The precipitation of θ' at high-angle boundaries in an Al-Cu alloy

✍ Scribed by D Vaughan

• Publisher: Elsevier Science
• Year: 1970
• Weight: 678 KB
• Volume: 18
• Category: Article
• ISSN: 0001-6160
• DOI: 10.1016/0001-6160(70)90082-9

✦ Synopsis

In the AI-Cu system precipitates of the intermediate 0' phase generally nualeate at low-angle boundaries and precipitates of the equilibrium 0 phase form at high-angle boundaries. A few exceptions oocur where 8' precipitates form at high-angle boundaries and these have been studied by transmission electron microscopy.

The determination of the crystallographia parameters of these boundaries by electron diffraction showed that they are normal high-angle boundaries.

It is believed that they are special boundaries only in the sense that 8' precipitates which nucleate on them can form low energy interfaces with both grains. This will reduce the free energy required to form a 8 nucleus of critical size at the boundary and it is suggested that in these eircumst~ces this energy might be less than that required to form a B nucleus. Two types of precipitate morphology have been observed both of which grow predominantly into one grain. It is shown that in each case growth into the other grain is restricted by the presence of a planar interface of low mobility which is almost parallel to the boundary plane.