Distribution Of Alloying Elements Research Articles

Microstructure, mechanical and corrosion study of friction stir processed Inconel 625 additive layers deposited via wire arc direct energy deposition

This study explores the application of friction stir processing (FSP) as an effective post-deposition surface treatment technique for improving the mechanical and corrosion properties of wire arc direct energy deposited (WA-DED) Inconel 625 additive layers. The coarse and cube-oriented microstructure observed in as-built Inconel 625 components results in anisotropic mechanical properties. The non-equilibrium solidification in WA-DED Inconel 625 leads to severe micro-segregation of alloying elements, forming large Nb and Mo-rich Laves and carbide phases in the inter-dendritic areas. This causes a heterogeneous distribution of vital alloying elements within the γ-Ni matrix of the material, adversely affecting its mechanical properties and corrosion resistance, thereby restricting the utility of this manufacturing technique in critical applications. The incorporation of FSP has been observed to successfully eradicate the presence of typical coarse and highly oriented microstructure through grain refinement, achieving a more uniform microstructure. Through severe plastic deformation (SPD), coarse eutectic phases are broken down and redistributed within the γ-Ni matrix, enhancing the uniformity of material properties. The research thoroughly investigates the changes in microstructure, mechanical performance, and corrosion resistance of both WA-DED and FSP-enhanced WA-DED Inconel 625 samples. A Thermo-Calc simulation using the classical Scheil model was conducted to understand the solidification pathway and the formation mechanism of the Laves phase in the WA-DED sample. The grain size was significantly reduced by 98.23%, from 138 µm in the WA-DED sample to 2.44 µm in the stir zone (SZ) of the FSP-treated area, due to dynamic recrystallization (DRX), particle-stimulated nucleation (PSN), and the Zener pinning effect. This grain refinement led to remarkable enhancements in the yield strength (YS) by approximately 113%, ultimate tensile strength (UTS) by about 37% and micro-hardness by around 60% compared to the WA-DED sample. In a 3.5 wt% NaCl solution, the FSP-treated sample demonstrated superior corrosion resistance by forming a stable, thicker passive film than the as-built sample. The results of this study will offer valuable insights into utilizing the FSP technique as post-weld surface treatment of WA-DED deposited IN625 superalloy.

Thermocapillarity transition-induced unconventional thermal behavior and dilution in laser welding of metals with dissimilar sulfur content

An enhanced three-dimensional transient Thermal-Fluid-Dilution model, integrating a sub-model that accounts for surface tension, is proposed to investigate the unconventional thermal behavior and dilution induced by the surface-active element (sulfur) during the laser joining process of 304SS with higher sulfur content and pure nickel with lower sulfur content. Surface tension is modeled as a function dependent on local temperature and the concentration of the surface-active element (sulfur) at the free surface. The temperature and sulfur-dependent surface tension initially generate an unconventional driving force, subsequently leading to the transitions of heat transfer, flow pattern, and species dilution. Specifically, the inclusion of the sulfur effect results in a redistribution of larger surface shear stress along the transition boundary, causing unconventional flow behavior. The temperature coefficient of surface tension (TCST) is the coexistence of TCST (-) and TCST (+), leading to a novel flow pattern with combined inward-outward flows. Moreover, the anomalous flow exhibits observed phenomena such as the rotation of the major axis (RA) and center line shift (CLS) within the melt pool, showing more reasonable simulated melt pool dimensions when accounting for the sulfur effect. Additionally, the dilution model integrated with the unconventional flow pattern presents a more uniform concentration distribution compared to the conventional dilution. Finally, the simulated distribution of alloy elements is validated effectively by experimental data obtained from Energy Dispersive Spectrometer (EDS) analysis.

Influence of Alloying Elements on the Carburizing Behavior in Acetylene Atmosphere

Three steel types (AISI 1020, AISI 8620, AISI 4120) with similar carbon content and different Cr content were used as test specimens to closely examine the effect of alloying elements for carbon penetration and diffusion on the steel surface during vacuum carburizing. The carbon mass gain according to the carburizing time was measured using a microbalance, and the average carbon flux, which is an indicator of the carbon penetration rate, was calculated using the measured weight as a variable. The outermost surface of the carburized specimen was observed by scanning electron microscopy (SEM) and Raman spectroscopy (RS), and the reason for the change in carburization rate according to the steel type was identified in relation to the equilibrium carbon contents calculated from Thermo-Calc. The overall carbon distribution and distribution of alloy elements on the outermost surface were quantitatively analyzed using an electron probe microanalyzer (EPMA). On the surfaces of the AISI 1020 and AISI 4120 carburized specimens, graphite layers and grain boundary carbide were formed during the carburizing process, which hindered the carburization rate, while no abnormal layer was observed on the surface of the AISI 8620 carburized specimens, so the overall carburization results were excellent.

A novel method for preparing ultrafine molybdenum‑rhenium alloy powders

To address the issues of large particle size and poor particle size uniformity in the traditional two-step hydrogen reduction method for preparing molybdenum‑rhenium alloy powders, this study innovatively employed glucose as the carbon source and successfully prepared ultrafine molybdenum‑rhenium alloy powders through wet-wet mixing, evaporative crystallization, calcination, carbothermal pre-reduction, and hydrogen deep reduction steps. The results demonstrate that when the C/(Mo + Re) molar ratio is 0.7, the powders synthesized through carbon‑hydrogen synergistic reduction exhibit a spherical shape, with particle sizes distributed in the sub-micrometer range and an average particle size of 173 nm. The phase composition of the reduction powders consists predominantly of molybdenum, rhenium and χ phases, with a uniform distribution of alloy elements. In contrast, the powders synthesized using the traditional two-step hydrogen reduction method exhibit irregular, porous and loosely-packed structures, with particle sizes in tens of microns range and slightly larger than those of the precursor. This method is highly suitable for preparing high-purity, ultrafine, and highly homogeneous binary alloy powders, like MoRe, MoW, WRe, ect.

Differences in mechanical properties and high temperature deformation behavior between TiBw/Ti65 and TiBw/TA15 composites with network structure

In this paper, the differences in mechanical properties and high temperature (HT) deformation behavior between TiBw/Ti65 and TiBw/TA15 composites with network structure were studied. The alloy element distribution and microstructure of TiBw/Ti65 and TiBw/TA15 composites were characterized by the electron probe micro analyzer and transmission electron microscopy. The microstructure evolution during HT deformation was analyzed by electron back scatter diffraction. The mechanical properties of two composites were tested at room temperature and 600–750 °C. Arrhenius and artificial neural network models were developed to predict the peak stress and flow stress, respectively. The results show that the multiple alloying elements and silicide in TiBw/Ti65 refined the grains. TiBw/Ti65 composites had higher deformation activation energy and higher strength under the same deformation conditions. Based on the analysis of differences in microstructure, the strengthening mechanisms of TiBw/Ti65 compared to TiBw/TA15 was mainly from fine grain strengthening, dislocation density strengthening, and Orowan strengthening of silicide. The initial recrystallization temperatures for TiBw/TA15 and TiBw/Ti65 were 700 °C and 750 °C with strain rate of 0.001 s−1, respectively. The above results show that TiBw/Ti65 had better HT deformation resistance.

Study on the solid solution temperature of achieving ultra-high strength in wire-arc additive manufactured Al-Zn-Mg-Cu aluminum alloy

Al-Zn-Mg-Cu aluminum alloys are typically heat-treatable aluminum alloys. The heat treatment has a significant effect on the microstructure and mechanical properties of Al-Zn-Mg-Cu alloy. In this study, the solid solution temperature of achieving ultra-high strength in wire-arc additive manufactured 7B55 aluminum alloy was systematically investigated. The results showed that the microstructure of the as-deposited 7B55 aluminum alloy was composed of equiaxed grains with an average grain size of 4.2 ± 0.5 μm. A large number of the second phases were continuously distributed along grain boundaries. The precipitated phases within grains were mainly composed of the larger η phases and the smaller η′ phases, and the amount of precipitated phases was fewer. The second phases distributed along grain boundaries gradually dissolved into α-Al matrix with the increase of solid solution temperature, resulting in a higher supersaturation of the α-Al matrix and more homogeneous distribution of alloy elements. Combined with the results of DSC analysis, the optimal solid solution temperature of the 7B55 aluminum alloy was determined to be 480 °C. After solid solution of 480 °C，the microstructure was still composed of equiaxed grains with an average grain size of 4.8 ± 0.4 μm. The size of the grain did not grow significantly. A larger number of nanoscale fine GP zones, η′ phases and secondary Al3(Sc,Zr) particles were precipitated within the grains during subsequently artificial aging process, resulting in a significant increase in tensile properties. The ultimate tensile strength (UTS), yield strength (YS) and elongation (EL) reached 621 MPa, 555 MPa and 5.73%, respectively, which was significantly higher than the strength level of WAAM aluminum alloy reported among all the existing literature.

Unusual interface phase transformation during continuous additive manufacturing of maraging steel and Co–30Cr–7Mo alloy

The high strength and hardness of maraging steel (MS1) can be functionally integrated with the thermal stability and toughness of Co–30Cr–7Mo alloy (MP1) through multi-material additive manufacturing via laser powder bed fusion. However, appropriate heat treatment is necessary to stabilize the multi-phase interface post-printing and achieve desired material properties. In the present study, we investigate the effects of solution and aging heat treatment on the interface characteristics and mechanical properties of MS1-MP1 multi-material components. The results reveal that a discontinuous martensitic transformation occurs in the interface after printing due to the combined effects of solute segregation, local stress distribution, and intermixed cellular growth. In contrast, consistent parallel martensite laths were observed after heat treatment due to the homogenized alloying element distribution, extensive residual stress relief and stable interface structure. Furthermore, the mechanical testing results revealed that the tensile strength of the MP1-MS1 alloy was maintained at about 1185 ± 18 MPa before and after heat treatment, complemented by an increase in elongation from 14.7 ± 1.3% to 27.1 ± 2.1%. The microstructure and mechanical properties obtained are then correlated based on phase boundary orientation relationships and simulated martensite start temperatures in different regions along the interface. Based on overall results, it can be concluded that MP1 forms a compatible interface with MS1. Heat treatment can still be performed to improve the strength of MS1 by precipitation strengthening without compromising the strength of MP1 and the MS1-MP1 interface.

Corrosion behavior and mechanism of 4004/Al-Mn-Cu-Mg-Si/4004 aluminum brazing sheet in sea water acidified accelerated test

The microstructure and corrosion properties of a novel 4004/Al-Mn-Cu-Mg-Si/4004 aluminum brazing sheet were investigated in comparison with the traditional 4004/3003/4004. It revealed that, the microstructure after brazing of two aluminum brazing sheets from outer to center were both residual Al-Si eutectic, precipitate-free zone (PFZ), band of dense precipitates (BDP) and core material, respectively. However, the alloying element distribution and the types and amounts of second phases were quite different. The sea water acidified accelerated test showed that 4004/Al-Mn-Cu-Mg-Si/4004 exhibited typical exfoliation corrosion, while the corrosion quickly spread deep into the core material of 4004/3003/4004. The formation of Cu concentration gradient and the strip distribution of Al-Mg-Cu-Si precipitates in the BDP region contributed to the exfoliation corrosion of 4004/Al-Mn-Cu-Mg-Si/4004. The corrosion behaviors of Al-Mn-Cu-Mg-Si and AA3003 core materials are both in form of intergranular corrosion (IGC)，and the later was more severe than the former. For Al-Mn-Cu-Mg-Si core material, high-density fine dispersed cathodic α-Al(Mn, Cu)Si precipitates promoted the formation of a profusion of micro-galvanic cells in the Al matrix, which would retard any effects between the grain boundary precipitations and the adjacent relatively PFZs. Hence, the IGC susceptibility of Al-Mn-Cu-Mg-Si core material was decreased. Besides, less large-sized α-AlFeMn(Cu)Si phases in core material also reduced the localized corrosion attack. At last, the corrosion in depth direction of 4004/Al-Mn-Cu-Mg-Si/4004 was retarded, compared to its counterpart.

Depth distribution analysis of alloying and impurity elements in Ni-Ti alloy thin films using secondary ion mass spectrometer

Ni-rich Ni-Ti thin films of various compositions and thickness (69 nm - 141 nm) were deposited on Si (111) substrate by magnetron sputtering system using equiatomic NiTi alloy sputtering target. X-ray reflectivity analysis of the thin films deposited at room temperature showed the presence of a layered structure as: NiO/Ni-Ti/NiO/SiO2 on Si substrate. Secondary ion mass spectrometry (SIMS) was used to determine the qualitative (intensity) depth distribution of elements Ni, Ti, O and Si in the films using MCs+ approach. Relative sensitivity factor values were utilized to convert the qualitative depth profiles to concentration depth profiles. Surface and depth distribution of alloying elements in the deposited films were investigated. It was observed that the films deposited at high sputtering power and working pressure resulted in more non-uniform depth distribution of alloying elements compared to films deposited at low sputtering power and working pressure. SIMS depth profile data showed the presence of high oxygen contaminations at the surface and at the interface of the films. The Ti concentration in the deposited films depends upon the background oxygen contamination present in the deposition chamber during sputtering process. The concentration of Ni in the films deposited under similar working pressure increases with increase in the sputtering power. However, with increase in working pressure during deposition process results in decrease in the concentration of both Ni and Ti in the deposited films. In order to study the effect of insitu substrate heating on the distribution of alloying and impurity elements, one of the film was deposited on heated Si substrate. The film deposited on heated substrate represents the layer structure as NiTiO3 on Si substrate. The concentration of oxygen in the film deposited on heated substrate is comparatively higher than those deposited at room temperature.

Surface characteristics of AC PEO coatings fabricated on commercial Al alloys

The effect of alloying elements on coating characteristics was explored in the current work, which involved the fabrication of ceramic oxide coatings on commercial aluminium alloys (AA2024, AA6061, and AA7075) using the plasma electrolytic oxidation (PEO) process. The PEO coatings were fabricated by an AC power source with an exchange current density of about 300 mA/cm2. Field emission scanning microscopy (FESEM) was used to examine the surface, cross-sectional morphology, and alloying elements distribution. X-ray diffraction was used to investigate the phase composition. All PEO coatings were primarily composed of γ-Al2O3 and α-Al2O3 phases. As compared to PEO treated AA6061, PEO treated AA7075, and PEO treated AA2024 suppress the formation of α-Al2O3, resulting in a relatively higher fraction of γ-Al2O3, attributed to the alloying elements residing in the coatings. Because of its dense inner layer and high thickness (51 ± 1 μm), as well as its higher contact angle (114 ± 2°). PEO coated AA6061 sample exhibited superior corrosion resistance with lower icorr = 8.91(±0.24) E-6 mA/cm2 and impedance (Ω-cm2) to the order of 107 in 3.5 wt% aqueous NaCl corrosive medium. The PEO-coated AA6061 sample evinced greater hardness, scratch and wear resistance than the other samples, ascribed to its relatively higher α-Al2O3 phase, lower residual alloying elements, and thick and dense inner layer.

Development of friction stir powder deposition process for repairing of aerospace-grade aluminum alloys

This paper presents development of a novel friction stir powder deposition (FSPD) process for potential repairing applications of aerospace-grade aluminum alloy AA6061-T6. Powder form of the deposition material was thermo-mechanically processed at a temperature below its melting point. Influence of various process parameters on thermal cycles, deposition quality, deposition height, microstructure, and mechanical properties have been studied. Higher degree of deformation resulted in a dynamically recrystallized fine-grained microstructure which gave better mechanical properties. EDS study revealed uniform distribution of the major alloying elements throughout the deposition. Best quality deposition showed maximum microhardness and wear rate 0.84 and 1.07 times respectively than the substrate AA6061-T6 alloy. FSPD process is found to be capable of depositing maximum height of 0.45 mm, maximum deposition efficiency of 22% with an energy consumption of 73.7 J/mm 3 per unit deposition material consumption. Moreover, it used current in the range of 5-7 Ampere. This research shows that FSPD process can provide considerable cost and energy savings over fusion-based additive manufacturing processes making it a viable alternative for repairing aerospace-grade aluminum alloys. • Developed friction-stir powder deposition as a solid-state AM process for aerospace-grade Al alloys. • Max. deposition height: 0.45 mm; deposition efficiency: 22%; Avg. peak temperature: 293 °C. • Higher deformation gave dynamically recrystallized fine-grained microstructure. • Uniform distribution of alloying elements in the deposition. • Deposition microhardness and wear rate are 0.84 and 1.07 times than substrate AA6061-T6.

Exploring temperature-controlled friction stir powder additive manufacturing process for multi-layer deposition of aluminum alloys

This paper presents preliminary study on multi-layer deposition of aerospace grade Al 6061 alloy by novel friction stir powder additive manufacturing process. Minimum temperature of deposition was in-situ maintained using close loop temperature-controlled system for minimizing thermal gradient in the build direction. Maximum temperature during the deposition was monitored in-situ using pyrometer and thermal imaging camera. Use of a tool with circumferential and radial grooves and continuous external heating facilitated smooth three-layer deposition of Al 6061 alloy with 60% deposition efficiency and 417°C as maximum deposition temperature. Larger value of temperature at deposition zone improved material flowability and deposition quality. Microstructure of multi-layer deposition found to consist of fine sub-grains. Element analysis showed uniform distribution of major alloying elements in it. Phase analysis revealed Al along with Mg2Si hardening precipitates. Tensile strength and microhardness were close to the commercially available wrought AA6061-T4 alloy. It showed ductility with 16% elongation. The presented process is a viable alternative to fusion-based additive manufacturing processes for multi-layer depositions of aerospace grade and other lightweight alloys which are difficult-to-additively-manufacture.

Novel insights on the near atomic scale spatial distributions of substitutional alloying and interstitial impurity elements in Ti-6Al-4V alloy

The present study explores the near atomic scale spatial distributions of substitutional alloying elements (aluminium and vanadium) and interstitial impurities (oxygen and carbon) in the microstructures of Ti-6Al-4V and its boron modified counterpart (Ti-6Al-4V-0.1B) alloys using transmission electron microscopy (TEM) and atom probe tomography (APT) techniques. The latter alloy possesses zero solubility of boron in α-Ti and high oxygen concentration around TiB particles. The results suggest that aluminium and vanadium atoms enrich α and β phases, respectively due to strong elemental partitioning between these phases, to an extent that the atomic scale concentrations of various elements considerably differ from the bulk compositions of the two alloys. Furthermore, oxygen atoms are preferentially distributed within the α phase where other interstitial impurities (carbon) also segregate. Substitutional aluminium atoms share an inverse interrelation with interstitial oxygen atoms while vanadium atoms reside besides the impurity-rich regions for both the alloys. The size differences for these elements (substitutional vs. interstitial) with host titanium atoms and related lattice distortion is (partially) held responsible for the atomic scale elemental distributions and the observed interrelations within the α phase. These arguments are further substantiated from DFT results previously obtained for Ti-6Al-4V alloy.

Microstructure and mechanical properties of ultra-high strength Al-Zn-Mg-Cu-Sc aluminum alloy fabricated by wire + arc additive manufacturing

Ultra-high strength 7xxx series aluminum alloys are widely used in aerospace applications due to their exceptional high specific strength. Wire + Arc Additive Manufacturing (WAAM) is a combination of arc and wire feeding additive manufacturing technology including either the gas tungsten arc (GTA) or the gas metal arc (GMA) process. And this technology has been applied in the aerospace manufacturing industry to reduce the time of product development and “buy-to-fly” ratios. However, the existing Al-Zn-Mg-Cu aluminum alloy filler wires are not suitable for WAAM process due to their high susceptibility to hot cracks. In this study, a novel Al-Zn-Mg-Cu-Sc aluminum alloy wire named 7A55-Sc with ultra-high strength and excellent hot-crack resistance has been successfully prepared by optimizing the composition of Al-Zn-Mg-Cu alloying elements and adding appropriate amounts of inoculants Sc and Zr elements during the smelting process. And then, thin-wall components without any hot cracks were successfully fabricated by using cold metal transfer (CMT) process. Results indicated that the microstructure of the as-deposited 7A55-Sc alloy consists of predominantly fine equiaxed grains and the average size of the grains is between 5.0 and 6.0 μm. The eutectics composed of α (Al), η phase and S phase were distributed along the grain boundaries. The Al3Sc and Al3 (Zr, Sc) particles precipitated within grains act as heterogeneous nucleation nuclei, promoting the formation of the equiaxed grains. After T6 heat treatment, most of the second phases distributed within grains and grain boundaries were dissolved into the α(Al) matrix. The distribution of alloy elements became more homogeneous. The average ultimate tensile strength, yield strength and elongation of T6 heat-treated 7A55-Sc alloy in the horizontal direction were 554 MPa, 488 MPa and 1.7% respectively, whereas 523 MPa, 469 MPa and 1.4% in the vertical direction. The lower ductility was considered due to the existence of a large number of pores in the 7A55-Sc alloy fabricated by the CMT process.

Structure Formation in Antifriction Composites with a Nickel Matrix and Its Effect on Properties.

The paper is devoted to studying the chemical elements distribution in the material’s structure depending on the manufacturing technological parameters and their effect on properties of a new self-lubricating antifriction composite based on powder nickel alloy EP975 with CaF2 solid lubricant for operation at temperature 800 °C and loads up to 5.0 MPa, in air. The study is focused on the features of alloying elements distribution in the composite matrix, which depends on the manufacturing technology. A uniform distribution of all alloying elements in the studied composite was shown. The chemical elements’ uniform distribution in the material is associated with one of the most important preparatory technological operations in the general manufacturing technology used. This is a technological operation of mixing powders with subsequent analysis of the finished mixture. The uniform distribution of chemical elements determines the uniform arrangement of carbides and intermetallics in the composite. General manufacturing technology, which includes the main operations, such as hot isostatic pressing technology and hardening heat treatment, contributed to the obtainment of a practically isotropic composite with almost the same properties in the longitudinal and transverse directions. Because of the composite’s structural homogeneity, without texturing, characteristics are isotropic. Improving the material’s structural homogeneity helps to keep its mechanical and anti-friction qualities stable at high temperatures and stresses in the air. The performed studies demonstrated the correctness of the developed manufacturing technology that was confirmed by the electron microscopy method, micro-X-ray spectral analysis, mechanical and tribological tests. The developed high-temperature antifriction composite can be recommended for severe operating conditions, such as friction units of turbines, gas pumping stations, and high-temperature units of foundry metallurgical equipment.

Influence of changes in alloying elements distribution and retained Austenite (RA) on mechanical properties of high boron alloy during quenching and partitioning(Q&P) process

The quenching and partitioning (Q&P) process has been adopted innovatively to improve the toughness and wear resistance of Fe-0.44C-1.54B-3.97Mn-0.79Al-0.95Si alloy, and the microstructure, distribution of alloying elements, mechanical properties and dry sliding wear behavior of this alloy in as-cast and heat-treated by Q&P process were systematically investigated. The results show that test alloy consists mainly of martensite, retained austenite (RA) and eutectic boride phases. After being treated by Q&P process, the distribution of alloying elements in the microstructure becomes uniform and the impact toughness increases from 4.02 J cm-2 to 6.82 J cm-2, while the mass loss of the alloy is also decreased from 0.064 g to 0.051 g in dry sliding wear test. The improvement of the mechanical properties is attributed to the changes in the during Q&P process, especially the increase in the volume fraction of thin-film RA, as well as the fracture and spheroidization of part of the net-like boride.

Dilution rate and wear-resistance performance of assisted wire filling cable-type welding wire GMAW of surfacing layer

Surfacing technology is widely used in material surface modification and repair industries, with the advantages of low dilution rate and high wear-resistance performance. The assisted wire filling (AWF) of cable-type welding wire (CWW) gas metal arc welding (GMAW) is an innovative surfacing method, using CWW as the consumable electrode. The dilution rate and wear-resistance performance were studied in this paper. The results show that the weld penetration of the AWF-CWW-GMAW surfacing layer increased with the increase of welding current, which was consistent with the method of CWW GMAW. The dilution rate of the surfacing layer was about 19% lower than that of the CWW-GMAW with the same parameters. Comparing with the CWW-GAMW method, the sample treated by AFW-CWW-GAMW had a smaller dilution rate of surfacing layer, a less wear loss, a smaller friction coefficient and a higher hardness under the same welding parameters. The alloy element distribution of the surfacing layer was higher than that of CWW-GMAW from the weld to the base metal.

Microstructure and Mechanical Properties of Al-Cu-Mg Alloy Fabricated by Double-Wire CMT Arc Additive Manufacturing

The high cracking sensitivity of Al-Cu-Mg alloy limits its application in wire + arc additive manufacturing (WAAM). In this paper, a double-wire cold metal transfer (CMT) arc additive manufacturing system was applied. ER2319 and ER5183 wires were selected as feedstocks and a new type of high-strength, crack-free Al-Cu-Mg alloy was manufactured. T6 (solution and artificial aging) heat treatment was conducted to further improve the mechanical properties. The microstructure, the second phase, distribution of main alloy elements and fracture morphology of Al-Cu-Mg alloys in both as-deposited and T6 heat-treated conditions were analyzed by optical micrographs (OM), X-ray diffraction (XRD), and scanning electron microscopy (SEM), respectively. The micro-hardness and tensile properties of WAAM Al-Cu-Mg alloy in both as-deposited and T6 heat-treated conditions were tested. The results demonstrated that the microstructure of the as-deposited Al-Cu-Mg alloy was composed of short rod-shaped columnar grains, equiaxed grains in the inter-layer region, and coarsen equiaxed grains in the inner-layer region; most of the second phases were continuously distributed along the grain boundaries. After the T6 heat treatment, α(Al) grains became coarsened, most of second phases were dissolved, and the Cu and Mg elements were distributed homogeneously in the aluminum matrix. The micro-hardness and strength were significantly improved but the elongation was reduced.

Elemental mapping and quantitative characterization of dendrite structure in IN718 supperalloy based on micro beam X-ray fluorescence and EPMA

Micro beam X-ray fluorescence (μ-XRF) has been applied to characterize the quantitative distribution of elements in the dendrite structure of IN718 superalloy for the first time with the advantage of simple sample preparation, no requirement for conductivity, high spatial resolution and non-destructive surface. Dendrite structure is an important microstructure in cast polycrystalline superalloys such as IN718 superalloy. In this paper, the distribution characterization of Ni, Cr, Fe, Nb, Mo and Ti in the dendrite structure of superalloy was performed by μ-XRF with the improvement of the quantitative method. The elemental mapping with higher spatial resolution in the dendrite structure was obtained by electron probe micro-analysis (EPMA). The elemental content distribution on primary dendrite arm, secondary dendrite arm and inter-dendritic zone of superalloy was investigated and the segregation ratios of different elements have been obtained. It was found that the elemental distribution in dendrite structure of IN718 alloy was inhomogeneous and the content of Nb, Mo and Ti was much higher than that on dendrite arm and the elements of Fe,Cr and Ni have the opposite distribution tendency. Severe micro segregation of Nb has been revealed on the dendrite structure. The minimum Nb value of 2.90 wt%, the mean Nb value of 4.90 wt% and the maximum value of 8.84 wt% in the tested IN718 superalloy sample determined by μ-XRF have good agreement with the composition data of key nonequilibrium point in the Pseudo-binary solidification constitution diagram of Inconel 718. The content distribution of alloy elements (Mo, Nb and Ti) presents a sine distribution between the secondary dendrite arm and inter-dendritic region and the average SDAS value obtained from the line content distribution figure is about 70–80 μm. The segregation ratio of different elements has obtained and the SR values of Nb and Ti are much greater than 1. There were some large precipitates particles containing Nb and Ti elements distributed on the inter-dendritic zone, which led to the fluctuation of Nb and Ti contents.

A novel research on the solute redistribution phenomenon of sub-rapid twin-roll cast Al-50 wt.% alloy treated by semi-solid heat treatment

In this study, a vertical twin-roll cast (TRC) thermal-fluid coupling model was established to determine a suitable roll-casting velocity. A slab of 0.9 mm thick roll-cast Al-50 wt.% Si alloy with a two-phase zone width of 473 °C was prepared at a velocity of 20 m/min for the first time. In addition, the finite element simulation showed that the average heat transfer rate had a positive correlation with the roll-casting velocity. When the roll-casting velocity increased to 20 m/min, the average heat transfer rate reached 1260 K/s, at which point, the average size of the primary Si was merely 16.5 μm. This was a decrease of approximately 90% when compared with the size of alloys cast with conventional methods. After carrying out semi-solid heating, an observation on the distribution of alloy elements identified a novel phenomenon of solute redistribution, i.e., inverse segregation. This inverse segregation process was highly significant in further controlling solute redistribution in the alloy. Additionally, it provided a new concept for improving roll-cast segregation.