Change in Electrical Resistivity of Polycrystalline Aluminium Stretched at -196°C

Abstract

It is known that lattice defects are introduced in the specimen of metallic material by cold stretching, which results in the change in electrical resistivity. The increase Δρ/ρ of the resistivity is usually represented in terms of strain e byΔρ/ρ=Aen, where A and n are constants depending on the various conditions of the specimen.In order to study the effect of the grain size and the prior deformation on the change in resistivity, 99.998% aluminium wires were deformed in tension at the liquid nitrogen temperature. Three groupes of specimens having the grain size of about 18, 80 and 800μm were provided after annealing them in vacua for 2hrs at 200, 300 and 500°C, respectively.The results obtained are as follows;(1) The constants n and A in the above equation increase from 1.27 to 1.84 and from 0.1 to 0.55, respectively, with increase in grain size.(2) Similar emprical equation is valid for the specimen pre-stretched at 15°C, where the constants n and A depend on the amount of pre-strain.(3) The square root (Δρ/ρ)1/2 of the increase of resistivity at -196°C is proportional to the applied tensile stress σ. The gradient of the (Δρ/ρ)1/2/σ relation increases from 0.049 to 0.059mm2/kg with the increases of the grain size.(4) The relation between Δρ/ρ and d is represented by(Δρ/ρ)1/2=P+Qd-1/2, where P and Q are constants, and d is the grain size.(5) Nearly 60% of the total change in resistivity by cold stretching is attributed to the presence of point defects. The ratio is almost the same standing regardless of the grain size or of the amount of pre-strain.