Abstract
Several types of very high strength copper nickel alloys are tested with respect to environment sensitive mechanical properties which include hydrogen embrittlement and exposure to sulfide and ammonium compounds. It is found that Cu-Ni-Al-Mn-Nb alloys with nickel content up to 25wt% are resistant to hydrogen embrittlement, sulfide stress corrosion and stress corrosion in ammonium environments, whereas Cu-Ni-Sn materials demonstrate susceptibility to stress corrosion. A study of factors controlling stress corrosion susceptibility of Cu-Ni-Al and Cu-Ni-Al-Mn-Nb alloys shows the principal influences to be the degree of age hardening, the grain size and the iron content. Thus it is found necessary to control the production process of very high strength Cu-Ni-Al-Mn-Nb alloys such that high mechanical strengths are achieved with the material’s possessing a fine grain size and being in an under-aged condition. The use of the NACE TM-01-98-98 slow strain rate tensile test is advocated as a production test method for very high strength copper alloys to verify resistance to stress corrosion cracking susceptibility.
