Synthesis and elastic and mechanical properties of Cr2GeC

Herein we report on the synthesis and characterization of Cr2GeC, a member of the so-called M(n+1)AX(n) (MAX) phase family of layered machinable carbides and nitrides. Polycrystalline samples were synthesized by hot pressing pure Cr, Ge, and C powders at 1350 degrees C at similar to 45 MPa for 6 h. No peaks other than those associated with Cr2GeC and Cr2O3, in the form of eskolaite, were observed in the x-ray diffraction spectra. The samples were readily machinable and fully dense. The steady-state Vickers hardness was 2.5 +/- 0.1 GPa. The Young's moduli measured in compression and by ultrasound were 200 +/- 10 and 245 +/- 3 GPa, respectively; the shear modulus and Poisson's ratio deduced from the ultrasound results were 80 GPa and 0.29, respectively. The ultimate compressive strength for a similar to 20 mu m grain size sample was 770 +/- 30 MPa. Samples compressively loaded from 300 to similar to 570 MPa exhibited nonlinear, fully reversible, reproducible, closed hysteretic loops that dissipated similar to 20% of the mechanical energy, a characteristic of the MAX phases, in particular, and kinking nonlinear elastic solids, in general. The energy dissipated is presumably due to the formation and annihilation of incipient kink bands. The critical resolved shear stress of the basal plane dislocations-estimated from our microscale model-is similar to 22 MPa. The incipient kink band and reversible dislocation densities, at the maximum stress of 568 MPa, are estimated to be 1.2 x 10(-2) mu m(-3) and 1.0 x 10(10) cm(-2), respectively.