マグネシウムをドープしたチタン銅合金の不連続析出挙動

抄録

Discontinuous precipitation (DP) generated in an age-hardenable copper-titanium (Cu-Ti) alloy and its magnesium (Mg)-doped analog were thoroughly explored in a comparative study by advanced electron microscopy using focused ion beam specimens extracted from the bulk. Transmission electron microscopy (TEM) as well as scanning transmission electron microscopy (STEM) in combination with energy-dispersive X-ray spectroscopy (EDS) allowed us to describe and differentiate real microstructures of the DPs formed in the alloys. The Cu₉₆Ti₄ solid-solution alloy, when subjected to a prolonged aging treatment at 450°C for 100 h, had lamellar aggregates resulting from DP along the grain boundaries, consisting of an FCC-Cu solid-solution phase (denoted by α-Cu_ss) and a stable Cu₄Ti intermetallic phase (β-Cu₄Ti), while those in the ternary Cu₉₄Ti₄Mg₂ counterpart also had similar lamellar aggregates, but consisting anomalously of two distinct FCC-Cu solid-solution phases with different Ti-solute contents, without causing the β-Cu₄Ti plates to coexist. On the basis of these observations, the possible effects of Mg-doping on the DP behavior in the Cu-Ti alloy were elucidated and the structural environment of the DPs, which may result in relatively higher mechanical capabilities, was also discussed.