As-deposited Condition Research Articles

Grain refinement and mechanical properties improvement of additively manufactured Al-Cu alloy through pre-deformation in thermo-mechanical treatment

Inferior mechanical properties induced by porosity and coarse grains of wire-arc additively manufactured Al-Cu alloy restrict its industrial application. The inter-layer cold rolling, conventional heat treatment (T6) and thermo-mechanical heat treatment (T8) was applied to Al-Cu alloy, and the effect of pre-stretched strain in T8 treatment was investigated. The pre-stretched strain induces equal increments of hardness and YS for both the as-deposited and cold-rolled conditions before aging treatment, while the increments for cold-rolled samples are larger after aging treatment. The cold-rolled sample shows better tensile properties than the as-deposited sample with the same pre-stretched strain in T8 treatment, proving that T8 treatment further increased the strengths compared to the T6 treatment. It shows the best tensile properties with the pre-stretched strain of 5 %, exceeding the properties of 2219-T87 plate. With the increased pre-stretched strain, the density of the θ′ phases significantly increases; while further increase to 10 % pre-stretched strain induces severe coarsening of θ′ phases. Therefore, an optimized pre-stretched strain leads to high-density and tiny dispersed θ′ phases, thus resulting in the best tensile properties. Grain refinement induced by inter-layer cold rolling and uniformly precipitated phases resulted from proper pre-stretched strain both contribute to the strengths enhancement. The strengthening mechanism of hybrid additive manufacturing and inter-layer cold rolling followed by T8 treatment was discussed.

Investigating the influence of post-deposition heat treatment (PDHT) on the characteristic changes in wire arc additively manufactured 410 martensitic stainless steel thin-wall structure

Obtaining the desired material characteristics of an as-deposited martensitic stainless steel (MSS) structure fabricated by wire arc additive manufacturing (WAAM) is challenging due to several factors like inhomogeneity, precipitation, phase transition, etc. This investigation elucidates the impact of post-deposition heat treatment (PDHT) on the microstructural and mechanical properties of the WAAM-processed 410 MSS thin-wall structure and compares it with the as-deposited 410 thin-wall structure. The MSS thin-wall structure consists of retained austenite (γ), delta (δ) ferrite, martensite laths and Cr-rich M23C6 type carbide. The M23C6 volume fraction increases by up to 18 %, and the γ-phase fraction reduces by up to 40 % by applying PDHT. The PDHT process significantly changed the texture from {110}<011> to {001}<110>. The PDHT process increases the dislocation density (1.974 × 10−15 m−2) than the as-deposited condition (0.924 × 10−15 m−2). The total low energy boundary (LAGB+CSL) contribution of the as-deposited sample is 19.5 %, whereas the PDHT sample demonstrated a higher fraction of low energy boundaries of 32.4 %. The PDHT sample showed a much smaller distribution of grains with an average grain size of 11 μm compared to the as-deposited condition. The overall hardness increases from 468 HV to 487 HV after PDHT compared to the as-deposited condition with lower inhomogeneity across the build direction. The mean 0.2 % proof stress, ultimate tensile stress, and elongation of the PDHT sample increased by 17 %, 5 %, and 60 %, respectively, compared to the as-deposited sample.

Microstructure and mechanical properties of 7075/5356 aluminum alloy laminated composite fabricated by wire arc additive manufacturing

A 7075/5356 aluminum alloy laminated composite was fabricated by alternately depositing a 7075 wire and a 5356 wire layer by layer using wire arc additive manufacturing (WAAM). The microstructure and mechanical properties of the produced components under as-deposited and heat-treated conditions were investigated. The results revealed that the grain morphology of the specimen was mainly composed of equiaxed grains in each layer, while the grain size of the interlayer region was reduced due to the heterogeneous nucleation relying on the partially remelted previous layer. Moreover, a reduced amount of second phase was observed due to decreased Zn and Cu alloying elements content in this region, which resulted in a gradient change in microhardness distribution. The tensile strength and elongation of the heat-treated samples in vertical and horizontal directions were 321 MPa, 10.12 %, and 377 MPa, 9.72 %, respectively. The results indicated good comprehensive mechanical properties, which is promising for further application of WAAM fabricated laminated metal composite.

Hybrid manufacturing approach for landing gear applications: WAAM Ti–6Al–4V on forged Ti–5Al–5Mo–5V–3Cr

High-strength metastable β-titanium alloys like Ti-5553 (Ti–5Al–5Mo–5V–3Cr) are frequently used in highly loaded aerospace components. Such aerospace parts tend to be expensive to traditionally manufacture due to current industry process limitations such as inflexibility for complex geometries, costs related to tooling for large forgings, extended lead times, poor machinability and high material waste. These challenges are leading to increased interest in exploring alternative manufacturing routes. This work investigates the use of additive manufacturing to deposit cost-effective and machinable Ti-64 (Ti–6Al–4V) alloy onto a forged Ti-5553 alloy substrate. The microstructure evolution, microhardness and tensile properties have been investigated for both the as-deposited as well as for stress relief heat-treated conditions. The results confirmed the formation of coarse columnar β grains with a fine basketweave α structure. The heat affected zones (HAZs) developed in the Ti-5553 substrate material from the cyclic thermal fluxes introduced from the melt-pool were characterized by a gradient microstructure of dissolving constituent phases with nearing proximity to the fusion zone. Tensile testing in the as-deposited condition was characterised with a UTS of 884 MPa and a ductility of 15%. Tensile samples extracted across the substrate-deposit interface all failed in the WAAM Ti-64 material and demonstrated comparatively greater strength but poorer ductility. A band of tensile residual stresses was imparted along the substrate, but was adequately stress relieved after heat-treatment at 600 °C. The heat-treatment led to the formation of more homogeneous α-phase laths throughout the HAZ of the Ti-5553 material and provided overall improvements to the strength and ductility.

Enhanced surface finish and reduced porosity of TiC nanoparticles reinforced 2219 aluminum alloy deposit fabricated via oscillating laser-arc hybrid additive manufacturing

Additive manufacturing (AM) of ceramic particle reinforced aluminum alloy has drawn increasing attention due to the refined microstructure and improved mechanical properties in as-deposited condition. However, it is still challenging to make defect-free ceramic particle reinforced aluminum alloy deposit with desirable surface finish using wire-based AM technique because of the special thermophysical properties of the incorporated ceramic particles. In this work, a novel oscillating laser-arc hybrid additive manufacturing (OLHAM) technique was developed to fabricate TiC nanoparticles reinforced 2219 aluminum alloy deposit. The surface finish and porosity were evaluated using optical microscope and 3D XCT, respectively. Compared with wire-arc additively manufactured (WAAMed) deposit, the surface roughness and volume porosity of OLHAMed deposit decreased by 46.0 % and 88.3 %, respectively. In-situ high-speed photography was used to observe the arc and molten pool behaviors to understand the mechanism of enhanced surface finish and reduced porosity. The enhanced surface finish was attributed to smaller layer width fluctuation and higher arc stability, which resulted from the action of the hybrid heat source. The elimination of large droplet transfer, which caused pores in the WAAMed deposit, and the promotion of molten pool fluidity resulted in much lower porosity of the OLHAMed deposit.

Effect of post-deposition heat treatment on microstructure and mechanical properties of NASA HR-1 cold spray coatings

The primary goal of this work was to examine the impact of heat treatment on the evolution of microstructure and mechanical properties of NASA HR-1 cold spray coatings. Coatings were produced employing a high-pressure cold spray system using N2 and He process gases and the effect of process gas and deposition temperature on the microstructure and mechanical properties of the coatings was examined. Microstructural characterization was performed using optical microscopy, scanning electron microscopy, micro X-ray computed tomography, and electron backscatter diffraction. NASA HR-1 coatings produced with He process gas exhibited improved plastic deformation and resulted in the lowest porosity compared to those deposited with N2 process gas. All coatings showed brittle failure with limited ductility in the as-deposited condition. Heat treatment of the NASA HR-1 cold spray coatings was performed at 550 °C and 950 °C for 1 h to improve the mechanical strength of the coatings. Heat treatment improved the particle bonding and enhanced the mechanical properties of the cold spray coatings. Heat treatment performed at 550 °C resulted in higher mechanical strength of coatings, whereas the heat treatment performed at 950 °C resulted in recrystallized microstructure and improved ductility of the coatings. However, heat treatment at 950 °C resulted in forming the Eta (η) phase and Ni-Ti intermetallics in all the NASA HR-1 cold spray coatings. The overall results suggest that using He as process gas contributed to reduced porosity and enhanced mechanical properties of the cold spray coatings.

Additive friction stir deposition of super duplex stainless steel: Microstructure and mechanical properties

Additive Friction Stir Deposition (AFSD) is an emerging solid-state metal additive manufacturing (AM) process that offers several key benefits, including high deposition rates and wrought-equivalent mechanical properties even in the as-deposited condition. The work presented is the first study to report on the development of microstructure and mechanical properties of AFSD-processed duplex stainless steel (DSS2507). The banded microstructure of the starting material was remarkably affected by AFSD processing; the austenite grains exhibited a refined and equiaxed morphology, while the ferrite grains appeared slightly larger and elongated. Microstructural observations revealed that the potential mechanism of microstructure evolution in austenite was discontinuous dynamic recrystallization (DDRX), while in ferrite, it was continuous dynamic recrystallization (CDRX). The occurrence of multiple thermal cycles during the AFSD process resulted in σ phase precipitation, which in turn led to considerable variation in mechanical properties with respect to the build direction. The top region of the as-built part with an insignificant σ phase fraction showed improved tensile strength and ductility combination compared to the as-received DSS2507 as well as other AM-processed DSS2507 alloys.

Effect of heat treatment on mechanical compression properties of C250 maraging steel fabricated by directed energy deposition

The mechanical compression properties of C250 maraging steel fabricated by directed energy deposition (DED), in the as-deposited and post-fabrication heat-treated conditions, are investigated under quasi-static loading conditions. The microstructure of the material is studied using analytical transmission electron microscopy and a comparison is made between the DED fabricated and conventionally produced wrought materials. The results reveal that the DED fabricated material, in the as-deposited condition, exhibits lower yield and ultimate compressive strengths compared to the commercially heat-treated wrought alloy, due to the absence of strengthening precipitates and the presence of a retained austenite phase. However, post-fabrication thermal treatment significantly improves the compressive strengths of the as-processed material to levels comparable to those of the conventionally produced wrought material. This is attributed to the formation of nano-sized Ni3Mo strengthening precipitates, a reduction in the amount of austenite phase, and the refinement of prior-austenite grains during the thermal treatment. Moreover, the DED fabricated material, in the heat-treated condition, with the presence of an austenite phase shows higher ductility than the commercially heat-treated wrought material.

Corrosion characteristics of Ti and Al2O3/Ti thin films sputtered on 316LSS

In this work, two thin films (Ti and Al2O3/Ti) were deposited on 316LSS substrates by the physical vapor deposition (PVD) sputtering technique. Heat treatment was applied for thin films at 400 °C for 2 h. Thin films were divided into two groups, The First group cooled in the air (normalized), and the second cooled in the furnace (annealed). The electrochemical characteristics were investigated by potentiodynamic polarization (POT) and impedance spectroscopy (EIS) tests. The corrosion resistance (CRST) for all thin films before and after heat treatment was determined in 3.5% NaCl at room temperature (RT). Scanning electron microscope (SEM), and surface topography were studied for all thin films before and after heat treatment and corrosion tests. At as-deposited conditions, superior CRST belonged to Ti thin film. Meanwhile, after heat treatment, the annealed 316LSS/ Al2O3/Ti had the lowest corrosion rate 0.17 mm/y, and the highest CRST of about 3655 ohm.cm2.

Effects of nitride precipitation on delta phase formation in additively manufactured nickel superalloys

Additively manufactured Inconel 625 is particularly susceptible to the formation of niobium-rich δ-phase precipitates in the interdendritic regions during high temperature exposure. With specific minor alloying element combinations and nitrogen mass fractions on the order of 0.1 %, the formation of δ-phase can be suppressed through the precipitation of nitrides. For example, mass fractions of 0.39 % silicon and 0.03 % titanium led to the precipitation of Z-phase and η-nitrides, which consumed the excess niobium in the interdendritic regions and limited δ-phase formation. Even when holding the material at a temperature of 870 °C for 1000 h, the δ-phase volume fraction was approximately 2 %, which is far below the 6 % level observed in the wrought condition. When the titanium mass fraction was increased to 0.21 % and the silicon mass fraction decreased to 0.05 %, titanium-rich MN nitrides formed within the interdendritic regions instead. Since much of the Nb in these regions was not consumed by the nitrides, δ-phase formation was promoted and reached volume fractions above 10 %. The addition of a hot isostatic pressing step prior to high temperature exposure in both alloys produced a more uniform niobium distribution and minimized δ-phase formation at shorter times. At extended times, trends in the δ-phase volume fractions were similar to those observed in the as-deposited condition, with the initial alloy compositions driving differences in the distribution of excess niobium available for δ-phase formation.

Co-strengthening and deformation behaviors of hybrid additive manufactured U75V/15-5PH bimetal via optimized heat treatment

Bimetals composed of U75V pearlitic steel and 15–5 precipitation hardening (PH) steel were successfully processed by a hybrid additive manufacturing method. However, the U75V/15-5PH bimetal in the as-deposited condition showed inferior mechanical properties owing to the inhomogeneous microstructures. Herein, optimized heat treatment for the co-strengthening of U75V/15-5PH bimetal was designed by investigating the microstructural evolution and mechanical properties thoroughly. Results showed that the mechanical properties of the U75V steel region were recovered after solution treatment, reflected in the formation of lamellar pearlite. For the additive 15-5PH steel region, the formation of martensitic phase and NbC carbides contributed to the strengthening in the solution condition. Furthermore, this region was further hardened by the massive precipitation of Cu-riched precipitates induced by aging treatment. Due to the difference in yield strength of U75V/15-5PH bimetals with various locations, the deformation transfer phenomenon from U75V steel to 15-5PH stainless steel was detected during the uniaxial tensile tests. After heat-treated through the solution and aging treatment, the optimized yield strength, ultimate tensile strength, and elongation of the U75V/15-5PH bimetal achieved 878 MPa, 1201 MPa, and 11.2%, respectively. This study demonstrated experimentally that the mechanical performance of the U75V/15-5PH bimetal with various microstructures could be improved by designing a suitable solution and aging heat treatment.

Gamma prime precipitation in as-deposited Ni-based superalloy IN713LC

The as-deposited microstructure of an additively manufactured Ni-based superalloy fabricated using laser powder-bed-fusion has been investigated using atomic resolution transmission electron microscopy. It is shown that γ′ precipitates exist in the as-deposited condition, albeit in a non-equilibrium state. The precipitates are present as nano-structured domains throughout the microstructure. These domains exhibit clear L12 ordering but show highly irregular matrix-precipitate interfaces.

Corrosion resistance and microstructure analysis of additively manufactured 22% chromium duplex stainless steel by laser metal deposition with wire

Microstructure characteristics and pitting corrosion of a duplex stainless steel (DSS) manufactured by laser metal deposition with wire (LMDw) were studied. The layer-by-layer LMDw process resulted in a mixed microstructure of predominantly ferrite with 2% austenite and chromium-rich nitrides, and reheated regions with ∼33% austenite. The high cooling rate of LMDw restricted the distribution of Cr, Mo, and Ni, in ferrite and austenite, while N diffuses from ferrite to austenite. Subsequent heat treatment at 1100 °C for 1 h resulted in homogenized microstructure, dissolution of nitrides, and balanced ferrite/austenite ratio. It also led to the redistribution of Cr and Mo to ferrite, and Ni and N to austenite. At room temperature, cyclic potentiodynamic polarization measurements in 1.0 M NaCl solution showed no significant differences in corrosion resistance between the as-deposited and heat-treated samples, despite the differences in terms of ferrite to austenite ratio and elemental distribution. Critical pitting temperature (CPT) was the lowest (60 °C) for the predominantly ferritic microstructure with finely dispersed chromium-rich nitrides; while reheated area with ∼33% austenite in as-deposited condition achieved higher critical temperature comparable to what was obtained after heat treatment (73 and 68 °C, respectively). At temperatures above the CPT, selective dissolution of the ferrite after deposition was observed due to depletion of N, while after heat treatment, austenite preferentially dissolved due to Cr and Mo concentrating in ferrite. In summary, results demonstrate how microstructural differences in terms of ferrite-to-austenite ratio, distribution of corrosion-resistant elements, and presence of nitrides affect corrosion resistance of LMDw DSS.

Deciphering the role of W content, triple junctions, and heat treatment on the corrosion performance of Ni–W alloy coatings used for automotive applications

In this study we focus on understanding the influence of tungsten (W) content, heat treatment and grain size on the corrosion behaviour of Ni–W coatings. Using pulse and pulse reverse electrodeposition techniques, Ni–W coatings with different W contents (3, 7.5, 12, 17, 20 and 25 at.%) were deposited from a standard ammonia-citrate bath. Coatings were heat treated at 700 °C in vacuum for 1 h and then characterized to determine the surface morphology, grain size, and phase transformations. To evaluate the corrosion performance of the coatings, potentiodynamic polarization tests were performed in 0.6 M NaCl solution. Polarization test results indicated that as-deposited Ni–W coatings had better corrosion resistance compared to heat treated coatings. In the as-deposited condition, corrosion resistance increased up to 17 at.% W. However, further addition of W decreased the corrosion resistance due to high volume fraction of triple junctions and intercrystalline regions. On the other hand, heat treated coatings suffered from micro-galvanic corrosion due to the precipitation of Ni4W and NiW phases, and therefore showed higher corrosion rates compared to as-deposited coatings. The changes observed in the corrosion behaviour of as-deposited and heat treated Ni–W coatings were rationalized based on surface composition, mixed potential theory, and triple junction corrosion theory.

Predicting the Effect of Surface Waviness on Fatigue Life of a Wire + Arc Additive Manufactured Ti-6Al-4V Alloy.

This paper reports the effect of as-deposited surface conditions on the fatigue strength of an additively manufactured titanium alloy, Ti-6Al-4V (WAAM Ti64). First, the local stress concentration caused by the surface waviness was quantified using a metrology technique and computer modelling. Fatigue tests were conducted under bending loads at a cyclic load ratio of 0.1. The applicability of two predictive methods was the focus of this study. The traditional notch stress method was unable to predict the correct S-N curve trend slope, which could be attributed to the early crack initiation from the troughs on the as-built surface, with crack propagation being the dominant failure mechanism. By treating the troughs as small cracks, the fracture mechanics approach delivered good predictions at every applied stress level. Surface machining and polishing may not always be practical or required; it depends on the applications and service load levels. This research demonstrated that the fracture mechanics approach can be used for predicting the fatigue life of WAAM titanium alloys in as-built conditions and, hence, can be a tool for decision making on the level of surface machining.

Refinement of Ti-6Al-4V prior-β grain structure in the as-deposited condition via process control during wire-direct energy deposition

Refinement of Ti-6Al-4V prior-β grain structure in the as-deposited condition via process control during wire-direct energy deposition

Experimental and DFT investigations on the influence of cetrimonium bromide (CTAB) on surface morphology and anti-tarnishing performance of pulse galvanostatically deposited gold coatings from a cyanide-free electroplating solution

In the present study, pulse galvanostatic electroplating method is used to produce mirror-bright gold (Au) deposits from a non-cyanide electroplating solution. Electrodeposition is carried out from two different solutions in the presence and absence of cetrimonium bromide (CTAB) to study the influence of the quaternary ammonium surfactant on the microstructure and the anti-tarnishing behaviour of the Au deposits. Electrochemical studies (cyclic voltammetry (CV) and chronoamperometry) are carried out to get an insight into the type of nucleation and growth occurring during the electrodeposition of gold. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies show that in the presence of CTAB, fine-structured coating with a compact and uniform morphology is obtained. The X-ray diffraction (XRD) studies show that in the presence of cetrimonium bromide, the growth of Au is favoured along the (111) lower index crystal surface, and with no cetrimonium bromide in the electroplating bath, the growth of Au is favoured along the (200) higher index crystal surface. The influence of cetrimonium bromide on the resistance to the tarnishing of the Au coating is initially predicted by quantum chemical calculations based on density functional theory (DFT). Electrochemical impedance spectroscopy (EIS) and static immersion test also confirm the less severity of tarnishing for the coating electrodeposited from the solution containing cetrimonium bromide (CTAB). Visual observation and the glossiness analysis confirm the difference in the physical appearance of the coating surface in the as-deposited condition and after tarnishing. The findings of this study demonstrate that the electrodeposition of Au with a crystal surface control, by using CTAB as a bath additive, can be used as a plausible technique for enhancing the anti-tarnishing performance of the coatings.

Heat treatment effects on the corrosion performance of wire arc additively manufactured ER316LSi stainless steel

Corrosion performance of a multi-layered ER316LSi wall deposited using wire and arc additive manufacturing was studied in the as-deposited condition and after stress relief heat treatment at 900 °C, in 3.5 wt% NaCl solution. It was found that the heat treatment is not suitable for WAAM ER316LSi components due to the complete transformation of the delta ferrite into sigma decreasing the corrosion performance. The delta ferrite to sigma transformation during heat treatment was facilitated by the cyclic reheating of the part during deposition. The electrochemical response of as-deposited WAAM differed from a wrought alloy with similar composition and linked to microstructural differences: as-deposited WAAM had a higher pitting potential due to the absence of sulfide inclusions and increased metastable-like activity due to the presence of the secondary delta ferrite causing elemental segregation.

Processing and characterization of AISI 316L coatings modified with Cu and CuO nanoparticles

Nanoparticles (NPs) have been used to benefit from Cu properties, due to their unique physicochemical characteristics caused by a high surface-to-volume ratio. However, to enable the deposition of hardfacing coatings with NPs, it is of interest to evaluate the processability of nanocomposite materials. The processability of hardfacing coatings, measured by their soundness, porosity, hardness, and solidification structure, is particularly relevant to assess the effects of adding Cu NPs and CuO NPs to AISI 316L. This study prepared and deposited powder mixtures of AISI 316L atomized steel with 5 wt% Cu microparticles (MPs), Cu NPs, and CuO NPs, individually, to process coatings by plasma transferred arc. Results showed that Cu additions alter the processability of AISI 316L and that both NPs influenced dilution and wettability of layers, requiring higher deposition energy to avoid lack of fusion. The interaction between the powder and the plasma arc depends on the features of the powder mixtures and a hypothesis for the behavior of the powder mixtures used across the plasma arc is put forward. The more significant evaporation during hardfacing with powder mixtures with NP particles induced a more significant loss in Cu and an increase in porosity in the austenitic coatings. Further impacts of the Cu-based nanoparticles in the deposited powders mixtures are revealed by the finer solidification structure. Regardless of the features of the powder mixtures, Cu-containing coatings showed a lower hardness associated with Cu being in solid solution on the as-deposited condition.

A performance comparison of additive manufactured creep-resistant superalloys

Creep-resistant nickel, cobalt based superalloys, selected for a high-speed flight application, deposited using Wire + Arc Additive Manufacturing (WAAM), was reported. Three different alloys, Haynes 188, Inconel 718, and Rene 41, were deposited, and tested for their high-temperature tensile properties, and the results compared with wrought data. The alloys were tested from ambient temperature to 1000°C in their as-deposited condition and after undergoing industry standard age-hardening and solutionising heat-treatments, to down select the best performing alloy under two different processing conditions. The mechanical strength of the alloys fell short of the maximum achievable in wrought condition. Precipitation-strengthened alloys, Inconel 718 and Rene 41 were found to have underperformed the most significantly, whereas solid-solution-strengthened Haynes 188 suffered the least due to WAAM.