The effect of grain boundaries on the athermal stress of tantalum and tantalum-tungsten alloys

Abstract

The temperature dependence of the yield stress of polycrystalline Ta, Ta-2.47 wt pct W (Ta-2.5W), and Ta-9.80 wt pct W (Ta-10W) was measured to study the effect of grain boundaries and tungsten concentration on athermal strength components. Compression tests were performed over a temperature range from 77 to 1223 K at strain rates of 10 Ϫ4 and 10 Ϫ1 s Ϫ1 . The test results show that the yield stress of Ta becomes independent of temperature above about 400 K, indicating an "athermal" regime. In contrast, the temperature dependence of yield stress was still significant for Ta-10W up to the maximum test temperature. An analysis of the test data using single-crystal data in conjunction with Taylor factors was performed to assess the effect of grain boundaries on the athermal component of flow stress at 600 K. The results indicated that the long-range athermal stress at the yield point due to grain boundaries is approximately 13 to 41 MPa for the study materials and decreases with an increase in tungsten concentration. These results are discussed with regard to constitutive modeling of flow stress.

On the room temperature deformation mechanisms of a TiZrHfNbTa refractory high-entropy alloy

“…The value of 2.75 has already been used in studies relative to the deformation of tantalum [32,33] and tantalum alloys [34].…”

Thermally activated dislocation mechanism in Mo studied by indentation, compression and impact testing

“…It is apparent from the diagram that the flow stress of Mo consists of an athermal (σ a ) and a thermal component (σ * ) . The athermal component is related to the long-range internal stresses and microstructural barriers [10,11]. However, the aforementioned nucleation and motion of kink pairs of the screw dislocations affects the thermal component most and is responsible for the strain rate sensitivity (SRS) m of Mo.…”

Multiscale modeling of plastic deformation of molybdenum and tungsten: I. Atomistic studies of the core structure and glide of 1/2〈111〉 screw dislocations at 0K

“…These aspects of yielding have been found in a broad variety of non-magnetic transition metals of the VB and VIB groups of the periodic table (e.g. [7][8][9][10][11][12][13][14][15][16][17][18][19][20], in iron and iron-silicon alloys [21][22][23][24][25][26][27][28] as well as in alkali metals [29][30][31][32][33][34]. Niobium, molybdenum and tantalum are the transition metals that were studied most extensively [7][8][9][10][11][12][13][14][15][16][17][18][19][20] while tungsten was investigated much less frequently.…”

“…[7][8][9][10][11][12][13][14][15][16][17][18][19][20], in iron and iron-silicon alloys [21][22][23][24][25][26][27][28] as well as in alkali metals [29][30][31][32][33][34]. Niobium, molybdenum and tantalum are the transition metals that were studied most extensively [7][8][9][10][11][12][13][14][15][16][17][18][19][20] while tungsten was investigated much less frequently. The main reason is that its purification is rather involved and preparation of single crystals is difficult owing to its extremely high melting temperature (3422 °C) and high brittle-to-ductile transition temperature [35,36].…”