Cu0.81 mass%Cr0.12 mass%Zr alloy was spun into ribbon and then aged at different temperatures for different time. The microstructure, microhardness and electrical conductivity were investigated. It is found that the mother alloy ingot solidified under conventional conditions consists of three phases: Cu matrix, Cr and Cu 5 Zr. Rapid quenching makes Cr and Zr fully dissolve into the copper matrix. As the aging proceeds, Cr and Cu 5 Zr phases precipitate again from the matrix. The ribbon aged at 773 K for 15 min possesses the best property: a microhardness of 212 HV and an electrical conductivity of 78.9% IACS. Compared with the conventional process (homogenization treatment of a bulk alloy ingot followed by aging), the use of rapid quenching doubles the microhardness while only slightly decreasing the electrical conductivity.

No abstract

No abstract

The impact toughness of Q&T Mn-Ni-Mo bainitic steel in the ductile-brittle transition temperature (DBTT) region was measured. The fracture micromechanism associated with the microstructural features was studied, by statistically analyzing the grain sizes of various structures. The results reveal that the cleavage fracture behavior is controlled by bainitic packets. There exists a critical bainitic packet size. When a microcrack formed in the bainitic packet with a size exceeding the critical size propagates into adjacent packets, brittle cleavage fracture occurs. The probability of finding the bainitic packets larger than the critical size dominates the impact toughness and its scattering. It is suggested that refining the bainitic packets and homogenizing their sizes is an effective method of improving the impact toughness and reducing its scattering in the DBTT region.

No abstract