Hot deformation behavior of nano-sized TiB reinforced Ti-6Al-4V metal matrix composites

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Hot deformation behavior of nano-sized TiB reinforced Ti-6Al-4V metal matrix composites Yuankui Cao , Yong Liu , Yunping Li , Bin Liu , Rongjun Xu PII: DOI: Reference:

S0167-6636(19)30446-6 https://doi.org/10.1016/j.mechmat.2019.103260 MECMAT 103260

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Mechanics of Materials

Received date: Revised date: Accepted date:

28 May 2019 26 October 2019 21 November 2019

Please cite this article as: Yuankui Cao , Yong Liu , Yunping Li , Bin Liu , Rongjun Xu , Hot deformation behavior of nano-sized TiB reinforced Ti-6Al-4V metal matrix composites, Mechanics of Materials (2019), doi: https://doi.org/10.1016/j.mechmat.2019.103260

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Highlights 

Nano-sized TiB whiskers distributed homogeneously in the α+β titanium matrix.



The fine microstructures result in low activation energy and good workability.



Instable deformation involves flow localization band, cracking and debonding of TiB.



Dynamic recrystallization is responsible for stable deformation.

1

Hot deformation behavior of nano-sized TiB reinforced Ti-6Al-4V metal matrix composites Yuankui Cao, Yong Liu*, Yunping Li, Bin Liu**, Rongjun Xu State Key Lab of Powder Metallurgy, Central South University, Changsha 410083, China * Corresponding author, ** Corresponding author E-mail addresses: [email protected] (Y. Liu), [email protected] (B. Liu)

Abstract: In situ Ti-6Al-4V/TiB composites with different contents of TiB were prepared by SPS. The flow behavior of the composites deformed at temperatures of 900~1200°C and strain rates of 0.001 to 10s-1 was studied. The constitutive equations and processing maps were established. Results show that the composites have fine microstructures, and nano-sized TiB whiskers distribute homogeneously in the α+β titanium matrix. The activation energy of the composites is low due to the fine microstructures, resulting in a good workability. The processing maps suggest that the instable deformation occurs at low temperatures and high strain rates. The flow localization band of Ti matrix, cracking and debonding of TiB whiskers are the reasons for the instable deformation. Dynamic recrystallization has been found in composites deformed at low strain rates, accounting for the stable deformation. Keywords: Titanium; Metal matrix composite; Hot deformation; Microstructure; Processing map

1. Introduction Titanium matrix composites (TMCs) have been wide applied in industrial fields due to their outstanding mechanical properties[1-4]. Ti-6Al-4V alloy is widely used as the matrix of TMCs, while ceramic phases such as TiC, TiB, SiC and Al2O3 are usually used as the reinforcements[5-7]. Xu et al.[8] demonstrated that TiB is the best reinforcement due to the excellent thermodynamic stability and compatibility to Ti. 2

The reinforcement phases can be introduced to Ti matrix either by addition of ceramics or by in situ formation. The in-situ process can produce fine reinforcements and clean reinforcement/matrix interfaces, and thus is more preferentially used. Huang et al.[6] prepared an in-situ nanostructured TiB strengthened Ti6Al4V composite via spark plasma sintering (SPS). The composite has a clean interface between Ti matrix and TiB whiskers, and resulting in a satisfied combination of strength and ductility. In recent years, microstructures and properties of TiB reinforced TMCs synthesized through in situ process have attracted more and more interests. The mechanical properties of TMCs can be significantly improved through thermo-mechanical processing (TMP)[9, 10]. TMP strategies, such as hot forging, hot isostatic pressing and hot rolling, are usually utilized to regulate the microstructures and properties of TMCs[9,

11]

. During TMP, the hot deformation behavior could

dramatically influence the workability and the microstructures, and thus should be strictly controlled. The hot deformation behavior of TMCs is affected by deformation conditions (i.e. temperatures and strain rates) and reinforcements. To date, there was numerous work on the hot deformation behavior under different deformation conditions, but few focused on the effect of reinforcements on the deformation mechanism of TMCs. For example, Zhang et al.[12] found the flow stress of the TiBw/Ti6Al4V composite decreases with the increase of temperature and the decrease of strain rate. Sun et al.[13] found that the optimal hot processing condition for the (TiB+La2O3)/Ti composite is around 900℃ and 0.01s-1. However, reinforcements could also affect the flow stress, and further influence the hot deformation behavior[12, 14]

. Ceramic reinforcements can lead to a high flow stress, which makes the TMCs

difficult to deform, and resulting in a poor workability. The size of reinforcements is 3

an important role in plastic deformation. In general, coarse reinforcements easily cause stress concentration and lead to an early fracture, while fine reinforcements usually bring about homogeneous deformation and result in good workability[15]. Though the reinforcements have great effect on hot deformation behavior, the effecting mechanism is not fully understood. Therefore, it is important to study the effect of reinforcements on hot deformation behavior of TMCs. The present work investigates the hot deformation behavior of Ti-6Al-4V/TiB composites with different contents of TiB prepared by SPS. The constitutive equations and processing maps were established, and the effect of the reinforcements on hot deformation behavior was discussed. 2. Experimental Ti-6Al-4V/TiB composites with 2.5~10% (in volume) TiB were in situ synthesized through SPS. Ti-6Al-4V powder, Ti powder and TiB2 powder were used as the raw powders. The average particle size of Ti-6Al-4V, Ti and TiB2 are 11μm, 39μm and 3.8μm, respectively. The TiB phase was in situ produced through the reaction: Ti + TiB2 → 2TiB (ΔG = -6.3kJ/mol). Based on the reaction, the relationship between the volume fraction of TiB and the mass fraction of TiB 2 was determined as: TiBvol.% = 1.63* TiB2wt.%. The corresponding powders were mixed for 2h by using a planetary ball mill. The weight ratio of the agate ball to the powder mixtures was 6: 1. The rotation speed was 400rpm, and ethanol was used as the protective medium. The powder slurry was dried by using a vacuum evaporator. The powder mixtures were then sintered by using a SPS system (HPD25/3 type, FCT). The specimens were sintered at 1100℃ for 5min at a pressure of 40MPa. After sintering, the specimen was cooled with a cooling rate of about 100℃/min.

4

Hot deformation of cylindrical specimens was performed at 900°C to 1200°C with an interval of 100°C and the strain rates from 0.001s-1 to 10s-1 on a dynamic thermal

simulation

testing

machine

(Gleeble-3000).

The

specimens

were

spark-machined from the sintered bulks with a dimensions of Ф6mm × 9 mm. The hot deformation tests were proceeded in vacuum (5 × 10-3Pa). The height reduction of specimens was controlled to be 55%. The specimen was cooled by water immediately after hot compression to maintain the deformed microstructures. The phase was analyzed by XRD (D/max 2550). The microstructures were investigated through SEM (Nova Nano SEM230) and TEM (JEM-2100F). 3. Results 3.1 Initial microstructures Fig. 1 shows the XRD patterns of the Ti-6Al-4V/TiB composites in the SPS status. The composites have a similar phase composition. Only α-Ti, β-Ti and TiB phase are detected in the composites, indicating that TiB2 has been depleted through the reaction. The intensity of TiB diffraction peaks increases with the addition of boride increasing (esp. at 2θ = 42°). The microstructures of the SPSed Ti-6Al-4V/TiB composites are presented in Fig.2. The phases could be clearly identified through morphology and contrast, i.e. the near-equiaxed phase is α-Ti (grey), the netted phase is β-Ti (white), and the rod-like phase is TiB (black). The grain size of the matrix is about 20μm. The grain size becomes finer with the content of TiB increasing. The TiB whiskers distribute homogeneously in the matrix. Fig. 2(d) shows the details of the fine TiB phase. The embedded images present the interface of TiB/matrix and the Selected Area Electron Diffraction (SAED) patterns of the TiB. The diameter of the TiB whisker is about 118nm. The interface is clean and well-bonded. No defects such as cracks or impurities can be found around the interfaces. The volume fraction of 5

TiB and β phase of the SPSed composites is shown in Table 1, the volume fractions of TiB are 2.3%, 4.7%, and 8.9%, respectively, which are lower than the theoretical values (2.5%, 5%, and 10%, respectively), suggesting that some boron may dissolve in the matrix. In addition, the fraction of β phase decreases with the content of TiB increasing, agreed with the results reported by Tamirisakandala et al[16].

Fig.1. XRD patterns of the Ti-6Al-4V/TiB composites prepared by SPS.

6

Fig. 2. Microstructures of the SPSed Ti-6Al-4V/TiB composites: (a) 2.5%TiB; (b) 5%TiB; (c) 10%TiB; (d) details of the TiB whiskers. Table 1 Volume fraction of TiB and β phases in the composites after SPS. Volume fraction (%) Phases Ti-6Al-4V/2.5%TiB

Ti-6Al-4V/5%TiB

Ti-6Al-4V/10%TiB

TiB

2.3

4.7

8.9

β phase

14.3

11.4

10.5

3.2 Hot deformation behavior The compressive curves of the composites deformed at 900~1200℃ and 0.001~10s-1 are shown in Fig. 3. The stress increases rapidly within a small strain, and then, decreases continuously after reaching the peak stress. In the final stage, the flow stress becomes stable and no longer change. Fig. 4 shows the corresponding peak stress obtained from the compressive true stress-true strain curves. The peak stress decreases with increasing temperatures and decreasing strain rates. The effects of TiB content on peak stress are dependent on the deformation conditions. When being deformed at low temperature or high strain rate (10s-1), the peak stress increases significantly with the content of TiB increasing. But, when being deformed at high temperatures (1100~1200℃) and low strain rate (0.001s-1), the values of peak stress show weak dependence on the contents of TiB.

7

Fig. 3. Compressive true stress-true strain curves of the Ti-6Al-4V/TiB composites deformed at: (a) 900℃; (b) 1000℃; (c) 1100℃; (d) 1200℃.

Fig. 4. Peak stress of compression test: (a) 900℃; (b) 1000℃; (c) 1100℃; (d) 1200℃. 8

For further understanding the hot deformation behavior and the deformation mechanism of the in situ Ti-6Al-4V/TiB composites, the activation energy was calculated. Since the α/β phase transition temperature for Ti-6Al-4V matrix is about 990℃, the activation energy of the composites is discussed in β phase field (1000℃~1200℃). The Arrhenius equation can be used to analyze deformation behavior and activation energy[17]: ̇

(1)

Where ̇, σ and T represent the strain rate, the flow stress and the temperature, respectively. The parameter A, α and n are the material constants, and R is the gas constant (8.314 J·mol-1·K-1). The parameter Q represents the deformation activation energy, and can be expressed as: α

̇

( [

)

̇

( ̇

(

)

]

)

(2) *

(

)

+ ̇

(3)

Fig.5 shows the linear dependence of the above parameters. The four plots all show a linear relationship approximately. Based on the linear regression analysis, the values of α are 0.026, 0.023 and 0.026, respectively, determined from Fig.5 (a) and (b). And, from Fig.5 (c) and (d), the activation energy, Q, was calculated to be 280 kJ/mol, 292 kJ/mol and 309 kJ/mol, respectively. The well-known Zenere-Hollomon parameter (Z) can describe the deformation condition during TMP process[18]: ̇

(4)

The linear dependence between the variable lnZ and ln[sinh(ασ)] is analyzed in Fig.6. Corresponding slope and intercept represent the parameter n and lnA, respectively. The values of linear correlation coefficient R are 97.0%, 97.4% and 98.5% for the composites with 2.5TiB%, 5%TiB and 10%TiB, respectively. The high R 9

values reflect that the flow behavior of the composites can be well described by the Arrhenius constitutive. Therefore, the Arrhenius constitutive equations of the current composites are established as follow: ̇

(for Ti-6Al-4V/2.5%TiB)

(5)

̇

(for Ti-6Al-4V/5%TiB)

(6)

̇

(for Ti-6Al-4V/10%TiB)

(7)

Fig. 5. Linear regression analysis of flow stress and deformation parameters: (a) ln ̇-lnσ; (b) ln ̇-σ; (c) ln ̇-ln[sinh(ασ)]; (d) ln[sinh(ασ)]-T-1.

10

Fig. 6. Linear dependence of the parameter Z on the ln[sinh(ασ)] for Ti-6Al-4V/TiB composites. 3.3 Processing maps Prasad et al.[19] developed a Dynamic Materials Model (DMM) to establish processing map. The processing map can give a direct evaluation of workability and provide suitable processing parameters for materials. Based on the DDM, the processing maps of the current composites were established, as shown in Fig. 7. The numbers in the processing maps represent the values of the efficiency of power dissipation (η, (%)). The processing maps of the composites with different contents of TiB show similar configuration: the domains with high values of η (η > 45%) mainly occurs at low temperatures with low strain rates (900~1000℃, 0.01~0.001s-1). And, the domains for instable deformation locate at low temperatures with high strain rates. With the content of TiB increasing, the maximum value of η increases from 48% to 57%, indicating the microstructural evolution is promoted by the addition of boride. The plastic flow instability domain also depends on the content of TiB. The instable domain for the composite with 2.5%TiB is located at 900℃~920℃ with strain rate from 1s-1~10s-1. With the content of TiB increasing, the instable deformation domain expands to the β phase field: the deformation instable domain for the composite with 11

5%TiB and 10%TiB are 900℃~1025℃, 0.1s-1~10s-1 and 900℃~1175℃, 0.01s-1~10s-1, respectively.

Fig. 7. Processing maps of the Ti-6Al-4V/TiB composites with: (a) 2.5%TiB; (b) 5%TiB; (c) 10%TiB. 3.4 Microstructural evolution To investigate the deformation mechanism in both stable and instable domains, the microstructures of the composites after hot deformation were studied. Fig. 8 shows the microstructural characteristics of the composites being deformed at high strain rate (10s-1). The composites all show features of flow localization when being deformed at 900℃ and 10s-1. The microstructures in the flow band present severe plastic deformation, as shown in Fig. 8(a~c). The α and β phases of the matrix are elongated to near 45° to the loading direction, and the TiB whiskers are broken within the band. The microstructures of the composites being deformed at 1000℃ and 10s-1 are shown in Fig. 8(d~f), in which homogeneous deformation can be observed. Both α and β phases are found in the matrix. Under this deformation condition, the composite 12

with 2.5%TiB exhibits stable deformation with the TiB whiskers distributed dispersively. However, with the content of TiB increasing, the whiskers turn to be clustered and broken. When being deformed at a high temperature (1100℃), the hot deformation becomes much more homogeneously, as shown in Fig 8(g~i). A microstructure of single β phase with TiB whiskers aligning near perpendicular to the compression direction can be observed. The TiB whiskers bond well with the matrix in the composites with 2.5%TiB and 5%TiB. But, the interfacial debonding between TiB and the matrix can be found in the composite with 10%TiB, as shown in Fig. 8(i). The microstructural characteristics in stable deformation domain were also studied. Fig. 9 shows the EBSD results of the composites deformed at low strain rate (900℃, 0.001s-1). The grain size is refined after hot deformation. An obvious dynamic recrystallization behavior is found in the composites.

Fig. 8. Microstructures of the Ti-6Al-4V/TiB composites deformed at 10s-1: (a) 2.5%TiB at 900℃; (b) 5%TiB at 900℃; (c) 10%TiB at 900℃; (d) 2.5%TiB at 1000℃;

13

(e) 5%TiB at 1000℃; (f) 10%TiB at 1000℃; (g) 2.5%TiB at 1100℃; (h) 5%TiB at 1100℃; (i) 10%TiB at 1100℃.

Fig. 9. EBSD images of the Ti-6Al-4V/TiB composites deformed at 900℃ and 0.001s-1: (a) 2.5%TiB; (b) 10%TiB. 4. Discussion 4.1 Flow behavior The flow curves of the in situ Ti-6Al-4V/TiB composites all present flow softening after peak stress, similar phenomenon has been reported in previous researches[13, 20]. The flow softening is attributed to the combined effects of work hardening and flow softening[14]. The flow stress increases with the content of TiB increasing. The reasons are as follows: i) the solution of boron may cause a decrease in β phase fraction[16]. Tamirisakandala et al.[16] reported that the supersaturated boron in the rapidly solidified alloy can cause a significant increase in β transus. In the present work, the majority of boron transforms into TiB during the in situ reaction, but a small number of boron can dissolve in the matrix and may cause a slight supersaturation due to the rapid cooling rate of SPS. Therefore, the composite with higher content of TiB shows lower fraction of β phase, as shown in Table 1. Because of the high activation energy of α phase, the deformation in α phase is more difficult than that in β phase[21]. Thus, the rising in flow stress of the composite with high TiB 14

content could be attributed to the reduced β phase. ii) the strengthening from the TiB whiskers. The hard TiB whiskers impede the dislocation motion and the grain-boundary sliding, which result in a high flow stress during hot deformation. iii) the TiB whiskers cause an increasing in geometrically necessary dislocation density demonstrated[22]. The TiB whiskers are rigid and do not deform, so the strain gradient along the interface between the whisker and the matrix needs to be offset through the generation of dislocations. Thus the high content of TiB results in a high dislocation density, which is one of the reason for the high flow stress of the composite with 10%TiB. However, the increasing in flow stress caused by the content of TiB becomes negligible when being deformed at high temperatures and low strain rates. The high deformation temperature leads to a formation of single β phase in the matrix, thus the difference caused by the fraction of β phase is mitigated. The low strain rate also helps to mitigate the stress concentration by providing sufficient time for dynamic softening. Therefore, the content of TiB has little effect on the flow stress when being deformed at 1100~1200℃ and 0001s-1. 4.2 Hot workability The activation energy reflects the necessary energy for plastic deformation, and can evaluate the workability of alloys. The activation energy is generally related to microstructures and deformation conditions. In the case of dual-phase titanium alloys, the activation energy is significantly affected by the α/β phase ratio, grain size and deformation conditions[23]. Table 2 gives the activation energy of TMCs with similar compositions prepared by different methods. In the β phases field, the values of activation energy of the Ti-6Al-4V/TiB composites (280~309 kJ/mol) are greater than that of the Ti-6Al-4V alloy (234 kJ/mol), which is caused by the strengthening effect of the TiB whiskers[23]. Compared with other TMCs, the composites prepared by SPS 15

exhibit relative low values of activation energy, which can be attributed to the fine microstructures. The low values of activation energy reflect a better workability of the composites. TMCs with high TiB content usually exhibit flow instability when being deformed in α+β phase field at low strain rate, due to cavitation or fracture of reinforcements. But, for the present composites, the hot deformation at 900℃ and 0.001s-1 was found to be stable. The deformation microstructures shown in Fig. 9 present significant DRX behavior, and no crack or breaking of TiB whiskers can be found. The improvement in hot workability of the composites is mainly benefited from the fine microstructures. A critical strain rate for ductile fracture was proposed by Koeller et al.[24], suggesting that the critical strain rate increases remarkable with decreasing in particle size. According to the model, grain refining can remarkably improve the flow stability of the composites. As for the present composites, the fast cooling rate during SPS results in a fine microstructure of TiB. Therefore, the present composites exhibit remarkable flow stability.

16

Table 2 Comparison of the values of activation energy of TMCs prepared by different methods. Deformation

Activation

temperature

energy

(℃)

(kJ/mol)

Preparation Composition

Ref.

method

Ti-6Al-4V

PM

1000~1100

234

Ref.[25]

Ti-6Al-4V/2.5%TiB

SPS

1000~1200

280

This work

Ti-6Al-4V/5%TiB

SPS

1000~1200

292

This work

Ti-6Al-4V/10%TiB

SPS

1000~1200

309

This work

Ti-6Al-4V/5%TiB

HIP

1010~1100

300

Ref.[26]

Ti-1100/5%(TiB+TiC)

VAR

1000~1150

334

Ref.[27]

Ti-6Al-2Zr-1Mo-1V/3.5%TiB

HP

1010~1040

345

Ref.[28]

4.3 Deformation mechanism The deformation mechanism of composites (both metal matrix composites (MMCs) and polymer matrix composites (PMCs)) are closely associated with the strain rate, deformation temperature and ceramic reinforcements[15, 29-31]. For example, the dispersion of nanoclay in the polyethylene matrix can reduces the severity of periodic scratch tracks and cracking during microscratching[32]. As for TMCs reinforced with TiB, the deformation characteristics are dependent on deformation conditions and the content of TiB. In the instable region, the deformation mechanism is usually associated with flow localization of matrix, cavitation, and fracture of TiB. When being deformed at low temperature and high strain rate, the composites present flow localization, which is related to adiabatic shearing[33]. The heat generated by deformation could not dissipate immediately during the limited deformation time at higher strain rates. The adiabatic heating promotes local deformation along the 17

maximum shear stress plane (45° to the loading direction), and thus leading to the flow localization. In the flow localization band, grains can be refined significantly, which further promotes plastic deformation in the shear band [34]. Therefore, the deformed composites present severe plastic deformation in the flow localization band with plenty of broken TiB whiskers (Fig. 8(c)). With temperature increasing, the plastic deformation becomes more homogenous. The strain rate sensitivity exponent, m (given by

)̇ , can reflects the homogeneity of deformation[20]. A

high value of m usually corresponds to a homogeneous deformation, and superplasticity may occur when m > 0.3. The strain rate sensitivity exponents of the composites at 900℃~1200℃ are determined, as shown in Table 3. The composites deformed at 900℃ show relatively low strain rate sensitivity exponents (m = 0.16). The exponent increases to about 0.2 when being deformed in β phase field. The content of TiB has little effect on the strain rate sensitivity exponents. The calculated results suggest that the plastic deformation becomes more homogenous when the temperature increases from 900℃ to over 1000℃. When being deformed at high temperatures and high strain rates, the deformation in matrix becomes stable, and the deformation instability mainly comes from the failure of TiB whiskers, as shown in Fig. 8(d~i). The breaking and debonding of the TiB whiskers are responsible for the flow instability. Such features are related to the content of TiB in the composites, i.e. the failure of TiB whiskers is more likely to occur in composite with high TiB content, mainly due to the stress concentration and interaction of whiskers themselves. During hot deformation, the stress concentration leads to local deformation in the composites. Once the local stress exceeds either the fracture strength of the TiB whisker or the strength of the interface of TiB/matrix, cracking or debonding will occur. The failure type also depends on the deformation 18

temperature. Cracking of TiB prefers to occurring at relatively low temperature while debonding of TiB occurs at high temperature. The Balakrishna criterion for determining the failure type is expressed as[35]: (for cracking) and

(for debonding)

(8)

where l is the length of the whisker, and d is the diameter of the whisker, σfiber and σmatrix are strengths of the whiskers and the matrix, respectively. With deformation temperature increasing, the matrix becomes soft obviously while the rigid TiB whisker keeps hard. Therefore, according to the criterion, the failure of the TiB whiskers may turns from breaking to debonding. Table 3 Strain rate sensitivity exponents of the composites at different temperatures. Strain rate sensitivity exponent Composites 900℃

1000℃

1100℃

1200℃

Ti-6Al-4V/2.5%TiB

0.16

0.20

0.19

0.19

Ti-6Al-4V/5%TiB

0.16

0.20

0.21

0.20

Ti-6Al-4V/10%TiB

0.16

0.19

0.21

0.21

5. Conclusions (1) The in situ Ti-6Al-4V/TiB composites prepared by SPS have fine microstructures, and the nano-sized TiB whiskers distribute homogeneously in the α+β titanium matrix. (2) The composites present continuous flow softening during hot deformation. The flow stress increases sharply with the content of TiB increasing, especially when being deformed at high strain rate. (3) The constitutive equations of the Ti-6Al-4V/TiB composites were established. The values of activation energy are low due to the fine microstructures, and increase with 19

the content of TiB increasing. The low activation energy further results in a good workability of the composites. (4) The instable deformation occurs at low temperature and high strain rate, and extends to higher temperature and lower strain rate with the content of TiB increasing. The flow localization band of Ti matrix, cracking and debonding of TiB whiskers are the reasons for the instable deformation of the composites. Dynamic recrystallization is responsible for uniform deformation of the composites in stable region. Acknowledgments This work was supported by the National Natural Science Funds for Distinguished Young Scholar of China (51625404), the Hunan Natural Science Foundation of China (2017JJ2311) and the Project of Innovation for Postgraduate of Hunan Province (CX2017B047). Reference [1] I. Montealegre Melendez, E. Neubauer, P. Angerer, H. Danninger, J.M. Torralba, Influence of nano-reinforcements on the mechanical properties and microstructure of titanium matrix composites, Composites Science and Technology, 71 (2011) 1154-1162. [2] P. Majumdar, S.B. Singh, M. Chakraborty, Fatigue behaviour of in situ TiB reinforced β-titanium alloy composite, Materials Letters, 64 (2010) 2748-2751. [3] Y. Lin, J. Yao, Y. Lei, H. Fu, L. Wang, Microstructure and properties of TiB2-TiB reinforced titanium matrix composite coating by laser cladding, Optics and Lasers in Engineering, 86 (2016) 216-227. [4] J. Wang, L. Li, C. Tan, H. Liu, P. Lin, Microstructure and tensile properties of TiCp /Ti6Al4V titanium matrix composites manufactured by laser melting deposition, Journal of Materials Processing Technology, 252 (2018) 524-536. [5] C. Cai, B. Song, C. Qiu, L. Li, P. Xue, Q. Wei, et al., Hot isostatic pressing of in-situ TiB/Ti-6Al-4V composites with novel reinforcement architecture, enhanced hardness and elevated tribological properties, Journal of Alloys and Compounds, 710 (2017) 364-374. [6] L. Huang, L. Wang, M. Qian, J. Zou, High tensile-strength and ductile titanium matrix composites strengthened by TiB nanowires, Scripta Materialia, 141 (2017) 133-137. [7] G. Huang, X. Guo, Y. Han, L. Wang, W. Lu, D. Zhang, Effect of extrusion dies angle on the microstructure and properties of (TiB+TiC)/Ti6Al4V in situ titanium matrix composite, Materials Science and Engineering: A, 667 (2016) 317-325. [8] X. Wang, L. Wang, L. Luo, H. Yan, X. Li, R. Chen, et al., High temperature deformation behavior of melt hydrogenated (TiB + TiC)/Ti-6Al-4V composites, Materials & Design, 121 (2017) 335-344. [9] X. Guo, L. Wang, M. Wang, J. Qin, D. Zhang, W. Lu, Effects of degree of deformation on the microstructure, mechanical properties and texture of hybrid-reinforced titanium matrix composites, Acta Materialia, 60 (2012) 2656-2667. 20

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Conflict of Interest The authors declared that they have no conflicts of interest to this work. We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.

Figure caption Fig. 1. XRD patterns of the Ti-6Al-4V/TiB composites prepared by SPS. Fig. 2. Microstructures of the SPSed Ti-6Al-4V/TiB composites: (a) 2.5%TiB; (b) 5%TiB; (c) 10%TiB; (d) details of the TiB whiskers. Fig. 3. Compressive true stress-true strain curves of the Ti-6Al-4V/TiB composites deformed at: (a) 900℃; (b) 1000℃; (c) 1100℃; (d) 1200℃. Fig. 4. Peak stress of compression test: (a) 900℃; (b) 1000℃; (c) 1100℃; (d) 1200℃.

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Fig. 5. Linear regression analysis of flow stress and deformation parameters: (a) ln ̇-lnσ; (b) ln ̇-σ; (c) ln ̇-ln[sinh(ασ)]; (d) ln[sinh(ασ)]-T-1. Fig. 6. Linear dependence of the parameter Z on the ln[sinh(ασ)] for Ti-6Al-4V/TiB composites. Fig. 7. Processing maps of the Ti-6Al-4V/TiB composites with: (a) 2.5%TiB; (b) 5%TiB; (c) 10%TiB. Fig. 8. Microstructures of the Ti-6Al-4V/TiB composites deformed at 10s-1: (a) 2.5%TiB at 900℃; (b) 5%TiB at 900℃; (c) 10%TiB at 900℃; (d) 2.5%TiB at 1000℃; (e) 5%TiB at 1000℃; (f) 10%TiB at 1000℃; (g) 2.5%TiB at 1100℃; (h) 5%TiB at 1100℃; (i) 10%TiB at 1100℃. Fig. 9. EBSD images of the Ti-6Al-4V/TiB composites deformed at 900℃ and 0.001s-1: (a) 2.5%TiB; (b) 10%TiB. Table 2 Comparison of the values of activation energy of TMCs prepared by different methods. Deformation

Activation

temperature

energy

(℃)

(kJ/mol)

Preparation Composition

Ref.

method

Ti-6Al-4V

PM

1000~1100

234

Ref.[25]

Ti-6Al-4V/2.5%TiB

SPS

1000~1200

280

This work

Ti-6Al-4V/5%TiB

SPS

1000~1200

292

This work

Ti-6Al-4V/10%TiB

SPS

1000~1200

309

This work

Ti-6Al-4V/5%TiB

HIP

1010~1100

300

Ref.[26]

Ti-1100/5%(TiB+TiC)

VAR

1000~1150

334

Ref.[27]

Ti-6Al-2Zr-1Mo-1V/3.5%TiB

HP

1010~1040

345

Ref.[14]

23