Microstructure tailoring of Al-containing compositionally complex alloys by controlling the sequence of precipitation and ordering

Fundamental Effects of Al and Ta on Microstructure and Phase Transformations in the Al–Cr–Mo–Ta–Ti Refractory Complex Concentrated Alloy System

“…This corresponds fairly well with a previously calculated C15 Laves phase solvus temperature of 1300 °C [ 18 ] and the experimental peaks determined here in the annealed alloys at 1178–1235 °C. As discussed extensively in prior work, [ 22 ] discontinuous phase transformations should exhibit more symmetrical peaks, whereas continuous transformations such as ordering should exhibit “lambda” shaped peaks, characterized by a sharp exponential increase followed by an abrupt return to the baseline calorimetric curve. In the case of the annealed alloy calorimetric data in Figure 10b, the first lower temperature peaks exhibit lambda‐shaped profiles, whereas the second higher temperature peaks are generally more symmetric.…”

“…Laube et al also examined the effect of Al (and Cr) on the order-disorder reaction in this system and determined that Al seemingly promotes the formation of the ordered bcc phase, and lower amounts of Al could lead to a disordered (A2) matrix with ordered (B2) precipitates. [22] Thus, this body of work reports on the independent effects of Al and Ta on the microstructure and equilibrium behavior of the base AlCrMoTaTi alloy system. Results of this study therein lead to a more detailed understanding of how this alloy system could be optimized for increased structural integrity, while retaining its unique degree of oxidation resistance for use in extreme environments.…”

“…Laube et al also examined the effect of Al (and Cr) on the order–disorder reaction in this system and determined that Al seemingly promotes the formation of the ordered bcc phase, and lower amounts of Al could lead to a disordered (A2) matrix with ordered (B2) precipitates. [ 22 ]…”

Compositional Modifications to Alter and Suppress Laves Phases in AlxCrMoTayTi Alloys

“…Initial thermodynamic calculations in this system focus on refined approaches based on CALPHAD results from prior work, [16] as well as other work that specifically evaluated the dependencies of Al, Cr, and Ta. [17][18][19] In this research, a critical driver for the success of the alloy includes long-term environmental and microstructural stability at 1000 °C. [2] As such, particular emphasis was placed on the equilibrium behavior of the alloy at this temperature as well as in the annealing regime (1300 °C).…”

“…Tuning Al and Cr ratios in the AlCrMoTaTi system was demonstrated, whereby sophisticated ordered structures could be directed, although these modifications did not demonstrate a disordered solid solution. [ 19 ] In relatable work on the AlCrMoNbTi alloy system, lattice distortion effects on numerous high entropy alloys (HEAs) were validated, including also the AlCrMoTi system which appeared as single‐phase body‐centered cubic (bcc) disordered structure in initial studies. [ 20 ] Disordered structures were later confirmed only in low‐aluminum concentrations (≤5 at%) in the AlCrMoTi quaternary system, with ordering well correlated by thermodynamic calculations.…”