Comparison of discontinuous precipitation behavior of Cu-15Ni-8Sn alloy with and without Co addition

The microstructure evolution, phase interface relationships, and corresponding hardness changes of dis-continuous precipitation in Cu-15Ni-8Sn alloy during the aging process were investigated. The samples were isothermally aged for 15 h at 500-700 degrees C to yield discontinuous precipitates with varying lamellar spacings. The results showed that discontinuous precipitation with a lamellar structure is composed of the alpha-Cu phase and gamma-DO3 phase, which has an incoherence interface and satisfies the K-S orientation re-lationship. With the increase of aging temperature, the lamellar spacing of the discontinuous precipitation increases, the length of lamellar shortens, and the lamellar nature weakens. Simultaneously, the dis-continuous coarsening reaction is accelerated. The addition of the trace Co element can inhibit the for-mation of discontinuous precipitation and discontinuous coarsening phase. Co enrichment was found in the gamma-DO3 phase, which can alter the lamellar spacing and then affect the hardness of the Cu-15Ni-0.5Co alloy. In addition, the hardness of discontinuous precipitation in the Cu-15Ni-8Sn-(0.5Co) alloy is negatively correlated with the lamellar spacing and can follow the Hall-Petch type relation.(c) 2022 Published by Elsevier B.V.