Engineering topics

Anderson, Iver

Publications and source records attributed to Anderson, Iver.

62 records · Page 4

DOE OSTI2012

Effects of Ag additions on melt-spun RE2Fe14B microstructure and texture

Control of microstructure and texture is of critical importance in forming rare earth (RE)-iron-boron particulate suitable for anisotropic polymer-bonded permanent magnets and anisotropic sintered permanent magnets. In this study, the selected approach to controlling grain size, while maintaining texture, is through stabilization and refinement of directional growth in melt-spun ribbons. Varying concentrations of Ag were added to melt-spun ribbons of composition (Y0.55Nd0.45)2.2Fe14B1.1. Effects on microstructure and texture were observed through scanning electron microscopy (SEM) and x-ray diffraction (XRD). It was determined that Ag stabilized columnar growth (compared to alloys with no Ag added) with additions as small as 0.3 at. %, but the Ag also produced a unique texture in the ribbons. In RE-Fe-B ribbons without Ag, strong <00l> texture is observed at the free surface and a mechanism has been established. In all Ag-containing ribbons, the observed texture is canted to both the c- and a-axes, but the mechanism remains unclear.

36 MATERIALS SCIENCE↗

DOE OSTI2012

Breakthrough: Lead-free Solder

Ames Laboratory senior metallurgist Iver Anderson explains the importance of lead-free solder in taking hazardous lead out of the environment by eliminating it from discarded computers and electronics that wind up in landfills. Anderson led a team that developed a tin-silver-copper replacement for traditional lead-tin solder that has been adopted by more than 50 companies worldwide.

36 MATERIALS SCIENCE↗

DOE OSTI2011

Advancements in Ti Alloy Powder Production by Close-Coupled Gas Atomization

As the technology for titanium metal injection molding (Ti-MIM) becomes more readily available, efficient Ti alloy fine powder production methods are required. An update on a novel close-coupled gas atomization system has been given. Unique features of the melting apparatus are shown to have measurable effects on the efficiency and ability to fully melt within the induction skull melting system (ISM). The means to initiate the melt flow were also found to be dependent on melt apparatus. Starting oxygen contents of atomization feedstock are suggested based on oxygen pick up during the atomization and MIM processes and compared to a new ASTM specification. Forming of titanium by metal injection molding (Ti-MIM) has been extensively studied with regards to binders, particle shape, and size distribution and suitable de-binding methods have been discovered. As a result, the visibility of Ti-MIM has steadily increased as reviews of technology, acceptability, and availability have been released. In addition, new ASTM specification ASTM F2885-11 for Ti-MIM for biomedical implants was released in early 2011. As the general acceptance of Ti-MIM as a viable fabrication route increases, demand for economical production of high quality Ti alloy powder for the preparation of Ti-MIM feedstock correspondingly increases. The production of spherical powders from the liquid state has required extensive pre-processing into different shapes thereby increasing costs. This has prompted examination of Ti-MIM with non-spherical particle shape. These particles are produced by the hydride/de-hydride process and are equi-axed but fragmented and angular which is less than ideal. Current prices for MIM quality titanium powder range from $40-$220/kg. While it is ideal for the MIM process to utilize spherical powders within the size range of 0.5-20 {mu}m, titanium's high affinity for oxygen to date has prohibited the use of this powder size range. In order to meet oxygen requirements the top size cut has traditionally been 45 {mu}m, and in some instances a bottom cut at +5 {mu}m is made to remove ultra-fine particles and reduce oxygen content. Predictably, use of irregular shaped or larger particle feedstock powder can reduce part quality as sintering shrinkage and part detail suffer. Thus, widespread production and technological use of Ti-MIM is limited due in large part to Ti alloy feedstock cost and availability, not MIM processing capability. Lower cost feedstock of fine, spherical Ti alloy powder with sufficient purity must be available in order to fully utilize the advantages of the Ti-MIM processing route allowing expansion of the market to small complex Ti parts in many high volume applications.

36 MATERIALS SCIENCE↗

DOE OSTI2011

Plasma Sprayed Pour Tubes and Other Melt Handling Components for Use in Gas Atomization

Ames Laboratory has successfully used plasma sprayed ceramic components made from yttria stabilized zirconia as melt pouring tubes for gas atomization for many years. These tubes have proven to be strong, thermal shock resistant and versatile. Various configurations are possible both internally and externally. Accurate dimensions are achieved internally with a machined fugitive graphite mandrel and externally by diamond grinding. The previous study of the effect of spray parameters on density was extended to determine the effect of the resulting density on the thermal shock characteristics on down-quenching and up-quenching. Encouraging results also prompted investigation of the use of plasma spraying as a method to construct a melt pour exit stopper that is mechanically robust, thermal shock resistant, and not susceptible to attack by reactive melt additions. The Ames Laboratory operates two close-coupled high pressure gas atomizers. These two atomizers are designed to produce fine and coarse spherical metal powders (5{mu} to 500{mu} diameter) of many different metals and alloys. The systems vary in size, but generally the smaller atomizer can produce up to 5 kg of powder whereas the larger can produce up to 25 kg depending on the charge form and density. In order to make powders of such varying compositions, it is necessary to have melt systems capable of heating and containing the liquid charge to the desired superheat temperature prior to pouring through the atomization nozzle. For some metals and alloys this is not a problem; however for some more reactive and/or high melting materials this can pose unique challenges. Figure 1 is a schematic that illustrates the atomization system and its components.

36 MATERIALS SCIENCE↗

DOE OSTI2011

Visualization of Atomization Gas Flow and Melt Break-up Effects in Response to Nozzle Design

Both powder particle size control and efficient use of gas flow energy are highly prized goals for gas atomization of metal and alloy powder to minimize off-size powder inventory (or 'reverb') and excessive gas consumption. Recent progress in the design of close-coupled gas atomization nozzles and the water model simulation of melt feed tubes were coupled with previous results from several types of gas flow characterization methods, e.g., aspiration measurements and gas flow visualization, to make progress toward these goals. Size distribution analysis and high speed video recordings of gas atomization reaction synthesis (GARS) experiments on special ferritic stainless steel alloy powders with an Ar+O{sub 2} gas mixture were performed to investigate the operating mechanisms and possible advantages of several melt flow tube modifications with one specific gas atomization nozzle. In this study, close-coupled gas atomization under closed wake gas flow conditions was demonstrated to produce large yields of ultrafine (dia.<20 {mu}m) powders (up to 32%) with moderate standard deviations (1.62 to 1.99). The increased yield of fine powders is consistent with the dual atomization mechanisms of closed wake gas flow patterns in the near-field of the melt orifice. Enhanced size control by stabilized pre-filming of the melt with a slotted trumpet bell pour tube was not clearly demonstrated in the current experiments, perhaps confounded by the influence of the melt oxidation reaction that occurred simultaneously with the atomization process. For this GARS variation of close-coupled gas atomization, it may be best to utilize the straight cylindrical pour tube and closed wake operation of an atomization nozzle with higher gas mass flow to promote the maximum yields of ultrafine powders that are preferred for the oxide dispersion strengthened alloys made from these powders.

36 MATERIALS SCIENCE↗

DOE OSTI2011

Innovative Powder Processing of Oxide Dispersion Strengthened ODS Ferritic Stainless Steels

An innovative gas atomization reaction synthesis technique was employed as a viable method to dramatically lower the processing cost for precursor oxide dispersion forming ferritic stainless steel powders (i.e., Fe-Cr-(Hf,Ti)-Y). During this rapid solidification process the atomized powders were enveloped by a nano-metric Cr-enriched metastable oxide film. Elevated temperature heat treatment was used to dissociate this metastable oxide phase through oxygen exchange reactions with Y-(Hf,Ti) enriched intermetallic compound precipitates. These solid state reactions resulted in the formation of highly stable nano-metric mixed oxide dispersoids (i.e., Y-Ti-O or Y-Hf-O) throughout the alloy microstructure. Subsequent high temperature (1200 C) heat treatments were used to elucidate the thermal stability of each nano-metric oxide dispersoid phase. Transmission electron microscopy coupled with X-ray diffraction was used to evaluate phase evolution within the alloy microstructure.

36 MATERIALS SCIENCE↗

DOE OSTI2011

Gas Atomization Precursor Powder Approach for Simplified Large-Scale Production of Oxide Dispersion

Oxide dispersion strengthened (ODS) Ni-based alloys show promise for future energy applications that require high-temperature and oxidation resistant properties. Gas atomization reaction synthesis (GARS), with a mixed (Ar/O{sub 2}) atomization gas, is being developed as a simplified route for producing ODS precursor powders. Internal oxidation studies determined Ni-Cr-Y-(Hf or Ti) containing systems are suitable for production of ODS alloys via hot consolidation, which is used to encourage oxygen exchange between the less stable surface oxide phase and reactive alloying elements, resulting in highly stable nano-metric dispersoid formation. Size control of powders is key to optimizing microstructural and strengthening features. Aspiration and, previously, water modeling experiments were used to develop atomization process parameters that encourage controlled powder production while maintaining reduced operating costs when implemented on an industrial scale. For an increase in pour tube extension: aspiration base pressure at any given operating pressure was found to decrease while wake closure pressure was found to increase. Aspiration hysteresis was observed as recorded previously in the literature. Light emission was observed above wake closure pressures.

36 MATERIALS SCIENCE↗

DOE OSTI2011

Advanced Electric Traction System Technology Development

As a subcontractor to General Motors (GM), Ames Laboratory provided the technical expertise and supplied experimental materials needed to assess the technology of high energy bonded permanent magnets that are injection or compression molded for use in the Advanced Electric Traction System motor. This support was a sustained (Phase 1: 6/07 to 3/08) engineering effort that builds on the research achievements of the primary FreedomCAR project at Ames Laboratory on development of high temperature magnet alloy particulate in both flake and spherical powder forms. Ames Lab also provide guidance and direction in selection of magnet materials and supported the fabrication of experimental magnet materials for development of injection molding and magnetization processes by Arnold Magnetics, another project partner. The work with Arnold Magnetics involved a close collaboration on particulate material design and processing to achieve enhanced particulate properties and magnetic performance in the resulting bonded magnets. The overall project direction was provided by GM Program Management and two design reviews were held at GM-ATC in Torrance, CA. Ames Lab utilized current expertise in magnet powder alloy design and processing, along with on-going research advances being achieved under the existing FreedomCAR Program project to help guide and direct work during Phase 1 for the Advanced Electric Traction System Technology Development Program. The technical tasks included review of previous GM and Arnold Magnets work and identification of improvements to the benchmark magnet material, Magnequench MQP-14-12. Other benchmark characteristics of the desired magnet material include 64% volumetric loading with PPS polymer and a recommended maximum use temperature of 200C. A collaborative relationship was maintained with Arnold Magnets on the specification and processing of the bonded magnet material required by GM-ATC.

36 MATERIALS SCIENCE↗