黒鉛とニッケルの固相接合に及ぼす接合圧縮応力の影響

Abstract

Graphite was bonded to nickel in a vacuum using an RF-induction furnace by changing conditions of temperature, keeping time and joining compressive stress. The bending strength of graphite/nickel joints and the changes of microstructure and hardness near the joining interface of nickel were investigated. Thermal stress induced in the joints was estimated by means of finite element analysis. On the basis of these results, the influences of joining compressive stress on bonding were examined.Joining compressive stress and temperature are important factors for close contact and strong bonding between joining surfaces of graphite and nickel. At high temperature, nickel is plastically deformed even under low joining compressive stress so that full contact and strong bonding are accomplished, while at low temperature, no strong bonding are attained when joining compressive stress is lower, because plastic deformation of nickel is restrained. Plastic deformation of nickel plays an important role in full contact and strong bonding.The strength of the joints increased as joining compressive stress increases, because of the following reasons: The plastic deformation of nickel near the joining interface increases with joining compressive stress so that graphite is elastically deformed in radial direction during annealing. Therefore, longitudinal compressive stress is induced on the graphite surface near the joining interface. Thermal tensile stress induced on the graphite surface after cooling is relaxed by this compressive stress.