This study compares the microstructure and properties of pure Cu and Cu-5 wt.% Al2O3 composites fabricated by spark plasma sintering under strictly identical processing conditions at 800-1000°C. Pure Cu samples achieved near-full densification and exhibited a bimodal grain structure dominated by coarse grains with increasing sintering temperature. In contrast, the composite samples showed lower density and non-monotonic densification behavior, with a minimum relative density at 900°C and significantly refined equiaxed grains due to strong grain-boundary pinning by nano Al2O3 particles. The higher fractions of high-angle boundaries and pronounced orientation disruption were observed in the composite samples, while high-resolution analysis confirmed the presence of grain-boundary Al2O3-rich regions that restricted Cu grain coalescence and continuity of grain boundary migration. X-ray diffraction results confirmed the absence of reaction phases in both materials. Hardness peaked at 900°C for both samples, and the composite samples showed consistently lower hardness due to retained porosity. The apparent electrical conductivity of the composite displays a non-linear temperature dependence, reflecting the competing influences of densification, microstructural recovery, and the insulating nature of Al2O3.

1. Introduction 
2. Experimental Section 
    2.1 Materials and Methods 
    2.2 Characterization 
3. Results and Discussion 
    3.1 Density and microstructure of sintered samples 
    3.2 Mechanical properties and electrical conductivity of sintered samples 
4. Conclusion 
Funding
Conflict of Interest 
Data Availability Statement 
Author Information and Contribution 
Acknowledgments
References

• Dinh Van Cong(School of Materials Science and Engineering, University of Ulsan, Ulsan 44610, Republic of Korea)
• Dong-Wan Lee(School of Materials Science and Engineering, University of Ulsan, Ulsan 44610, Republic of Korea)
• Su-Wan Lee(School of Materials Science and Engineering, University of Ulsan, Ulsan 44610, Republic of Korea)
• Jin-Chun Kim(School of Materials Science and Engineering, University of Ulsan, Ulsan 44610, Republic of Korea) Corresponding author
• Nguyen Minh Thuyet(Faculty of Materials Engineering, School of Materials Science and Engineering, Hanoi University of Science and Technology, Hanoi 100000, Vietnam) Corresponding author
• Nguyen Viet Hoang(Faculty of Materials Engineering, School of Materials Science and Engineering, Hanoi University of Science and Technology, Hanoi 100000, Vietnam)