拡散溶接における接合界面の電気抵抗の集中抵抗による解析

抄録

New equations giving constriction resistance R_C as a function of area S_M and number density n of true contact spots have been obtained from a model experiment, and applied to the analysis of the electric resistance of the bond interface ΔR for the diffusion-welded joint of titanium. The new equations obtained are described as
R_C= ρ/√n ⋅S ( √π/2 √S/√S_M -1.21) ……(1)
for (S_M/S)<1/4, and
R_C= ρ/√πn⋅S {√ S/S_M tan^-1(√ S/S_M -1)-0.842(1-√ S_M/S )} ……(2)
for (S_M/S)> 1/4, where ρ is the resistivity of base metal and S the apparent contact area. It can be seen from these equations that parameter A=(ΔR⋅S/ρ) depends only on (S_M/S) and n, if ΔR=R_C. Parameter A measured at temperatures from 77 K to room temperature for joints of titanium, however, decreased with a rise in the temperature of measurement, and its temperature dependence became less pronounced with the increase in welding temperature and time. On the other hand, area S_M and density n were estimated from fractured surfaces of joints on the assumption that spots where grooves caused by machining of the faying surface were annihilated corresponded to true contact spots. Parameter A estimated from S_M and n thus obtained using eqs. (1) and (2) was significantly smaller than that measured at 77 K and rather in good agreement with that measured at room temperature. This result indicates that not all the true contact spots observed on fractured surfaces corresponded to completely bonded spots having electrical properties identical with those of the base metal. The dependence of A on the temperature of measurement can be accounted for by a model that the bond interface consists of three characteristic spots: unbonded spot, completely bonded spot and incompletely bonded spot containing inclusions such as oxide films.