Search

Ni-16Mo and ODS alloys were fabricated by the powder metallurgical processes, and their microstructures and tensile properties were investigated. Ni-16Mo-7Cr and Ni-16Mo-7Cr-0.3Ti-0.35Y2O3 (in wt.%) alloys were prepared by mechanical alloying, uniaxial hot pressing, and heat treatment processes. Microstructural observations of these alloys revealed that the Ti and Y2O3 additions to a Ni-16Mo alloy were significantly effective to refine the grain size and form nano-sized Y-Ti-O oxide particles. Consequently, the tensile strengths at room temperature and 700°C were considerably enhanced. This improvement of tensile properties can be mainly attributed to the formation of nano-sized oxide particles, as well as the refined grain size. It is thus concluded that Ni-16Mo alloy with Ti and Y2O3 additions would be very effective in improving the mechanical properties especially at elevated temperatures.

YO dispersion strengthened iron-based powders and oxide dispersion strengthened (ODS) alloys were prepared by hydrothermal synthesis and spark plasma sintering (SPS), respectively. The effects of YO, vibratory milling treatment, and Ti element on the microstructure and mechanical properties of the materials were investigated by scanning electron microscope (SEM) and micro-electronic universal tester. The results show that the best mechanical properties are obtained with 1 wt.% YO addition. The size of agglomerated particles can be decreased to a certain degree by vibratory milling treatment. With the addition of Ti element, the tensile strength and hardness of the samples were improved. [ABSTRACT FROM AUTHOR]

Abstract: Oxide dispersion strengthened (ODS) tungsten heavy alloys have been considered as promising candidates for advanced kinetic energy penetrator due to their characteristic fracture mode compared to conventional tungsten heavy alloy. In order to obtain high relative density, the ODS tungsten heavy alloy needs to be sintered at higher temperature for longer time, however, induces growth of tungsten grains. Therefore, it is very difficult to obtain controlled microstructure of ODS tungsten heavy alloy having fine tungsten grains with full densification. In this study, two-stage sintering process, consisted of primary solid-state sintering and followed by secondary liquid phase sintering, was introduced for ODS tungsten heavy alloys. The mechanically alloyed 94W–4.56Ni–1.14Fe–0.3Y2O3 powders are solid-state sintered at 1300–1450°C for 1h in hydrogen atmosphere, and followed by liquid phase sintering temperature at 1465–1485°C for 0–60min. The microstructure of ODS tungsten heavy alloys showed high relative density above 97%, with contiguous tungsten grains after primary solid-state sintering. The microstructure of solid-state sintered ODS tungsten heavy alloy was changed into spherical tungsten grains embedded in W–Ni–Fe matrix during secondary liquid phase sintering. The two-stage sintered ODS tungsten heavy alloy from mechanically alloyed powders showed finer microstructure and higher mechanical properties than conventional liquid phase sintered alloy. The mechanical properties of ODS tungsten heavy alloys are dependent on the microstructural parameters such as tungsten grain size, matrix volume fraction and tungsten/tungsten contiguity, which can be controlled through the two-stage sintering process. [Copyright &y& Elsevier]

Abstract: The microstructure and mechanical properties of mechanically alloyed oxide dispersion strengthened (ODS) tungsten heavy alloys were investigated. Three different mechanical alloying processes, such as one-step mechanical alloying process, two-step mechanical alloying process, and mechanical alloying and mixing process, were performed in order to control the microstructure and mechanical properties of ODS tungsten heavy alloys. The partially stabilized zirconia (PSZ) dispersoids tend to be dispersed in tungsten grains rather than the binder matrix when the powders were prepared by two-step mechanical alloying or mechanical alloying and mixing process. The yield strength of ODS tungsten heavy alloy increased with decreasing the binder mean thickness, but was not dependent on location of oxide dispersoids. The elongation and high temperature strength of ODS tungsten heavy alloys increased with increasing the content of PSZ dispersoids. [Copyright &y& Elsevier]

This paper reviews both the thermo-mechanical architecture and the configuration of the thermal protection system (TPS) of the Pre-X vehicle, as presented at the System Concept Review that concluded the evaluation phase in June 2002. Pre-X is a first generation experimental re-entry vehicle. It aims mainly at gathering aerothermodynamics (ATD) data in the hypersonic regime and at testing reusable thermal protections and hot structures, currently available in Europe, which could be used for a RLV. The mechanical architecture, based on an aircraft like metallic structure, is presented, as well as the general configuration of the TPS. The experimentation plan on thermal protections is detailed; it includes ceramic matrix composite (CMC) hot structures, ceramic shingles and panels, metallic components, flexible blankets. The outcomes of the analyses already performed on critical issues are summarized (oxidation regime of C/SiC, radiation box analysis on the nose cap, windward and body-flaps pre-design and pre-sizing). Finally, guidelines are proposed for the development plan of the TPS and an outline is given on tasks which are under investigation. [Copyright &y& Elsevier]

The development of mechanical alloying (MA)-oxide dispersion strengthened (ODS) heat-resistant ferritic alloys of Fe−12%Cr with W, Ti and Y203 additions were carried out. Fe−12%Cr alloys with 3%W, 0.4%Ti and 0.25% Y203 additions showed a much finer and more uniform dispersion of oxide particles among the alloy system studied. Nano-sized oxides dispersed in the alloys suppress the grain growth during annealing at a high temperature and resulted in the remarkable improvement of creep strength. The oxide phase was identified as a complex oxide type of Y−Ti−O. [ABSTRACT FROM AUTHOR]

The medium W content W–Ni–Fe alloys have a combination of high strength and great ductility, revealing a promising future for widespread engineering applications. In order to fabricate medium W content W–Ni–Fe alloys with outstanding performances, W nano-powders prepared by a two-stage reduction method was employed as raw material. Meanwhile, the finely dispersed Al 2 O 3 particles have effective roles in restraining the growth of W grain. Electron back-scattered diffraction analysis identified that fine W grains were uniformly distributed in the γ matrix phase without any observable texture. Benefitting from the combination of fine-grain strengthening, oxide dispersion strengthening and precipitation strengthening, a highest tensile strength of 816 ± 11 MPa and a greatest elongation of 29.7 ± 1.2% are obtained for the sintered alloys of 75 W–1Al 2 O 3 and 50 W, respectively. It is also concluded that the main fracture modes of the currently manufactured alloys are ductile matrix rupture and W-matrix interface separation. • Fine-grained medium W content W–Ni–Fe alloys (<5 μm) was fabricated. • Nano W powder prepared by a two-stage reduction method was adopted. • EBSD analysis shows that fine W grains distribute evenly in γ matrix phase. • Addition of Al 2 O 3 markedly affects grain size of W and strength of alloy. • The prepared alloys have a high strength and a great elongation. [ABSTRACT FROM AUTHOR]