Al-Ni-Y三元共晶合金高压凝固组织

利用光学显微镜,扫描电镜,X射线衍射仪对不同压力(2,4,6 GPa)下凝固的Al-1Ni-3Y(%,原子分数)共晶合金组织形貌和相组成进行研究,并且与常压条件下合金凝固组织进行对比。实验结果表明,与常压凝固相比,在超高压力条件下凝固的合金的显微组织形貌发生了很大的改变,但是合金的相组成没有发生变化。常压凝固的合金具有共晶团组织,而高压下凝固的合金具有枝晶状亚共晶组织。高压凝固合金显微组织中出现了大量的初生α-Al相,这表明高压条件下凝固的合金共晶点发生偏移,使得常压共晶成分的合金在高压下变成亚共晶成分合金。同时,共晶组织的形貌发生了很大变化,常压下凝固的合金的组织为Al3Y相与α-Al相形成的菊花状的二元共晶和Al23Ni6Y4相与α-Al相形成的层片状的二元共晶,而高压下这两种共晶组织逐渐转化为离异共晶组织。随着压力的增大,共晶第二相的体积分数减小,α-Al的晶格常数增加。

Solidification Microstructure of Ternary Eutectic Al-Ni-Y Alloy under High Pressure

The eutectic microstructure and phase constituents of ternary eutectic Al-1Ni-3Y(%,atom fraction) alloy solidified under different high pressures(2,4,6 GPa) were analyzed by X-ray diffraction,OM and SEM,and compared with that of the alloy solidified under normal pressure.The results suggested that the microstructures changed,but the phase constituents did not change in the alloy solidified under high pressure compared to that solidified under normal pressure.A transition of the microstructure from eutectic to dendritic hypoeutectic could be observed in the alloy solidified under high pressure.The microstructure of the alloy solidified under high pressure contained a lot of primary α-Al,which suggested that the eutectic point of Al-Ni-Y alloy under high pressure shifted towards the Ni and Y directions in the phase diagram compared with that under normal pressure.Two kinds of two-phase eutectic structure could be observed in the alloys solidified under normal pressure as follows: one was chrysanthemum-like two-phase eutectic structure consisted of Al3Y phase and α-Al phase;the other was lamellar two-phase eutectic structure that consisted of Al23Ni6Y4 phase and α-Al phase.But these two kinds of two-phase eutectic structure transformed to divorced eutectic gradually with the increasing solidification pressure.The volume fraction of the second-phase decreased and the crystal lattice parameter of α-Al increased with the solidification pressure increasing.