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Using pure Ti powder with particle sizes from 300 to 500 µm prepared by the plasma rotating electrode process (PREP), porous pure Ti compacts for biomedical applications were synthesized by powder sintering, and microstructures and mechanical properties of the compacts were investigated in this study. Porous compacts having porosity of 19-35 vol% are successfully fabricated by controlling sintering condition. It is found that Young's modulus and compressive yield strength decrease linearly with increasing porosity, and porous Ti compacts having porosity of about 30-35 vol% exhibit identical Young's modulus of human bone.

Microstructures and mechanical properties of porosity-graded Ti compacts were investigated in this study. To fabricate the porositygraded compacts, Ti powders with three different particle sizes, 65, 189 and 374 mm were prepared by the plasma rotating electrode process (PREP) and the gas atomization process, and these powders were sintered with and without applied stress. Porosity and pore size of porositygraded Ti compacts decrease significantly with decreasing initial powder size and by applying stress. The most porous layer (374 mm) is severely deformed in compression tests compared to other layers. The compressive strength of porosity graded-compacts is found to be in fairly good agreement with the strength of most porous layer. Bend strength of compact sintered at 1223 K and 1 MPa (223.3 MPa) shows a higher value than that of human bone (156.9 MPa).

Hydroxyapatite (HA) coating was carried out by plasma spraying on bulk Ti substrates and porous Ti substrates having a Young's modulus similar to that of human bone. The microstructures and bond strengths of HA coatings were investigated in this study. The HA coatings with thickness of 200-250 microm were free from cracks at interfaces between the coating and Ti substrates. XRD analysis revealed that the HA powder used for plasma spraying had a highly crystallized apatite structure, while the HA coating contained several phases other than HA. The bond strength between the HA coating and the Ti substrates evaluated by standard bonding test (ASTM C633-01) were strongly affected by the failure behavior of the HA coating. A mechanism to explain the failure is discussed in terms of surface roughness of the plasma-sprayed HA coatings on the bulk and porous Ti substrates.

Diffusion pack coatings via Al-Si powders with an AlCl 3 chloride activator have been investigated in order to examine the surface protection effect on pure magnesium and magnesium alloys. Pure Magnesium and commercial AZ31 magnesium alloys have been subjected to diffusion coatings in an Al alloy powder for various time frames. When the pack coating was carried out at 823 K for 15 h, the Mg 17 Al 12 layer has been successfully synthesized on the pure magnesium substrate. Similarly, a pack annealing at 823 K for 15 h showed a synthesized Mg-Al layer on the AZ31 magnesium alloy as a coating layer. Mechanisms for the surface layer formation are discussed together with growth kinetics and microstructural observations.