Zirconium Tungsten Electrode Rod Processing

Obtained tungsten zirconium alloy bar by powder metallurgy, the electrode rod after swaging, drawing and a series of processing can obtain zirconium tungsten electrode. To carry hardness test on zirconium tungsten electrode found that the hardness value of work surface is similar to negative working surfaces hardness value, but the top edge hardness values is ​​significantly higher than the bottom edge hardness values, and therefore the electrode rod in the swaging is easily to form transverse cracks on bottom edge, and even breakage.

ZrO₂ is a reversible phase transition. During sintering process, the temperature changes will cause ZrO₂ phase transformation from monoclinic to tetragonal transformation and the volume change is substantially as follows:
△ V12 = (0.14045-0.13420) /0.14045≈4%
△ V13 = (0.14045-0.13178) /0.14045≈6%

When the monoclinic changes to tetragonal transformation, ZrO₂ volume declines by 4%. When the temperature is low, the tetragonal will change to monoclinic and the volume expansion rate of ZrO2 is about 4%. When the forging temperature at 2300 ℃, its volume shrinkage rate is about 6% and 6% volume expansion during cooling. Thus, around the ZrO₂ particle is easy to form small cracks or voids and these voids and cracks are one of the main reason that zirconium tungsten alloy bar brakeage during process. ZrO₂ chemical properties is stable and at high temperatures and hydrogen atmosphere it will not be reduced to zirconium, but at 1600 ℃, ZrO₂ will react with carbon to from ZrC in the grain boundaries. ZrC is more brittle and hard than ZrO₂, so it easy becomes brittle fracture sources. In addition, the negative work surface of electrode has low density on the edge, if cogging temperature is low, then the low-density edge of negative work surface is prone to form transverse cracking.

ZrO₂ phase change and uneven density are likely to cause cracks or fracture on electrode rod, affecting its processing performance, which has a certain impact on electrode subsequent use.

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