摘要
The microstructural evolution of a 18R single phase （S 18） alloy during annealing at 773 K for 100 h was investigated in order to reveal the formation mechanism of 14H phase. The results showed that the as-cast S 18 alloy was composed of 18R phase （its volume fraction exceeds 93%）, W particles and α-Mg phase. The 18R phase in S18 alloy was thermally stable and was not transformed into 14H long period stacking ordered （LPSO） phase during annealing. However, 14H lamellas formed within tiny α-Mg slices, and their average size and volume fraction increased with prolonging annealing time. Moreover, the 14H phase is nucleated within α-Mg independently on the basis of basal stacking faults （SFs）. The broadening growth of 14H lamellas is an interface-controlled process which involves ledges on basal planes, while the lengthening growth is a diffusion-controlled process and is associated with diffusion of solute atoms. The formation mechanism of 14H phase in this alloy could be explained as α-Mg＇→α-Mg＋14H.
为了揭示14H相的形成机理,制备并研究了18R LPSO单相Mg-Y-Zn(简称S18)合金经773 K退火100 h的显微组织演变。结果表明:铸态S18合金主要由18R相组成(其体积分数高于93%),并含有少量的W相和α-Mg相。退火时,S18合金中的18R相保持稳定,未转变成14H LPSO结构。然而,在α-Mg相内部形成了14H层片相,其尺寸和体积分数随着退火时间的延长不断增大。TEM分析表明,14H相在α-Mg内基面堆垛层错区域独立形核。14H层片的增厚生长是界面控制过程,与基面台阶的形成密切联系。而14H层片的伸长生长属于扩散控制,与溶质元素的扩散有关。该18R单相合金中14H相的形成机理可通过反应式α-Mg'→α-Mg+14H表示。
基金
Project(BK20160869)supported by the Natural Science Foundation of Jiangsu Province,China
Project(GY12015009)supported by the Nantong Science and Technology Program,China
Project(2015B01314)supported by the Fundamental Research Funds for the Central Universities,China
Project(51501039)supported by the National Natural Science Foundation of China
