**3. Results and discussions**

#### **3.1 X-ray diffraction analysis and microstructural study**

This section has been structured according to the employed reinforcement, in order to present the results and to perform their discussion clearly and concisely. Therefore, there have been three subparts taking into account the ceramic materials used as starting reinforcements in the TMC manufacturing.

#### *3.1.1 TiC*

*Inelastic X-Ray Scattering and X-Ray Powder Diffraction Applications*

only Ti, TiC, TiB2, and B4C, respectively.

Reinforcement material Volume

*Reinforcement percentages and processing parameters.*

[%]

*Diagram of the inductive hot-pressing cycle: time vs. temperature and piston displacement.*

**Ti matrix and reinforcement**

**Table 2.**

the most representative of the concentration of the analysed species.

the phase evolution of sintered TMCs. The reference intensity ratio (RIR) analysis was performed to semi-quantitatively determine the phases. This method is based on setting the diffraction data to the diffraction of standard reference materials. The intensity of a diffraction peak profile is a convolution of diverse factors, being

In **Figure 1**, the X-ray diffraction spectra of the starting materials (as-received) are shown. Based on the obtained diffraction patterns, these materials consist of

Previously in the TMC consolidation, the raw material blends were prepared according to the fixed percentages in volume (see **Table 2**). The mixing procedure was described in previous authors' work [28]. Next, the specimens were sintered. To consolidate the TMCs, a self-made hot pressing machine, inductive hot pressing (iHP) equipment of RHP-Technology GmbH & Co. KG (Seibersdorf, Austria), was used. This machine enabled the operational cycle time to be reduced thanks to its advantageous high heating rate, which in turn is due to its special inductive heating setup. The prepared powders were inserted in the graphite die; it was lined with thin graphite paper and a protective coating of boron nitride (BN). The same procedure and die were used for all the iHP cycles (punch Ø 20 mm). Methods based on this rapid hot consolidation are considered as preferred techniques for in situ fabrication of nearly fully dense TMCs [29]. In **Table 2**, the processing conditions are shown. Likewise, the curves of the process cycle are represented graphically in

**Processing parameters**

Time [min]

Pressure [MPa]

Temperature [°C]

TiC 10, 20, 30 1000, 1100, 1200 15 50 TiB2 10, 20, 30 1000, 1100, 1200 15 50 B4C 10, 20, 30 1000, 1100, 1200 15 50

**102**

**Figure 2.**

The X-ray diffraction spectra of TMCs made from TiC-Ti blends are shown in **Figure 3**. Based on the obtained diffraction patterns, these materials consist of Ti and TiCx phases. On the one hand, the X-ray analysis reveals that there are only Ti and TiC phases in specimens produced at 1000°C, regardless of whether the highest or the lowest TiC concentration (vol.%) was used in the starting blend. Likewise, only TiC stoichiometric phase is detected in specimens made from 10 vol.% of TiC, even in specimens produced at 1100 and 1200°C. On the other hand, the peak intensity of the Ti phase decreased; meanwhile, there was an apparition of slight diffraction peaks of nonstoichiometric TiC phase named TiC0.67. It suggested that there were possible reactions between the Ti and diffused C from the TiC particles at high concentrations (20 vol.% TiC and 30 vol.% TiC). The intensification of the nonstoichiometric TiC peaks from 1100 to 1200°C indicates the increase in the volume fraction of this phase, which can be confirmed by the RIR semi-quantification analysis. The results from RIR analysis are shown in **Table 3**. These results may lead to the assumption that the phenomenon of C diffusion was more significant at the highest TiC concentration (30 vol.%) and the highest operational temperature (1200°C). In agreement with the values of the RIR semi-quantification analysis in **Table 3**, the higher the TiC in starting materials was used, the higher the TiC phase values in the RIR analysis was detected.

To clarify the distribution of the nonstoichiometric TiCx phases in TMCs, energy-dispersive X-ray spectroscopy (EDS) analysis was performed. In **Figure 4**, the EDS result revealed that there were concentration gradients between the centres of the TiC particles and the matrix. This clearly demonstrated the value of the temperature and the starting material compositions as influencing factors in the final behaviour of the TMCs. Moreover, it can be observed from **Figure 4** that C was diffused in the region, which is rich in titanium. This is in accordance with the slight displacement of the Ti peaks in the TMC patterns when the specimens were consolidated especially at 1200°C.

#### **Figure 3.** *XRD patterns of TMCs reinforced using (a) 10 vol.% of TiC, (b) 20 vol.% of TiC and (c) 30 vol.% of TiC.*


#### **Table 3.**

*Reinforcement percentages and processing parameters.*

From the microstructural point of view, there were several differences observed in the specimens, which depended not only on the processing temperature employed but also on the starting reinforcement concentration. In this regard, the lower the concentration of TiC (10 vol.%), the fewer the pores observed in the TMC microstructure. Moreover, some agglomerations of the TiC particles could be clearly appreciated in specimens made from the blend with 30 vol.% of TiC; there are little pores observed

**105**

*3.1.2 TiB2*

**Figure 4.**

**Figure 5.**

*(b) 1200°C.*

*In Situ Titanium Composites: XRD Study of Secondary Phases Tied to the Processing Conditions…*

*On the left, SEM image of TMCs processed at 1200°C, with starting TiC composition of 20 vol.%. On the right,* 

in the centre of these ceramic particles' agglomerations in the titanium matrices (**Figure 5a**). The pores tended to close with the increase in temperature. In line with the diffusion phenomenon mentioned above, a possible reason for the porous reduction may be the diffusion of the C element and, consequently, the formation of TiCx phases. Furthermore, the cited pores could also be caused by material removal during the metallographic preparation, which suggested that major bonding between TiC particles and the matrix decreases the material removal. It indicates that the reaction between the C sourced by TiC particles and Ti from the matrix involved a strong interfacial bonding. Therefore, the rising of the temperature benefited, and it was very useful to obtain major densification. It is worth noting that the reinforcement agglomeration could be a problem as a barrier for affecting the diffusion phenomenon and the interfacial contact. For that reason, the pores are only observed in the centre

*SEM images of TMCs made from composition of 30 vol.% of TiC hot consolidated at (a) 1000°C and* 

**Figure 6** shows the XRD patterns of the TMCs reinforced with TiB2 particles. In this respect, particular attention will be devoted to the existence of peaks of Ti3B4, while there was an increment of the temperature from 1100 to 1200°C. Likewise, it can be seen that the XRD patterns of the specimens produced at 1000°C only contain strong diffraction peaks of TiB2 phase and slight diffraction peaks of TiB phase. The Ti3B4 peaks appear independently of the starting TiB2 concentration (vol.%),

**Table 4** shows the semi-quantification analysis of the TMCs reinforced by TiB2 particles. As many authors describe [9, 12, 13, 16, 19, 22, 29], there are reactions between B from TiB2 particles and the Ti matrix, resulting in the in situ TiB phase. Thus, it would be expected that the percentages of in situ TiB phase were proportional to the initial composition of TiB2 in the starting blend. However, observing the values presented in **Table 4**, the key parameter was the temperature instead of the concentration,

being only related to the processing temperature (1100 and 1200°C).

of the mentioned agglomerations (see **Figure 5**).

*DOI: http://dx.doi.org/10.5772/intechopen.88625*

*EDX analysis of three spots on the cross section of such TMC.*

*In Situ Titanium Composites: XRD Study of Secondary Phases Tied to the Processing Conditions… DOI: http://dx.doi.org/10.5772/intechopen.88625*


#### **Figure 4.**

*Inelastic X-Ray Scattering and X-Ray Powder Diffraction Applications*

From the microstructural point of view, there were several differences observed in the specimens, which depended not only on the processing temperature employed but also on the starting reinforcement concentration. In this regard, the lower the concentration of TiC (10 vol.%), the fewer the pores observed in the TMC microstructure. Moreover, some agglomerations of the TiC particles could be clearly appreciated in specimens made from the blend with 30 vol.% of TiC; there are little pores observed

**Temperature (°C) vol.% Ti (%) TiC (%) TiC0.67 (%)**

*XRD patterns of TMCs reinforced using (a) 10 vol.% of TiC, (b) 20 vol.% of TiC and (c) 30 vol.% of TiC.*

1200 10 94.6 3.6 1.8

20 96.3 6.4 30 88.5 11.5

20 91.9 8.1

30 84.4 15.6

20 91.4 8.6 30 81.0 19.0

1000 10 97.8 2.2

1100 10 96.9 3.1

*Reinforcement percentages and processing parameters.*

**104**

**Table 3.**

**Figure 3.**

*On the left, SEM image of TMCs processed at 1200°C, with starting TiC composition of 20 vol.%. On the right, EDX analysis of three spots on the cross section of such TMC.*

**Figure 5.**

*SEM images of TMCs made from composition of 30 vol.% of TiC hot consolidated at (a) 1000°C and (b) 1200°C.*

in the centre of these ceramic particles' agglomerations in the titanium matrices (**Figure 5a**). The pores tended to close with the increase in temperature. In line with the diffusion phenomenon mentioned above, a possible reason for the porous reduction may be the diffusion of the C element and, consequently, the formation of TiCx phases. Furthermore, the cited pores could also be caused by material removal during the metallographic preparation, which suggested that major bonding between TiC particles and the matrix decreases the material removal. It indicates that the reaction between the C sourced by TiC particles and Ti from the matrix involved a strong interfacial bonding. Therefore, the rising of the temperature benefited, and it was very useful to obtain major densification. It is worth noting that the reinforcement agglomeration could be a problem as a barrier for affecting the diffusion phenomenon and the interfacial contact. For that reason, the pores are only observed in the centre of the mentioned agglomerations (see **Figure 5**).

### *3.1.2 TiB2*

**Figure 6** shows the XRD patterns of the TMCs reinforced with TiB2 particles. In this respect, particular attention will be devoted to the existence of peaks of Ti3B4, while there was an increment of the temperature from 1100 to 1200°C. Likewise, it can be seen that the XRD patterns of the specimens produced at 1000°C only contain strong diffraction peaks of TiB2 phase and slight diffraction peaks of TiB phase. The Ti3B4 peaks appear independently of the starting TiB2 concentration (vol.%), being only related to the processing temperature (1100 and 1200°C).

**Table 4** shows the semi-quantification analysis of the TMCs reinforced by TiB2 particles. As many authors describe [9, 12, 13, 16, 19, 22, 29], there are reactions between B from TiB2 particles and the Ti matrix, resulting in the in situ TiB phase. Thus, it would be expected that the percentages of in situ TiB phase were proportional to the initial composition of TiB2 in the starting blend. However, observing the values presented in **Table 4**, the key parameter was the temperature instead of the concentration,

#### **Figure 6.**

*XRD patterns of TMCs reinforced in the starting blend with (a) 10 vol.% of TiB2, (b) 20 vol.% of TiB2, and (c) 30 vol.% of TiB2.*


#### **Table 4.**

*RIR semi-quantification analysis of TMCs made from Ti-TiB2 blends, manufactured at different temperatures (by iHP).*

**107**

**Figure 8.**

*(a) 10 vol.%, (b) 20 vol.%, and (c) 30 vol.%.*

**Figure 7.**

*In Situ Titanium Composites: XRD Study of Secondary Phases Tied to the Processing Conditions…*

promoting the apparition of TiB as in situ formed phase. Owing to the rising temperature, the diffusion mechanism was driven by the temperature increments of 100°C (from 1000 to 1100°C and from 1100 to 1200°C). The highest temperature (1200°C) played a major role in the formation of TiB, independently of the operational temperature. Obviously, at the same temperature, there was more TiB detected in specimens made from starting powder with the higher TiB2 composition (30 vol.% of TiB2). Microstructural study of these TMCs confirmed the visual existence of the in situ TiBx phases. Moreover, some pores were detected in areas where the TiB2 particles were slightly agglomerated. As mentioned in the results of the microstructural analysis of TMC reinforced by TiCx phases, the referred pores were located in the centre of particle agglomeration. The higher the concentration of particles and the lower the operational temperature, the more significant the apparition of pores in

The influence of the temperature was relevant once again to close these pores, as in similitude with the TiC. Many studies [31] attempted to show the importance of strong bonding between the matrix and the TiBx phases; the no contact between the reinforcement and the matrix, in addition to the inappropriate processing temperature, inhibited the formation of in situ secondary phases. By increasing the operational temperature, improvement in the diffusion phenomenon was expected. SEM images of the microstructure of TMCs processed at 1100°C are shown in **Figure 8**. The results about homogenous distribution and increase in the volume of reinforcements in the Ti matrix are in accordance to the RIR analysis. In **Figure 8a**, the reinforcements on the matrix can be easily recognized. Observing the microstructural evolution by increment of the composition, the smaller TiB2 particles were surrounded by the in situ formed phases when the starting composition of TiB2 was the lowest. However, in **Figure 8c**, coarse TiB2 particles were also sur-

the TMCs. In **Figure 7**, the commented pores can be recognized.

*SEM image of TMC reinforced with 30 vol.% of TiB2 particles consolidated at 1000°C.*

*SEM images of TMCs processed at 1100°C with different percentages of TiB2 in the starting blends:* 

*DOI: http://dx.doi.org/10.5772/intechopen.88625*

rounded by phases with minor size.

#### *In Situ Titanium Composites: XRD Study of Secondary Phases Tied to the Processing Conditions… DOI: http://dx.doi.org/10.5772/intechopen.88625*

promoting the apparition of TiB as in situ formed phase. Owing to the rising temperature, the diffusion mechanism was driven by the temperature increments of 100°C (from 1000 to 1100°C and from 1100 to 1200°C). The highest temperature (1200°C) played a major role in the formation of TiB, independently of the operational temperature. Obviously, at the same temperature, there was more TiB detected in specimens made from starting powder with the higher TiB2 composition (30 vol.% of TiB2).

Microstructural study of these TMCs confirmed the visual existence of the in situ TiBx phases. Moreover, some pores were detected in areas where the TiB2 particles were slightly agglomerated. As mentioned in the results of the microstructural analysis of TMC reinforced by TiCx phases, the referred pores were located in the centre of particle agglomeration. The higher the concentration of particles and the lower the operational temperature, the more significant the apparition of pores in the TMCs. In **Figure 7**, the commented pores can be recognized.

The influence of the temperature was relevant once again to close these pores, as in similitude with the TiC. Many studies [31] attempted to show the importance of strong bonding between the matrix and the TiBx phases; the no contact between the reinforcement and the matrix, in addition to the inappropriate processing temperature, inhibited the formation of in situ secondary phases. By increasing the operational temperature, improvement in the diffusion phenomenon was expected.

SEM images of the microstructure of TMCs processed at 1100°C are shown in **Figure 8**. The results about homogenous distribution and increase in the volume of reinforcements in the Ti matrix are in accordance to the RIR analysis. In **Figure 8a**, the reinforcements on the matrix can be easily recognized. Observing the microstructural evolution by increment of the composition, the smaller TiB2 particles were surrounded by the in situ formed phases when the starting composition of TiB2 was the lowest. However, in **Figure 8c**, coarse TiB2 particles were also surrounded by phases with minor size.

**Figure 7.** *SEM image of TMC reinforced with 30 vol.% of TiB2 particles consolidated at 1000°C.*

#### **Figure 8.**

*SEM images of TMCs processed at 1100°C with different percentages of TiB2 in the starting blends: (a) 10 vol.%, (b) 20 vol.%, and (c) 30 vol.%.*

*Inelastic X-Ray Scattering and X-Ray Powder Diffraction Applications*

*XRD patterns of TMCs reinforced in the starting blend with (a) 10 vol.% of TiB2, (b) 20 vol.% of TiB2, and* 

Temperature [°C] vol.% Ti (%) TiB2 (%) TiB Ti3B4 (%)

1100 10 90.2 4.1 3.9 1.8

1200 10 88.5 2.5 6.2 2.6

*RIR semi-quantification analysis of TMCs made from Ti-TiB2 blends, manufactured at different temperatures* 

20 78.2 19.0 2.8 30 68.3 28.1 2.9

20 77.9 12.0 6.8 3.3 30 65.0 24.8 7.4 2.8

20 76.7 3.9 12.3 7.1 30 72.9 3.5 20.9 3.4

1000 10 91.3 4.7 4.0

**106**

**Table 4.**

*(by iHP).*

**Figure 6.**

*(c) 30 vol.% of TiB2.*

**Ti matrix and TiB2**

**Figure 9.** *SEM image of TMC with 10 vol.% of TiB2 in the starting blend, processed at 1200°C.*

The rising in temperature was crucial for reactions between the matrix and the TiB2 particles. At 1200°C, there were major diffusion of B through the matrix and more formation of the in situ TiBx phases. **Figure 9** shows two different areas on a cross section (iHP at 1200°C), where the B distribution varied considerably; the darkest region in the centre corresponds with the highest concentration of B. It suggests that the dark grey areas were originally the TiB2 particles, which were surrounded by the in situ TiBx phases.
