**3. Results and discussion**

In this section, we studied the effect of Titania on the mechanical behavior of Alumina-10 wt.% TCP composite with different additive amounts (1 wt.%; 2.5 wt. %; 3 wt.%; 4 wt.%; 5 wt.%; 7.5 wt.% and 10 wt.%).

The particle size analysis of the Al2O3–10 wt.% TCP-TiO2 composites illustrated in **Figure 6** show that the particle distribution and the average grain size of the Al2O3–10 wt.% TCP-TiO2 mixtures vary a function of the amount of Titania additive.

The particle size distribution of composites without titania is narrow, while mixtures containing TiO2 exhibit a wide particle size dispersion. The median diameter (D50) is around 0.34 μm.

#### **3.1 Sintering behavior and densification effect**

**Figure 7** shows the densification behavior of various Al2O3–10 wt.% TCP- TiO2 samples that contain different amounts of Titania.

It is noted that the addition of Titania has been effective in improving the densification and lowering the porosity. In fact, the addition of TiO2 improves the density (by 30%) compared to that recorded without TiO2. The maximum recorded densification rate is around 90% following an addition of 5% TiO2 which is suitable for an optimum in the porosity of the order of 10%. Beyond this percentage, the density of these samples decreases slightly. So, a higher densification and a lower porosity for this composition indicates its good resistance.

#### **3.2 Mechanical proprieties**

In order to evaluate the material stiffness, ultrasound technique, is retained to estimate the elastic modulus E for different percentages of TiO2. The evolution of elastic modulus of Al2O3–10 wt.% TCP- TiO2 is illustrated in **Figure 8**. As can be seen, the elastic modulus increases with the amount of Titania additive until 194.96 GPa for 5 wt.% TiO2. Beyond the 5 wt.% TiO2, the overall stiffness falls

**Figure 6.** *Average particle size distribution plot composition for different amounts of TiO2.*

*Effect of Titania Addition on Mechanical Properties and Wear Behavior… DOI: http://dx.doi.org/10.5772/intechopen.99253*

**Figure 7.** *Relative density and porosity of specimens added with different amounts of Titania.*

#### **Figure 8.**

*Elastic modulus and hardness of Alumina-10 wt.% TCP-TiO2 versus percentage of Titania sintered at 1600 °C for 1 h.*

gradually. The Vickers indenter was applied to determine the hardness. On the other hand, at the same filler content of 5 wt % Titania, it was found that this composite provides the highest hardness values than those given by Alumina-10 wt% TCP (**Figure 8**).

Regarding the mechanical stresses, these were determined via bending, compression and Flattened Brazilian tests. The results are presented in **Figure 9**.

The tensile, flexural and compressive strength appears as being dependent on the amount of Titania additive.

It is observed that the tensile strength σ<sup>t</sup> switches from 26.68 MPa for Alumina-10 wt.% TCP to 86.65 MPa with the addition of 5 wt.% TiO2. For the results of the bending test, the flexural strength σ<sup>f</sup> relative to the Alumina- 10 wt.%TCP-TiO2 composite reaches 98 MPa.

On the other hand, and for the variation in the compressive strength σ<sup>c</sup> of the elaborated specimens with different percentages of the Titania, one notices an

**Figure 9.**

*Tensile strength, flexural strength and compressive strength Alumina-10 wt.% TCP-TiO2 versus percentage of Titania sintered at 1600 °C for 1 h.*

improvement in the compressive resistance σ<sup>c</sup> whose maximum value reached is of the order of 352 MPa in the presence of 5 wt.% Titania (**Figure 9**).

**Figure 10** shows the fracture toughness of different amounts of Titania added to Alumina-10 wt% TCP composite. As sintered at 1600°C/1 h, the toughness is improved to 13 MPa m1/2 after 5 wt% TiO2 adding.

#### **3.3 Friction and wear behavior results**

Likewise, the impact of adding Titania on the tribological properties of alumina-10 wt% TCP was explored with various TiO2 percentages.

Representative plots the evolution of friction coefficients (COF) as a function of the time for different percentages of Titania tested under normal loading of 9 N at a sliding speed of 200 rpm are displayed in **Figure 11a**.

All friction curves display similar tendency for the different samples.

COF was found to increase abruptly at the beginning of the sliding test. This can be attributed to the topography of the initial surface roughness or fresh surface that has an influence on the contact intensity. Then, the variations in the curves become approximately constant and the COF values stabilized. This constant values

**Figure 10.** *Fracture toughness of different amounts of Titania added to alumina-10 wt.% TCP composite.*

*Effect of Titania Addition on Mechanical Properties and Wear Behavior… DOI: http://dx.doi.org/10.5772/intechopen.99253*

#### **Figure 11.**

*(a) Plots of coefficient of friction (COF) versus time for Alumina-10 wt.% TCP-Titania composites in dry ambient condition. (b) The average steady COF as a function of % Titania.*

corresponds to the average steady state value of the COF [33]. This step is named: stable wear stage.

**Figure 11b** presents the evolution of the friction coefficient versus the different compositions of samples during one hour (1 h) of sliding.

It is observed that a significant difference was noted between Alumina-10 wt.% TCP and Alumina-10 wt.% TCP- TiO2 composites. Actually, the specimens were found to behave distinguishable depending on the percentage of titania under the explored conditions. In fact, the specimen of Alumina-10 wt.% TCP recorded maximum COF-values around 0.49, while Al2O3–10 wt.% TCP-TiO2 specimens showed lowest COF-values about 0.325.

After each test, wear resistance and wear volume were estimated for different specimens.

The evolution of the wear rate and wear volume of Alumina-10 wt.% TCP-TiO2 as a function of different Titania percentages is presented in **Figure 12**. According to this figure, it is noticed that the increasing of Titania content can lead to an increase in the wear resistance. The significant increase of this resistance is observed for 5 wt.% of Alumina- 10 wt.% TCP-TiO2.

For the optimum composition, the wear volume decreases four times compared to Alumina- 10 wt.% TCP. Likewise, the lowest wear volume (0.26) was recorded for the Al2O3–10 wt.% TCP-5 wt.% TiO2 composite.

#### **Figure 12.**

*Wear volume and wear rate of different samples (Alumina- 10 wt.% TCP- TiO2) composites.*

These low wear volumes are expected by the significantly higher values of the micro-hardness of the composites which go from 3800 MPa for Al2O3–10 wt.% TCP, to reach 9000 MPa, in the presence of 5% TiO2 with a tenacity of the order of 13 MPa m1/2. Indeed, the good densification of Al2O3–10% TCP-5% TiO2 composite is due to mass transfers in liquid phase sintering. In this study, the liquid phase corresponds to an eutectic transformation between the initial powder (TCP) and the additive (TiO2).

The tribological behavior of the biomaterials and specially the biocoating depends on the geometry of the contact, the tensile strength and also the surface roughness. The topography and surface roughness is an essential parameter during sliding contact which influences factors that govern sliding and wear behavior, the contact mode and the behavior of the interfacial medium.

The presence of pores in materials decreases the actual contact area between the two materials in contact, thus appears the cracks between the pores, causing wear debris to form. The wear resistance is thus reduced. The increase of the wear of these composites was probably due to the poor porosity of the Al2O3–10 wt% TCP– 5 wt% TiO2 (10%) (**Figure 7**).

To provide more information on wear mechanisms, microscopic observations of the worn surfaces are retained.

The specimens were analyzed by SEM after a duration of 1 hour and at a sliding speed of 200 rpm under a load of 9 N. **Figure 13** presents typical damages such as wear scars, micro-cracking, mechanical fracture and abrasion marks on the surfaces of all samples.

By co1mparing the **Figure 13a-c** and **e**, it is observed that the area of wear scar was smaller on the Al2O3–10 wt.%TCP-TiO2 composite surface than Al2O3–10 wt.% TCP composite. This confirms that the addition of Titania to Al2O3–10 wt.%TCP enhances the wear resistance and tribological behavior [34]. For Al2O3–10 wt.% TCP-Titania composites, the debris became less deep and often compacted (**Figure 13b**, **d** and **f**).

#### **3.4 Physicochemical characterization**

The mechanical and tribological behavior confirms that a significant improvement in mechanical and tribological properties in the presence of 5 wt.% titania.

*Effect of Titania Addition on Mechanical Properties and Wear Behavior… DOI: http://dx.doi.org/10.5772/intechopen.99253*

**Figure 13**

*.*

*SEM images of worn surfaces after testing against zirconia ball under 9N of (a) and (b) Al2O3- 10 wt.% TCP (c) and (d) Al2O3-10 wt.% TCP-5 wt.% TiO2, (e) and (f) Al2O3-10 wt.% TCP-10 wt.% TiO2.*

In order to find an explanation for this improvement, an in-depth physicochemical study was carried out to obtain more information, in particular, the microstructural changes of the samples.

**Figure 14** exhibits XRD patterns of Al2O3–10 wt.% TCP, and Alumina-10 wt.% TCP-5 wt.% Titania composites sintered for 1 h at 1600°C. A new information was added about solid-state reactivity in the ternary system Al2O3-TCP-TiO2. In fact, the spectra indicate the presence of traces of β-TCP, α-Al2O3, and new phases relative to β-Al2TiO5: aluminum titanate (**Figure 14**). This is an intermetallic compound relating to (βAl2TiO5) in the binary system Al2O3-TiO2. It is a thermodynamically stable compound above 1280°C, formed as a result of a reaction between α- Al2O3 and TiO2 in an oxidizing atmosphere. Note also that the intensity of the peak increases with the TiO2 content in the Al2O3 composite – 10 wt.% TCP.

The micrograph (**Figure 15a**) displays a continuous phase and the spherical pores in the Al2O3–10 wt.% TCP composites. The microstructure of the Al2O3–10 wt.% TCP composites sintered with Titania show a high densification (**Figure 15b-d**).

#### **Figure 14***.*

*XRD patterns of different composites Alumina-10 wt.% TCP-Titania versus percentage of Titania sintered at 1600 °C for 1 h.*

For Al2O3–10 wt.% TCP-2.5 wt.% TiO2 composite, we notice a high intergranular porosity (**Figure 15b**).

An important improvement of the characteristic performances of the Al2O3– 10 wt.% TCP-5 wt.% TiO2 composite was obtained by the addition of titania.

The microstructural analysis of the Al2O3–10 wt.% TCP-5 wt.% TiO2 composite reveal high densification (90%) of the specimens. The creation of a liquid phase (between TCP and TiO2) (**Figure 15c**) that can induce a higher wear and mechanical strength through the transition from solid sintering to liquid sintering. In summary, a small amount of liquid phase due to the presence of a TCP-TiO2 eutectic caused the densification of the composites and the improvement of the mechanical properties of the Al2O3–10 wt.% TCP-5 wt.% TiO2 composite.

On the other hand, the addition of high percentages of TiO2 hinders densification was found that the intragranular pores and the growth of the grains are more important, consequently decreases in mechanical properties. For the composite Al2O3–10 wt.% TCP-10 wt.% TiO2 composite (**Figure 15d**), it was found that there are intragranular pores and grain growth.

When increasing TiO2 content in Al2O3–10 wt.%TCP composites, the mechanical and wear resistance of the Alumina-10 wt.% TCP composites were enhanced. In fact, the wear volume and the mechanical stresses of the Al2O3–10 wt.% TCP composites decreased to a minimum value with 5 wt.% Titania. In our research, the mechanical and tribological behavior of Alumina-TCP- TiO2 bioceramics is

*Effect of Titania Addition on Mechanical Properties and Wear Behavior… DOI: http://dx.doi.org/10.5772/intechopen.99253*

#### **Figure 15.**

*SEM micrographs of the Alumina-10 wt.% TCP-Titania composites sintered at 1600 °C for 1 h: (a) Al2O3- 10 wt.% TCP, (b) Al2O3- 10 wt.% TCP-2.5 wt.% TiO2 (c) Al2O3-10 wt.% TCP-5 wt.% TiO2, (d) and (e) Al2O3-10 wt.% TCP-10 wt.% TiO2.*

enhanced by incorporating TiO2, that's agrees well with other similar works [34, 35].

An important improvement of the characteristic performances of the Al2O3– 10 wt.% TCP-5 wt.% TiO2 composites were successfully obtained by the addition of titania oxide.

This important improvement can be explained by the high densification of the samples (90%), the creation of a liquid phase (between TCP and TiO2) (**Figure 15c**).

#### **4. Conclusion**

In this chapter, we have focused on the effect of Titania on mechanical and tribological characterizations of Alumina-10 wt.% TCP biomaterials manufactured as coating for orthopedic implant.

After the sintering process, Alumina-10 wt.% TCP-Titania composites have been characterized by using X-ray diffraction and SEM analysis. The mechanical properties have been investigated by the Flattened Brazilian test, compression test, semicircular bending test and NanoIndenter. A pin-on-disk tribometer was used to ensure sliding and wear experiments under dry condition and against zirconia ball. A 2D profilometer was retained to measure the wear volume.

The main results are summarized as follows:

The produced Al2O3–10 wt.% TCP-TiO2 composites with different percentages of Titania (1 wt.%; 2.5 wt.%; 3 wt.%,4 wt.%,5 wt.%,7.5 wt.% and 10 wt.%) exhibited much better mechanical properties than the reported values of Alumina-TCP without titania.

After the sintering process at 1600°C for 1 hour, the Al2O3–10 wt.% TCP composites showed a higher elastic modulus, compressive strength, flexural strength, and fracture toughness which certainly increased with the Titania content and reached the optimum value with 5 wt.%. However, no cracks were observed in the microstructure of this composition.

In terms of tribological properties, the composite Alumina-10 wt.% TCP-5 wt.% Titania presents excellent wear rate and wear volume. Accordingly, the lowest wear volume (0.003%) was recorded for this composite. The mechanical properties and wear behavior of Alumina-TCP-TiO2 biomaterial is enhanced by incorporating Titania. This important improvement can be explained by the high densification of the composite (90%) and the creation of a liquid phase (between Tricalcium Phosphate and Titania).
