Effect of Mechanical Alloying Time on CoCrFeNiTi High-Entropy Sintered Alloys

High-entropy alloys (HEAs) are promising for advanced structural applications because they can achieve a unique combination of strength, damage tolerance, and environmental resistance.In powder-metallurgy processing routes, mechanical alloying (MA) may introduce carbon contamination, which significantly influences phase evolution and microstructural development.Carbon uptake, phase evolution, and mechanical response in a CoCrFeNiTi HEAs processed by mechanical alloying followed by spark plasma sintering were found to be strongly dependent on MA time.The carbon content in milled powders was quantified by combustion analysis.Phase constitution and lattice parameters were analyzed using X-ray diffraction (XRD), with lattice constants determined by Nelson-Riley extrapolation and crystallite size and lattice strain evaluated by Williamson-Hall analysis.Dislocation density was estimated using a Burgers-vector-based formulation.The sintered compacts were characterized by XRD, scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), electron probe microanalysis (EPMA), and electron backscatter diffraction (EBSD).Mechanical properties were evaluated using micro-Vickers hardness and nanoindentation, from which the performance indices H/E and H 3 /E 2 were derived.Carbon uptake increased monotonically with MA time and tended to saturate at longer milling durations.The milled powders formed a predominantly BCC solid solution after MA, accompanied by crystallite refinement and increased lattice strain/dislocation density.After SPS, the microstructure evolved into an FCC-dominant matrix with TiC-related regions and Cr-rich phases.Grain refinement and increased Geometrically Necessary Dislocations (GND) were observed with longer MA time.Mechanical properties showed a hardness drop at short MA time followed by recovery and stabilization at longer MA time, while nanoindentation-based performance indices suggested an optimal intermediate MAtime window.These results demonstrate that MA time controls not only alloying/defect states but also carbon-mediated precipitation and phase balance, providing a practical guideline for optimizing MA-SPS processing of Ti-containing HEAs.