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The development research of Cu--Ti alloys for electrical engineering applications copes with two crucial problems. First, Ti solutes in the Cu matrix result 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 conditions of 450°C for 100 h and hydrogen pressure of 0.6 MPa, were investigated using various electron microscopy and microanalytical techniques. 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 βA-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. [ABSTRACT FROM AUTHOR]

The development research of Cu-Ti alloys for electrical engineering applications copes with two crucial problems. First, Ti solutes in the Cu matrix result 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 conditions of 450°C for 100 h and hydrogen pressure of 0.6 MPa, were investigated using various electron microscopy and microanalytical techniques. 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 βA-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 βA-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. [ABSTRACT FROM AUTHOR]

Herein, the isothermal aging behavior of coppertitaniummagnesium (CuTiMg) supersaturated solid-solution alloys, with different compositions, under test conditions of 450°C for 100 h, has been thoroughly investigated in a comparative study using various electron microscopy and microanalytical techniques. The Vickers hardness and electrical conductivity of the ternary alloys were recorded at slightly elevated (during aging) and reduced levels than their binary counterparts without Mg doping. Hence, it is proposed that the hardness and conductivity values are approximated from the superposition effect of precipitation hardening stimulated by Ti solutes and solution hardening by both Ti and Mg solutes. Furthermore, the tensile tests for these ternary specimens have demonstrated that Mg doping has a substantial effect on the improvement of the tensile strength and fracture elongation properties of binary CuTi alloys. Aberration-corrected high-angle annular darkfield scanning transmission electron microscopy imaging combined with atomic-resolution energy-dispersive X-ray spectroscopy mapping analysis confirmed that the same metastable precipitate phase is responsible for peak hardening in ternary and CuTi binary alloys. In addition, a large part of the Mg solutes is homogeneously distributed over the matrix regions, while there is also a smaller part of those present in the precipitates. The potential effects of Mg doping on the microstructures of CuTi alloys were elucidated and the structural environment, which may yield relatively high mechanical properties, was discussed using the aforementioned observations. [ABSTRACT FROM AUTHOR]

In magnetic skyrmion crystals (SkXs), the quality of skyrmion ordering affects the motion under electric current and temperature gradient. However, the crystalline nature itself remains an open issue. We report the observation of skyrmion polycrystallization in FeGe1−xSix as a function of x by Lorentz transmission electron microscopy. With increasing x, the SkX changes from single crystalline to polycrystalline, concomitantly with the formation of the interfaces referred to as domain boundaries. In situ observations have revealed that the domain boundary formation competes the tendency to accommodate the differences between orientations of the SkX. [ABSTRACT FROM AUTHOR]