| The TiAl-Cr alloys compositions were chosen from the γ-phase stability region up to maximum 5 at.% chromium. The elemental powders were initially blended to desired composition of Ti-49Al-49Cr-2 and Ti-48Al-47Cr-5 (numbers indicate at.%). The ball milling process was performed in a high energy planetary mill Fritsch Pulverisette P5/4. Formation of mixture of amorphous and nanocrystaline Cr(Ti, Al) solid solutions was observed after 40 hours of milling. Two consolidation methods of milled powders were applied: hot pressing (HP) at 1273K at 35 MPa under argon flow and pulse plasma sintering (PPS). The conditions of the latter method were optimized for pressure and voltage by application of temperature and shrinkage measurements during the process. The micro-hardness of consolidated samples was about 860 HV1 and only small differences were observed between samples obtained by both methods. The mean density of pulse plasma sintered compact was about 98% of the theoretical value while hot pressed samples had lower density close to 95% of the theoretical one. The TEM observation of consolidated samples revealed that pulse plasma sintered samples have a grain size in the range of tens of nanometers while the grains in the hot pressed samples are larger, of size below 1 micron. The compression tests performed in the temperature range between RT and 1073K with deformation rate of 4x10-4s-1 demonstrated higher ductility and strength of PPS samples at room temperature, due to a different level of densification and grains size. |
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