The rate of bubble deformation during tungsten wire drawing

Comparison of K-doped and pure cold-rolled tungsten sheets: As-rolled condition and recrystallization behaviour after isochronal annealing at different temperatures

“…Since these are not observable in Wpure, we interpret them as K-bubbles. The break-up of K-bubbles, which is also known from K-doped W lamp wires and described by the Plateau-Rayleigh instability [23,28,29], seems to take place in our rolled W sheets during annealing at 1400 °C for 2 h as well, despite having theoretically much lower strains ( log = 3.7 in this sample) than usually achieved in wires. The critical aspect ratio needed for the break-up of the bubbles by the Rayleigh instability should be ≥ 8.89 [63].…”

“…During wire drawing, the K-bubbles are co-deformed with the tungsten matrix into long ellipsoids. During intermediate temperature treatments, these ellipsoids break up into rows of bubbles, following the mechanism of the Plateau-Rayleigh instability [23,28,29]. The formation of rows of bubbles from elongated ellipsoids is the result of the tendency of minimizing surface energy under the given restriction of material transport, a phenomenon also observed e.g.…”

“…That observation and the large pore volume (up to 500 nm) fits to the circumstance that we investigated the sheet in as-rolled condition and not in annealed condition. We suspect that during annealing a break-up of the bubbles into rows of smaller bubbles will occur and dispersion will improve, as known from K-doped tungsten wires [26,29]. The pores are mostly decorated with surrounding dislocations.…”

“…Both aspects combined, it can be concluded that, despite the WK sheet with highest strain has no benefit compared to the sheet with lowest strain at 900 °C due to higher loss of hardness, severe rolling of K-doped W sheets leads to an improved inhibition behaviour at temperatures above 1270 °C. This influence of the degree of deformation on the RX inhibition effectiveness of K-doping can be explained by the finer dispersion of K-bubbles: Further rolling leads to more elongated Kbubbles with higher aspect ratio, which break up into longer rows of smaller bubbles after annealing [23,28,29]. If we assume a pinning mechanism of grain boundaries similar to incoherent particles and apply the approximation of Zener and Smith [64,65] to describe the pinning force (or Zener pressure) M N of K-bubbles that are present in a sample volume, the relationship of the pinning force to the bubble radius O is reciprocal:…”

The Study of Fine Tungsten Rhenium Thermocouple Wires in the Temperature Measurement of the Molten Steel

“…After sintering, rotary forging, drawing and annealing treatment, the Fine Rare Earth Oxide particle dispersed in grain boundaries, which causes little impact to the thermoelectric potential homogeneity. Because of added Si, Al, K elements in the traditional W-Re thermocouple wire, the large number of K-bubble were dispersed in the grain and grain boundaries [10][11][12] , which has very adverse effect to the thermoelectric potential homogeneity of W-Re thermocouple wires and reduce the temperature measurement accuracy of W-Re thermocouple wires.…”