Wen Wen Yang

Reaction Synthesis of TiAl/Ti2AlC In Situ Composites

Full dense and highly pure TiAl/Ti2AlC in situ composites were successfully synthesized by reactive synthesis from the powder mixtures of Ti, Al and carbon black by hot-press-assisted reaction process. The reaction process, microstructure and bending strength of the TiAl/Ti2AlC in situ composites were investigated in detail. The results show that the as fabricated composites posses three phases, namely, TiAl, Ti3Al and Ti2AlC. The matrix phases are mainly equiaxed TiAl with a minor lamellar Ti3Al phase. Ti2AlC particles with size less than 1 μm are distributed uniformly in matrix grains as a reinforcing phase. When C content is 0.44 wt %, the flexural strength reaches 426.21 MPa, which is increased by 35 %.

Effect of Carbon Addition on the Microstructure and Mechanical Properties of the In Situ Formed TiAl/Ti2AlC Composites

TiAl/Ti2AlC composites were successfully fabricated by hot-press-assisted reactive synthesis method from elemental powder mixtures of Ti, Al and C. The effect of C addition on the microstructures and mechanical properties of TiAl/Ti2AlC composites was investigated in detail. The results show that the Rockwell hardness, flexural strength and fracture toughness of the composites are modified by incorporation of in situ formed Ti2AlC. When the C content was 0.44 wt %, the flexural strength and the fracture toughness reach the maximum values of 658.7 MPa and 10.03 MPa•m1/2, respectively. The reinforcing mechanism was also discussed.

Fabrication of TiAl/Ti2AlC Composite by Reaction Hot Pressing

TiAl/Ti2AlC in situ composite was successfully fabricated by hot-press-assisted reaction process from the mixture of Ti, Al and carbon black. The phase formation and transformation were investigated in detail by X-ray diffraction (XRD) and the morphology characteristics were also studied by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results show that when the mixed powders were hot pressed at 1300 °C for 1 h, full dense and highly pure TiAl/Ti2AlC composite was synthesized. The TiAl was the matrix phase and the in situ synthesized Ti2AlC was reinforcing phase. The reaction process was also discussed.

Influence of Cr2O3 Addition on the Properties of TiAl Composites

Using Ti, Al and Cr2O3 as starting materials, Al2O3 particulate reinforced TiAl composites have been fabricated by in-situ reaction synthesis method. Effects of the Cr2O3 addition on the microstructures and mechanical properties of the TiAl/Al2O3 composites were investigated in detail. The results show that the composites have a matrix of TiAl, Ti3Al, and minor Cr containing phases, and a second reinforcement Al2O3. The addition of Cr2O3 effectively refined the structure of the matrix, and as a result, the mechanical properties of TiAl composites are improved. At Cr2O3 7.36 wt%, the flexural strength and fracture toughness reach the maximum values of 634.62 MPa and 9.79 MPa·m1/2, which are increased by 80% and 30%, respectively. The strengthening mechanism is also discussed.

Reaction Synthesis of TiAl-Al2O3 Composites from Ti-Al-Cr2O3

Titanium aluminide composite reinforced with in situ formed submicron Al2O3 has been prepared by a reactive hot press method using Cr2O3, Al and Ti powder as starting materials. The reaction synthesis processing is particularly investigated. Results show that the matrix of the as-prepared material is a mixture of TiAl and a small amount of Ti3Al and Cr containing phase. Fine Al2O3 particles that act as reinforcing phase are dispersed along the interface of the matrix. The formation of TiAl/Al2O3 composite involves many transitional stages. Firstly, TiAl3 and Ti3Al intermediates were produced, then reducing reaction of Cr2O3 by Al formed Al2O3, and finally, the competitive solid-state diffusing reactions among Ti3Al, TiAl and TiAl3 produced the matrix phases of the TiAl/Al2O3 composite.

Effect of Si Addition on the Microstructures and Mechanical Properties of TiAl Intermetallics

TiAl/Ti5Si3 in situ composites were successfully fabricated by reactive hot-press method from powder mixtures of Ti, Al and Si. The influence of the Si addition on the microstructures and mechanical properties of TiAl/Ti5Si3 composites was investigated in detail. The results show that an appropriate amount of addition of Si refined the matrix structure obviously due to the in situ formed Ti5Si3, and as a result, the flexural strength and fracture toughness of the composites are modified. When the Si content is 1.82 wt %, the flexural strength and the fracture toughness reach the maximum value of 685.67 MPa and 9.02 MPa·m1/2, respectively. The enhancing mechanism was also discussed.

Synthesis of Al2O3 Reinforced TiAl Composites from Ti-Al-Nb2O5

TiAl/Al2O3 in situ composites have been prepared by a reactive hot pressing method from Ti, Al and Nb2O5 powders. The phase transformation and the mechanism of synthesis were studied by differential scanning calorimeter (DSC) of starting powers and X-ray diffraction (XRD) of samples hot press sintered at different temperatures from 500 °C to 1300 °C. Scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS) was utilized to investigate the morphology characteristics of the products. The resultant in situ formed TiAl/Al2O3 composites exhibited multiplex structures containing TiAl, Ti3Al, Al2O3and NbAl3 phases. Fine Al2O3 particles that act as reinforcing phase are dispersed along the interface of the matrix. The formation of TiAl/Al2O3 composite involves many transitional stages. Firstly, Ti and Al reacted to form TiAl3 and Ti3Al intermediates, then Nb2O5 was reduced by Al to form the Al2O3, and finally, the competitive solid-state diffusing reactions among Ti3Al, TiAl and TiAl3 produced the final matrix phases of the resultant composite.

Reactive Synthesis of TiAl/Ti5Si3 In Situ Composites

Full dense and highly pure TiAl/Ti5Si3 in situ composite was successfully synthesized by reactive synthesis from the powder mixtures of Ti, Al and Si. The reaction process was investigated in detail by the X-ray diffraction analysis (XRD) and differential scanning calorimetry (DSC). The microstructural characteristics of the TiAl/Ti5Si3 in situ composite were also studied by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results show that the as fabricated composite possesses three phases, namely, TiAl, Ti3Al and Ti5Si3. The matrix phases are mainly equiaxed TiAl with a minor lamellar Ti3Al phase. Ti5Si3 particles with size less than 1 μm are distributed uniformly in matrix grains as a reinforcing phase.

Effect of TiO2 Addition on the Microstructures and Mechanical Properties of γ-TiAl Intermetallics

Al2O3 Particulate reinforced TiAl based composites have been fabricated by hot press-assisted reaction synthesis (HPRS) method using Ti, Al and TiO2 as starting materials. Effect of the TiO2 addition on the microstructures and mechanical properties of the TiAl/Al2O3 composites were detailedly investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and universal properties tests. The results show that the TiO2 addition has evident effect on phase composition and microstructure of the TiAl intermetallics, as a result, the mechanical properties of TiAl composites are improved. When the TiO2 content is 10.58 wt %, the flexural strength and fracture toughness reach the maximum values of 537.34 MPa and 9.38 MPa·m1/2, which are increased by 70% and 23%, respectively. The strengthening mechanism is also discussed.