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Key engineering materials
Trans Tech Publications Ltd.
Key engineering materials

Trans Tech Publications Ltd.

半月刊

1013-9826

Key engineering materials/Journal Key engineering materials
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    Consolidation Process in Near Net Shape Manufacturing of Armstrong CP-Ti/Ti-6Al-4V Powders

    Yukinori YamamotoJim O. KiggansMichael B. ClarkStephen D. Nunn...
    103-111页
    查看更多>>摘要：This paper summarizes our recent efforts to develop the manufacturing technologies of consolidated net-shape components by using new low-cost commercially pure titanium (CP-Ti) and Ti-6Al-4V alloy powders made by the Armstrong process. Fabrication processes of net shape/ near net shape components, such as uniaxial die-pressing, cold isostatic pressing (CIP), sintering, roll compaction and stamping, have been evaluated. The press-and-sinter processing of the powders were systematically investigated in terms of theoretical density and microstructure as a function of time, pressure, and temperature. Up to 96.4% theoretical density has been achieved with the press-and-sinter technology. Tensile properties of the consolidated samples exhibit good ductility as well as equivalent yield/ultimate tensile strengths to those of fully consolidate materials, even with the presence of a certain amount of porosity. A consolidation model is also under development to interpret the powder deformation during processing. Net shape components made of the Armstrong powder can successfully be fabricated with clearer surface details by using press-and-sinter processing.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    The Impact of Diffusion on Synthesis of High-Strength Titanium Alloys from Elemental Powder Blends

    Orest M. IvasishinDmytro G. Savvakin
    113-121页
    查看更多>>摘要：High strength near-beta titanium alloys are being increasingly used in industry due to their excellent combination of properties. Blended elemental powder metallurgy (BEPM) allows to produce the above alloys and parts from them in a cost-effective manner. However, the alloy synthesis is complicated by a big amount (up to 18 wt.%) of alloying elements which diffusional redistribution between alloying particles and titanium matrix has a strong impact on microstructure evolution. In this paper synthesis of the high-strength alloys from the powder blends based on hydrogenated titanium was studied. It was found that hydrogen strongly affects diffusion controlled processes upon synthesis, such as chemical homogenization, densification and grain growth through its influence on phase composition and defect structure of the blends. Optimization of the processing parameters allowed to produce uniform, nearly-dense alloys with reduced grain size, which mechanical properties met the requirements of corresponding specifications.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Investigation of pressing and sintering processes of CP-Ti powder made by Armstrong Process

    Wei ChenYukinori YamamotoWilliam H. Peter
    123-130页
    查看更多>>摘要：This work used in-situ and ex-situ techniques to investigate the pressing and sintering processes of commercially pure (CP) Ti powder made by the Armstrong process. The objective is to simulate the actual manufacturing process of near net shape Ti components. Ti powders were uniaxially pre-pressed at designated pressures up to 100 ksi to form disk samples with different theoretical densities. Compression tests were performed in an SEM at different temperatures to obtain the mechanical properties and deformation behavior of these samples. Ex-situ technique was used to track the powder deformation process of disk samples from low pressure to high pressure. In-situ sintering was also performed in an SEM to record the morphology change of the porosities on the sample surface during the sintering process. The results will provide valuable information for optimizing the manufacturing process of high-density near net shape Ti components.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Microwave Sintering and Melting of Titanium Powder for Low-Cost Processing

    Ralph W. BruceArne W. FlifletHugo E. HueyChad Stephenson...
    131-140页
    查看更多>>摘要：The emerging reduction technologies for titanium from ore produce powder instead of sponge. Conventional methods for sintering and melting of titanium powder are costly, as they are energy intensive and require high vacuum, 10~(-6) Torr or better, since titanium acts as a getter for oxygen at high temperature, adversely affecting mechanical properties. Other melting processes such as plasma arcs have the additional problem of electrode consumption, and direct induction heating of the titanium powder is problematic. Microwave sintering or melting in an atmospheric pressure argon gas environment is potentially cost effective and energy efficient due to the possibility of direct microwave heating of the titanium powder augmented by hybrid heating in a ceramic casket. We are investigating this approach at the Naval Research Laboratory using an S-Band microwave system. The experimental setup and the results of melting and sintering experiments will be described including a rough estimate of energy usage.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Microwave sintering of titanium

    Shudong LuoC.J. BettlesM. YanG. B. Schaffer...
    141-147页
    查看更多>>摘要：Effective sintering of titanium requires the use of a high sintering temperature (≥1200℃), preferably in high vacuum (< 10~(-2) Pa). This confines the heating and cooling rates to ～ 4℃/min because of the limited thermal shock resistance of ceramic tube furnaces. Consequently, it leads to lengthy sintering cycles (10-12 hr). This work presents an assessment of microwave (MW) sintering of titanium. Titanium powders in the size ranges of <20 μm, 45-63 μｍ, and 100-150 μm were used to make green samples with compaction pressures ranging from 200-800 MPa. Sintering was carried out at 1200℃ for 2 hr in a 3 kW MW furnace with a 2.45 GHz multimode cavity under a vacuum of 2-6×10~(-3) Pa. The characteristics of MW heating of green titanium samples in vacuum are described in terms of the heating rate, vacuum fluctuations, and sparking discharge. The actual M W heating rate achieved from 350℃ to 1200℃ was 34℃/min. The attendant densities are comparable to those attained by conventional vacuum sintering. Cross-sectional examinations revealed a fairly uniform pore distribution in MW-sintered samples made from either the coarse or fine titanium powder.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Reaction Assisted Ultrasonic Consolidated TiNi

    M.KulakovH. J. Rack
    149-155页
    查看更多>>摘要：This investigation has examined the feasibility of fabricating near-net shape components containing TiNi shape memory constituents by combining the attributes of ultrasonic consolidation and reaction heat treatment. An optimization design of experiment was conducted to determine the ultrasonic consolidation control parameters, e.g., sonotrode rotational velocity, amplitude and normal force, which would result in the maximum weld quality as defined by the linear weld density. Subsequent thermal treatment of the consolidated compact resulted in the formation of a graded Ti-TiNi-Ni microstructure.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Titanium and Titanium Alloy via Sintering of TiH_2

    Hongtao WangMichael LeflerZ. Zak FangTing Lei...
    157-163页
    查看更多>>摘要：Blended elemental (BE) powder metallurgy (PM) is a promising low cost approach for manufacture titanium and titanium alloy components. Conventional BE method relies on sintering of pure titanium metal powder, while the new approach examined in this investigation produces bulk titanium materials by sintering titanium hydride powder. Dehydrogenation and densification of TiHi powders with different particle sizes and TiH_2-6Al-4V alloy powder was studied using thermogravimetric and dilatometric techniques. The results show that the dehydrogenation of TiH_2 leads to very rapid shrinkage of α-Ti during sintering. In contrast, densification TiH_2-6Al-4V requires dissolution of alloy elements which occurs during sintering above its beta transus temperature.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Structure Formation during Preparation of Variable Porosity Titanium Foams by Solid State Replication

    Yu. OrlovaK. MaekawaH.J. Rack
    165-170页
    查看更多>>摘要：Fabrication of variable porosity titanium foams through incorporation of sacrificial sodium chloride powder has been investigated. A three-dimensional solid foam pore skeleton containing macro-(200-400μn), micro- (5-10μm) and sub-micropores (< 1.5μm) was formed during high temperature sintering of commercial purity titanium powder containing sacrificial sodium chloride particles, faceting of the interior pore powder surface being noted throughout. The largest macro-pores had a cubical topography representative of the sodium chloride powder that had been vaporized during heating to the sintering temperature. Formation of the smaller micro-pores appeared to have occurred during the compaction process these being retained in the specimen body due to incomplete sintering of the host powder. Finally formation of the smallest sub-micropores was associated with high temperature gas evolution and entrapment during sodium chloride vaporization.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Microstructure and Mechanical Properties of a' Martensite Type Ti-V-Al Alloy after Cold- or Hot Working Process

    Hiroaki MatsumotoHiroshi YonedaKazuhisa SatoToyohiko J Konno...
    171-177页
    查看更多>>摘要：Ti alloys are widely utilized for industrial applications due to their excellent mechanical properties combined with low density. In general, Ti alloys are classified as α, α+β and β alloys, with further subdivision into near α and metastable β alloys. Quite recently, we have presented new type structural a' martensite (H.C.P.) Ti alloys with low Young's modulus, high strength and excellent ductility at room temperature. In this work, we examined the microstructure and mechanical properties of a' martensite type Ti-V-Al alloy after cold- or hot working process. Then, we found that deformation behavior of a' initial microstructure as compared with (α+β) initial microstructure was different based on the results of stress-strain curves and Processing Maps under the hot working process. Further, cold rolled a' martensite microstructure exhibited the refined equiaxed dislocation cell structure, thereby resulting in high strength. This result suggests the new type deformation processing (for both cold- and hot work processing) utilizing a' martensite in industrial Ti alloys.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Effect of Oxygen on Phase Precipitation and Mechanical Functionality in Ti-29Nb-13Ta-4.6Zr

    MITSUO NIINOMIMASAAKI NAKAITOSHIKAZU AKAHORIHARUMI TSUTSUMI...
    179-184页
    查看更多>>摘要：Oxygen plays very important roles in titanium and its alloys. Solute oxygen in titanium alloys leads to solid solution strengthening, suppressing the precipitation of the athermal omega or orthorhombic martensite phase, enhancing the formation of the a-case, etc. The proper using oxygen is effective to improve the mechanical functionalities of titanium alloys. However, the role of oxygen in titanium alloys is still not well understood. Therefore, the effect of oxygen on the mechanical functionalities such as strength-ductility balance, hardness, and Young's modulus in Ti-29nb-13Ta-4.6Zr was investigated.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd