Thoriated Tungsten Electrode Second Phase Research after Machining Deformation

Thorium tungsten electrode after machining deformation, the second phase had some obvious different changes. By analyzing the second phase changes after recrystallization, 202 rotary swaging and finished electrode, understand the impact of deformation on second phase of electrode.

After recrystallization, more second phase of thorium tungsten electrode had maintained spherical shape and small showed elongated rugby-ball like shape, or broken. This is mainly because a lot of residual stress disappeared after recrystallization annealing, so the internal stress of the electrode was in equilibrium, and tungsten matrix grains in the recovery and recrystallization process, the second phase showed spherical shape. Spherical shape is in favor of reducing electrode stress, in subsequent processing to prevent internal cracks. In addition, the spherical shape of second phase can be better deformation with the tungsten matrix to improve the mechanical properties of the electrode. Meanwhile, spherical second phase distribution in grain boundaries of tungsten matrix can effectively inhibit the cracks expansion in grain boundary.

And small second phase showed rugby-ball like mainly because during hot rolling cogging there were excessive external force, making the second phase not time moved to tungsten matrix, but it creates plastic deformation. Besides, there was fragmentation in the axial direction.

After 202 rotary swaging, the second phase elongation along with axial direction and most showed rice-like shape. When the deformation isn’t large, it can still maintain the ability to deformation with tungsten matrix. And a part of the second phase particles will be broken, mainly because deformation increased and deformation temperature reduced, so tungsten matrix deformation capacity will gradually decrease. And recovery and recrystallization grains will gradually shift to the dislocation cells, then if the second phase affected by the significant external force will occur fragility fracture.

With the deformation increased, tungsten matrix showed significant fibrous tissue. The second phase particles interrupted distributed in tungsten matrix with fibrous tissue. With the degree of deformation increased, the deformation ability has been behind the tungsten matrix, and easy to occur brittle fracture. Making rice-like second phase broke into smaller particles while leaving a large hole, which is not suitable for further processing. Otherwise it will generate a lot of cracks.

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