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On the go-and-stop motion of the discontinuous precipitation front

Chronowski M., Zięba P.

Archives of Civil and Mechanical Engineering

2020

Vol. 20, no. 2

73--79

The growth of lamellar structure during discontinuous precipitation occurs frequently by so-called go-and-stop fashion. The results of simulation combined with the changes of Cahn’s parameter C revealed two types of such motion. The process takes place in the successive stages which can be distinguished judging from the value of C parameter. For lower values of linear growth rate (v = 10÷20 nm/s) and smaller α lamella thickness (100÷200 nm), the full cycle with relaxation takes 4–6 s. The faster movement of the reaction front (v = 30 nm/s) resulted in dramatic decrease of the full cycle to τtotal = 0.8 s. The same behavior is observed if the α lamella thickness increases beyond 200 nm at constant v equal to 10 nm/s. Both predicted types of go-and-stop motion can experimentally be observed during growth or dissolution of discontinuous precipitates. What is the reason that particular type prevails is unknown, and this is invitation for further studies especially using high-resolution transmission electron microscope operating in in situ mode.

Recent Developments on Discontinuous Precipitation

Zięba P.

Archives of Metallurgy and Materials

2017

Vol. 62, iss. 2A

955--968

The discontinuous precipitation (DP) belongs to a group of diffusive solid state phase transformations during which the formation of a new phase is heterogeneous and limited to a migrating reaction front (RF). The use of analytical electron microscopy provided reliable information that there is no differences in the diffusion rate at the stationary grain boundary and moving RF of DP reaction. On the other hand, the use of “in situ” transmission electron microscopy observations indicated the importance of stop- go motion or oscillatory movement of the RF. During 2004-2016 period more or less 280 papers were published in which the terms “discontinuous precipitation, “cellular precipitation”, discontinuous coarsening” appeared either in the abstract or in key-words. In the present contribution, the research on the DP reaction will be reviewed taking into account new aspects of theories and modelling, new evidences and findings, effect of various factors including third element, external stresses, plastic deformation and GB orientation, occurrence in less known systems and alloys like: superalloys, nitrided Fe-based alloys and Cu-based alloys. Finally, some suggestions for the future research will be formulated.