Evolution of Nickel Base Alloys – Modification to Traditional Alloys for Specific Applications

摘要

Nickel alloys have been used for many demanding applications for over 100 years now. In the early days most of the alloy families that we are now familiar with were established, such as Ni- Cu, Ni-Cr-Mo, Ni-Mo, Ni-Cr-Fe, and Ni-Fe-Cr-Mo alloys, of which some are still used today. These fundamental alloy families have been the basis for numerous new alloys, each targeted for specific applications. As nickel alloys are today a very mature field of study, most recent developments have been evolutionary in nature rather than revolutionary. This paper describes two recent developments that show how changes still can be made to established nickel alloys to further improve their performance in certain applications. The first example is a Ni-Fe-Cr-Mo-Cu alloy (UNS N08031) that was modified to improve the fabrication characteristics of the material with the result of new alloy chemistry. It is important that when improving the fabrication characteristics the corrosion behavior of the material is maintained or even slightly improved. This requirement was met with the modified new alloy version of UNS N08031. The second example is a new Ni-Cr-Mo alloy (UNS N06058) that was developed with improved localized corrosion resistance and increased uniform corrosion resistance in certain acids over the Ni-Cr-Mo alloys in common use up until now. In this case corrosion resistance and mechanical properties were deliberately improved, while good fabrication and weldability characteristics were maintained. Alloy UNS N06058 is the most recent member of the so called C-family of alloys and the first Ni-Cr-Mo alloy to contain nitrogen as an alloying constituent. In addition, it contains the highest molybdenum content (around 19%) of this alloy family resulting in an excellent corrosion resistance in reducing environments. Together with the chromium and the increased molybdenum content the alloying of nitrogen results in a pitting resistance equivalent number (PREN) of about 86, surpassing all other Ni-Cr-Mo alloys.