Abstract
In this research, the 2nd part of a series of papers on the processing and characterization of TiAl–Ti3AlC2 composites, the phase evolution during the manufacturing process was investigated by X-ray diffraction (XRD) analysis and Rietveld refinement method. Metallic Ti and Al powders with different amounts of previously-synthesized Ti3AlC2 additives (10, 15, 20, 25 and 30 wt%) were ball-milled and densified by spark plasma sintering (SPS) under 40 MPa for 7 min at 900 °C. Before the sintering process, XRD test verified that the powder mixtures contained metallic Ti and Al as well as Ti3AlC2 and TiC (lateral phase synthesized with Ti3AlC2) phases. In the sintered composites, the in-situ synthesis of TiAl and Ti3Al intermetallics as well as the presence of Ti3AlC2 and the formation and Ti2AlC MAX phases were disclosed. The weight percentage of each phase in the final composition of the samples and the crystallite size of different phases were calculated by the Rietveld refinement method based on the XRD patterns. The size of Ti3AlC2 crystallites in sintered samples was compared with the crystallite size of synthesized Ti3AlC2 powder.
Highlights
TiAl-based composites have gained researcher’s attentions because of their unique characteristics including low density, high melting point, as well as excellent corrosion properties, good creep and oxidation resistance [1,2,3,4,5,6]
The first three ones, the metallic and MAX phases, were added directly to the powder mixture, but the detection of the TiC was due to impurities along with the synthesized Ti3AlC2 phase
Our previous published report and calculations [40], using the Rietveld refinement method, showed that the purity of the Ti3AlC2 phase synthesized in our laboratory was 85 wt%, and the presence of about 15 wt% TiC in the MAX phase is cognizable
Summary
TiAl-based composites have gained researcher’s attentions because of their unique characteristics including low density, high melting point, as well as excellent corrosion properties, good creep and oxidation resistance [1,2,3,4,5,6]. Low-temperature ductility and weak formability of TiAl matrix materials have led to limitation of their application and development [7,8,9,10]. Different tricks such as choosing appropriate manufacturing method and addition of reinforcements have been used to dominate such shortcomings [11,12,13]. Protective surface layer formation of Al2O3 as a result of adding Nb or Ta to TiAl matrix improved oxidation resistance at high temperatures [25]. It is reported that Ru has an effective impact on both ductility and strength of TiAl materials through grain refinement mechanism [28]
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