Body-centred tetragonal martensite formed from Au7Cu5Al4 β phase

Determination of the 76 wt.% Au section of the Al–Au–Cu phase diagram

“…The structures of some of the less familiar phases were subsequently determined, and are reported elsewhere [9][10][11]. The degree of ordering of the AuCu-I phase was primarily determined by computation of the ratio a/c, determined for a four-atom fct (a/c>1) or bct unit cell (a/c<1).…”

“…In contrast, laths were barely evident or absent in the as-cast, arc-melted and unmounted state. X-ray diffraction studies conducted at ambient and elevated temperatures revealed that the lathy phase at room temperature has the structure of a nominally tetragonal martensite [10], the atomic positions of which are further modulated [11]. The parent phase for this martensite is a little-known ternary β electron phase, with the nominal composition Au 7 Cu 5 Al 4 and an e/a ratio of 1.48 [9].…”

Thin Films of AuCuAl Shape Memory Alloy for Use in Plasmonic Nano-actuators

“…At higher magnification, fringes spaced at about 1.54 nm become visible in this film. If a nominal spacing of the close-packed planes of 0.222 nm is accepted [10,18], then a martensite phase of the 7R type is indicated by the presence of these fringes [10]. The lack of crystallinity when the (Au 0.58 Cu 0.42 ) 1-x Al x films were deposited at room temperature is similar to the situation found for very thin, nanoscale films of TiN [14].…”

Phase diagram of Au-Al-Cu at 500 °C

“…The ε phase contained 25 to 33.4 at.% of Cu and 62.4 to 65 at.% of Al. Ten three-phase equilibria were determined in this study, namely, Al-AuAl 2 -Al 2 Cu, A1 2 Cu-ε-AlCu, AuAl 2 -ε-AlCu, AuAl 2 -AuAl-γ, AuAl-δ (Au 2 Al)-γ, δ (Au 2 Al)-α-β, Au 8 Al 3 -δ (Au 2 Al)-Au 4 Al, AlCu-AuAl 2 -Al 9 Cu 11 , Al 9 Cu 11 -AuAl 2 -Al 2 Cu 3 , and Al 2 Cu 3 -AuAl 2 -γ. Four three-phase equilibria, namely, β-δ (Au 2 Al)-γ, α-β-γ, α-δ (Au 2 Al)-Au 4 Al, and AuA1 2 -ε-Al 2 Cu were estimated to meet the criteria for phase relationships.…”

“…A β (Au 7 Al 4 Cu 5 ) phase exhibiting martensite-like properties was developed [3][4][5]. The embossed and fine-layered surface of this material, which originates from a martensitic transformation, exhibits a characteristic shining color and is used in Spangold jewelry.…”