快速凝固Al—Li─Cu—Mg—Zr合金中H相和Z相的TEM研究

TEM STUDY OF H AND Z PHASES IN RAPIDLY SOLIDIFIED Al-Li-Cu-Mg-Zr ALLOY

用ＨＲＴＥＭ、ＴＥＭ及ＥＤＡＸ分析研究了Ａｌ─Ｌｉ—Ｃｕ—Ｍｇ—Ｚｒ合金中的一种新相（暂名Ｈ相）和六角Ｚ相的结构，确定Ｈ相具有四方点阵，点阵参数为α＝２．８ｎｍ，ｃ＝２．４ｎｍ，ＥＤＡＸ分析表明Ｈ相和Ｚ相均含Ａｌ、Ｍｇ、Ｃｕ发现Ｈ相与Ｚ相的共存取向关系为［１００］‖［１１２０］Ｚ，［１０１０］Ｈ‖［０００１］Ｚ。

luminum-Lithium alloys is of considerate interest to the aerospace community due to their high strengths and stiffness. Basic research in the Al-Li based systems was stimulated once more since the icosadral quasicrystal T2-A16Cu3Li was observed in the Al-Li-Cu alloys. Recently,the defect structures of several new stable intermetallic compounds in the vicinity A10.6(Cu,Zn)0. 1(Li,Mg)0.3, namely the so-called R, Z, C andτ phasaes, as well as the relations among them, have been studied in detail due to their intimate structural relation to T2 quasicrystal phase. A special rotation domain in Z phase was observed in our experiment. Other new intermetallic phases possessing similar structural units with R, Z, C and τ phases should form, resulting from many elements and complex phase compositions,especially the adoption of rapidly solidification technique in our exprimental alloy, and this paper also reports a new tetragonal H phase possessing a intimate structural relation with Z phase.The detailed analysis to the sequence of SAD patterns, which was taken by rotating H phase around the [010] * axis from the [001] zone,displays that H phase belongs to a tetragonal lattice with parameters of a=2.8num, c=2.4nm, c / a=0.866. From the HREM image showing the coexistence of H and Z phases, an orientation relationship between the two phases can be given by:[100]H.‖ [1120]z. [010]H.‖[0001]Z. and no obvious phase interface between them could be detected.A plenty of experiments on the speimen display that Z phase of larger size appears relatively more frequently than H phase of smaller size coexisting with Z phase, and EDAX energy sacrum quantitative analysis shows that both of them contain with some elements such as Al, Cu, Mg of similar content to each other, so it is reasonable that H phase aught be the metastable phase corresponding to Z phase.A particular 90°rotation domain structure exists in Z phase and the domain boundary is apparent to ie relatively flat. HREM image displays that the orientation relationship between two domains in z phase could be described as [0001]A ‖[1120]B. [1100]A‖[1100]B, coinciding with the interfaCe on (1100)A‖(1100)B. In fact the domain 'A' is linked with 'B' by 90°with each other around the [1100]B. direction. The absence of any defeCt structure inside 'A' and 'B', and coherency at the interface, indicates that the length of the c axis should be that of the a axis for the hexagonal Z phase.