TWI Industrial Member Report Summary 570/1996
I A Bucklow, S B Dunkerton and P L Threadgill
Joining creep-resistant oxide- dispersion-strengthened (ODS) alloys poses the challenge of making the joint microstructure indistinguishable from the parent material.
Iron or nickel-based ODS alloys exhibit excellent corrosion resistance and mechanical properties at elevated temperature. They are made by mechanical alloying, powders of the constituent materials being compacted into a protective atmosphere. The composite powder is packaged into sealed containers which are hot worked into simple primary shapes, and the resultant product is then recrystailised at about 1280-1350 degrees C when large and highly elongated grains form. The mechanical alloying process may also cause a quantity of the protective atmosphere gas to be occluded in the powder.
The creep resistance of these alloys stems from the dispersion of oxide particles, and from the massive and elongated grain structure. However, ODS materials can be made only in fairly simple shapes and any complex component must be made by joining. This presents a challenge if the finished article is required to have the coarse-grained microstructure through the joint, and the original dispersion of oxide particles is to be preserved.
In the present work, application of a number of joining processes was explored. Diffusion bonding of an Fe-based ODS alloy was carried out with the objective of producing a coarse-grained joint with epitaxial growth across the interface. Study was made on Fe-based material of low gas content to assess the potential for fusion welding by the laser and TIG processes, and friction welds were produced in a Ni- based ODS alloy.
To assess the feasibility of producing joints in iron and nickel-based ODS alloys with minimum degradation of parent material microstructure.