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<p>Functionally graded materials (FGMs) offer a practical route for integrating the low density and deformability of aluminum with the hardness and dimensional stability of alumina. However, in Al-Al<sub>2</sub>O<sub>3</sub> FGMs, densification is often limited by particle-scale packing incompatibility, disrupted metallic continuity, and route-sensitive pore retention, particularly in transition layers. This study compares the metallurgical response of a five-layer Al-Al<sub>2</sub>O<sub>3</sub> functionally graded pellet fabricated by sequential powder stacking and consolidated by vacuum sintering and spark plasma sintering (SPS). The pellet architecture consisted of 100/0, 75/25, 50/50, 25/75, and 0/100 Al/Al<sub>2</sub>O<sub>3</sub> layers. Powder size distribution, X-ray diffraction, SEM, porosity, density, microhardness, and compression behavior were used to establish a processing-structure–property relationship. Both routes preserved the designed five-layer architecture and retained the dominant FCC Al and α-Al<sub>2</sub>O<sub>3</sub> phases without evidence of major reaction-driven phase transformation. Vacuum sintering produced a non-linear porosity profile of 9.12, 15.26, 10.26, 16.23, and 15.36% across Layers 1–5, whereas SPS yielded 5.32, 7.23, 10.23, 13.35, and 15.28%, indicating a reduced tendency for pronounced pore accumulation in the transition layers. Layer-wise porosity analysis showed that SPS reduced pore retention in the Al-rich and intermediate layers compared with vacuum sintering, although the ceramic-rich layer remained difficult to densify under both routes. Vacuum sintering generated a hardness increase from 44.6 to 703.0 HV0.1, while SPS increased hardness from 57.8 to 624.7, with greater improvement in the Al-rich and intermediate layers. Under compression, the SPS pellet reached a peak stress of 114.3&#xa0;MPa at 17.0% strain, whereas the vacuum-sintered pellet reached 85.4&#xa0;MPa at 13.47% strain. The SPS specimen also retained higher residual stress at the end of the test, indicating improved load-bearing stability. Within this exploratory comparison, SPS showed a more favorable densification response by reducing porosity in selected Al-rich and transition layers and improving compressive load-bearing stability under the tested conditions.</p>

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Comparative Densification, Microstructure, and Mechanical Response of Five-Layer Al-Al2O3 Functionally Graded Materials Processed by Vacuum Sintering and Spark Plasma Sintering

  • 期刊论文

  • 发表日期：

    2026年7月16日

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  • Satyasaibaba Pitta,
  • Ranga Janardhana Ginka,
  • Balakrishna Bhanavathu

摘要

Functionally graded materials (FGMs) offer a practical route for integrating the low density and deformability of aluminum with the hardness and dimensional stability of alumina. However, in Al-Al2O3 FGMs, densification is often limited by particle-scale packing incompatibility, disrupted metallic continuity, and route-sensitive pore retention, particularly in transition layers. This study compares the metallurgical response of a five-layer Al-Al2O3 functionally graded pellet fabricated by sequential powder stacking and consolidated by vacuum sintering and spark plasma sintering (SPS). The pellet architecture consisted of 100/0, 75/25, 50/50, 25/75, and 0/100 Al/Al2O3 layers. Powder size distribution, X-ray diffraction, SEM, porosity, density, microhardness, and compression behavior were used to establish a processing-structure–property relationship. Both routes preserved the designed five-layer architecture and retained the dominant FCC Al and α-Al2O3 phases without evidence of major reaction-driven phase transformation. Vacuum sintering produced a non-linear porosity profile of 9.12, 15.26, 10.26, 16.23, and 15.36% across Layers 1–5, whereas SPS yielded 5.32, 7.23, 10.23, 13.35, and 15.28%, indicating a reduced tendency for pronounced pore accumulation in the transition layers. Layer-wise porosity analysis showed that SPS reduced pore retention in the Al-rich and intermediate layers compared with vacuum sintering, although the ceramic-rich layer remained difficult to densify under both routes. Vacuum sintering generated a hardness increase from 44.6 to 703.0 HV0.1, while SPS increased hardness from 57.8 to 624.7, with greater improvement in the Al-rich and intermediate layers. Under compression, the SPS pellet reached a peak stress of 114.3 MPa at 17.0% strain, whereas the vacuum-sintered pellet reached 85.4 MPa at 13.47% strain. The SPS specimen also retained higher residual stress at the end of the test, indicating improved load-bearing stability. Within this exploratory comparison, SPS showed a more favorable densification response by reducing porosity in selected Al-rich and transition layers and improving compressive load-bearing stability under the tested conditions.