Microstructure and mechanical properties of ODS tungsten heavy alloys

Abstract

The microstructure and mechanical properties of oxide dispersion strengthened (ODS) tungsten heavy alloys were investigated. The ODS tungsten heavy alloys were fabricated by mechanical alloying, sintering, heat-treatment, swaging and annealing processes. The static mechanical properties of ODS tungsten heavy alloy were characterized by using the tensile test and high temperature compressive test. The dynamic mechanical properties of ODS tungsten heavy alloy were characterized by using Charpy impact test and Hopkinson pressure bar test. Three new alloy systems were designed as $94W-4.56Ni-1.14Fe-0.3Y_2O_3$, $94W-3.65Ni-0.91Fe-1.14Mo-0.3Y_2O_3$ and $94W-4.56Ni-1.14Co-0.3Y_2O_3$ alloys. Among three alloy systems, $94W-4.56Ni-1.14Co-0.3Y_2O_3$ alloy showed higher strength at room and elevated temperature, while showed lower elongation and impact energy than those of other alloys. The location of oxide dispersoids in sintered ODS tungsten heavy alloys can be controlled by controlling the mechanical alloying process. The yield strength of ODS tungsten heavy alloys was not affected by the location of oxide dispersoids. However, elongation of ODS tungsten heavy alloys can be enhanced by control of the location of oxide dispersoids when prepared by modified mechanical alloying processes such as two-step mechanical alloying process or mechanical alloying and mixing process. Two-stage sintered ODS tungsten heavy alloys showed finer tungsten grain size and higher tensile strength compared to the conventional liquid phase sintered ones. The yield strength and ultimate tensile strength of ODS tungsten heavy alloys can be improved by two-stage sintering process due to their finer microstructure with higher matrix volume fraction. Cyclic heat-treatment process was introduced to control the mechanical properties by controlling the tungsten/tungsten contiguity due to the mismatch of thermal expansion coefficients between tungsten and matrix phase. The cyclic heat-treatment resul...