Papers by Author: Fen Wang

Abstract: As the new structural material, TiAl intermetallic compound has great potential application in aerospace engine, energy and automotive fields. But the bottleneck problems including poor room temperature ductility and high-temperature oxidation resistance limit its application. Ti₂AlC possesses an unusual combination of the merits of both metals and ceramics, which is considered the best reinforcement for TiAl intermetallic compound. In the present work, Ti₂AlC/TiAl matrix intermetallic compound was successfully fabricated by in situ hot pressing method from the mixture of Ti/Al/TiC. The phase transitions were investigated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The microstructure of the product was studied by scanning electron microscopy (SEM). Ti reacted with Al liquids to form Ti-Al intermetallics below 900 °C firstly. With increasing temperature (above 900 °C), a part of TiAl intermetallics reacted with TiC to form Ti₂AlC reinforcement. The as-sintered product presented dense and typical lamellar structure. The in-situ synthesized fine Ti₂AlC contributed to improve the strength of TiAl matrix intermetallic compound.

Abstract: Al₂O₃/TiAl composites doped with Cr and V₂O₅ were successfully prepared from Ti, Al, TiO₂, Cr and V₂O₅ by in situ hot-pressing. The synthesis process and the microstructures of as-fabricated samples were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the reaction process could be divided into three stages: firstly, Ti reacted with Al to form TiAl₃, then TiO₂ and V₂O₅ were reduced by Al to form Al₂O₃, and finally TiAl and Ti₃Al occur from the competitive solid-state diffusion reactions. The as-synthesized composites mainly consist of V and Cr doped matrix phases of γ-TiAl and α₂-Ti₃Al and dispersive Al₂O₃ phase. The in situ formed fine Al₂O₃ particles mainly disperse on the boundaries of TiAl. Compression strength shows a peak value of 1096.22 MPa at 7.54 at.% Al₂O₃ content.

Abstract: Al₂O₃/TiAl composites were successfully fabricated by hot-press-assisted exothermic dispersion method with powder mixtures of Ti, Al, TiO₂ and Cr₂O₃ as raw materials. The effect of sintering temperature on the microstructures and mechanical properties of Al₂O₃/TiAl composites has been investigated. The results show that the Rockwell hardness and density of the composites increased with increasing sintering temperature. But the flexural strength and fracture toughness peaked at 825 MPa and 7.29 MPa·m^1/2, respectively, when the sintering temperature reached to1300 °C.

Abstract: Elemental mixture of Ti, Al and C was high energy milled in a planetary ball mill under high-purity nitrogen gas protection and then hot pressed. The fully dense bulk layered ternary Ti2AlN0.5C0.5 with sub-micron grain size was successfully obtained. The phase formation and transformation in high energy milling and subsequently hot press sintering were studied in detail by using X-ray diffraction (XRD). Scanning electron microscopy (SEM) linked with energy dispersive spectroscopy (EDS) was used for the structural and compositional analysis. The formation mechanism was also discussed.

Abstract: Al₂O₃/TiAl composites were successfully fabricated by hot-press-assisted exothermic dispersion method with elemental powder mixtures of Ti, Al, TiO₂ and Cr₂O₃. The effect of Cr₂O₃ addition on the microstructures and mechanical properties of Al₂O₃/TiAl composites has been characterized. The results show that the Rockwell hardness, flexural strength and fracture toughness of the composites increase with increasing Cr₂O₃ content. When the Cr₂O₃ content is 3.5 wt %, the flexural strength and the fracture toughness reach the maximum value of 658.7 MPa and 7.2 MPa•m^1/2, respectively. The improvement of mechanical properties is firstly associated with a more homogeneous and finer microstructure developed by addition of Cr₂O₃; secondly, it is related to the increase of the ratio of α₂-Ti₃Al/γ- TiAl matrix phases.

Abstract: In this work, the composites were fabricated by in-situ synthesis reaction and hot-pressing using Ti, Al, TiO₂ and Eu₂O₃ as starting materials. Effects of the sintering temperature on the microstructures and properties of the Al₂O₃/TiAl composites were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and universal properties tests. The result shows that the sintering temperature had effect on improving the mechanical properties of TiAl composites. The phase of the composites composed of γ-TiAl/_α2-Ti₃Al matrix and reinforcing phases of Al₂O₃ and EuAlO₃. The grain size of composite was smaller than 0.5 µm at 1200 °C. And the mechanical properties reached to the maximum value (477.96 MPa and 9.73 MPa•m^1/2). The properties decreased with grain growth at 1300 °C.

Abstract: The dense layered ternary Ti₂AlN ceramics were successfully synthesized by a combination of mechanical alloying and hot press sintering from the mixture of Ti and Al in nitrogen milling atmosphere. The phase transformation and morphology characteristics in mechanical alloying and subsequently hot press sintering were studied by using XRD and SEM as well as EDS. The results show that Ti(Al,N) amorphous powders were synthesized successfully by mechanical alloying. When the as milled powders were hot pressed at 1200 °C for 1 h, full dense and highly pure layered ternary Ti₂AlN ceramic was synthesized.

Abstract: The nanocrystalline TiC_1-xN_x powders were synthesized by high energy milling from the mixture of Ti and carbon black in nitrogen milling atmosphere. The phase transformation and powder morphology characteristics were studied by using XRD and SEM. The results show that nanocrystalline TiC_1-xN_x powders were fabricated successfully by milling for 24 h at a rotational speed of 450 rpm in planetary ball-mill. The formation mechanism was mechanically induced self-propagating reactive synthesis (MSR). According to changing the mole ratio of C to Ti, serial TiC_1-xN_x powders can be produced, including TiC₇N₃, TiC₅N₅, and TiC₃N₇.

Abstract: A novel method of the combination of high energy milling and hot pressing was adapted to fabricate dense titanium nitride-alumina (TiN/Al2O3) in situ composites using Ti, Al and TiO2 as raw materials. Full dense and pure TiN/Al2O3 composites were fabricated at 1300 °C for 1 h under 10 MPa. The composition, microstructure and mechanical properties of the as-fabricated products were investigated. The results show that the synthesized TiN/Al2O3 composites possess high purity. The TiN/Al2O3 composites have a good combination of mechanical properties of hardness of 18.0 GPa, the flexural strength of 500 MPa, and the fracture toughness (KIC) of 5.2 MPa•m1/2. The strengthening and toughening mechanisms are also discussed.

Abstract: Highly pure Ti3AlC2 powder was fabricated by combination of high energy milling and heat treatment with Ti, C and Al as starting materials. The details of reactions and phase evolution in fabrication process were investigated. The results shown that the Ti-Al intermetallics, Ti3AlC2 and TiC were formed in high energy milling. The as-milled powders were heat treated subsequently, and the Ti3AlC2 powder with high purity was produced from the reaction among Ti-Al intermetallics, Ti3AlC2 and TiC at relative low temperature (1100 °C).