This study is investigated on weldability of TD nickel, especially on the behavior of dispersed particles in welded zone at the first step of the study on weldability of dispersion hardening alloys.
In previous report, the following results was obtained.
In case of fusion welding of TD nickel, fusion zone is micrographically separated into three different regions. Even if melting-solidification time is about 1/6 sec, its separation is occured.
So, in this report it was confirmed by the transmission electron microstructures of various fusion welded zone that the previous three regions were separated by distribution of ThO
2 particles. And it was investigated the propriety of fusion welding for dispersion hardening alloys.
The results obtained from this study are summarized as follows.
(1) By transmission electron microstructures of various fusion welded zone, it became evident that the previous three regions are separated by distribution of ThO
2 particles. Namely, in Region I, ThO
2 particles make agglomeration and growth to some degree and form the honeycomb structure. In Region II, ThO
2 particles make agglomeration and growth larger than in Region I. In Region III, ThO
2 particles are excluded when matrix nickel is melted and solidified, and so it has the solidified structure of pure nickel.
(2) At the point of view of wettability of metal-oxide system and work of adhesion, it is considered about the phenomena based on the behavior of ThO
2 particles. And its propriety on consideration of exclusion of ThO
2 particles is confirmed by the experiment of melting of SAP.
(3) The tensile properties of TIG welded and EBW joints, having the previous three regions in fusion zone, are lower than those of base metal.
(4) As the results of consideration for the propriety of fusion welding to welding of dispersion hardening alloys, it is concluded that it is impossible to obtain the dispersion hardening effect at the joint by existing fusion welding.
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