2023 年 62 巻 1 号 p. 6-11
The development research of Cu–Ti alloys for electrical engineering applications copes with two crucial problems. First, Ti solutes in the Cu matrix results in serious loss of electrical conductivity； second, discontinuous precipitation (DP) results in the deterioration of the mechanical properties of the alloy. In this connection, the effect of isothermal aging in a hydrogen atmosphere on the microstructure of an Mg–doped Cu–Ti alloy, under test condition of 450 ˚C for 100 h and hydrogen pressure of 0.6 MPa, were investigated using various electron microscopy and microanalytical technique. During the early stage of aging, the ternary alloy showed almost the same levels of the Vickers hardness as well as the electrical conductivity as those of the binary counterpart without Mg doping. Through this stage, fine needle–shaped metastable β’–Cu4Ti precipitates were continuously formed, as in the case of the binary alloys subjected to conventional aging in air (or vacuum). After 10 h of aging when the peak–hardness was reached, the Vickers hardness and electrical conductivity of the ternary alloy were recorded at more reduced and elevated levels respectively than in the case of vacuum aging. On further aging, the ternary alloy had the β’–precipitates replaced more increasingly by stable TiH2 precipitates in the matrix than the binary counterpart, resulting in a more rapid increase of electrical conductivity. It is, thus, suggested that the combined treatments of Mg doping and aging in hydrogen atmosphere can affect significantly the microstructures of Cu–Ti alloys to effectively reduce the negative impact of the Ti solutes in matrix as well as of the DP reaction.
