Fundamental Aspects and Modeling Powder Metal Synthesis and Processing: Titanium and Advanced Materials
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Powder Materials Committee
Program Organizers: Paul Prichard, Kennametal; Eugene Olevsky, San Diego State University; Iver Anderson, Ames Laboratory

Monday 8:30 AM
February 27, 2017
Room: 16A
Location: San Diego Convention Ctr

Session Chair: Paul Prichard, Kennametal

8:30 AM  
Engineering the Microstructure and Mechanical Properties of Titanium Alloys via Hydrogen Sintering and Phase Transformation (HSPT): James Paramore1; Brady Butler1; Jonathan Ligda1; Z. Zak Fang2; Matt Dunstan2; 1United States Army Research Laboratory; 2University of Utah
    Hydrogen sintering and phase transformation (HSPT) is a powder metallurgical process that utilizes hydrogen-enabled phase transformations to refine microstructure during sintering. This process has been shown to produce unique ultra-fine grained microstructures in titanium alloys in the as-sintered state with exceptional mechanical properties. Additionally, the as-sintered microstructure may be further evolved via simple heat treatments to produce a range of traditional wrought-like microstructures without requiring energy-intensive thermomechanical processing. This allows for low-cost microstructural engineering to produce a range of application-tailored mechanical properties. Evidence gained from advanced microscopy techniques regarding the unique mechanisms for microstructural evolution during sintering and subsequent heat treatments will be presented. Additionally, the exceptional strength, ductility, and fatigue performance of titanium alloys produced via this low-cost process will be discussed in the context of microstructure and processing.

8:50 AM  
Titanium Hydrides Enhancing Improvement of Ductility of PM α-Ti Material: Katsuyoshi Kondoh1; Takafumi Mimoto1; Junko Umeda1; Hisashi Imai1; 1Osaka University
    In general α-Ti material shows a local deformation in tensile because a lot of {10-12} tensile deformation twins are introduced near the fractured area. PM α-Ti material containing a small amount of titanium hydrides (TiHx), which are prepared by sintering TiH2 raw powder, obviously indicates the propagation of the deformation twins is completely stop by needle-like hard TiHx dispersoids. As a result, the local deformation is obstructed, and elongation to failure is significantly improved in PM Ti with hydrogen materials.

9:10 AM  
Particle Charging during Electron-beam Additive Manufacturing: Zachary Cordero1; Harry Meyer1; Peeyush Nandwana1; Ryan Dehoff1; 1Oak Ridge National Laboratory
    Electrons injected into the build envelope during electron-beam additive manufacturing can accumulate on the irradiated particles and cause them to repel each other. In extreme cases, these electrostatic forces can grow so large that they drive the particles from the powder-bed in a process termed “smoking”. Here we will describe a model of powder bed charging that can identify the conditions under which a given powder will smoke. We will compare this model’s predictions with various trends that have been observed in practice, and provide examples of how these predictions can be used in quality control and process design in order to suppress smoking.

9:30 AM  
Titanium-Based Alloys with Gradient Structures Fabricated by Blended Elemental Powder Metallurgy (BEPM): Dmytro Savvakin1; Pavlo Markovsky1; Orest Ivasishin1; Sergey Prikhodko2; 1G.V. Kurdyumov Institute for Metal Physics, National Academy of Science of Ukraine; 2University of California, Los Angeles
    High specific strength of Ti-based alloys makes them desirable materials for various structural applications including anti-ballistic protection. Essential anti-ballistic properties of materials can be attained by formation of the gradient microstructures that combines high strength at the surface of the alloy parts with sufficient toughness in their core. Our present study reports results on layered structures of Ti-based alloys fabrication by means of Blended Elemental Powder Metallurgy (BEPM) using hydrogenated titanium and alloying elements powders. Combined multi-layered structures of CP Ti, Ti-6Al-4V, Ti-1Al-8V-5Fe (wt.%) alloys, some strengthened with inclusions of fine TiB2 and TiC particles were sintered. Further heat or thermomechanical treatment was used to modify alloys’ microstructure and porosity to optimize their mechanical properties.

9:50 AM Break

10:10 AM  
Characterizing the Effect of Powder Properties on In-Machine Performance in Powder Bed Direct Metal Additive Manufacturing: Ross Cunningham1; Ola Harrysson2; Jack Beuth1; Fred Higgs III1; Anthony Rollett1; 1Carnegie Mellon University; 2North Carolina State Univ.
    This talk outlines an on-going project supported by America Makes that seeks to expand the range of powders available for both selective laser melting (EOS) and electron beam melting (Arcam) AM processes. Multiple material systems of interest with varying size distributions and morphologies were investigated. Size and morphology were characterized using SEM analysis and image analysis software, as well as 3D XCT. Rheological behavior was analyzed on a Freeman FT4 Rheometer. Process variables were adjusted as needed in order to achieve successful builds. Successful results from two new Ti-6Al-4V powders in the Arcam were obtained, one of which has a much larger size distribution than the standard powder, demonstrating the ability to significantly broaden the range of available powders. Porosity in printed material is related to porosity in the powders. Porosity can be reduced via varying the process conditions.

10:30 AM  
Sintering of Titanium-Magnesium Alloys with Stable Nanocrystalline Structure: Kathrin Graetz1; Christopher Schuh1; 1Massachusetts Institute of Technology
    Nanocrystalline metals have certain advantages over their microcrystalline counterparts due to the large volume fraction of grain boundaries. However, nanocrystalline metals have primarily been processed as thin films, as retaining nanoscale grains in processing a bulk material is much more difficult. Recently, a low-temperature, accelerated sintering mechanism of supersaturated, nanocrystalline powders was developed by our group to make bulk nanocrystalline W-Cr alloys. Here we show that this processing route may be extended to Ti-Mg alloys. Titanium powders with different additions of magnesium powders (10, 20, 30 at.% Mg) were mechanically alloyed via ball milling, cold compressed and subsequently annealed in a thermomechanical analyzer. The sintering kinetics were analyzed using the master sintering curve and the microstructure of the powders and the resulting compacts were characterized. This talk will discuss the sintering behavior and thermal stability of the alloys based on the experimental results.

10:50 AM  
Enhanced Texture and Magnetic Energy Product in Alnico Magnets Utilizing Solid State Processing: Aaron Kassen1; Emma White1; Wei Tang1; Lin Zhou1; Matthew Kramer1; Iver Anderson1; 1Iowa State University
    Commercial production of aligned anisotropic alnico requires costly processing like directionally solidified casting which often is inefficient and results in significant amounts of waste material from machining to final shape. In contrast, current sintered alnico, produced from elemental powder blends or granulated alnico, often has inferior magnetic properties to cast counterparts due to isotropic fine grained microstructures and retained porosity. In response, a new technique is being developed for pre-alloyed powder-processed bulk magnet production using compression molding and sintering to near-final shapes. This technique utilizes an abnormal grain growth mechanism with an applied stress bias to create uniform large grain textures. These bulk magnets were characterized to verify density and analyze microstructure using FE-SEM, OIM/EBSD. The influence of microstructure and grain texture on bulk magnetic properties is discussed with hysteresisgraph measurements, as a function of heat treatment variations. Work funded by USDOE-EERE-VT-EDT program through Ames Lab contract no. DE-AC02-07CH11358.

11:10 AM  
Size-Scaled High-Performance Alnico Magnets with Enhanced Mechanical Properties and Near-Final Shape: Liangfa Hu1; Iver Anderson1; Aaron Kassen1; Emma White1; Wei Tang1; Lin Zhou1; Matt Kramer1; 1Ames Laboratory
    The prospect of scaling up a near-final shape manufacturing process for alnico magnets using pre-alloyed powder was examined. Pre-alloyed powder processing is being developed to manufacture large, up to 66 mm (2.6 in.) in length, bulk magnets of a modified alnico 8 composition. Existing results showed that partially aligned anisotropic alnico magnets in near-final shapes could be made by a binder-assisted compression molding method from spherical, pre-alloyed powder by de-binding, sintering, a novel biased grain growth method, magnetic annealing, and drawing. A new systematic study of processing parameters for producing magnets of greatly enlarged near-final shapes suggested an effective set of conditions to minimize density gradients in the bulk magnets and to achieve improved alignment. Both magnetic and mechanical tests suggested enhanced properties of the present alnico magnets in comparison with commercial counterparts. Work funded by USDOE-EERE-VT-EDT program through Ames Lab contract no. DE-AC02-07CH11358.

11:30 AM  
Self-propagating High-temperature Synthesis for Synthesizing Tantalum Carbide from Ta Metal Scraps: Jae-Jin Sim1; Sang-Hun Choi1; Won Ju1; Won-Jung Choi1; Basit Ali1; Tae-Hyuk Lee2; Kyung-Mook Lim1; Bum-Sung Kim1; Taek-Soo Kim1; Kyoung-Tae Park1; 1Korea Institute of Industrial Technology; 2Department of Materials Science & Engineering, University of Sheffield
    For the grain refinement, Tantalum carbide (TaC) have been applied as the addictive in the field of WC base cemented materials. In this study, Self-propagating High-temperature Synthesis (shortly SHS) is selected and researched for preparation of TaC. Comparing with general carbothermic solid-state synthesis, SHS could achieved that it is more faster, need no more heat inducing without first ignition. In case of TaC synthesis adiabatic combustion temperature reaches to ca. 2,400C at that time it is possible to remove volatile impurities. Ta powders produced from metal scraps are used as the raw material of synthesis. Purity of Ta powder is around 98% because of using the scrap which origin is from turning, plate, target and critical impurities are Cu, Ti, Al, Zn, Fe and Nb. Focuses of this study are that impurities removing ability during the synthesis, optimum ratio of reductant, graphite powder, morphology of synthesized TaC particles.