Predicting Microstructure From Thermal History During Additive Manufacturing for Ti-6Al-4V

2016 ◽  
Vol 138 (11) ◽  
Author(s):  
Jeff Irwin ◽  
Edward W. Reutzel ◽  
Pan Michaleris ◽  
Jay Keist ◽  
Abdalla R. Nassar
Keyword(s):  
Thermal History ◽  
Deposition Process ◽  
Beta Phase ◽  
Processing Parameters ◽  
Simplex Algorithm ◽  
Alpha Phase ◽  
Process Understanding ◽  
Microstructural Model ◽  
Lath Width ◽  
Optimized Model

Due to the repeated thermal cycling that occurs with the processing of each subsequent layer, the microstructure of additively manufactured parts undergoes complex changes throughout the deposition process. Understanding and modeling this evolution poses a greater challenge than for single-cycle heat treatments. Following the work of Kelly and Charles, a Ti-6Al-4V microstructural model has been developed which calculates the phase fractions, morphology, and alpha lath width given a measured or modeled thermal history. Dissolution of the alpha phase is modeled as 1D plate growth of the beta phase, while alpha growth is modeled by the technique of Johnson–Mehl–Avrami (JMA). The alpha phase is divided into colony and basketweave morphologies based on an intragranular nucleation temperature. Evolution of alpha lath width is calculated using an Arrhenius equation. Key parameters of the combined Kelly–Charles model developed here are optimized using the Nelder–Mead simplex algorithm. For the deposition of two L-shaped geometries with different processing parameters, the optimized model gives a mean error over 24 different locations of 37% relative to experimentally measured lath widths, compared to 106% for the original Kelly–Charles model.

scholarly journals Structural Factors Inducing Cracking of Brass Fittings

Materials ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3255
Author(s):  
Lenka Kunčická ◽  
Michal Jambor ◽  
Adam Weiser ◽  
Jiří Dvořák
Keyword(s):  
Chemical Composition ◽  
Plastic Flow ◽  
Beta Phase ◽  
Alpha Phase ◽  
Structural Factors ◽  
Transmission Electron ◽  
Medical Gas ◽  
Hot Die Forging ◽  
Multiple Step

Cu–Zn–Pb brasses are popular materials, from which numerous industrially and commercially used components are fabricated. These alloys are typically subjected to multiple-step processing—involving casting, extrusion, hot forming, and machining—which can introduce various defects to the final product. The present study focuses on the detailed characterization of the structure of a brass fitting—i.e., a pre-shaped medical gas valve, produced by hot die forging—and attempts to assess the factors beyond local cracking occurring during processing. The analyses involved characterization of plastic flow via optical microscopy, and investigations of the phenomena in the vicinity of the crack, for which we used scanning and transmission electron microscopy. Numerical simulation was implemented not only to characterize the plastic flow more in detail, but primarily to investigate the probability of the occurrence of cracking based on the presence of stress. Last, but not least, microhardness in specific locations of the fitting were examined. The results reveal that the cracking occurring in the location with the highest probability of the occurrence of defects was most likely induced by differences in the chemical composition; the location the crack in which developed exhibited local changes not only in chemical composition—which manifested as the presence of brittle precipitates—but also in beta phase depletion. Moreover, as a result of the presence of oxidic precipitates and the hard and brittle alpha phase, the vicinity of the crack exhibited an increase in microhardness, which contributed to local brittleness.

scholarly journals Development of an Additive Manufacturing System for the Deposition of Thermoplastics Impregnated with Carbon Fibers

2019 ◽  
Vol 3 (2) ◽  
pp. 35 ◽  
Author(s):  
Miguel Reis Silva ◽  
António M. Pereira ◽  
Nuno Alves ◽  
Gonçalo Mateus ◽  
Artur Mateus ◽  
...  
Keyword(s):  
Tensile Strength ◽  
Additive Manufacturing ◽  
Carbon Fibers ◽  
Low Cost ◽  
Deposition Process ◽  
Processing Parameters ◽  
Yarn Diameter ◽  
Thermoplastic Matrix ◽  
Anisotropic Mechanical Properties ◽  
Long Carbon Fiber

This work presents an innovative system that allows the oriented deposition of continuous fibers or long fibers, pre-impregnated or not, in a thermoplastic matrix. This system is used in an integrated way with the filamentary fusion additive manufacturing technology and allows a localized and oriented reinforcement of polymer components for advanced engineering applications at a low cost. To demonstrate the capabilities of the developed system, composite components of thermoplastic matrix (polyamide) reinforced with pre-impregnated long carbon fiber (carbon + polyamide), 1 K and 3 K, were processed and their tensile and flexural strength evaluated. It was demonstrated that the tensile strength value depends on the density of carbon fibers present in the composite, and that with the passage of 2 to 4 layers of fibers, an increase in breaking strength was obtained of about 366% and 325% for the 3 K and 1 K yarns, respectively. The increase of the fiber yarn diameter leads to higher values of tensile strength of the composite. The obtained standard deviation reveals that the deposition process gives rise to components with anisotropic mechanical properties and the need to optimize the processing parameters, especially those that lead to an increase in adhesion between deposited layers.

scholarly journals Phase and power modulations on the amplitude of TMS-induced motor evoked potentials

PLoS ONE ◽  
2021 ◽  
Vol 16 (9) ◽  
pp. e0255815
Author(s):  
Lukas Schilberg ◽  
Sanne Ten Oever ◽  
Teresa Schuhmann ◽  
Alexander T. Sack
Keyword(s):  
Evoked Potentials ◽  
Diagnostic Tool ◽  
Primary Motor Cortex ◽  
Motor Evoked Potentials ◽  
Single Pulse ◽  
Beta Phase ◽  
Alpha Phase ◽  
Individual Variability ◽  
Oscillatory Activity ◽  
Alpha Power

The evaluation of transcranial magnetic stimulation (TMS)-induced motor evoked potentials (MEPs) promises valuable information about fundamental brain related mechanisms and may serve as a diagnostic tool for clinical monitoring of therapeutic progress or surgery procedures. However, reports about spontaneous fluctuations of MEP amplitudes causing high intra-individual variability have led to increased concerns about the reliability of this measure. One possible cause for high variability of MEPs could be neuronal oscillatory activity, which reflects fluctuations of membrane potentials that systematically increase and decrease the excitability of neuronal networks. Here, we investigate the dependence of MEP amplitude on oscillation power and phase by combining the application of single pulse TMS over the primary motor cortex with concurrent recordings of electromyography and electroencephalography. Our results show that MEP amplitude is correlated to alpha phase, alpha power as well as beta phase. These findings may help explain corticospinal excitability fluctuations by highlighting the modulatory effect of alpha and beta phase on MEPs. In the future, controlling for such a causal relationship may allow for the development of new protocols, improve this method as a (diagnostic) tool and increase the specificity and efficacy of general TMS applications.

Mechanical behavior of fine-grained Mg-6.5Li at elevated temperature

1994 ◽  
Vol 9 (6) ◽  
pp. 1392-1396 ◽  
Author(s):  
Eric M. Taleff ◽  
Oleg D. Sherby
Keyword(s):  
Stress Exponent ◽  
Solute Drag ◽  
Beta Phase ◽  
Alpha Phase ◽  
Dislocation Creep ◽  
Creep Process ◽  
Strain Rate Change ◽  
Fine Grained ◽  
Diffusion Controlled ◽  
Average Grain Size

A Mg-6.5 wt. % Li alloy containing 80% hep alpha phase and 20% bcc beta phase was processed to achieve an average grain size of 5.9 μm. Strain-rate-change tests were performed in the temperature range from 398 K to 573 K. Two types of creep behavior were observed. A stress exponent of five, obtained at low temperatures and high stresses, is attributed to a diffusion-controlled dislocation creep process in the alpha matrix. A stress exponent of three, obtained at high temperatures and low stresses, is attributed to a solute-drag controlled dislocation creep process in the alpha matrix.

Effect of Deposition Conditions on Intrinsic Stress, Phase Transformation and Stress Relaxation in Tantalum Thin Films

1991 ◽  
Vol 239 ◽  
Author(s):  
A. Mutscheller ◽  
L. A. Clevenger ◽  
J.M.E. Harper ◽  
C. Cabrai ◽  
K. Barmakt
Keyword(s):  
Thin Films ◽  
Phase Transition ◽  
Phase Transformation ◽  
Stress Relaxation ◽  
Compressive Stress ◽  
Stress Relief ◽  
Beta Phase ◽  
Alpha Phase ◽  
Intrinsic Stress

AbstractWe demonstrate that the high temperature polymorphic tantalum phase transition from the tetragonal beta phase to the cubic alpha phase causes complete stress relaxation and a large decrease in the resistance of tantalum thin films. 100 nm beta tantalum thin films were deposited onto thermally oxidized <100> silicon wafers by dc magnetron sputtering with argon. In situ stress and resistance at temperature were measured during temperature-ramped annealing in purified He. Upon heating, films that were initially compressively stressed showed increasing compressive stress due to thermo-elastic deformation from 25 to 550°C, slight stress relief due to plastic deformation from 550 to 700°C and complete stress relief due to the beta to alpha phase transformation at approximately 700–800°C. Incomplete compressive stress relaxation was observed at high temperatures if the film was initially deposited in the alpha phase or if the beta phase did not completely transform into alpha by 800°C. This incomplete beta to alpha phase transition was most commonly observed on samples that had radio frequency substrate bias greater than -100 V. We conclude that the main stress relief mechanism for tantalum thin films is the beta to alpha phase transformation that occurs at 700 to 800°C.

Towards Computational Modeling of Temperature Field Evolution in Directed Energy Deposition Processes

2018 ◽  
Author(s):  
Jianyi Li ◽  
Qian Wang ◽  
Panagiotis (Pan) Michaleris
Keyword(s):  
Temperature Field ◽  
Thermal History ◽  
Energy Deposition ◽  
Deposition Process ◽  
Final Part ◽  
Laser Source ◽  
Heat Sources ◽  
Analytical Computation ◽  
Directed Energy Deposition ◽  
Directed Energy

In modeling and simulating thermo-mechanical behavior in a directed energy deposition process, it often needs to compute the temperature field evolved in the deposition process since thermal history in the deposition process would affect part geometry as well as microstructure, material properties, residual stress, and distortion of the final part. This paper presents an analytical computation of temperature field evolved in a directed energy deposition process, using a single-bead wall as an illustrating example. Essentially, the temperature field is computed by superposition of the temperature fields generated by the laser source as well as induced from each of the past beads, where the transient solution to a moving heat source in a semi-infinite body is applied to describe each individual temperature field. For better characterization of cooling effect (temperature contribution from a past bead), a pair of positive and negative virtual heat sources is assigned for each past bead. In addition, mirrored heat sources through a reflexion technique are introduced to define the adiabatic boundaries of the part being built and to account for the substrate thickness. In the end, three depositions of Ti-6AL-4V walls with different geometries and inter-layer dwell times on an Optomec® laser engineered net shaping (LENS) system are used to validate the proposed analytical computation, where predicted temperatures at several locations of the depositions show reasonable agreement with the in situ temperature measurements, with the average prediction error less than 15%. The proposed analytical computation for temperature field in directed energy deposition could be potentially used in model-based feedback control for thermal history in the deposition, which could affect microstructure evolution and other properties of the final part.

Study of the Metallurgy of a Dissimilar Ti-6Al-4V – Stainless Steel Linear Fiction Welded Joints

2015 ◽  
Vol 651-653 ◽  
pp. 1427-1432 ◽  
Author(s):  
Filomena Impero ◽  
Fabio Scherillo ◽  
Antonello Astarita ◽  
Kathryn A. Beamish ◽  
Michele Curioni ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Intermetallic Compounds ◽  
Weld Line ◽  
Beta Phase ◽  
Alpha Phase ◽  
Parent Material ◽  
Grain Structure ◽  
Linear Friction ◽  
Aisi 316 ◽  
Welding Processes

This paper deals with the investigation of the metallurgy of a dissimilar Ti-6Al-4V-stainless steel joint linear friction welded. In particular two different stainless steel were considered: AISI 304 and AISI 316. These two alloys differs in the Molybdemun content. Metallographic observations, EDS analysis and Vickers Microhardness measurements were carried out, particular attention was focused on the study of the intermetallic compounds and on the microstructures of the different zones produced by the process. As usual for solid state welding processes, three different zones can be identified: the parent material, the heat affected zone (HAZ) and the thermo-mechanical affected zone (TMAZ), furthermore a very thin joining line, rich of intermetallic compounds, was also observed. In this zone diffusive phenomena also occurred resulting in a variation of the alpha phase content on the titanium side.In the TMAZ, the bimodal microstructure of the parent material was deformed and the presence of elongated alpha grains with broken beta-phase particles was established. Moreover it was observed that in the weld region, exposure to supertransus temperatures (995°C) combined with hot-deformation working and rapid cooling after joining induced the recrystallization of a martensitic beta grain structure. Concerning the joint between Ti-6Al-4V and AISI 316 some cracks were observed within the weld line, this due to the presence of brittle intermetallics compounds in this zone. The formation of these intermetallics was promoted by the presence of Molybdenum.

Sputter-Deposited Bcc Tantalum on Steel with the Interfacial Tantalum Nitride Layer

2001 ◽  
Vol 697 ◽  
Author(s):  
Anamika Patel ◽  
Leszek Gladczuk ◽  
Charanjeet Singh Paur ◽  
Marek Sosnowski
Keyword(s):  
Corrosive Wear ◽  
Beta Phase ◽  
Nitride Layer ◽  
Alpha Phase ◽  
Tantalum Nitride ◽  
Nuclear Reaction Analysis ◽  
Sputtered Films ◽  
Bcc Structure ◽  
Two Phases ◽  
Sputter Deposited

AbstractTantalum has mainly two phases: alpha phase (bcc structure) and beta phase (tetragonal structure). The meta-stable beta phase is usually obtained in sputtered films. Alpha phase is preferred over the beta for some applications as beta phase is very brittle. One of such application is to protect steel from the erosive and the corrosive wear. It was found that with the intermediate layer of tantalum nitride the preferred alpha phase was grown on steel by DC magnetron sputtering technique. Electrical and structural properties of these films were studied by four-point probe measurement and x-ray diffraction (XRD). Stoichiometry of the interfacial tantalum nitride layer was investigated by nuclear reaction analysis (NRA). Influence of the interfacial film thickness and the ratio of argon and nitrogen gas during reactive deposition of tantalum nitride on the tantalum phase were investigated. This work also reports on the dependence of tantalum phase on the substrate temperature (100-400°C) during sputtering in Ar and Kr gases.

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