Kinetics in Solid State Bonding of Superplastic Steel 一 Effect of Geometrical Factors of Surface Asperity on Contacting Modes and Bonding Mechanisms 一

摘要

The solid state bonding of fine-grained high carbon steel with different initial void shapes (surface asperities) was carried out. The contacting modes and predominant bonding mechanisms were investigated. The interfacial contacting process was influenced by the geometrical factor: initial void shape with the surface asperity angle a0. The surface asperity angle changed the initial void shape on the bonding interface. When a0 =10 ?15 deg, the initial void shape was Lens-type. While a0 = 40 ?45 deg, it was Massif-type by the observation of cross section on the bonding interface. Lens-type contacting process was controlled by surface folding mode, which showed a high bonding rate. On the other hand, Massif-type contacting process was controlled by both surface folding and interfacial expansion modes, which inhibited the contacting rate. In spite of two modes, it was found that superplastic deformation could be the predominant bonding mechanism if the bonding conditions, temperature and pressure were appropriate. In other words, it was identified from the stress exponent n value and the activation energy Q value of each bonding mechanism that superplastic flow played a dominant role in the interfacial contacting process from a bonding ratio of 30% to 40%, under the conditions of bonding temperature T=1023 ?1053 K and bonding pressure P = 35 ?45 MPa.