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B2结构的NiAl具有高熔点、低密度和优异的耐蚀性能,因而有希望成为一类新型的高温结构材料。但低的室温塑性是这类材料走向实用化的主要障碍。采用快速凝固的方法细化晶粒是已知能有效地改善其室温塑性的方法之一。Gaydosh等研究了熔体旋转快速凝固NiAl薄带,性能测试表明NiAl快速凝固后的弯曲断裂应变从铸态的0增加到0.9％～1.3％,进一步在1273K退火1h后应变提高到2.25％,热处理能够明显地提高塑性表明存在其它因素影响快速凝固NiAl合金的塑性,但这一问题却一直未能澄清。近年来,随着长程有序金属间化合物研究的深入,一些研究者相继在快速凝固的强有序化相Ni_3Al,Ti_3Al,FeAl等铝系金属间化合物中发现存在亚稳组织,同样作为强有序化相的NiAl,由于其有序转变的临界温度与液固温度基本重合,因而尚未见在单相成分范围内存在亚稳组织的报道。最近,我们发现接近化学计量的快速凝固NiAl合金中存在亚稳的调幅组织,而这一现象尚未见前人报道。另外,亚稳的调幅组织的发现也使热处理提高快速凝固NiAl合金塑性的现象得到了合理的解释。
B2 structure of NiAl with high melting point, low density and excellent corrosion resistance, and therefore hope to become a new type of high temperature structural materials. However, low room temperature plasticity is a major obstacle to the practical application of this type of material. The use of rapid solidification to refine grains is one of the known methods that can effectively improve the room temperature plasticity. Gaydosh et al. Studied the rapid solidification of NiAl ribbons by melt spinning. The results show that the flexural strain after rapid solidification increases from 0 to 0.9% ~ 1.3% as-cast and further increases to 2.25% after annealed at 1273K for 1h. The ability to significantly improve the plasticity indicates that there are other factors that affect the plasticity of the rapidly solidified NiAl alloy, but this problem has not been clarified. In recent years, along with the research of long-range ordered intermetallic compounds, some researchers have found metastable structures in rapidly solidified ordered intermetallic compounds such as Ni 3 Al, Ti 3 Al and FeAl, NiAl, a ordered phase, has not been reported as a metastable structure in the single-phase composition due to the fact that the critical temperature of its ordered transition substantially coincides with the liquid-solid temperature. Recently, we found metastable AM structures in rapidly solidified NiAl alloys near stoichiometry, a finding not previously reported. In addition, the discovery of a metastable AM system has also led to a reasonable explanation of the fact that the heat treatment increases the plasticity of the rapidly solidified NiAl alloy.