2 HV, respectively. The as-deposited WMoTaNbTi RHEA formed at a scanning speed of 2.5 m/s displays ultimate strength of 1312 MPa.

Selective laser melting of novel 7075 aluminum powders with internally dispersed TiC nanoparticles

7075 aluminum alloy (AA7075) has been extensively used in the aerospace and defense industries owing to its supreme mechanical performance. As a promising platform to fabricate metallic components with complex structures, selective laser melting (SLM) has been successful in manufacturing aluminum alloys such as Al-Si-Mg. However, high-strength AA7075 is difficult to be manufactured by SLM due to its tendencies toward hot cracking and elemental vaporization. Here, specially designed AA7075 powders with internally dispersed TiC nanoparticles are produced by gas atomization. Through parameter optimization, novel AA7075 powder has been successfully laser printed to form dense parts with homogenous microstructures containing equiaxial grains, delivering a tensile strength of up to 550 MPa and ductility of over 6.5%. After heat treatment, the tensile strength further increased to approximately 650 MPa. TiC nanoparticles play a crucial role in SLM to refine grains while eliminating hot cracks.

Formation mechanism of Al-Zn-Mg-Cu alloy fabricated by laser-arc hybrid additive manufacturing: Microstructure evaluation and mechanical properties

A novel additive manufacturing followed by a hybrid process involving pulsed laser and tungsten inert gas (TIG) arc was proposed to balance the element vaporization, microstructure uniformity, and mechanical properties of the Al-Zn-Mg-Cu alloy. The amount of vaporized Zn in the laser-arc hybrid additive manufacturing (LAHAM) reduced by merely 2.5%, whereas the Zn vaporization loss of the WAAM specimens reached up to 8.3%. Compared with the grain sizes of specimen obtained via WAAM, those obtained via LAHAM decreased by approximately two times. The < 100 > texture in the LAHAM specimen was decreased significantly, due to the appearance of equiaxed grains and grain refinement. Furthermore, in contrast to WAAM specimen, the eutectics contained Al, Zn, Mg and Cu were evenly distributed in the LAHAM specimen, resulting in uniform element distribution. Nano-precipitates were dispersedly distributed within the grains in the LAHAM specimen, whereas they merely appeared around the grain boundaries in the WAAM specimen. Owing to microstructure changes, LAHAM improved the ultimate tensile strength and yield strength by up to 11.4% and 29.9%, as compared with WAAM. The substantial improvement in yield strength was primarily attributed to precipitation strengthening, instead of grain boundary strengthening or solid solution strengthening.

Estimation of the possibility of controlling the temperature of an electrothermal atomizer by the signals of the element absorption

The current system of the temperature control for the electrothermal atomizer (ETA) used in atomic absorption spectrometers for simultaneous multielement analysis, is unable to provide high characteristics of the analysis when the calibration of the built-in optical pyrometer becomes irrelevant due to the natural wear of graphite cells upon operation. As the control of the ETA efficiency using an external calibrated pyrometer is laborious, it is advisable to use the dependence of temperature on the time of appearance of atomic vapors of elements. We have studied the possibility of controlling the temperature of graphite cells in the electrothermal atomizer of a multielement atomic absorption spectrometer with a continuous spectrum source by the time dependence of absorption signals of chemical elements. The correctness of the calibration was checked by recording the absorption signals of a sample containing chemical elements of different volatility with subsequent evaluation of the time and the corresponding temperature of the appearance of atomic vapors of the elements. The obtained temperatures of the appearance of atomic vapors of Al, Cd, In, Mn, Ni, Pb and V ranged within 640 – 1940°C. When the heating rate is changed by a factor of more than 3, the vapor appearance temperature for the selected elements differs by less than 5%. Using a deliberate change in the calibration of the built-in optical pyrometer, we have simulated a situation in which the relevance of the calibration was lost, e.g., due to the wear of a graphite cell. The experiment revealed a shift of the correlation graph between the actual and measured temperatures of the appearance of vapors of elements in the case of incorrect calibration of the feedback pyrometer in the coordinates «Real temperatures» — «Measured temperatures». The method presented in the study can be used to check the correctness of the calibration of the built-in pyrometer and to determine the necessity of replacing a worn graphite cell.

Blackbox optimization for approximating high-fidelity heat transfer calculations in metal additive manufacturing

Heat transfer simulations play an important role in predicting solidification conditions that determine microstructure properties of additive manufactured products. High-fidelity heat transfer models, e.g., Truchas [1], provide a numerical framework capable of resolving many desired physics (e.g., thermal radiation, elemental vaporization, gas-solid-liquid interactions, etc.), but they are often too computationally expensive to simulate the solidification conditions at the AM process-scale. Recently, Stump et al. [2] proposed a low-fidelity analytical heat conduction model capable of simulating solidification conditions on the process-scale. This model makes the problem analytically tractable by neglecting many important physics that may have an impact on the accuracy of the predicted solidification conditions. An effective way of improving the accuracy of the analytical with little computational effort is to determine an optimal set of parameters that minimize the discrepancy between the low-fidelity analytical model and a high-fidelity numerical model. In this work, a model approximation problem is formulated which can be solved by leveraging blackbox optimization methods. Multiple heat sources are used in the analytical model to improve the calibration performance in a flexible framework. Two blackbox optimization methods, i.e., Bayesian optimization and directional Gaussian smoothing methods, are employed to address the challenge that the gradient of the loss function is inaccessible during optimization. The results show that the single-beam analytical model has limitations in fitting the high-fidelity model, but the proposed multi-beam analytical model provides satisfactory approximations to the high-fidelity temperature and melt pool fields.

Influence of laser power on precipitate formation and multiple step transformation kinetics in NiTi shape memory alloy weld joints

NiTi shape memory alloys are considered to be one of the fastest-growing materials with vast potential. However, the broader applications in intricately designed components are limited due to difficulties faced during welding processes such as degradation of functional and mechanical properties, precipitate formation, and selective vaporization of elements. In this study, the effect of laser power on precipitates formation and subsequent transformation temperatures on NiTi shape memory alloy was investigated by testing 0.8 kW, 1.0 kW and 1.2 kW welded specimens. The microstructures revealed the formation of Ni4Ti3 precipitates in the fusion zone and energy dispersive X-ray spectroscopy assessment exhibited preferential Ni evaporation. Differential scanning calorimetry analysis revealed the evolution of multiple step transformations (3-step / 3-step) after laser welding. Furthermore, enthalpy change in peak transformations was evaluated and increasing order of enthalpy change was recorded for weld joints with increasing laser power. The kinetics of martensite transformation was evaluated by placing emphasis on average activation energy. High laser power welded joints showed easy martensitic transformation compared to low laser power welded joints. X-ray diffraction assessment also validated the existence of Ni4Ti3 precipitates and martensitic phase in NiTi alloy after laser welding. The electron backscattered diffraction maps of welded joints revealed the grain growth in the fusion zone and heat affected zone, and the unindexed black region emphasized the formation of distorted interphase of austenite/martensite and additional martensite phase at the fusion zone/heat affected zone interface.

Effect of ER5356 Welding Wire on Microstructure and Mechanical Properties of 5083 Aluminum Alloy GTAW Welded Joint

Automatic gas tungsten arc welding experiments of 5083 aluminum alloy were completed, to analyze the weld microstructure and mechanical properties. The influences of welding current, travel speed, frequency, and arc length on weld forming and mechanical properties were studied. When the welding current was 160 A, the travel speed was 380 mm/min, the frequency was 100 Hz, the arc length was 4 mm, and the maximum tensile strength of the welded joint was 296.9 MPa, which was 86.8% of the base metal’s tensile strength. The fracture elongation was 7.8%. No porosity was formed in the weld, but there were poor fusion problems. ER5356 welding wire can improve the problem of poor weld fusion and accommodate Mg element vaporization losses. When the wire feeding speed was 1200 mm/min, the tensile strength of the welded joint can be improved to 315.2 MPa, which was 92.2% of the base material’s tensile strength, and the fracture elongation was 8.5%. The tensile specimens fractured in the heat-affected zone. The fracture surface was characterized as plastic fracture. Introduction Specific strength of aluminum alloy is high, so aluminum alloys reduce the weight of the structure compared with steel structures. Aluminum alloys have a broad application prospect in aerospace, automotive, and marine industries based on their good corrosion resistance, low temperature resistance, good processability, and rich alloy system (Kuk et al. 2004; Wang &amp; Zhang 2015; Canepa et al. 2018; Gaur et al. 2018; Qiang &amp; Wang 2019). In recent years, to reduce the weight of the structure such as trimaran hull and improve speed, aluminum alloys have been more and more applied in shipbuilding. But there are many problems in the welding of aluminum alloy.