粉末冶金Cu-15Ni-8Sn合金时效组织的演变行为

Effect of different aging time at 400℃ on microstructure and properties of powder metallurgy Cu-15Ni-8Sn alloy was investigated after hot extrusion and solution treatment. The results show that: the tensile strength increases initially and then decreases, the elongation decreases initially and then increases with increasing aging time. And the maximum tensile strength value of 918 MPa is obtained after aging at 400℃ for 1.5 h. Aging about 2 h at 400℃ is the best way to get a better performance in both strength and toughness. Scanning electron microscope (SEM) was employed to study the tensile fracture mode. The results show that: the tensile fracture mode evolves from predominance on intergranular fracture to trans-granular fracture after aging from 1h to 3 h at 400℃. The microstructural evolution of powder metallurgy Cu-15Ni-8Sn alloy with different aging time (1?3 h) at 400℃ and its effect on strength and plasticity were studied by transmission electron microscopy (TEM), and the results show that in the under aged condition, the Sn-rich regions form the metastable state (CuxNi1?x)3Sn particles of DO22 by continuous precipitation in the under-aged condition. The microstructure evolves from FCC to DO22 structure, the tensile strength increases widely and the plasticity decreases. In the peak-aged condition, DO22 evolves into L12, and the tensile strength increases furthermore. As the lamellar discontinuous precipitation structure grows from the grain boundary to the inside of grains, and the tensile strength decreases. What’s more, the lamellar structure grows from grain boundary to the inside of grain extensively in the over aged condition, and DO22 evolves into L12. The extension of lamellar structure is the main factor of influence on the strength, and the strength decreases. In the late stage of aging, the spinodal structure is consumed by the lamellar structure. The coarsening and breaking of the lamellar structure can be observed, and DO3is constantly formed. But the procedure is rather slow and requires more composition fluctuation, so that the lamellar structure is the main microstructure, and it is not obviously noticed the changes of the strength and plasticity.