Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN, 37996-2200, USA.
Lujan Center, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
Sci Rep. 2017 Apr 7;7:45965. doi: 10.1038/srep45965.
The ferritic Fe-Cr-Ni-Al-Ti alloys strengthened by hierarchical-NiTiAl/NiAl or single-NiTiAl precipitates have been developed and received great attentions due to their superior creep resistance, as compared to conventional ferritic steels. Although the significant improvement of the creep resistance is achieved in the hierarchical-precipitate-strengthened ferritic alloy, the in-depth understanding of its high-temperature deformation mechanisms is essential to further optimize the microstructure and mechanical properties, and advance the development of the creep resistant materials. In the present study, in-situ neutron diffraction has been used to investigate the evolution of elastic strain of constitutive phases and their interactions, such as load-transfer/load-relaxation behavior between the precipitate and matrix, during tensile deformation and stress relaxation at 973 K, which provide the key features in understanding the governing deformation mechanisms. Crystal-plasticity finite-element simulations were employed to qualitatively compare the experimental evolution of the elastic strain during tensile deformation at 973 K. It was found that the coherent elastic strain field in the matrix, created by the lattice misfit between the matrix and precipitate phases for the hierarchical-precipitate-strengthened ferritic alloy, is effective in reducing the diffusional relaxation along the interface between the precipitate and matrix phases, which leads to the strong load-transfer capability from the matrix to precipitate.
通过在铁素体 Fe-Cr-Ni-Al-Ti 合金中析出纳米级 NiTiAl/NiAl 或单相 NiTiAl 析出相，开发出了具有分级结构的析出相强化铁素体合金，其抗蠕变性能优于传统铁素体钢，因此受到了广泛关注。虽然在分级析出强化铁素体合金中显著提高了抗蠕变性能，但是深入了解其高温变形机制对于进一步优化微观结构和力学性能，以及推进抗蠕变材料的发展至关重要。本研究采用原位中子衍射技术研究了在 973K 下拉伸变形和应力松弛过程中基体和析出相的弹性应变演变及其相互作用，如析出相与基体之间的载荷传递/载荷松弛行为，这为理解控制变形机制提供了关键特征。采用晶体塑性有限元模拟定性比较了在 973K 下拉伸变形过程中弹性应变的实验演变。结果表明，对于分级析出强化铁素体合金，由于基体和析出相之间的晶格失配而在基体中产生的共格弹性应变场可有效降低沿析出相与基体相界面的扩散松弛，从而导致从基体到析出相的强载荷传递能力。
