Effect of Yttrium Oxide Dispersion on the Microstructure and Properties of Tungsten Heavy Alloys
Tungsten heavy alloys are considered as two phase composites with 88 to 97 wt% tungsten interspersed in a matrix of relatively low melting elements such as nickel, iron and cobalt. The mechanical properties of these alloys are greatly influenced by the microstructural features such as tungsten grain size, tungsten-tungsten contiguity and matrix volume fraction. Oxide dispersion strengthening (ODS), refinement of tungsten grain size, cyclic heat treatment, addition of alloying elements like Cr, Mo, and Co are some of the methods investigated to improve the microstructural features and thereby the mechanical properties of tungsten heavy alloys. Among these methods ODS has been considered as a promising processing technique since the tungsten grain size observed in ODS alloys is finer compared to the conventional alloys and more importantly the dynamic fracture mode changes from adiabatic shear band to brittle fracture. The present study is mainly focused on investigating the effect of 0.3 wt% yttrium oxide (Y2O3) dispersion on the microstructure and consequently the tensile properties of 90W-6Ni-2Fe-2Co alloy. With 0.3 wt%Y2O3, the ODS alloy (89.7W-6Ni-2Fe-2Co-0.3Y2O3) is processed by two-stage sintering with subsequent thermo-mechanical treatment which includes vacuum heat treatment and swaging. ODS alloy and the conventional alloy (without oxides) are compared based on the microstructures and tensile properties obtained after liquid phase sintering and after final processing.
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