Application to the Aluminum-Lithium system

The decomposition of a supersaturated solution of Li in A1 usually leads to disp er-sion of coherent precipitates of the metastable phase A Ni within the disordered matrix which hinders the subsequent transformation into the stable phase AlNi [72, 73]. From a qualitative point of view, this behavior takes place mainly because of the coherence between the metastable phase and the matrix yielding a small interface energy. We studied this practical example of the Al-Li alloy using the data from experiments [70-73, 77-79]. Experiments show that Al(Li) alloys with more than 5 

For industrial appHcations, Alilii is an unwanted phase because of the deterioration of mechanical and corrosion properties of the Al(Li) alloy. The characteristic feature of AliLii phase formation is that around the AliLii phase regions there is no metastable AI3 Lii phase. It is also found experimentally that the elastic modulus increase is well related to the presence of the intermediate metastable AliLii phase [70, 77-79]. It would be interesting to define whether it is possible to stabilize the metastable AliLii phase because of small particles or some other way. The basic results of this section were published first in [58, 59, 66]. 

Our analysis leads to the main conclusion that there exists the possibility of formation and total stabilization of the metastable AliLii phase instead of the stable Alilii phase in small particles of A1 -5/50 at.% Li alloys. This suggests that too high an interface energy 021 (between AliLii and AliLii) may hinder the subsequent transformation from the metastable phase AliLii to the stable phase Alilii in particles of nanometric scale (R = 2 nm). 

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