HIGH STRENGTH COPPER NICKEL-OPTIMISATION OF MECHANICAL STRENGTH AND MARINE CORROSION RESISTANCE FOR USE IN NAVAL ARCHITECTURE AND OFFSHORE OIL GAS

摘要

Copper nickel alloys which are able to harden by precipitation reactions involving aluminium are described. The main precipitation species is Ni_3Al present as 10 nm - 15 nm size particles, and strengths above 750 N/mm~2 proof stress have been achieved. Two such alloys have been commercialised and they demonstrate higher corrosion resistance to marine environments than standard cupronickels, most probably due to the passivating influence of aluminium. The reaction of one of these alloys with sodium chloride both with and without the presence of sulphides has been studied, using weight loss, Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) and these techniques indicate a greater degree of passivity for this alloy than for copper or standard cupronickels in sulphide environments. The age-hardenable cupronickels also display complete freedom from hydrogen embrittlement and resistance to biofouling. Service experience with these high strength copper-nickel alloys for highly loaded critical components in naval shipbuilding and offshore oil and gas application is discussed.