# Preparation and Electron-Beam Surface Modification of Novel TiN Material for Medical Applications
## 3 Results and Discussion  
### Structure and Composition  
As previously described [30], the initial powder represented with particles of 100-200 \(\upmu\)m had two types of surface morphology, i.e., sponge-like and compact types. The particles of the former type were found to consist primarily of TiNi phase, while the latter compact particles contained large TiNi grains surrounded with Ti\({}_{2}\)Ni phase [30]. As a first preparation step, initial TiNi powder was placed onto a TiNi monolithic plate surface and thermally treated to form a porous coating (Scheme 1). During this stage, because of high temperature, the powder particles formed contact zones that prevented any motion of the latter particles when the samples were further processed by HCPEB. The photographs of prepared samples are presented in Figure 1.  
The phase composition of two HCPEB-treated samples (TN-20 and TN-30), as well as that of their non-treated counterpart (TN), was studied by the XRD method. The results presented as patterns in Figure 2 revealed that all three samples contained the following phases: TiNi (phases B2 and B19\({}^{\prime}\) with PDF-4 cards 01-076-3614 and 01-078-2550, respectively), Ti\({}_{3}\)Ni\({}_{4}\) (PDF-4 card 04-001-1903), and Ti\({}_{2}\)Ni (PDF-4 card 04-007-1531). This finding implies that the pulse electron beam treatment applied in this work did not affect the composition of phases within the formed surface layer, but rather influenced fractions of such phases (see Table 1). For both treated samples TN-20 and TN-30, their TiNi content increased, while that of Ti\({}_{2}\)Ni decreased when compared with untreated sample TN. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Phase**} & \multicolumn{3}{c}{**Content in the Samples (wt\%)**} \\  & **TN** & **TN-20** & **TN-30** \\ \hline TiNi & 73 & 87 & 78 \\ Ti\({}_{3}\)Ni\({}_{4}\) & 13 & 7 & 14 \\ Ti\({}_{2}\)Ni & 14 & 6 & 8 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Phase composition of the samples as evaluated by XRD. Figure 1: Photographs of samples TN, TN-20 and TN-30. Interestingly, whereas in sample TN-20 the fraction of phase Ti\({}_{3}\)Ni\({}_{4}\) dropped to 7 wt%, its content was again back to 14 wt% in sample TN-30, as more energy was applied (Table 1). It is possible that the phase evolution observed in sample TN-30 could be caused by material aging due to additional heating under more energetic HCPEB, which is known to be associated with formation of phase Ti\({}_{3}\)Ni\({}_{4}\)[3]. Indeed, since sample TN-30 was subjected to more intense high-energy impact, its top-layer could be more prone to aging and precipitation of phase Ti\({}_{3}\)Ni\({}_{4}\). Figure 3 presents SEM images of sample surfaces, with insets depicting more details at higher magnification. Sample TN is seen in Figure 3a to inherit the morphology of initial powder, containing two types of particles, sponge-like and compact ones (presented as insets and indicated with arrows in Figure 3a). The average roughness (R\({}_{\text{a}}\)) was evaluated for this material to be around 80 \(\upmu\)m (Table 2). HCPEB treatment with 20 keV is seen in Figure 3b to result in surface smoothening and homogenization, which is also confirmed by roughness measurements (see Table 2). It was expected that HCPEB treatment would cause some smoothening of single particles, as well as filling of cracks and pores on the surface. The high-energy beam led to surface melting of TiNi particles, also increasing their contact areas and giving rise to newly recrystallized surface layers forming upon cooling down. In agreement with surface smoothening observed in Figure 3b, the average roughness of sample TN-20 was found to decrease by 12.5% (Table 2). Figure 3: SEM images (SE mode) of sample surface: (**a**) untreated sample TN, and HCPEB-treated samples (**b**) TN-20, and (**c**) TN-30. Figure 2: XRD patterns of samples prepared in this study from TiNi powder and monolith TiNi substrates.