Effects of Nb/Ti additions and heat treatment on the microstructure evolution and hardness of as-cast and directionally solidified NiAl–Cr(Mo) alloy
Effects of Nb/Ti additions and heat treatment on the microstructure evolution and hardness of as-cast and directionally solidified NiAl–Cr(Mo) alloy
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DOI：
10.1016/j.jmrt.2020.12.089
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发表时间：
2021
期刊：
影响因子：
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通讯作者：
Z. Shang;Qianwei Zhang;Jun Shen;H. Bai;Xiao Dong;Wen-Shan Bai;L. Zhong;Gang Liu;Yunhua Xu
中科院分区：
文献类型：
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作者：
Z. Shang;Qianwei Zhang;Jun Shen;H. Bai;Xiao Dong;Wen-Shan Bai;L. Zhong;Gang Liu;Yunhua Xu
研究了Nb、Ti的加入和热处理对铸态和定向凝固NiAl-Cr(Mo)合金组织演变和硬度的影响。Nb主要固溶于Cr(Mo)相中，而Ti主要固溶于NiAl相中。形成了Cr2Nb和Ni2AlTi析出相，主要分布在晶胞边界。随着Nb含量的增加，初生Cr(Mo)相显著增多，不再出现枝晶组织。共晶耦合生长受到抑制，片层组织变得不规则。定向凝固NiAl-Cr(Mo)-Nb和NiAl-32Cr-6Mo-1Ti-1Nb合金完全共晶组织中没有初生Cr(Mo)相，定向凝固NiAl-32Cr-6Mo-3Ti-3Nb合金中有枝晶组织。热处理后，Nb和Ti重新分布。共晶组织变得相对均匀，析出相变得细小弥散。Nb和Ti的加入通过固溶强化和析出强化提高了合金的硬度。随着Nb含量的增加，硬度进一步增加。定向凝固合金的硬度高于铸态合金，这是由于定向凝固合金组织规则所致。热处理后，由于显微组织形态和相分布的变化，特别是NiAl析出物的粗化和Cr(Mo)相中位错的存在，所有合金的硬度都有所下降。
The effects of the addition of Nb and Ti and heat treatment on the microstructure evolution and hardness of the as-cast and directionally solidified NiAl–Cr(Mo) alloy were studied. Nb mainly solubilizes in the Cr(Mo) phase while Ti basically solubilizes in the NiAl phase. Precipitated phases of Cr2Nb and Ni2AlTi are formed and mainly distributed at the cell boundary. With the increasing Nb content, the primary Cr(Mo) phase increases significantly and does not show dendritic morphology. The eutectic coupled growth is suppressed and the lamellar microstructure becomes irregular. Fully eutectic microstructure with no primary Cr(Mo) phase is obtained in the directionally solidified NiAl–Cr(Mo)–Nb and NiAl–32Cr–6Mo–1Ti–1Nb alloys while dendrites + eutectic is observed in the directionally solidified NiAl–32Cr–6Mo–3Ti–3Nb alloy. After heat treatment, Nb and Ti are redistributed. The eutectic microstructure becomes relatively uniform and the precipitated phases become fine and dispersed. The addition of Nb and Ti can increase the hardness of the alloy due to the solid solution strengthening and precipitation strengthening. As the Nb content increases, the hardness further increases. The hardness of the directionally solidified alloys is higher than the as-cast alloys attributing to the regular microstructure. After heat treatment, the hardness of the all alloys decreases due to the varying microstructure morphology and phase distribution, especially the coarsening of NiAl precipitates and the existence of dislocations in Cr(Mo) phase.