MICROSTRUCTURE AND COMPRESSIVE PROPERTY OF Ni3Al ALLOYS

This paper investigated the microstructure and compressive property of cast NisAl alloys produced by button furnace and vacuum induction melting (VIM) furnace, as well as annealed NisAl produced by VIM. The phase structure, microstructure and characteristic of fracture were analyzed by means of X-ray diffraction, optical microscopy, scanning election microscopy (SEM) and transition electron microscopy (TEM). By means of kikuchi couples, characteristic distribution of boundaries in cast NiaAl alloys produced by button furnace was analyzed. The results showed that:There was a lot of dislocation and stacking fault (SF) in cast NisAl alloys produced by button furnace. The distinct characteristic of dislocation was that there were all-pervading dislocation walls built up of low angle boundaries (LAB) that had not clear relative orientation. In NiaAl, SF was mostly complex stacking fault (CSF) produced by shear of 眎/6[Ti2] and?i / 6[i2i ] -High density of dislocation was the result of supersaturated voids and heat stress.Analysis of relative orientation by kikuchi couples showed that grain boundaries were mostly composed of high angle boundaries (HAB). For #l-Ni74.7Ah5.3, the percentage for LAB was 16.7in the cross sections, 41.7 ininthe vertical sections; for #!-Ni76.iAl23.9, the percentage for LAB was 12.5 and 37.5 respectively.Compression test showed that yield strength a 0.2 and compression strength o b as well as compression ration ?increased with increasing Al contents. At the same time, fracture mode changed from Vertical fracture to shear fracture. After homogenizing of Ni3 Al, yield strength o 0 2 increased, and compression strength o b as well compression ration e reduced. Brittleness of Ni3Al increased somewhat after homogenizing. The major cause for these changes was that the percentage for LAB increased and cross slip became easier as a result of decreasing stacking energy with increasing Al contents.With regard to the disputed Ni-Al two-phase diagram, we took figure 5-2 for granted on basis of our experiments. In the peritectic reaction, L and y phases transformed into Y -Ni3Al at 1382.3癈; In the eutectic reaction, L transformed into Y '-Ni3Al and 0 -NiAl at 1381.4癈. About 1378癈, 23.5-23.88at.%A1 was in the Y -Ni3Al phase region.