Visible Observation and Formation Mechanism of Porous TiAl 3 Intermetallics During the Continuous Sintering Process
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https://doi.org/10.1007/s11837-020-04294-2 Ó 2020 The Minerals, Metals & Materials Society
TECHNICAL ARTICLE
Visible Observation and Formation Mechanism of Porous TiAl3 Intermetallics During the Continuous Sintering Process XINYANG JIAO,1,2 XUANRU REN,1,3 and PEIZHONG FENG1,4 1.—School of Materials Science and Physics, China University of Mining and Technology, Xuzhou 221116, People’s Republic of China. 2.—School of Chemical Engineering and Technology, China University of Mining and Technology, Xuzhou 221116, People’s Republic of China. 3.—e-mail: [email protected]. 4.—e-mail: [email protected]
The formation mechanism of porous TiAl3 intermetallics from Ti-75 at.% Al powder compact was explored through a continuous sintering process. The exothermic behavior, temperature changes and open porosity were investigated by ranging the sintering temperature from 600°C to 700°C. Results show that a thermal explosion (TE) occurs once the sample temperature reaches to 675°C, upon which it rapidly climbs to 1148°C within 10 s. Visual observation was achieved and revealed the exothermic state at every step, showing the overall heating and instantaneous reaction of TE. The open porosity increased significantly from 24.8% to 58.7% by increasing the sintering temperature from 670°C to 675°C. The reaction mechanism of porous TiAl3 materials in the Ti-75 at.% Al system indicates that sintering at 600°C, 650°C, and 670°C was controlled by atomic diffusion, diffusion-induced TE, and liquid-induced TE reaction, respectively. The diffusion reaction activation energy was 161.5 kJ mol1 for diffusion-controlled growth of the TiAl3 reaction layer.
INTRODUCTION Porous Al-based intermetallics have been widely investigated as potential functional materials owing to their excellent properties including low density, good oxidation resistance, and controllable porosity and permeability, which provide opportunities toward the development of their applications in areas of filtration, catalytic carriers, and heat insulation.1–5 Combustion synthesis (CS) is the typical sintering process employed for preparing porous intermetallic compounds, and it has the advantages of low-energy consumption, fast production, and simple equipment.6–12 CS can be categorized into two different modes, depending on the heating procedure: (1) self-propagating high-temperature synthesis (SHS) refers to the process in which the sample is ignited by localized heating and then quickly propagated to the other end of the sample, and (2) the thermal explosion (TE) mode means that the whole sample is heated at a constant (Received July 14, 2019; accepted July 15, 2020)
heating rate until combustion behavior occurs.13–15 Several porous Al-based intermetallics (Cu-Al, FeAl, Ni-Al, Nb-Al, and Ti-Al) were successfully fabricated by our research group in a TE process.16–19 Among Ti-Al systems, the TiAl3 equilibrium phase has a relatively low density (3.3 g/cm3) and higher oxidation resistance compared to Ti3Al and TiAl phases.20 Furthermore, TiAl3 is a thermodynamically sta
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