INFLUENCE OF HEAT-TREATMENTS ON MICROSTRUCTURE AND MECHANICAL-PROPERTIES OF CU-15NI-8SN PREPARED BY SPRAY FORMING

An alloy of composition (wt-%) Cu-15Ni-8Sn produced by the Osprey proc ess has been examined after a range of thermomechanical treatments wit h the aim of achieving high strength combined with reasonable ductilit y. Extensive cold working and an anneal in a two phase region for recr ystallisation, followed by spinodal decomposition, leads to a high str ength with reasonable tensile elongation because of the small grain si ze. Yield stresses in excess of 1100 MPa ale obtained by contributions of grain size hardening, spinodal hardening by the internal strain am plitudes created during decomposition, and progressive ordering at tin rich sites. Alternatively, very short high temperature anneals or med ium short low temperature anneals for recovery or partial recrystallis ation of the cold worked state lead to materials with very high yield stresses, between 1250 an 1450 MPa, maintaining similar values of tens ile elongation. (C) 1997 The Institute of Materials.