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<p>This study systematically investigated the microstructural evolution of binary Ni-Cu alloys (Cu55Ni45, Cu60Ni40, and Ni65Cu35) under deep undercooling conditions. The controlled rapid solidification experiments combined with optical microscopy and electron backscatter diffraction (EBSD) analysis demonstrate that increasing undercooling (Δ<i>T</i>) can induce a consistent sequence of microstructural transitions: coarse dendrites, fine equiaxed grains (first refinement), oriented fine dendrites, and fine equiaxed grains (second refinement). Two distinct grain refinement events are identified, with critical undercooling thresholds (Δ<i>T</i>) dependent on composition: increasing Cu content increases the critical undercooling Δ<i>T</i>* required for the second refinement (Cu55Ni45: 227 K; Cu60Ni40: 217 K; Ni65Cu35: 200 K). The BCT (Bridgman Crystal Growth) model quantitatively elucidates this behavior, revealing a shift from solute-diffusion-dominated growth at low undercooling to thermally dominated diffusion at high undercooling (Δ<i>T</i>). Crucially, refined grains at high undercooling exhibit smaller sizes (10 µm) and higher uniformity than those at low undercooling (20 µm). These findings provide fundamental insights into non-equilibrium solidification mechanisms and establish a foundation for designing high-performance Ni-Cu alloys via deep undercooling processing.</p>

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Microstructural Evolution of Rapidly Solidified Ni-Cu Alloys

  • 期刊论文

  • 发表日期：

    2025年11月27日

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  • Shuwei Qu,
  • Zejun Li,
  • Hongfu Wang,
  • Xiaoguang Tian,
  • Zhike Qian,
  • Ruiqin Li,
  • Wei Yao

摘要

This study systematically investigated the microstructural evolution of binary Ni-Cu alloys (Cu55Ni45, Cu60Ni40, and Ni65Cu35) under deep undercooling conditions. The controlled rapid solidification experiments combined with optical microscopy and electron backscatter diffraction (EBSD) analysis demonstrate that increasing undercooling (ΔT) can induce a consistent sequence of microstructural transitions: coarse dendrites, fine equiaxed grains (first refinement), oriented fine dendrites, and fine equiaxed grains (second refinement). Two distinct grain refinement events are identified, with critical undercooling thresholds (ΔT) dependent on composition: increasing Cu content increases the critical undercooling ΔT* required for the second refinement (Cu55Ni45: 227 K; Cu60Ni40: 217 K; Ni65Cu35: 200 K). The BCT (Bridgman Crystal Growth) model quantitatively elucidates this behavior, revealing a shift from solute-diffusion-dominated growth at low undercooling to thermally dominated diffusion at high undercooling (ΔT). Crucially, refined grains at high undercooling exhibit smaller sizes (10 µm) and higher uniformity than those at low undercooling (20 µm). These findings provide fundamental insights into non-equilibrium solidification mechanisms and establish a foundation for designing high-performance Ni-Cu alloys via deep undercooling processing.