MS&T'11 Poster Session: Materials-Environment Interactions
Program Organizers: Chris Wood, TMS

Tuesday 11:00 AM
October 18, 2011
Room: Exhibit Hall C
Location: Greater Columbus Convention Center


150 Analysis of Hf-Ta Alloys for Oxidation Protection in Ultra High Temperature Environments: Otto Lu-Steffes1; Elizabeth Colon1; Ridwan Sakidja1; John Perepezko1; 1University of Wisconsin-Madison
    Materials with in-situ thermal protective coatings at high temperatures are of great interest for advanced aerospace applications. Hf-Ta alloys are being considered due to their attractive high-temperature materials properties. The oxide scale formation of Hf-Ta was studied at 1650°C through torch testing and 1200-1300°C through air furnace oxidation. The results show that the oxide scale is composed of HfO2 and between the interface of the scale and the alloy substrate there is a reaction zone that is composed of HfO2 and a Hf-Ta-O ternary oxide. The oxidation tests show that Ta additions to Hf significantly reduce the oxide thickness. The XRD results confirm that oxidized Hf-Ta alloys form monoclinic HfO2 and orthorhombic Hf7Ta2O19. Analysis of the results indicates that the beneficial effect of Ta is due to a reduced oxygen mobility in the ternary Hf-Ta oxides that form superstructures of the alpha PbO2 crystal prototype.

151 Characterization of the Oxidation Behavior of Nb-20Si-20Cr Alloy: Daniel Voglewede1; Shailendra Varma1; 1The University of Texas at El Paso
    Nb-20Si-20Cr alloy has been subjected to static oxidation for 24 hours (short term oxidation, STO) and then subjected to 7 cycles of 24 hours (long term oxidation, LTO) in a range of temperature from 700 to 1400°C. Internal oxidation appears to be controlling the oxidation at 900°C while pesting is the oxidation mechanism at 1100°C. Spalling begins to take place at 1200°C and continues until 1400°C. The alloy survives the oxidation in air up to 1400°C. The results will be compared with the published work on Nb-20Si-20Cr-5Al to determine the effect of Al on the oxidation behavior. Oxide scale and microstructures in the as-cast and after oxidation have been characterized using SEM, EDS, x-ray mapping and XRD.

152 Comparative Analysis of NiAl Alloys Used as Resistant Coating at High Temperatures Deposited by Powder Flame Spraying and HVOF Process: Lucas Aguiar1; Émillyn Trevisani1; André Capra2; Helio Padilha1; Gustavo Sucharski1; Ramón Paredes1; 1Federal University of Paraná; 2Lactec
    Components that work at high temperatures require that your materials show oxidation resistance in agreement to the service conditions. Intermetallics compounds like NiAl alloys have excellent resistance at high temperatures due to formation of a protective layer of alumina, high melting point, low density and high hardness. It will be deposited NiAl alloys by Powder Flame Spraying, with pre and post heating, and HVOF process on substrates of AISI 304 austenitic steel. The samples were submitted for tensile, wear and oxidation tests. Preliminary results of the analysis obtained by optical microscopy, X-ray diffraction and microhardness of coatings showed high adhesion, low porosity and wear resistance at elevated temperatures. Although the coatings obtained by HVOF process show best results in the oxidation tests, the samples deposited by Flame Spraying also present a low level of oxides and porosity becoming an alternative to the application of high temperatures resistant coatings.

153 Comparative Study of the Deposition of NiCoCrAl Alloys Used as Bond Coat Deposited by HVOF and Air Plasma Spray Processes: Lucas Aguiar1; Gustavo Sucharski1; Émillyn Trevisani1; André Chicoski2; André Capra2; Ramón Paredes1; 1Federal University of Paraná; 2Lactec
    TBC are often used to achieve an increase in the work temperature of compounds exposed to aggressive service conditions at high temperatures. It’s constituted of a ceramic coating resistant to thermal shocks ad a Bond Coat(BC), responsible for the corrosion and oxidation resistance at high temperatures. In order to qualify and optimize the TBCs deposited by Thermal Spray it was deposited YSZ ceramic alloys by Air Plasma Spray, and as bond coat was deposited the NiCoCrAl superalloy by the HVOF and APS processes. Tests were performed of microhardness, adhesion for tensile test, hot wear and oxidation resistance. The samples were evaluated by their porosity, micro and macrostructure and chemical composition. The BC deposited by HVOF present low porosity and oxides, high oxidation resistance and adherence while the coatings deposited by APS show a higher porosity without affecting their adherence, which may suggest a higher thermal isolation.

154 Comparison of Oxidation Behavior of Nb-20Si-20Cr-5Hf and Nb-20Si-20Cr-5Al Alloys: Brenda Arellano1; Amanda Gutierrez1; Alma Vasquez1; David Alvarez1; Shailendra Varma1; 1The University of Texas at El Paso
    The oxidation behavior of two alloys from the Nb-Si-Cr system containing hafnium and aluminum has been investigated under isothermal conditions. Nb-20Si-20Cr-5Hf and Nb-20Cr-20Si-5Al (in atomic pct) were oxidized in air in a temperature range from 700-1400°C. The as-cast alloys and oxidation products were characterized using SEM, EDS, x-ray mapping, and XRD. Catastrophic oxidation occurred at 700°C for 5Al alloy indicating pesting behavior compared to the 5Hf at 700°C which showed excellent oxidation behavior. Internal oxidation was detected from 1100-1400°C in the 5Al alloy. Partial pesting was observed for 5Hf alloy at 800°C. A weight gain per unit area as a function of oxidation temperature was used to determine the oxidation kinetics. In addition, the microstructures were compared in the as-cast condition and after oxidation for the two alloys at the specified temperature range.

155 Environmental Degradation of Coated Metals: severine cambier1; 1Fontana Corrosion Center
    Organic coated metals are often exposed to accelerated laboratory tests to determine coating protectiveness and ultimately to predict lifetimes. However, discrepancies with field exposures are sometimes observed. Ultimately, we would like to develop an accelerated laboratory test that can reliably predict coating lifetime using a known acceleration factor. In this work, effects of UV, O3, and RH are studied using PVB coatings on 1018 steel as a model system. The primer/substrate interface degradation is analyzed by measuring cathodic delamination with a Scanning Kelvin Probe (SKP) and IR spectroscopy. Exposure to UV, O3, and RH was performed for 4 days in a weathering chamber and the cathodic delamination rate was then measured in the SKP chamber during exposure to lab air with 95% RH. Cathodic delamination was accelerated when the sample was first degraded in the weathering chamber or during exposure in coastal environment.

156 Environmentally Friendly Tin Oxide Coating through Aqueous Solution Process: Yoshitake Masuda1; Tatsuki Ohji1; Kazumi Kato1; 1National Institute of Advanced Industrial Science and Technology (AIST)
     Aqueous solution process was developed for the hybrid materials in this study. It was environmentally friendly and had advantages of low energy consumption, low cost and an organic solvent free process. Nucleation and crystal growth were well controlled to realize tin oxide nano-structure coatings on flexible polymer films. Polytetrafluoroethylene (PTFE) films were successfully coated with tin oxide nano-crystals. Tin oxide was crystallized in aqueous solutions to form nano-sheet assembled films. They were about 10 nm to 50 nm in size and about 5 nm in thickness. Large sheets of about 200 nm to 300 nm in size and about 10 nm in thickness were also crystallized on the surfaces. PTFE films coated with tin oxide were transparent in the range from 400 nm to 850 nm. Hybrid tin oxide-PTFE composites are useful for increasing the potential application of tin oxide film as flexible electronics.

157 Examination of the Machining Affected Zone in Gamma Titanium Aluminide Machining: sajjad kolahdouz1; 1Amirkabir university of technology
    

158 How Coagulant Changes with Corrosion Inhibitors Help Reduce Costly Water Main Breaks: Glenn Terrell1; Jason Heberling1; Patricia Barron1; 1Birmingham Water Works Board
    Because corrosion is a major cause of costly water main breaks, Birmingham Water Works Board has used a corrosion inhibitor to minimize water corrosive potential. An applicability study for using alternative corrosion inhibitors, primarily-silicate based, has been identified and is being evaluated using a flow-through study. These results will be evaluated against the current inhibitor to see if a decrease in corrosion potential can be realized using silicate-based inhibitors. In addition to inhibitors, the impact of changing the primary coagulant change from aluminum sulfate to ferric sulfate, with its impact on metal leaching is currently being evaluated. Decreasing the potential for leaching metal from the distribution system is projected to have a positive effect on the reduction of main breaks and minimize corrosion.

159 Oxide Scale Development in Select Alloys from the Nb-Mo-Cr-Si-B System: Eduardo Soto1; Katherine Thomas1; Benedict Portillo1; Shailendra Varma1; 1The University of Texas at El Paso
    The development of oxide scales was examined on three alloys from the Nb-Mo-Cr-Si-B system with compositions in atomic percent of Nb-10Mo-25Cr-15Si-5B, Nb-15Mo-25Cr-20Si-5B, and Nb-20Mo-25Cr-15Si-10B. The oxide scales were developed during the ramping of each sample to temperatures between 700 and 1300°C, after which samples were held at temperature for 10 minutes then removed from the furnace. The oxide scales were characterized by various scanning electron microscopy techniques including secondary, back scatter mode, energy dispersive (X-Ray) spectroscopy, and x-ray mapping. Surface oxides were characterized by x-ray diffraction. Results will be presented in the poster.

160 Protective Coatings for Molybdenum Alloys: Travis Sossaman1; Ridwan Sakidja1; John Perepezko1; 1University of Wisconsin-Madison
    Molybdenum based alloys such as TZM and Mo-rich Mo-Si-B alloys have great potential for structural applications at elevated temperatures due to their high melting point and high temperature strength. Their limitations have been poor oxidation resistance in TZM and an extended transient oxidation stage in Mo-Si-B alloys. Previous works have concentrated on MoSi2 coatings which exhibit oxidation resistance. However, CTE mismatch between the coating and substrate and the lack of a barrier to prevent Si diffusion into the substrate are the main challenges. In the current study, the synthesis and performance are evaluated for two Mo-based pack cementation coatings. The borosilicide coating is comprised of a three layer structure: borosilica, Mo-rich silicide, and Mo-rich borosilicide. The aluminosilicide coating is composed mainly of Al-saturated Mo silicide and Mo-poor aluminide layers. These coatings exhibit significant improvement in the oxidation protection of Mo alloys versus the disilicide coatings under various oxidation conditions.

161 Synthesis and Performance of PGM Modified βNiAl Coatings: Kevin Severs1; Pratik Ray1; Travis Brammer1; Matthew Kramer1; Mufit Akinc1; 1Ames Laboratory
    A new coating/substrate system is proposed, comprised of a platinum group metal (PGM) modified βNiAl coating on a two phase βNiAl+(Mo) substrate. This system will utilize the high melting temperature and superior high temperature strength of the molybdenum along with the oxidatively stable βNiAl. Utilizing βNiAl in both the base alloy and coating eliminates interfacial incompatibility both mechanically and chemically . This will promote better coating adhesion and thermodynamic stability. The PGM modified βNiAl has also been shown to increase oxidation resistance compared to the unmodified βNiAl. Synthesis of the coating using both a combination of electroplating and pack cementation will be discussed along with comparison of isothermal and cyclic oxidation resistance at 1200°C with competing alloy systems.

162 The Characteristics of High Strength and Lead-Free Machinable α-β Duplex Phase Brass Cu-40Zn-Cr-Fe-Sn-Bi Alloy: Haruhiko Atsumi1; Hisashi Imai1; Shufeng Li1; Katsuyoshi Kondoh1; Yoshiharu Kousaka2; Akimichi Kojima2; 1osaka university; 2San-etsu Co., Ltd.
    High strength and lead-free machinable α-β duplex phase brass Cu-40Zn-0.3Cr-0.2Fe-0.6Sn (mass%) alloys with 1-3 mass% Bi (Cu-40Zn-Cr-Fe-Sn-Bi) were prepared by casting process, and their microstructures, mechanical properties, and machinability were investigated. The extruded Cu-40Zn-Cr-Fe-Sn-Bi alloy consisted of fine and uniform α-β duplex phases dispersed with fine Bi particles. The number of their Bi particles was 1500-3000 /mm2 in the transversal cross-section of the extrusion direction. Yield strength (YS) and ultimate tensile strength (UTS) of the extruded Cu-40Zn-Cr-Fe-Sn-Bi alloy were an average value of 288 MPa and 601 MPa, respectively. This extruded alloy revealed an increment of 29 % YS and 40 % UTS compared to the traditional machinable brass Cu-40Zn with 3.2 mass% Pb (Cu-40Zn-Pb). Since the machinability of the extruded Cu-40Zn-Cr-Fe-Sn-Bi alloy also maintained 75 % of that of Cu-40Zn-Pb, they remarkably deviated from the traditional trade-off balance between hardness and machinability in the conventional machinable brass materials.

163 The Mechanism of Metallic Iron Aggregation and Effect of Addition Agent on the Aggregation of Metallic Iron during the Self-Reduction of High Basicity Coal Mixed Briquettes: zhao dong-nan1; xue zheng-liang1; 1china
    This research takes use of the recycled dust containing iron from iron&steel plant completely, so reduces the environment pollution a lot. The mechanism of iron nugget aggregation and the effect of addition agent on the aggregation of iron nuggets during the self-reduction of high basicity coal mixed briquettes have been investigated. It’s pointed that: 1) The nascent metallic iron is carburized during the self-reduction of high basicity coal mixed briquettes at low the melting point of metallic iron. By the driving of the surface tension of iron and the pressure of slag phase volume shrinkage because of slag sintering, the metallic iron diffuses through the capillary pore from inner to outside of slag phase, 2) During the self-reduction of high basicity coal mixed briquettes, all the factors which lower surface tension of slag phase or increase interfacial tension between slag and metal phase can accelerate the aggregation of metal phase.