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

Abstract

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 suggested the segregation of Sn element at grain boundary could be alleviated to a certain degree with B addition. After being solution-treated at 850 °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 °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 excess 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 deterioration as long as 18 h during the aging process, which suggests the tremendous enhancement of softening 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.