A study on the microstructure of D023 Al3Zr and L12 (Al+12.5 at.% Cu)3Zr intermetallic compounds synthesized by PBM and SPS

The spark plasma sintering (SPS) of L12 phase Al3Zr and (Al+12.5 at.% Cu)3Zr powders with a nanocrystalline microstructure has been studied to produce bulk intermetallic compounds which maintain metastable structures such as L12 structure and nanocrystalline microstructure. The powders were prepared by 10 h planetary ball milling (PBM). Full-density L12 (Al+12.5 at.% Cu)3Zr intermetallic compounds were obtained by SPS for 0 min at 600 °C. The specimens prepared with a longer holding time than 0 min at 600 °C or a higher temperature than 600 °C had local melting areas where micro-cracks were found. They had a lower relative density than the specimen SPS sintered at 600 °C for 0 min. The smallest grain size was obtained in the specimen prepared at 600 °C for 0 min, which was 20–30 nm as confirmed by TEM observation. This was the smallest grain size ever reported in the trialuminide specimens processed by various consolidations of nanocrystalline powders. Accordingly, the highest micro-hardness, 989.5 HV, was obtained in the specimen and this value was three times higher than those of the specimens with micro grain sizes. Full density Al3Zr intermetallics were prepared by SPS at 700 °C for 0 min. However, their crystal structure was D023 and micro-hardness was 778.1 HV. By using SPS, the sintering time can be reduced within 10 min. It was thought that the decrease in sintering temperature for the PBM Al3Zr and (Al+12.5 at.% Cu)3Zr powders by 200–300 °C compared with the conventional sintering temperature resulted in the refinement of microstructure to the nano-size level.