Study of mechanisms of crack formation on tungsten composites using the three-point method

Abstract

The aim of this study was evaluated the ductile-to-brittle transition temperature (DBTT) and microstructure of miniaturized
tungsten composites by three point bending method. Tungsten and tungsten composites are the best technical materials candidates for
the manufacture of a diverter in the future fusion reactor ITER (International Thermonuclear Experimental Reactor). Because tungsten
has the highest melting point off all metals, it is candidate for plasma-facing materials. The ITER plasma temperatures to between 150
and 300 million °C, so it is important to study the effect of temperature on materials.
The effect of temperature on the mechanical properties of tungsten composites was studied by performing a number of three point
bending tests at different temperatures (100-600 С). Three different types of materials were assessed: first one – IGP commercial pure
tungsten (W > 99,97%), grades produced according to International Thermonuclear Experimental Reactor specifications in Europe
and China and two laboratory types W - 0.5%ZnC, W - 2%Y2O3. The resulting DBTT ranges depending on the type of material,
grain orientation affects and rolled. The IGP and W - 0.5%ZnC were rolled and tested in two different orientations of grains (L and
T): WZC_L, WZC_T, IGP_L, IGP_T. It is shown that the temperature transition from brittle to plastic fracture occurs sharply for
composites WZC_L (120-180 ° C) and IGP_L (160-180 ° C), slower for WZC_T (260-380 ° C) and (350-500 °C). The yield stress
decrease linearly with temperature. The materials tested in the L- orientation of the grains have a higher elasticity and better strength
characteristics. There are two types of fracture researched in work. After the crack has initiated in a metal it grows through the grains,
which is called transgranular fracture (WZC_L, WZC_T, IGP_L, IGP_T), or along the grain boundaries, known as intergranular
fracture (W-YO), or by a combination of transgranular and intergranular fracture (WZC_L, WZC_T, IGP_T).