Conventional Powder Metallurgy Process and Characterization of Porous Titanium for Biomedical Applications

Abstract

Commercially pure titanium (c.p. Ti) is one of the best metallic biomaterials for bone tissue replacement. However, one of its main drawbacks, which compromises the service reliability of the implants, is the stress-shielding phenomenon (Young's modulus mismatch with respect to that one of the bone). Several previous works attempted to solve this problem. One alternative to solve that problem has been the development of biocomposites implants and, more recently, the fabrication of titanium porous implants. In this work, porous samples of c.p. Ti grade 4 were obtained using conventional powder metallurgy technique. The influence of the processing parameters (compacting pressure and sintering temperature) on the microstructure features (size, type, morphology, and percentage of porosity), as well as on the mechanical properties (compressive yield strength, and conventional and dynamic Young's modulus) were investigated. The results indicated that there is an increment in density, roundness of pores, and mean free path between them as compacting pressure and/or sintering temperature is increased. The Young's modulus (conventional and dynamic) and yield strength showed the same behavior. Better stiffness results, in the central part of cylindrical samples, were obtained for a uniaxial compression of 38.5 MPa using a sintering temperature of 1273 K and 1373 K (1000°C and 1100°C). An evaluation of porosity and Young's modulus along a cylindrical sample divided in three parts showed that is possible to obtain a titanium sample with graded porosity that could be used to design implants. This approach opens a new alternative to solve the bone resorption problems associated with the stress-shielding phenomenon.

Processing, characterization and biological testing of porous titanium obtained by space-holder technique

“…NH 4 HCO 3 ], with a NH 4 HCO 3 concentration of 50 vol.%, were prepared using a Turbula Ò T2C blender for 40 min to ensure good homogenization. This NH 4 HCO 3 content was chosen according to the previous works by the authors with conventional PM [35] and space-holder results with NaCl [45] based on the optimum porosity to match the Young's modulus of cortical bone. The compacting step was carried out using an Instron 5505 universal machine to apply the pressures used (200, 400, 600 and 800 MPa).…”

“…The compacting loading rate was 6 kN/s, dwelling time was 2 min and unloading time was 15 s for decreasing load up to 150 N. Elimination of NH 4 HCO 3 from green samples was performed thermally by placing the samples in an oven at 100°C for 10 h. The sintering process was performed in a Carbolyte Ò STF 15/75/450 ceramic furnace with a horizontal tube at 1250°C for 2 h using high vacuum (*5Á10 -5 mbar). Diameter of compaction die (8 mm) and powder mass were selected to obtain samples in which the effect of compaction pressure was minimized [35]. These parameters were kept constant for compression tests (height/diameter = 0.8 [46]).…”

“…There are several manufacturing processes for the latter, among which are highlighted: the electron beam melting process [16], creep expansion of argon-filled pores [17], directional aqueous freeze casting [18], rapid prototyping techniques [19], laser-engineered net shaping [20], electric current activated/assisted sintering techniques [21,22], conventional powder metallurgy [23] and space-holder techniques [24]. In this last process, most of the space-holders (ammonium bicarbonate [25][26][27][28], carbamide [29] and PVA [30]) are completely evaporated at low temperatures, whilst others (e.g., sodium chloride [31][32][33][34][35]) are removed by a dissolution process, generally in water.…”

Porous Metallic Biomaterials Processing (Review) Part 1: Compaction, Sintering Behavior, Properties and Medical Applications

“…The yield strength was 234 MPa, and 421 MPa for the Fe-35%Mn alloy and Fe-20%Mn alloy, respectively, elongation for Fe-35%Mn alloy was 32% but for Fe-20%Mn was 7.5%. The magnetic susceptibility in the quenched condition for these type of alloys was similar and remains constant after plastic deformation, with 33 Brought to you by | MIT Libraries Authenticated Download Date | 5/9/18 8:57 PM exception of Fe-20%Mn alloy. In comparison with pure iron, the corrosion rate was slightly higher.…”

“…Torres et al [33] have researched on Porous Titanium for Biomedical applications obtained by Conventional P/M process, and studied the influence of pressing and sintering parameters on structure and mechanical characteristics of CP Ti grade 4 porous specimens. The microstructure was investigated from porosity point of view (the type , shape, size and quantity of pores).…”