Duplex phase hexagonal-cubic multi-principal element alloys with high hardness

Abstract

We report on the influence of Mn additions on the microstructure and properties of (CoCrCuTi)100−xMnx multiprincipal element alloys (MPEAs) containing 5, 10, 15, and 20% Mn prepared by arc-melting. It was observed that the alloys containing less than 10 at.% Mn contained BCC dendrites and a Cu-rich face centered cubic (FCC) interdendritic matrix. In contrast, alloys containing Mn ≥ 10 at.%, consisted of a hexagonal dendritic Laves phase (C14, hexagonal, P63/mmc) with small amounts of Cr-rich and Ti-rich dendrites, and a Cu-rich FCC interdendritic matrix. Isopleths of the CoCrCuMnTi system were generated using the ThermoCalc software with TCHEA3 database in order to elucidate phase formation in these alloys. In addition, the particular composition Co22Cr18Cu20Mn16Ti24 was found to consist of Laves C14 phase hexagonal dendrites in a Cu-rich FCC interdendritic matrix with very small dispersed Ti-rich dendrites. Selected area electron diffraction of the dendritic phase in Co22Cr18Cu20Mn16Ti24 was found to have lattice parameters approximated to be a = 4.8Å and c = 7.5Å based on fitting the d-spacing of the indexed patterns to previously published data on the Cr2Ti intermetallic phase. The Vickers mircohardness of the hexagonal dendritic phase of Co22Cr18Cu20Mn16Ti24 was found to be 996.6 ± 57.2 HV 0.01, while the Cu-rich interdendritic matrix has hardness of 457.3 ± 7.0 HV 0.01 and overall hardness of both regions equaling 480.2 ± 21.4 HV 1. The overall Rockwell hardness was found to be 43 ± 2 HRC. The compressive strength of Co22Cr18Cu20Mn16Ti24 was measured to be 1430 MPa, while wear rate was measured as 2.64 × 10−5 mm3/m·N.