Embrittlement Phenomena in Copper and Cupronickel Alloys

 

D. Empl, V. Laporte, L. Felberbaum and A. Mortensen

The goal of this study, funded by a collaboration between the Swiss agency KTI/CTI and the Swissmetal company was to improve our understanding of cracking phenomena observed in the hot deformation processing of Cu-Ni alloys that may contain further alloy elements, in particular lead. The main axes of enquiry were: (i) measurement of capillary forces at inclusions of added lead using a newly developed technique based on three-dimensional reconstruction of the inclusion/matrix interface; (ii) mechanical tests between room temperature and 900 °C over a wide range of strain rates.
Laboratory grade alloys are cast in an argon atmosphere. The material is successively extruded, cold drawn, heat treated and tensile or creep tested at intermediate temperature.
Liquid as well as Solid Metal Embrittlement are operating in alloys containing lead, depending on temperature and strain rate used in the mechanical test. The ductility and strength of the alloy are much reduced around 400°C as compared to Cu OFHC. Alloys of Cu-Ni-Si are prone to grain boundary embrittlement by oxygen and sulfur at low strain rates.

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