High temperature compressive behavior of dense Cr2AlC and Ti3AlC2 Max phases obtained by SPS (reactive) sintering

Marteleur, Matthieu [UCL] Jacques, Pascal [UCL] et al.

Ternary layered compounds of transition metal carbides and nitrides, commonly known as MAX phase materials with the general formula of Mn+1AXn (M being an early transition metal, A being a group IIIA or IVA element, X being either C or N, and n=1-3) offer a unique combination of metal and ceramic properties. In the present work, the high temperature compressive behavior of dense compacts of Cr2AlC and Ti3AlC2 MAX phases has been assessed in the temperature range 800-1000 °C. In the case of Cr2AlC, the compacts were obtained by SPS sintering a relatively high purity powder (CroMAX) for 5 min at 1200 °C under 50 MPa. In the case of Ti3AlC2, high purity (i.e. > 95%) dense compacts have been obtained by reaction SPS sintering for 15 min at 1325 °C under 15 MPa a TiC/Al/Ti powder mixture of molar composition 1:1,1:1. Prior to the mechanical characterization, the microstructure of the investigated compacts has been has been assessed by FIB-SEM-EBSD analysis. The typical microstructure of the Ti3AlC2 samples consisted of plate like grains with average size of 2-4 µm and length of 15-20 µm, that of Cr2AlC samples consisted of equiaxed grains with average size of 8-10 µm with traces of Cr7C3 and Al2O3. In both materials, only a slight degree of preferential crystallographic orientation was observed in the as sintered compacts resulting from the uniaxial loading in the SPS. The assessment of the high temperature compressive behavior has been carried out by plasto-dilatometry. Cylindrical and parallelepiped samples were machined from SPS compacts by EDM. Samples were heated with a heating rate of 4°C/s by induction under vacuum. After stabilization, samples were deformed with a displacement rate of 0.01 mm/s up to various strain levels. The first results show that the flow stress of the material is significantly affected by the macroscopic deformation mode activated. On one hand, plastic deformation starts at very low flow stress under the occurrence of barreling, while on the other hand a high stress level is required when deformation occurs by shear banding. Finally, analysis of the damage level and mechanism in increasingly deformed samples were performed and discussed.