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

Abstract

Porous materials with interconnected porosity have widespread applications in many fields of engineering. [1] Bulk porous metallic materials (honeycomb, foam, and hollow spheres) are known for their interesting combinations of the advantages of a metal (strong, hard, tough, electrically, and thermally conductive, etc.) with the functional properties of porous structures (lightweight with adjustable properties by selecting the density. [2] Because of this, porous metals are interesting for a number of engineering applications such as structural panels, energy absorption devices, acoustic damping panels, compact heat exchangers, and biomedical implants etc. [3] Porous titanium (Ti) and its alloy were widely used in the biomedical field due to their outstanding mechanical properties, low density, chemical resistance, and biocompatibility. As a kind of long-term load-bearing implant, the porous structures of Ti and its alloy could lead to a reliable anchoring of host tissue into the porous structure, and allow mechanical interlocking between bone and implant. [4] The ingrowths of bone into the porous structure could ensure a good transfer of mechanical forces. Therefore, a porous structure is preferable for the Ti and its alloys using as bone scaffolds.However, porous Ti and its alloys are difficult to be produced from the liquid state, due to the high melting point, the high reactivity at high temperature above 1000 8C and the contamination susceptibility. Thus, fabrication processes for porous Ti has to date focused on the powder metallurgy (PM) route and avoided the liquid route. [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. [12] However, most of SPS researches were performed on dense materials; fewer studies were on porous materials. [13] The SPS studies on porous Ti alloys were mainly using low temperature and low pressure to decrease the relative density of samples. [14][15][16][17][18][19] The samples exhibited pore sizes of some tens of micrometers and a porosity in the range of 20-45%. As bone foams, high porosity (>50%) and macropore size (>200 mm) are essential requirements for the bone growth and the osteoconduction. [20,21] Macroporous nanostructured tricalcium phosphate scaffolds have been successfully COMMUNICATION [*] Dr. for his support in mechanical testing.Macroporous pure titanium (Ti) foams with...

Porosity and Mechanical Properties of Porous Ti by Spark Plasma Sintering under Different Applied Produced Pressures

“…Furthermore, the sharp and well-defined shape of the diffraction peaks suggests a high degree of crystallization [38]. No β-Ti phase was observed in the samples when the solidification temperature was below 882 °C, which is consistent with previous studies [39][40][41][42]. It is common for there to be a discernible temperature variation between the die's surface and the actual interior of the sample during the sintering process.…”

“…The radial temperature gradient in the conductive samples is approximately 79 °C for a sample diameter of 20 mm [43]. Moreover, the control of the sintering temperature is achieved by maintaining the temperature difference between the sample core and the thermometer below 5 °C [42,44]. The temperature gradient, which is smaller than 79 °C, remains lower than the melting temperature of NaCl (802 °C).…”

Sintering and Heat Treatment of Titanium Alloys by Pulsed Electric Current Sintering

“…In this study, the Ti6Al4V foams were fabricated by using PECS at controlled porosity followed by dissolution of NaCl phase and post heat treatment at 1100 o C. Previous investigations showed that high-density pure Ti foams can be fabricated with NaCl as spacer by the PECS at 700 o C for 8 min under 50 MPa [11]. However, the Ti6Al4V/NaCl mixture cannot be densified at the same condition.…”

A Review on Biomedical Titanium Alloys: Recent Progress and Prospect

“…Current studies on the preparation of porous Ti alloys by SPS mainly focus on the conditions of low temperature and low pressure that can easily sinter Ti and its alloys in powders, because high current discharge produces ionization in the plasma can melt the local oxide film on the particles surface and allow the formation of junctions between particles. The porous CP–Ti prepared at 700 °C for 8 min under 50 MPa by combining SPS with NaCl dissolution method (NaCl can be easily removed by dissolution in water) showed a yield strength from 27 to 94 MPa and elastic modulus from 6.2 to 36.1 GPa and represented the highly interconnected structure and uniform distribution of pores . The typical microstructures of porous CP–Ti with the porosity of 55% but various pore sizes are represented in Figure .…”

“…The porous CP–Ti prepared at 700 °C for 8 min under 50 MPa by combining SPS with NaCl dissolution method (NaCl can be easily removed by dissolution in water) showed a yield strength from 27 to 94 MPa and elastic modulus from 6.2 to 36.1 GPa and represented the highly interconnected structure and uniform distribution of pores . The typical microstructures of porous CP–Ti with the porosity of 55% but various pore sizes are represented in Figure . Porous Ti–5Mn was also prepared by using SPS technique associated with ammonium hydrogen carbonate and by blowing agent TiH 2 under a low‐pressure condition at different temperatures for 5 min .…”