Fatigue crack initiation and propagation behaviors of solution-treated and air-cooled Cu-6Ni-1.5Si alloy strengthened by precipitation hardening

Abstract

Fatigue tests were conducted on round bar specimens of a solution-treated and air-cooled Cu-Ni-Si alloy with high solute concentrations of 6% Ni and 1.5% Si. This alloy was strengthened by disc-shaped Ni2Si precipitates, a few tens of nanometers in diameter, formed during air cooling. The results were compared with those of a conventional solution-treated Cu-Ni-Si alloy cooled by water quenching. The correlation between the tensile and fatigue strengths of the two alloys differed completely from the general tendency that enhanced tensile strength brings an increase in fatigue strength. Indeed, the fatigue strength of the air-cooled Cu-Ni-Si alloy was 1.1 times higher than that of the water-quenched alloy, while the tensile strength was only 75% that of the water quenched alloy. Moreover, the electrical conductivity of the air-cooled specimens in International Annealed Copper Standard (LACS) percentage points was 1.7 times higher than that of the water-quenched specimens. The physical background for the superior fatigue strength of the air-cooled Cu-Ni-Si alloy, including the role of microstructure, is discussed.