The influence of the Nb:Ta ratio on the microstructural evolution in refractory metal superalloy systems

Refractory metal high-entropy superalloys (RSA), which possess a nanoscale microstructure of B2 and bcc phases, have been developed to offer high temperature capabilities beyond conventional Ni-based alloys. Despite showing a number of excellent attributes, to date there has been little consideration of their microstructural stability, which is an essential feature of any material employed in high temperature service. Here, the stability of the exemplar RSA AlMo0.5NbTa0.5TiZr is studied following 1000 h exposures at 1200, 1000 and 800 °C. Crucially, the initial nanoscale cuboidal B2 + bcc microstructure was found to be unstable following the thermal exposures. Extensive intragranular precipitation of a hexagonal Al-Zr-rich intermetallic occurred at all temperatures and, where present, the bcc and B2 phases had coarsened and changed morphology. This microstructural evolution will concomitantly change both the mechanical and environmental properties and is likely to be detrimental to the in-service performance of the alloy.

Download Full-text

Microstructural Evolution in Reduced TiO2

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100097089 ◽

1981 ◽

Vol 39 ◽

pp. 74-75

Author(s):

W. T. Donlon ◽

S. Shinozaki ◽

E. M. Logothetis ◽

W. Kaizer

Keyword(s):

Microstructural Evolution ◽

Point Defects ◽

Extended Defects ◽

Small Deviations ◽

Controlled Atmospheres ◽

Limited Solubility ◽

Thin Foils ◽

Heat Treated ◽

Porous Polycrystalline ◽

Crystallographic Shear

Since point defects have a limited solubility in the rutile (TiO2) lattice, small deviations from stoichiometry are known to produce crystallographic shear (CS) planes which accomodate local variations in composition. The material used in this study was porous polycrystalline TiO2 (60% dense), in the form of 3mm. diameter disks, 1mm thick. Samples were mechanically polished, ion-milled by conventional techniques, and initially examined with the use of a Siemens EM102. The electron transparent thin foils were then heat-treated under controlled atmospheres of CO/CO2 and H2 and reexamined in the same manner.The “as-received” material contained mostly TiO2 grains (∼5μm diameter) which had no extended defects. Several grains however, aid exhibit a structure similar to micro-twinned grains observed in reduced rutile. Lattice fringe images (Fig. 1) of these grains reveal that the adjoining layers are not simply twin related variants of a single TinO2n-1 compound. Rather these layers (100 - 250 Å wide) are alternately comprised of stoichiometric TiO2 (rutile) and reduced TiO2 in the form of Ti8O15, with the Ti8O15 layers on either side of the TiO2 being twin related.

Download Full-text

Corrosion Behavior and Microstructural Evolution of Magnesium Powder with Milling Time Prepared by Mechanical Milling

Korean Journal of Metals and Materials ◽

10.3365/kjmm.2011.49.6.454 ◽

2016 ◽

Vol 49 (6) ◽

Keyword(s):

Corrosion Behavior ◽

Microstructural Evolution ◽

Mechanical Milling ◽

Milling Time ◽

Magnesium Powder

Download Full-text

The influence of Mo/B atomic ratio on microstructural evolution and mechanical properties of Mo2FeB2-based cermets

International Journal of Materials Research (formerly Zeitschrift fuer Metallkunde) ◽

10.3139/146.111778 ◽

2019 ◽

Vol 110 (7) ◽

pp. 664-671

Author(s):

Jiajie Zhang ◽

Yong Zheng ◽

Wei Zhou ◽

Guotao Zhang ◽

Zheng Ke ◽

...

Keyword(s):

Mechanical Properties ◽

Microstructural Evolution ◽

Atomic Ratio

Download Full-text

WIELAND DURO TANTALUM

Alloy Digest ◽

10.31399/asm.ad.ta0014 ◽

2020 ◽

Vol 69 (11) ◽

Keyword(s):

High Temperature ◽

Powder Metallurgy ◽

Physical Properties ◽

Tensile Properties ◽

Refractory Metal ◽

Temperature Performance

Abstract Wieland Duro Tantalum is unalloyed tantalum that is produced from powder metallurgy consolidated ingots. It is a versatile refractory metal that is used in demanding applications requiring resistance to high temperature and corrosion. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on low and high temperature performance as well as machining and joining. Filing Code: Ta-14. Producer or source: Wieland Duro GmbH.

Download Full-text