ドープW線のNi誘起再結晶とNiの浸透挙動

抄録

Nickel-induced recrystallization of tungsten wire was investigated using a lamp-grade tungsten wire of 1mm diameter having a 40 μm thick layer of nickel formed by electrolytic plating. The wire was exposed to hot argon environments of 1 200 to 1 300°C and the resulting microstructural changes were examined in correlation with the distribution of nickel atoms detected by electron probe microanalysis (EPMA).
The examination revealed two different microstructural states corresponding to the primary and the secondary recrystallization. In the primary-recrystallized region extending inwards from the wire periphery, the presence of nickel atoms was detected by EPMA. Individual grains therein were hardly visible with standard technique of optical metallography but clearly observed on a room-temperature fractograph of the wire. These grains had the < 110 > preffered orientation. The secondary recrystallization, on the other hand, was characterized by a coarse grain structure. By applying an immage processing tech nique to one of the EPMA results, it was demonstrated that nickel atoms were enriched in and around the grain boundaries. Although the high temperature strength of the wire was little affected by the recrystal lizations, the ductile brittle transition temperature (DBTT) considerably increased. While DBTT was as low as 200°C for the nickel-free wire even after heat treatment at 1 300°C for 100 h, it was around 400°C and 900°C for the nickel-coated wire after the primary and the secondary recrystallization, respectively.