Faculty News

TMS 2013 142nd Annual Meeting & Exhibition

142nd Annual Meeting & Exhibition
Henry B. Gonzalez Convention Center
San Antonio, Texas  USA

Our Members Who Attended

Professors

Diran Apelian, Diana Lados and Richard Sisson, Jr.

Graduate Students

Luke Bassett, Danielle Belsito, Andrew Biro, Ye Cao, Xiang Chen, Shaymus Hudson, Baillie McNally, Yuwei Zhai, Antastasios Gavras (Post Doc)

Presentations

Thermodynamic and Kinetic Model-Based Processing of Light Weight Al Alloys

Danielle Belsito1, Victor Champagne2, Richard D. Sisson, Jr.1
1Worcester Polytechnic Institute, 2Army Research Laboratory
(presentation)

The U.S. Military requires structural materials that offer significant weight reduction with improved performance, multi-functionality, durability, and cost reduction to enhance the lethality and survivability of the individual Soldier and advanced weapon systems.  To meet that need, new high strength, high toughness, light weight alloys are being developed.  The primary focus of this effort is to develop an aluminum alloy powder that can be consolidated by the cold spray process, as well as by more conventional means.  This will be accomplished through discovering primary process conditions and environment windows to establish the optimum multiscale chemistries and microstructures of the material before thermomechanical processing.   Secondary thermomechanical process parameters will also be manipulated in order to maximize the aluminum-based heterogeneous material.  Initial efforts involve the development of multi-component phase diagrams, isotherms, and isopleths using thermodynamic and kinetic software, Thermo-Calc, Pandat and TC-PRISMA®, to predict the microstructure and performance of these alloys.

Microstructure, Mechanical Properties, and Failure Mechanisms in Parts Made by Additive Manufacturing

Yuwei Zhai and Diana A. Lados
Worcester Polytechnic Institute, Integrative Materials Design Center
(presentation)

Additive Manufacturing (AM) is an advanced material manufacturing technology that relies on the principle of "Layered Forming".  Three-dimensional near-net shape, fully-dense components with good properties can be directly fabricated from unit materials (powders, wires, etc.) in a layer-by-layer fashion using CAD models.  This technology eliminates materials removal, which is the basis of traditional subtractive manufacturing technologies such as machining.  A variety of AM techniques, including Laser Engineered Net Shaping (LENS), Electron Beam Free Form Fabrication (EBF3), and LaserCUSING have been developed to fabricate precise non-ferrous and ferrous parts.  These techniques were used in this study to produce parts using commercially significant alloys including Ti-6Al-4V.  The resulting microstructures of the studied alloys were extensively characterized and correlated to the processing parameters characteristic to each method.  In addition, room temperature tensile and fatigue crack growth tests were conducted to obtain static mechanical properties and identify crack-microstructure interactions at various growth stages.

Microstructure and Crack Size Effects on Fatigue Crack Growth Behavior of Non-Ferrous and Ferrous Structural Materials

Anastasios Gavras, Diana Lados
Worcester Polytechnic Institute, Integrative Materials Design Center
(presentation)

Fatigue crack growth studies at various stress ratios were performed on cast and wrought aluminum alloys (A535 and 6061), wrought titanium alloys (Ti-6Al-4V), and cast irons (flake and compacted graphite irons). Microstructures were altered through chemistry, heat treatment, and processing to shed light on the effects of materials’ intrinsic characteristic features on crack growth. The mechanisms of small and long fatigue crack growth at the microstructural scale of the studied materials were identified and will be discussed. In this context, the effects of the initial crack size on the fatigue crack growth response of the materials will also be discussed. The differences between various types of cracks were identified, and an integrated new methodology that accounts for these differences will be proposed together with examples of its validation and use in design.

Cold Spray Modeling: A method for predicting bulk properties of cold spray deposits

Luke Bassett; Richard Sisson, Jr.
(poster)

Cold spray deposition is a rapidly growing material consolidation process in which ductile particles, typically metal, are accelerated by a high velocity gas stream and impinged onto a substrate with sufficient energy to induce bonding.  The subsequent consolidated structure has very high strength and hardness when compared to a similar wrought alloy, and can be built up to any reasonable desired thickness.  Predictive modeling has been carried out for various portions of the process, however there is currently no all-encompassing model that can calculate the final microstructure and bulk properties based on process parameters and material characteristics.  The goal of this project is to develop a complete model that integrates existing models with new predictive calculations to fill in portions that are currently lacking or inadequate.  The resulting model will be validated using experimental results.

Finite Process Control Modeling of the Laser Ablation Cold Spray Technique

Aaron Birt; Diran Apelian
(poster)

Cold spray is a deposition process whereby particles are accelerated via a high temperature and pressure gas through a DeLaval nozzle to supersonic speeds. The particle then impacts a substrate and adheres due to extreme localized conditions. These particles can range from metals and cermets, to polymers and composites, and can be deposited to generate either a coating or a free-standing structure. The cold spray process has many applications including corrosion repair, antimicrobial surfaces, structural repair of damaged systems, and additive manufacturing. However, cold spray has only recently become a mainstream process thus there are gaps in the knowledge bases for many applications. This thesis will focus on increasing the ability of the end user to control the deposition process by developing a series of models to control parameters such as particle velocity, temperature , and composition so that rather than estimating the parameters needed to achieve a desired quality the user may consciously choose the parameters. In order to have an added measure of control over the conditions of the substrate and particles, a high-powered laser will be attached directly to the cold spray nozzle so that the laser can preheat the substrate, ablate the existing oxide layer, or preheat the particles depending on the its exact orientation. The development of numerical and experimental models for the Laser Assisted Cold Spray process will enable the user to match the precise parameters needed to generate a deposit of the quality and size desired.

Novel Applications of Friction Stir Welding and Processing in Aluminum and Magnesium Alloys

Ye Cao; Andrew L. Biro; Diana Lados
Worcester Polytechnic Institute, Integrative Materials Design Center
(presentation)

Friction Stir Welding (FSW) of wrought 6061 aluminum to various light metal alloys including cast A356 aluminum, wrought 6061 and 7055 aluminum, and cast ZE41A magnesium has been systematically investigated in this study. The effects of processing parameters and post-weld heat treatment on the microstructure, microhardness, tensile properties, and fatigue crack growth behavior of both similar and dissimilar welds were studied. Complementary studies on ceramic particle additions by Friction Stir Processing (FSP) to create uniformly distributed local material reinforcement and enhance mechanical properties have also been conducted. Four material systems were processed: wrought 6061 aluminum and three cast aluminum alloys (hypoeutectic A356 and 319 and hypereutectic 390). The alloys were judiciously selected to understand the effects of Si level, type, and morphology and strengthening precipitates type, as well as their interaction and combined effects with the reinforcing ceramic particles. The results of these studies will be presented and discussed.

Effects of Hot Compressive Dwell on Fatigue Crack Growth Behavior of Cast Aluminum Alloys

Xiang Chen1; Diana Lados1; Richard Pettit2
1
Worcester Polytechnic Institute; 2Fracture Lab
(poster)

Fatigue crack growth under Hot Compressive Dwell (HCD) conditions is an important failure mode in many high temperature applications, such as cylinder heads used in internal combustion engines. Tensile residual stresses gradually building up at the crack root are considered a key factor contributing to crack growth under HCD conditions. To understand and quantify this effect, both at elevated and room temperatures, an analytical model was developed, in which the residual stress contributions are added to the elastic response of the material to predict the behavior under HCD conditions. Cyclic stress relaxation tests were conducted to model tensile residual stress accumulation. A Blunt Compact Tension (BCT) specimen was designed and analyzed using Franc2D to determine the elastic behavior. Finally, crack growth tests on BCT specimens under HCD conditions were performed to validate the model. These results will be presented and discussed for 319 cast aluminum alloys used in engine applications.

Microstructural Characterization and Analysis of Cold Spray Al Alloys

Baillie McNally; Richard Sisson, Jr.
(poster)

The U.S. Military requires structural materials that offer significant weight reduction with improved performance, multi-functionality, durability, and cost reduction to enhance the lethality and survivability of military vehicles and advanced weapon systems.  To meet that need, new high strength, high toughness, lightweight alloys are being developed.  The primary focus of this effort is to develop an aluminum alloy powder that can be consolidated by the cold spray process, as well as by more conventional means.  Thermomechanical process parameters will be manipulated in thermodynamic and kinetic models to establish the optimum microstructure of the material.  Current work focuses on the experimental characterization used to verify and enhance our thermodynamic and kinetic modeling efforts.  Microstructural analyses of powder and consolidated cold spray Al 6061 will be presented through optical, scanning electron and transmission electron microscopy, and x-ray diffraction techniques.

April 3, 2013

 
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