Distribution Of Alloying Elements Research Articles

A Strain Integrated Gas Infusion Process (SIGI) for Magnesium Alloy Castings

This study presents a Strain Integrated Gas Infusion Process (SIGI) to manufacture high-performance cast AZ91 magnesium alloys without the addition of secondary alloying elements/reinforcements or secondary processing. The current SIGI process involves a combination of agitation and localized rapid heat extraction via strain integration and high-energy gas infiltration. The SIGI casting process has been compared systematically with conventional techniques. The critical process parameters, including hole diameter, bubble diameter, and flow rate, have been optimized through numerical calculations, simulations, extensive experiments, and comprehensive analysis. The study also focused on investigating the effect of gas bubbles on the molten metal and established the mechanisms involved in improved solidification. Gas infusion combined with strain integration impacts the solidification process, ensuring uniform alloying element distribution and reducing segregation and microporosity. This manufacturing strategy eliminates casting defects such as segregation and microporosity, resulting in a non-dendritic homogeneous microstructure. The significant refinement in morphologies of both primary (α-Mg dendrites) and secondary (β-Mg17Al12 phase) phases highlights the success of the current SIGI process. Compared to the conventional casting processes, a remarkable improvement in strength-ductility synergy is achieved in the current SIGI process. The scientific know-how and efficiency of the current SIGI process are established and discussed in detail, providing a promising solution to address the existing challenges encountered in magnesium alloy billet castings. The SIGI process improves the mechanical properties and corrosion resistance of billet-cast magnesium alloys. The SIGI process is suitable for the billet casting, offering significantly improved properties but faces limitations in complex mold casting applications. The billets casted by SIGI process can be used as a high-quality precursors for downstream processes to create industrial components.

Effect of water quenching into strength, hardness and microstructure of the welded AA 6061 plates

Purpose The purpose of this study is to find the effect of heat treatment on the mechanical proeprties of aluminum. Aluminum exhibits a good response to heat treatment, especially quenching, according to the mechanical property improvement. The presence and orientation of secondary phases (Al-Fe-Mn-Si) are greatly affected by the quenching process. Design/methodology/approach The present work deals with the effect of water quenching on the mechanical properties of welded AA 6061 plates which were joined by using metal inert gas (MIG) welding, tungsten inert gas welding and friction stir welding (FSW). Three tests like tensile, bending and hardness were considered. The microstructural variation was analyzed by optical microscopy and elemental mapping through field emission scanning electron microscope. Findings A significant enhancement in the tensile strength and hardness was achieved on postquenched specimens. This improvement in mechanical properties is caused by the distribution of fine alloying elements throughout the metal solution rather than precipitation at the grain boundaries. In comparison to the “untreated specimens,” an improvement of 76.7%, 25.32% and 56.81% in the tensile strength of quenched TIGW, MIGW and FSW specimens, respectively, was observed. Originality/value The quenching process has increased the strength of the MIG welded joint over the base metal. The MIG welded joint has a larger flexural modulus than the other two welded plates, according to the results of the bending test. Furthermore, a uniform distribution of hardness was observed in postquenched welded specimens. It was found that welded zone was harder than heat-affected zone. Out of all the specimens, the base metal zone has the lowest hardness.

Influence of the oxidizing technique on the biocompatible and corrosion properties of Ti6Al4V in a physiological environment

This work aims to evaluate the corrosion and biocompatibility properties of oxide films generated on Ti6Al4V alloys using both traditional and novel methods. Oxide films were generated by anodization and plasma treatment to achieve a blue surface finish. The oxide films were then characterized and compared to a native film formed on the Ti6Al4V.Electrochemical tests, incorporating potentiodynamic tests and electrochemical impedance spectroscopy, were employed to define the electrochemical resistance of oxides in an environment simulating biological exposure. In vitro tests were conducted to study ion release and biocompatible properties over a 6-week period of exposure to a 0.9 wt% NaCl solution, at body temperature. Various spectroscopic techniques, including ToF-SIMS, XRD, and Raman analysis, were used to study the structure and chemistry of the oxide films. The sub-surface layer was analysed by microstructural investigation.The type of oxidation was found to have a key influence on the oxide composition, especially with respect to the depth distribution of the individual alloy elements through the oxide film. The oxidation process determines which of the alloying elements are released into the environment, as a result of the corrosion reactions.

Weld Pool Flow Characteristics in Double-Wire Arc Welding of Aluminum Alloys: Research by Numerical Simulations

Double-wire arc welding involves simultaneously feeding two wires into a molten pool, improving the efficiency and flexibility of traditional welding techniques. However, the interactions between the two wires and the molten pools are complex, which increases the difficulties in process and composition control. This work focuses on the weld pool flow characteristics in double-wire TIG arc welding. A CFD model incorporating a liquid bridge transfer model was developed to simulate the fluid flow phenomenon. Results show that the bead-forming appearances and flow characteristics of double-wire arc welding show no significant differences from single-wire arc welding. Welding current and welding speed have significant effects on the weld bead dimensions, while only welding current has effects on the flow characteristics. Wire feed XOZ angles show no significant influences on weld bead forming appearances and molten pool flow characteristics. Wire feed XOY angles influence the symmetry of the weld bead and the fluid flow. In 5B71/7055 heterogeneous double-wire arc welding, achieving a uniform distribution of alloy elements is difficult due to the complex convection patterns within the molten pool.

The effect of interfacial alloy formation on the mechanical properties of the additively manufactured Ti6Al4V/Ti1Al8V5Fe microstructurally graded material

Multi-material (MM) structures have been shown in the past to be potential candidates for future high performance high strain rate applications. With the advancement of MM additive manufacturing (AM), there is a renewed push to explore the vast array of materials combinations to deliver advanced protective capabilities. At the same time, many fundamental issues are still plaguing MM assemblies, primarily linked to the often-poor quality of the MM interface. Here, we present a novel approach to obtain microstructural and mechanical properties gradient without interface defects by leveraging the link between the chemical composition and complex grain/phase morphology in titanium alloys. We used additive manufacturing (AM) to combine α+β-titanium alloy Ti6Al4V with metastable β-titanium alloy Ti1Al8V5Fe (which belong to different alloy classes but share common alloying elements), into a microstructurally graded material (MGM). Uniquely, the classic MM interface was replaced by the two additional intermixed alloy layers with unique chemical composition, microstructure and mechanical properties, with both ultimately making a significant contribution to the overall performance. The properties of these interface alloys are affected by many factors, such as thermal properties of the substrate, process parameters, alloying element distribution and post-manufacturing heat treatment. As a result, we showed that a superior combination of the strength and ductility could be achieved in the hybrid material after heat treatment compared to the original materials or the as-built hybrid material, which was ultimately attributed to the formation of the interface alloys. The presented approach is not limited to titanium alloys and could be extended to other materials systems and is expected to contribute to the development of a deeper understanding of the intermixing phenomena and its effects on microstructure and mechanical performance of MGMs, opening the door to a range of unique solutions in alloy and MM structural design for high performance applications.

Effects of volumetric energy density on melting modes, printability, microstructures, and mechanical properties of laser powder bed fusion (L-PBF) printed pure nickel

Volumetric energy density (VED) is a fundamental criterion for the laser powder bed fusion (L-PBF) process, influencing various forming characteristics. This study employed L-PBF to print pure nickel (Ni) using different VEDs across various melting modes. The thermodynamics in the different melt pools, obtained microstructural features, and tensile properties were characterized and investigated. The results reveal a higher likelihood of keyhole mode melt pool formation than the conduction mode due to the peak temperature exceeding 3005 K. The larger size and slower cooling rate of the keyhole mode melt pool facilitate the formation of cellular subgrains in the central zone and the overall grain coarsening. Compared to the conduction mode, the microstructure in the keyhole mode exhibits a higher dislocation density and a distinct distribution pattern for each type of dislocation. Unlike the L-PBF of commercial Ni alloys, where alloy element distribution significantly impacts tensile performance, the tensile performance of L-PBF Ni is governed by the interaction between grain morphology, dislocation density and distribution.

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.

Research on short process rolling of high performance wear resistant steel/carbon steel clad plate

An innovative short process rolling has been proposed to produce high performance clad plates of wear-resistant steel/carbon steel with lower production costs. The NM400 and Q345B cast billet instead of traditional hot-rolled plates were chosen to prepare composite steel ingots. The interface morphology, microstructure, and mechanical properties of clad plates with 45%, 60%, and 70% reduction ratios were analyzed and detailed using metallographic microscopy, scanning electron microscopy, and energy dispersive spectroscopy. The results demonstrate that the improvement of the reduction ratio effectively promotes the grain refinement of clad plates and the metallurgical bonding of dissimilar metals. The bonding interface of the clad plate is straight and clear when the reduction ratio is 70%, the distribution of alloy elements is uniform, and the grain refinement is apparent. The tensile strength of the clad plate rolling by the short process rolling reaches 626 MPa, the bonding strength reaches 484 MPa, and the elongation reaches 21%. These results exceed national, international, and industry standards.

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.