## 3 Results
### Microstructural and Mechanical Analysis Results  
Optical microscopy images of the polished cross-sections of the prepared samples of both feedstocks are shown in Figure 10.  
It was found that samples made by the coarse Ti powder had much larger micropores with less sphericity. These micropores are formed due to incomplete sintering and bonding amongst the adjacent Ti particles. In comparison, samples processed by commercial feedstock had much finer micropores and more spherical sizes that tend to increase towards the outer edges of the specimens. The average pore diameter for the commercial feedstock was about 17 \(\upmu\)m with a sphericity of about 0.63, whereas the average pore diameter for the current feedstock was about 57 \(\upmu\)m with a sphericity of about 0.49. Hence, it is expected that samples processed by commercial feedstock have better mechanical properties than those processed with the coarse Ti powder.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Contaminant**} & **Sintered Sample from** & **Sintered Sample in the** & **Ti Powder** \\  & **Commercial Feedstock (wt \%)** & **Current Study (wt \%)** & **(wt \%)** \\ \hline C & 0.044 & 0.079 & 0.006 \\ O & 0.273 & 0.277 & 0.093 \\ N & 0.033 & 0.023 & 0.010 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Chemical analysis results.  
Nevertheless, the relatively large micropores in the samples processed by the coarse Ti powder are well suited for biomedical applications, where pore sizes greater than 50 \(\upmu\)m are required for rapid osteeoconduction [25]. It should be noted that the optimum pore size range for bone ingrowth, cell attachment and proliferation is 100-500 \(\upmu\)m [26]. However, pore sizes in the samples could be increased with the introduction of a space holder material in the feedstock mixture and removing it at a later stage during sintering [8; 27].  
The results of mechanical tests for the samples are presented in Figure 11.  
The compression test results indicate that samples processed by the commercial feedstock have a significantly higher yield strength compared to those processed by the coarse Ti powder,  
Figure 11: Results of the mechanical tests showing: (**a**) stress-strain curves of the sintered samples; (**b**) samples processed by the coarse powder after compression.  
Figure 10: Optical micrographs of the polished samples for: (**a**) sample sintered using the current study feedstock; (**b–d**) centre and edges of a sample sintered using commercial feedstock.  
where the average yield strengths (\(\sigma_{0.2}\)) for the samples were about 473 and 191 MPa, respectively. However, the energy absorbed by the samples processed by the coarse Ti powder was notably higher than that absorbed by the samples made with the commercial feedstock, and this is one of the unique characteristics for porous materials, as the samples processed by the coarse powder had an average volume percentage of porosity around 20%. Yet, the stress-strain curve for these porous samples did not show any plateau stress, such as that classically expected during testing of porous materials. The samples after testing did not show nor develop any cracks and showed some signs of barrelling, which is typically observed during compression testing, as seen in Figure 11.