Fabrication of Ti–Al Micro/ Nanometer‐Sized Porous Alloys through the Kirkendall Effect

Abstract

Porous metals are of great interest as a potential engineering material in various industrial fields because of their unique properties such as their impact energy absorption capacity, their gas and liquid permeability, thermal conductivity, and electrical insulating properties.[1] However, their poor oxidation resistivity, poor corrosion resistance, and intolerance at elevated temperatures restrict their potential applications in much wider fields, such as high-temperature gas separation and as catalysis in rugged environments. It is well known that Ti-Al alloys are notable examples of intermetallic compounds containing a mixture of metallic and covalent bonds [2] that provide sound mechanical properties with outstanding corrosion resistance [3] and excellent oxidation resistance at elevated temperatures-particularly over 600°C. [4] In this Communication, we introduce a novel technique, based on the Kirkendall effect, to fabricate Ti-Al micrometer/nanometersized porous alloys with adjustable pore sizes ranging from several tens of micrometer to several tens of nanometers. In the late 1930s, Kirkendall et al. [5] discovered that the interface between copper and zinc in brass moved at an elevated temperature due to their different diffusion rates. This phenomenon was later referred to as the Kirkendall effect. It has been well documented that the Kirkendall effect leads to pore formation in materials. [6][7][8] In general, these pores impact negatively on the mechanical properties, so that significant efforts have been devoted to remove these pores for engineering applications. [9] However, in recent years, the Kirkendall effect has been used to fabricate special structures, such as hollow nanocrystals [7] and hierarchical porous iron oxide films. [8] In this regard, the Kirkendall effect can be used to produce porous alloys if there exists great diffusion-rate discrepancies between components in the alloy system. Two procedures for fabricating porous Ti-Al alloys via the Kirkendall effect are illustrated in Figure 1a. In the first procedure, commercial Ti and Al elemental powders were mixed and cold pressed into both disc and tubular compacts, followed by the solid sintering process (in which the Kirkendall effect occurs). Considerable expansion of these compacts has been observed and their examples are shown in Figure 1b and c. The final shape of a compact with the porous structure is important for practical applications. Through the precise control of the sintering process and the avoidance of the formation of the liquid phase, we have managed to preserve the sintered compacts in their original shapes (as shown in Fig. 1b and c) even though a great volume expansion occurred. Under an identical sintering condition (initially sintered at 600°C for 60 min and then sintered at 1300°C for 30 min), the porous materials of three structures of Ti-Al alloys (i.e., a 2 -Ti 3 Al, c-TiAl, and TiAl 3 ) could be fabricated when different ratios of Al and Ti powders were mixed. A typical example of the alloy with the nominal...

Synthesis and characterization of porous Fe–25 wt.% Al alloy with controllable pore structure

“…First, Fe 2 Al 5 forms at the interface between aluminum and iron powders by solid state interdiffusion below 648°C [20]. Simultaneously, pores are formed because of the different intrinsic diffusion coefficients of Al in Fe and Fe in Al, based on the Kirkendall effect [14]. In addition, the intensity of the reaction decreases due to decrease of the iron / aluminum contact area and the content of aluminum [21].…”

“…So FeAlbased functional materials such as cellular filter not only broaden their applications, but also make the mechanical properties not an important issue. Our recent studies [14][15][16] have demonstrated that porous Fe-Al and Ti-Al structures can be fabricated through reactive syntheses of commercial Fe and Al or Ti and Al mixed powders based on the Kirkendall effect and used for the filtration purposes. The aim of this paper is to report a detailed study of the influence of the preparation parameters on the synthesis of porous FeAl alloy, in order to obtain the optimal parameters to synthesize porous FeAl alloy with controllable pore structure.…”

“…produce porous alloys if the diffusion-rate differences exist between components in the alloy systems [14]. So FeAlbased functional materials such as cellular filter not only broaden their applications, but also make the mechanical properties not an important issue.…”

Effect of pressure on pore structure of porous FeAl intermetallics

“…Porous intermetallics, which include Ti-Al, Fe-Al and Ni-Al, have been fabricated in our previous work by reactive synthesis using element powders as raw materials [1][2][3][4]. Among the new porous materials with B2 structure, porous FeAl intermetallics present certain unique physical, chemical and mechanical properties.…”

Spark Plasma Sintering, Microstructures, and Mechanical Properties of Macroporous Titanium Foams

“…[5] Many techniques have been applied to produce porous Ti and its alloy implants in recent years. [6][7][8][9][10] Nevertheless, there are still problems to be solved in the field of porous Ti for biomedical applications [11] : the difficulty to create controlled porosity and pore sizes, the insufficient knowledge of porous structureproperty relationships, the requirements of new sintering techniques with rapid energy transfer, and less energy consumption and so on.Spark plasma sintering (SPS) as one of the field assisted sintering techniques, is a relative new sintering technique for PM and ceramics. SPS is a high efficient and energy saving powder consolidation and sintering technology capable of processing conductive and non-conductive materials.…”