On the influence of non-steady state velocity on interlamellae concentration profiles in discontinuous precipitation

Discontinuous and continuous precipitation in magnesium–aluminium type alloys

“…Additionally, as could be expected, the time necessary for nucleation and growth of precipitates decreases with ageing temperature. As well known, the volume fraction of regions transformed by discontinuous precipitation essentially depend on reaction front velocity, interlamellar spacing, average composition of the solutedepleted ␣ lamellae, temperature, solute content and conditions of the grain boundaries [25,26,29,[33][34][35][36][37]. The phase transformation during continuous precipitation is mainly described as the sequential or simultaneous processes of nucleation, growth and impingement [13,15,17].…”

“…Discontinuous precipitation is described by Sundquist, Cahn, Hillert, Turnbull or Petermann-Hornbogen models [25,[33][34][35][36] whereas continuous precipitation by the Austin and Ricket (A-R) [19,25,27] data. equation or the well-known Avrami equation, which is also known as the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation [13,18].…”

Recent Developments on Discontinuous Precipitation

“…6 is the value of Cahn parameter equal to 2, such value was not obtained from any microanalytical scans performed across the α lamellae at 428 K [8]. Other issues associated with DP like influence of jerky motion on the solute concentration profiles across the α lamellae [9], the importance of the solute drag effect at the moving RF [10] were thoroughly discussed by Zieba [11] and conclusions taken are invitation for the further research. Finally, in the paper by Klinger, Brechet and Purdy [12] dealing with discontinuous homogenization in multilayers, the interesting case was taken into account.…”

Discontinuous precipitation of β-Ru phase in Ni–18Ru alloys

“…The transition between the two states shown in Fig. 3a, b requires the recrystallization of the a phase in the regions between the b-Ru nuclei [12], and such discontinuous precipitation processes are normally thought to proceed by rapid short-range diffusion at the resultant incoherent interface(s) between the colony and the adjacent undecomposed matrix grains (e.g., [13,14]). Thus, the supersaturated matrix remains unchanged until swept over by the incoherent transformation front [10,11].…”

“…Although the findings presented here demonstrate that the strength (and indeed the homogeneity) of the Ni-18Ru alloy can be improved dramatically by homogenization and aging, the fact that the precipitation is discontinuous may limit the ability to tailor the properties of the alloy further. Since the precipitation initiates at a small number of potent grain boundary nucleation sites, the only way in which the microstructure can be refined further without changing the precipitation mechanism is to reduce the temperature to limit diffusion at the incoherent transformation front (e.g., [13,14]). Our attempts to exploit this effect by reducing the aging temperature to 550, 500, and 450°C were thwarted because there was little effect on the interlamellar spacing but a profound reduction in the overall transformation rate so that unfeasibly long aging times were required for the supersaturated a phase to decompose completely (data not shown here).…”