Characterization of Spatter and Sublimation in Alloy 718 during Electron Beam Melting

Due to elevated temperatures and high vacuum levels in electron beam melting (EBM), spatter formation and accumulation in the feedstock powder, and sublimation of alloying elements from the base feedstock powder can affect the feedstock powder’s reusability and change the alloy composition of fabricated parts. This study focused on the experimental and thermodynamic analysis of spatter particles generated in EBM, and analyzed sublimating alloying elements from Alloy 718 during EBM. Heat shields obtained after processing Alloy 718 in an Arcam A2X plus machine were analyzed to evaluate the spatters and metal condensate. Comprehensive morphological, microstructural, and chemical analyses were performed using scanning electron microscopy (SEM), focused ion beam (FIB), and energy dispersive spectroscopy (EDS). The morphological analysis showed that the area coverage of heat shields by spatter increased from top (<1%) to bottom (>25%), indicating that the spatter particles had projectile trajectories. Similarly, the metal condensate had a higher thickness of ~50 μm toward the bottom of the heat shield, indicating more significant condensation of metal vapors at the bottom. Microstructural analysis of spatters highlighted that the surfaces of spatter particles sampled from the heat shields were also covered with condensate, and the thickness of the deposited condensate depended on the time of landing of spatter particles on the heat shield during the build. The chemical analysis showed that the spatter particles had 17-fold higher oxygen content than virgin powder used in the build. Analysis of the metalized layer indicated that it was formed by oxidized metal condensate and was significantly enriched with Cr due to its higher vapor pressure under EBM conditions.

Download Full-text

Additive Manufacturing of Alloy 718 via Electron Beam Melting: Effect of Post-Treatment on the Microstructure and the Mechanical Properties

Materials ◽

10.3390/ma12010068 ◽

2018 ◽

Vol 12 (1) ◽

pp. 68 ◽

Cited By ~ 14

Author(s):

Arun Balachandramurthi ◽

Johan Moverare ◽

Satyapal Mahade ◽

Robert Pederson

Keyword(s):

Electron Beam ◽

Additive Manufacturing ◽

Electron Beam Melting ◽

Elevated Temperatures ◽

Microstructural Analysis ◽

Solution Treatment ◽

Post Treatment ◽

Alloy 718 ◽

Machined Surface ◽

Contour Region

Alloy 718 finds application in gas turbine engine components, such as turbine disks, compressor blades and so forth, due to its excellent mechanical and corrosion properties at elevated temperatures. Electron beam melting (EBM) is a recent addition to the list of additive manufacturing processes and has shown the capability to produce components with unique microstructural features. In this work, Alloy 718 specimens were manufactured using the EBM process with a single batch of virgin plasma atomized powder. One set of as-built specimens was subjected to solution treatment and ageing (STA); another set of as-built specimens was subjected to hot isostatic pressing (HIP), followed by STA (and referred to as HIP+STA). Microstructural analysis of as-built specimens, STA specimens and HIP+STA specimens was carried out using optical microscopy and scanning electron microscopy. Typical columnar microstructure, which is a characteristic of the EBM manufactured alloy, was observed. Hardness evaluation of the as-built, STA and HIP+STA specimens showed that the post-treatments led to an increase in hardness in the range of ~50 HV1. Tensile properties of the three material conditions (as-built, STA and HIP+STA) were evaluated. Post-treatments lead to an increase in the yield strength (YS) and the ultimate tensile strength (UTS). HIP+STA led to improved elongation compared to STA due to the closure of defects but YS and UTS were comparable for the two post-treatment conditions. Fractographic analysis of the tensile tested specimens showed that the closure of shrinkage porosity and the partial healing of lack of fusion (LoF) defects were responsible for improved properties. Fatigue properties were evaluated in both STA and HIP+STA conditions. In addition, three surface conditions were also investigated, namely the ‘raw’ as-built surface, the machined surface with the contour region and the machined surface without the contour region. Machining off the contour region completely together with HIP+STA led to significant improvement in fatigue performance.

Download Full-text

Can Appropriate Thermal Post-Treatment Make Defect Content in as-Built Electron Beam Additively Manufactured Alloy 718 Irrelevant?

Materials ◽

10.3390/ma13030536 ◽

2020 ◽

Vol 13 (3) ◽

pp. 536 ◽

Cited By ~ 1

Author(s):

Sneha Goel ◽

Kévin Bourreau ◽

Jonas Olsson ◽

Uta Klement ◽

Shrikant Joshi

Keyword(s):

Electron Beam ◽

Process Optimization ◽

Electron Beam Melting ◽

Phase Distribution ◽

Hot Isostatic Pressing ◽

Alloy 718 ◽

Proof Of Concept ◽

Defect Content ◽

Enhancing Production ◽

Hardness Values

Electron beam melting (EBM) is gaining rapid popularity for production of complex customized parts. For strategic applications involving materials like superalloys (e.g., Alloy 718), post-treatments including hot isostatic pressing (HIPing) to eliminate defects, and solutionizing and aging to achieve the desired phase constitution are often practiced. The present study specifically explores the ability of the combination of the above post-treatments to render the as-built defect content in EBM Alloy 718 irrelevant. Results show that HIPing can reduce defect content from as high as 17% in as-built samples (intentionally generated employing increased processing speeds in this illustrative proof-of-concept study) to <0.3%, with the small amount of remnant defects being mainly associated with oxide inclusions. The subsequent solution and aging treatments are also found to yield virtually identical phase distribution and hardness values in samples with vastly varying as-built defect contents. This can have considerable implications in contributing to minimizing elaborate process optimization efforts as well as slightly enhancing production speeds to promote industrialization of EBM for applications that demand the above post-treatments.

Download Full-text

The Effects of Alloying Elements on the Ductility of Electron Beam Melted Molybdenum (Electron Beam Melting of Refractory Metals (V))

Journal of the Japan Institute of Metals and Materials ◽

10.2320/jinstmet1952.30.1_38 ◽

1966 ◽

Vol 30 (1) ◽

pp. 38-42 ◽

Cited By ~ 2

Author(s):

Tetsuya Takaai

Keyword(s):

Electron Beam ◽

Electron Beam Melting ◽

Refractory Metals ◽

Alloying Elements

Download Full-text

Encapsulation of Electron Beam Melting Produced Alloy 718 to Reduce Surface Connected Defects by Hot Isostatic Pressing

Materials ◽

10.3390/ma13051226 ◽

2020 ◽

Vol 13 (5) ◽

pp. 1226 ◽

Cited By ~ 1

Author(s):

Yunus Emre Zafer ◽

Sneha Goel ◽

Ashish Ganvir ◽

Anton Jansson ◽

Shrikant Joshi

Keyword(s):

Electron Beam ◽

Electron Beam Melting ◽

Surface Defects ◽

High Surface ◽

Hot Isostatic Pressing ◽

Coated Sample ◽

Alloy 718 ◽

Isostatic Pressing ◽

Before And After ◽

X Ray Computed

Defects in electron beam melting (EBM) manufactured Alloy 718 are inevitable to some extent, and are of concern as they can degrade mechanical properties of the material. Therefore, EBM-manufactured Alloy 718 is typically subjected to post-treatment to improve the properties of the as-built material. Although hot isostatic pressing (HIPing) is usually employed to close the defects, it is widely known that HIPing cannot close open-to-surface defects. Therefore, in this work, a hypothesis is formulated that if the surface of the EBM-manufactured specimen is suitably coated to encapsulate the EBM-manufactured specimen, then HIPing can be effective in healing such surface-connected defects. The EBM-manufactured Alloy 718 specimens were coated by high-velocity air fuel (HVAF) spraying using Alloy 718 powder prior to HIPing to evaluate the above approach. X-ray computed tomography (XCT) analysis of the defects in the same coated sample before and after HIPing showed that some of the defects connected to the EBM specimen surface were effectively encapsulated by the coating, as they were closed after HIPing. However, some of these surface-connected defects were retained. The reason for such remnant defects is attributed to the presence of interconnected pathways between the ambient and the original as-built surface of the EBM specimen, as the specimens were not coated on all sides. These pathways were also exaggerated by the high surface roughness of the EBM material and could have provided an additional path for argon infiltration, apart from the uncoated sides, thereby hindering complete densification of the specimen during HIPing.

Download Full-text

Purification of Niobium by Electron Beam Melting

High Temperature Materials and Processes ◽

10.1515/htmp-2014-0218 ◽

2016 ◽

Vol 35 (6) ◽

pp. 621-627 ◽

Cited By ~ 3

Author(s):

M. Sankar ◽

K.V. Mirji ◽

V.V. Satya Prasad ◽

R.G. Baligidad ◽

A.A. Gokhale

Keyword(s):

Electron Beam ◽

Electron Beam Melting ◽

Alkali Metals ◽

High Vacuum ◽

Input Power ◽

Combined Effect ◽

Electron Gun ◽

Pure Niobium ◽

Interstitial Impurities ◽

Melting Technique

AbstractPure niobium metal, produced by alumino-thermic reduction of niobium oxide, contains various impurities which need to be reduced to acceptable levels to obtain aerospace grade purity. In the present work, an attempt has been made to refine niobium metals by electron beam drip melting technique to achieve purity confirming to the ASTM standard. Input power to the electron gun and melt rate were varied to observe their combined effect on extend of refining and loss of niobium. Electron beam (EB) melting is shown to reduce alkali metals, trace elements and interstitial impurities well below the specified limits. The reduction in the impurities during EB melting is attributed to evaporation and degassing due to the combined effect of high vacuum and high melt surface temperature. The % removal of interstitial impurities is essentially a function of melt rate and input power. As the melt rate decreases or input power increases, the impurity levels in the solidified niobium ingot decrease. The EB refining process is also accompanied by considerable amount of niobium loss, which is attributed to evaporation of pure niobium and niobium sub-oxide. Like other impurities, Nb loss increases with decreasing melt rate or increase in input power.

Download Full-text

Identifying the crossover between growth regimes via in-situ conductance measurements in focused electron beam induced deposition

Nanofabrication ◽

10.2478/nanofab-2014-0009 ◽

2014 ◽

Vol 1 (1) ◽

Cited By ~ 2

Author(s):

M. Winhold ◽

P. M. Weirich ◽

C. H. Schwalb ◽

M. Huth

Keyword(s):

Genetic Algorithm ◽

Electron Beam ◽

Elevated Temperatures ◽

Ion Beam ◽

Optimization Procedure ◽

Ternary Systems ◽

Deposition Process ◽

Algorithm Optimization ◽

Electron Beam Induced Deposition

AbstractFocused electron beam induced deposition presents a promising technique for the fabrication of nanostructures. However, due to the dissociation of mostly organometallic precursor molecules employed for the deposition process, prepared nanostructures contain organic residues leading to rather low conductance of the deposits. Post-growth treatment of the structures by electron irradiation or in reactive atmospheres at elevated temperatures can be applied to purify the samples. Recently, an in-situ conductance optimization process involving evolutionary genetic algorithm techniques has been introduced leading to an increase of conductance by one order of magnitude for tungsten-based deposits using the precursor W(CO)6. This method even allows for the optimization of conductance of nano-structures for which post-growth treatment is not possible or desirable. However, the mechanisms responsible for the observed enhancement have not been studied in depth. In this work, we identified the dwell-time dependent change of conductivity of the samples to be the major contributor to the change of conductance. Specifically, the chemical composition drastically changes with a variation of dwelltime resulting in an increase of the metal content by 15 at% for short dwell-times. The relative change of growth rate amounts to less than 25 % and has a negligible influence on conductance. We anticipate the in-situ genetic algorithm optimization procedure to be of high relevance for new developments regarding binary or ternary systems prepared by focused electron or ion beam induced deposition.

Download Full-text

Kinetics of Evaporation of Alloying Elements under Vacuum: Application to Ti alloys in Electron Beam Melting

High Temperature Materials and Processes ◽

10.1515/htmp-2015-0220 ◽

2017 ◽

Vol 36 (8) ◽

pp. 815-823 ◽

Cited By ~ 2

Author(s):

Wonjin Choi ◽

Julien Jourdan ◽

Alexey Matveichev ◽

Alain Jardy ◽

Jean-Pierre Bellot

Keyword(s):

Electron Beam ◽

Activity Coefficient ◽

Electron Beam Melting ◽

Liquid Pool ◽

Alloying Elements ◽

Surface Boundary ◽

Surface Boundary Layer ◽

Experimental Distribution ◽

High Vapor ◽

Titanium Processing

AbstractVacuum metallurgical processes such as the electron beam melting are highly conducive to volatilization. In titanium processing, it concerns the alloying elements which show a high vapor pressure with respect to titanium matrix, such as Al. Two different experimental approaches using a laboratory electron beam furnace have been developed for the estimation of volatilization rate and activity coefficient of Al in Ti64. The first innovative method is based on the deposition rate of Al on Si wafers located at different angles θ above the liquid bath. We found that a deposition according to a cos2(π/2−θ) law describes well the experimental distribution of the weight of the deposition layer. The second approach relies on the depletion of aluminum in the liquid pool at two separate times of the volatilization process. Both approaches provide values of the Al activity coefficient at T=1, 860 °C in a fairly narrow range [0.044–0.0495], in good agreement with the range reported in the literature. Furthermore numerical simulation of the Al behavior in the liquid pool reveals (in the specific case of electron beam button melting) a weak transport resistance in the surface boundary layer.

Download Full-text

ELECTRON-BEAM MELTING OF INGOTS OF TiAl SYSTEM INTERMETALLICS

MATEC Web of Conferences ◽

10.1051/matecconf/202032110004 ◽

2020 ◽

Vol 321 ◽

pp. 10004

Author(s):

S.V. Akhonin ◽

V.A. Berezos ◽

A.Yu. Severyn

Keyword(s):

Electron Beam ◽

Mathematical Models ◽

Titanium Aluminide ◽

Electron Beam Melting ◽

Liquid Pool ◽

Alloying Elements ◽

Technological Parameters ◽

Heat State ◽

Initial Charge ◽

Scientific Technical

Performance of scientific-technical researches at the E. O. Paton Electric Welding Institute of the NAS of Ukraine have been directed on development of technology for manufacture of titanium aluminide –based alloys using the method of electron-beam melting (EBM). The mathematical models of heat state and evaporation of alloying elements in EBM were developed. The results of calculations of heat state using the mathematical model allowed determining a dependence of depth of liquid pool on different melting rates. The mathematical models of processes of evaporation in EBM of titanium aluminide ingots were used for plotting the nomograms, which help to determine the necessary content of alloying element of the alloy in the initial charge for acquiring the necessary concentration of this element in ingot at set technological parameters of melting. In scopes of designed mathematical models there were investigated different technological modes of electron-beam melting of ingots based on titanium aluminide. The optimum EBM modes, at which a solidification front approaches to flat, were determined. At that, more uniform distribution of the additives on ingot section and volume is provided as well as level of stressed state is reduced. The works were carried out on manufacture of titanium aluminide based-ingots with addition of refractory as well as volatile alloying elements. Composition and structure of produced ingots were examined. It is shown that electron-beam melting allows getting chemically homogeneous ingots based on titanium aluminide and is a perspective method for production of such class materials.

Download Full-text