Microstructural evolution of Cu-1 at% Ti alloy aged in a hydrogen atmosphere and its relation with the electrical conductivity

Copper alloys with titanium additions between 1 and 6 at% Ti emerge currently as attractive conductive materials for electrical and electronic commercial products, since they exhibit superior mechanical and electrical properties. However, their electrical conductivity is reduced owing to the residual amount of Ti solutes in the Cu solid solution (Cuss) phase. Since Cu shows only poor reactivity with hydrogen (H), while Ti exhibits high affinity to it, we were inspired by the idea that hydrogenation of Cu–Ti alloys would influence their microstructure, resulting in a significant change of their properties. In this contribution, the influence of aging under a deuterium (D2) atmosphere of Cu-1 at% Ti alloys on their microstructure is investigated to explore the effects on the electrical conductivity. The specimens were investigated by means of transmission electron microscopy (TEM), field ion microscopy (FIM), computer-aided field ion image tomography (cFIIT), and atom probe tomography (APT). early aging stage at 623 K in a D2 atmosphere of 0.08 MPa, ellipsoidal α-Cu4Ti precipitates are formed in the alloy, and during subsequent aging, δ-TiD2 is competitively nucleated instead of growth of α-Cu4Ti particles. The co-precipitation of α-Cu4Ti and δ-TiD2 efficiently reduces the Ti concentration of Cuss matrix, particularly in the later aging stages in comparison to the aging in vacuum conditions. The electrical conductivity of the alloy aged in the D2 atmosphere increases steeply up to 48% International Annealed Copper Standard (IACS) after 1030 h, while it saturates to approximately 20% IACS in the alloy aged in vacuum. The outstanding increase of electrical conductivity during aging in D2 atmosphere can be basically explained by the reduction of Ti solute concentration in Cuss matrix.