Amorphous Particles Embedded in hcp Mg Grains of Melt-Quenched Mg_<98>Cu_1Gd_1 Alloys
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Unique precipitates with novel structures have been found in melt-quenched (MQ) Mg<SUB>98</SUB>Cu<SUB>1</SUB>Gd<SUB>1</SUB> alloys by transmission electron microscopy (TEM). Amorphous spherical particles with 50–200 nm sizes are uniformly embedded in Mg grains of an MQ Mg<SUB>98</SUB>Cu<SUB>1</SUB>Gd<SUB>1</SUB> alloy prepared with a relatively higher cooling rate. So-called <I>LAL</I> precipitates, which consist of an amorphous core sandwiched by long period stacking (LPS) phase, are formed in an MQ Mg<SUB>98</SUB>Cu<SUB>1</SUB>Gd<SUB>1</SUB> alloy prepared with a lower cooling rate. TEM observations show that <I>LAL</I> precipitates transform into LPS phases by annealing above 450 K. DSC results show that amorphous cores in <I>LAL</I> particles and amorphous particles crystallize at around 450 K, and partial melting of the LPS phase occurs at around 710 K prior to the melting of the Mg matrix. The composition of amorphous particles is 68 at%Mg, 26 at%Cu and 6 at%Gd, which is close to that having the highest glass forming ability (Mg<SUB>65</SUB>Cu<SUB>25</SUB>Gd<SUB>10</SUB>). Limited solubility of Cu and Gd in Mg and large negative mixing enthalpy between Cu and Gd are responsible for the formation of unique precipitates in rapidly solidified Mg-Cu-Gd alloys.
- Materials Transactions, JIM
Materials Transactions, JIM 49(2), 387-389, 2008-02-01
The Japan Institute of Metals and Materials