Synthesis, microstructure and mechanical properties of (Ti,Mo)Al/Al 2 O 3 in situ composites by reactive hot pressing
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i,Mo)Al/Al2O3 composites were successfully synthesized utilizing in situ reactive hot pressing method with Ti, Al, and MoO3 powders as starting materials. A possible synthesis mechanism was proposed to explain the formation of (Ti,Mo)Al/Al2O3 composites. The investigation results indicate a probable reaction process that molten Al reacted with MoO3 to form Al2O3 and Mo, and the TiAl matrix grains were refined increasingly by Al2O3 with the addition of MoO3 increased, accompanying with a small quantity of Mo containing phase AlMoTi2 formed in the fabricated composites. Meanwhile, the microstructure and mechanical properties of the (Ti,Mo) Al/Al2O3 composites were characterized. The as-synthesized composites exhibited lamellar structure of TiAl intermetallic compound and the in situ formed fine Al2O3 particles dispersed at the stratified TiAl matrix grain boundaries hindering the growth of the grain size of the matrix. And the Rockwell hardness, flexural strength, and fracture toughness of the as-prepared (Ti,Mo) Al/Al2O3 composite were 44.08 HRC, 684 MPa, 7.63 MPam1/2, which improved by 57.4%, 107.3%, and 38.7% compared to monolithic TiAl, respectively. The reinforcing mechanism of the material was also discussed.
I. INTRODUCTION
The intermetallic compounds based on Ti–Al binary alloys have been widely considered to be a kind of promising light-weight structure material due to their excellent properties, such as low density, high hardness, attractive fracture strength, good oxidation resistance, and high creep resistance at room temperature, and elevated temperatures.1–8 Because of these brilliant properties mentioned above, the compounds of TiAl based alloys own good application potentials in the aerospace, automotive, and turbine power generation markets.4 But the poor ductility and flexural toughness have prevented their further practical application in the fields mentioned above.5–7 Many works have been performed to investigate the strengthening of TiAl intermetallic compounds.8–18 And considerable investigations have shown that incorporation of second phase and micro-alloying are doable and resultful to control the microstructure and improve the mechanical properties of TiAl intermetallics.10–18 On one hand, ceramic particles, for instance, Si3N4,10 TiB2, TiC,11 Al2O313 as well as Ti5Si315 as effective reinforcements have been performed in many researches. Rao et al.15 have successfully synthesized TiAl–Ti5Si3 in situ composites by hot isostatic pressing (HIP), which showed Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.60
that the yield strengths of TiAl based alloys obtained with the technique adopted in the study were significantly high even at an elevated temperature of 800 °C. Zhu et al.17 have found out the combining aluminothermic reduction of Nb2O5 into the synthesis process to produce in situ formed Al2O3 particles were considered as an appropriate reinforcing method for the TiAl matrix, which was attributed to the out
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