Heterogeneous nucleation of β-type precipitates on nanoscale Zr-rich particles in a Mg-6Zn-0.5Cu-0.6Zr alloy
Zirconium (Zr) is an important alloying element to Mg-Zn-based alloy system. In this paper, we report the formation of the β-type precipitates on the nanoscale Zr-rich particles in a Mg-6Zn-0.5Cu-0.6Zr alloy during ageing at 180°C. Scanning transmission electron microscopy examinations revealed that the nanoscale Zr-rich [0001]α rods/laths are dominant in the Zr-rich core regions of the as-quenched sample after a solution treatment at 430°C. More significantly, these Zr-rich particles served as favourable sites for heterogeneous nucleation of the Zn-rich β-type phase during subsequent isothermal ageing at 180°C. This research provides a potential route to engineer precipitate microstructure for better strengthening effect in the Zr-containing Mg alloys.
Structural characteristics of β1′ precipitates in Mg–Zn-based alloys
β 1 ′ precipitates in an Mg 97 Zn 2.5 Y 0.5 alloy are shown to have a complex domain structure based on the structure of monoclinic Mg 4 Zn 7 phase. All domains are oriented with [0 1 0]∥[0 0 0 1] Mg and one of the four planar matches with the matrix. Two of these orientations are related to two others by twinning on the (0 0 1) plane of the Mg 4 Zn 7 phase. These orientations are brought about by crystallographic constraints from the matrix. An ordering of the domains creates a new structure.
The fine structure F. C. C. /B. C. C. boundaries in a Cu-0. 3% Cr alloy
Abstract The interfacial structures of overaged b.c.c. precipitates in a Cu-0.3%Cr alloy have been studied with transmission electron microscopy using weak-beam and lattice imaging techniques and the results have been compared with theoretical structures obtained with the “O”-lattice calculation. Lattice imaging showed that one set of close-packed planes in the structures were accurately parallel and using normal diffraction and Kikuchi line measurements the precipitates were observed to have a range of orientation relationships varying from Nishiyama-Wasserman to Kurdjumov-Sachs and beyond. All precipitates showed at least one fine dislocation array with spacings f.c.c. habit plane of the lath precipitate was also obtained.