Effect of B addition on microstructures and properties of Cu-15Ni-8Sn alloy

The effect of B addition on microstructures and properties of as-cast, solution-treated and aged Cu-15Ni-8Sn alloy was systematically investigated in the present study. It is found that the micron-scale Ni6.67SnB2 phase is identified in as-cast microstructure for B-containing Cu-15Ni-8Sn-xB alloys. Moreover, it is sug-gested the segregation of Sn element at grain boundary could be alleviated to a certain degree with B addition. After being solution-treated at 850 degrees C for 4 h, the Ni6.67SnB2 phase is still existed in the matrix, thereby resulting in a significant influence on the microstructures and properties during subsequent aging process. Results demonstrate that, during aging treatment at 400 degrees C, the transformation of DO22 ordered phase into L12 ordered phase can be increasingly inhibited with increase of B content and completely prevented for 0.3 and 0.5 wt% B addition. Additionally, the appropriate B addition (0.04, 0.08, 0.1 wt%) could remarkably suppress the formation and growth of the discontinuous precipitation. Nevertheless, with ex-cess B addition (0.3, 0.5 wt%), the discontinuous precipitation is instead promoted. More importantly, alloys with appropriate B addition (0.04, 0.08, 0.1 wt%) could also maintain the peak hardness without dete-rioration as long as 18 h during the aging process, which suggests the tremendous enhancement of soft-ening resistance. It is believed that the suppression of discontinuous precipitation by Ni6.67SnB2 phase should be responsible for such enhancement of softening resistance. It is anticipated that the current work could provide guidance for the multi-component design of high-performance Cu-Ni-Sn alloy.(c) 2023 Elsevier B.V. All rights reserved.

Automated summary

In this study, the effect of B addition on the microstructures and properties of Cu-15Ni-8Sn alloy in different states was investigated. The presence of Ni6.67SnB2 phase was observed in the as-cast microstructure, and B addition could alleviate the segregation of Sn at the grain boundary. Solution treatment did not eliminate the Ni6.67SnB2 phase, leading to significant influences during aging. Increasing B content inhibited the transformation of DO22 phase into L12 phase and suppressed discontinuous precipitation. Appropriate B addition maintained peak hardness during aging, indicating enhanced softening resistance. These findings provide guidance for the design of high-performance Cu-Ni-Sn alloys.