Microstructure and mechanical properties of AlCoCrNiTi-C High Entropy Alloy processed through Spark Plasma Sintering

AlCoCrNiTi-C High Entropy Alloy (HEA) fabricated through mechanical alloying (10 h) and Spark Plasma Sintering (SPS) at 1000 degrees C develops a mixture of NiAl B2 phase, Cr rich phase and fine TiCs. Transmission Electron Microscope (TEM) images before and after milling confirms the presence of BCC phases in the alloy. Carbon Hydrogen and Nitrogen (CHN) analysis reveal the presence of carbon content in milled powders after 10 h. Back Scattered Electron (BSE) images and elemental mapping indicates the presence of TiCs along grain boundaries of NiAl B2 phase. Microstructural characterization before and after heat treatments reveals the fact that there is an increase in the volume fraction of Cr rich phase. Moreover the alloy develops a good room temperature compressive strength of 2750 +/- 4.3 MPa, high temperature strength of 871 +/- 3.1 MPa at 800 degrees C along with micro hardness of 860 +/- 7.8 HV0.5. Nano indentation results shows that the major contribution to hardness and strength comes from NiAl phase which has a value of 10.2 +/- 2.1 GPa. Enhanced properties of the alloy can be attributed to the presence of NiAl B2, disordered Cr rich BCC phase along with fine TiCs.

Automated summary

AlCoCrNiTi-C High Entropy Alloy processed through mechanical alloying and Spark Plasma Sintering shows a mixture of NiAl B2, Cr rich phase, and TiC. The alloy exhibits good room temperature and high temperature strength, with hardness primarily contributed by the NiAl phase.