High-strength and tunable plasticity in sputtered Al–Cr alloys with multistage phase transformations

Anisotropic Mechanical Properties of 2-D Materials

“…Figure 1 shows the structure zone diagram after energetic deposition of a thin film on a substrate, indicating that columnar grains preferentially being generated at different generalized temperature T/T m and argon pressure [14]. The columnar structure could even exist in amorphous Al-Cr thin films prepared by the sputtering technique as a result of chemical segregation [15]. These 2D metal coatings or thin films have higher hardness and strength, abiding by the wellknown Hall-Petch relationship.…”

Achieving strong and stable nanocrystalline Al alloys through compositional design

“…Most of our studied binary Al-rich systems experienced a two-stage phase transformation, i.e., FCC-to-amorphous transition, as solute concentration increased, on condition that matrix element is predominant. In one exceptional system, Al-Cr exhibits a multistage transformation from FCC to intermetallic Al 7 Cr to amorphous phase [34]. For liquidquenched amorphous alloys, larger T g /T m (T g is glass transition temperature), difference in atomic radius and mixing enthalpy in general lead to a higher glass-forming ability [65], and this suggests that the amorphization is highly composition-and rate dependent [66,67].…”

“…For liquidquenched amorphous alloys, larger T g /T m (T g is glass transition temperature), difference in atomic radius and mixing enthalpy in general lead to a higher glass-forming ability [65], and this suggests that the amorphization is highly composition-and rate dependent [66,67]. An amorphous phase started to form as Fe content (C Fe ) reached ~ 8% in Al-Fe, C Cr ~ 13% in Al-Cr and C Zr ~ 15% in Al-Zr system [29,34,36]. Ophus et al revealed that 12% Mo was the onset of composition for the amorphous formation [68].…”

“…Figure 2c shows the composition effects on hardness of various binary NC Al alloys and it clearly suggests that Co [37], Ni [40] and Fe [35] are more effective in strengthening Al than other solutes. With 5-6 at% solutes, Al-Co, Al-Ni and Al-Fe produce hardnesses as high as 5.5-6 GPa, whereas the hardnesses of Al-X (X = Ag [35], Cr [34], Mg [38], Mo [35,71], Ti [39], Zr [36] or W [35]) alloys could hardly exceed 3 GPa.…”

“…In contrast, electrodeposited Ni-W achieved 5-7 nm grain size, but was classified as a metastable/unstable NC system [26]. In the course of our recent developments of various binary NC Al alloys with supersaturated solid solution using sputtering technique, moderate addition of Co, Ni, or Fe has manifested exceedingly high effectiveness in shrinking the grain size of Al down to a few dozens of or a few nanometers, in striking contrast to Ag, Cr, Mg, Mo, Ti, W, and Zr [34][35][36][37][38][39][40]. Notwithstanding these NC Al-TM alloys endowed with strengths greater than 1.5 GPa, first principles calculations in combination with the NC stability criterion suggest that those Al-TM systems are subjected to very large weighted fraction of unstable segregated GBs, reflective of low propensity for good thermal stability [41].…”