Residual microstructure associated with impact crater in Ti–6Al–4V meshes reinforced 5A06Al alloy matrix composite

Micron 43 (2012) 201–204

Contents lists available at ScienceDirect

Micron journal homepage: www.elsevier.com/locate/micron

Residual microstructure associated with impact crater in Ti–6Al–4V meshes reinforced 5A06Al alloy matrix composite Q. Guo a,∗ , G.Q. Chen a , L.T. Jiang a , M. Hussain b , X.L. Han a , D.L. Sun a , G.H. Wu a a b

School of Materials Science and Engineering, Harbin Institute of Technology, No. 92 West Da-Zhi Street, Harbin 150001, China Department of Material Science and Chemical Engineering, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy

a r t i c l e

i n f o

Article history: Received 30 June 2011 Received in revised form 17 July 2011 Accepted 17 July 2011 Keywords: Composites Impact Microstructure

a b s t r a c t In this paper, TC4m /5A06Al composite was hypervelocity impacted by 2024 aluminium projectile with the diameter of 2 mm and with the impact velocity of 3.5 km/s. The residual microstructure was observed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HREM). The TC4–Al interface before impact was composed of TiAl3 phase and Ti3 Al phase. Near the pithead, separation of TC4 fibers and Al matrix occurred along the impact direction. Around the middle of the crater, TC4 fibers were sheared into several sections. Near the bottom of crater, adiabatic shear band (ASB) occurred in TC4 fiber, while the angle between shear plane and cross section was 45◦ . The crack propagated along TC4–Ti3 Al interface during impact and some Ti3 Al phase at the TC4–Al interface transformed to amorphous with few nanocrystals after hypervelocity impact. © 2011 Elsevier Ltd. All rights reserved.

1. Introduction Hypervelocity impact behaviors and micro-damage of alloys (e.g., Al alloys and Ti alloys) and composites are being paid more and more attentions due to increase of space debris. It was observed that micro-cracks, microvoids and adiabatic shear bands (ASB) were the typical damage characteristics surrounding the hypervelocity impact crater for the Al–6Mg alloy (Zhen et al., 2005). Besides, Ye et al. (2010) investigated the residual microstructure of Al–Sc and Al–Ti semi-infinite targets impacted by high-speed projectiles with velocities of up to 4 km/s. The results showed that deep columned craters with hemispherical bottoms were formed in the Al–Ti target, while or relatively shallower craters with near-hemispheroidal were found in the Al–Sc alloy. The different microstructures of Al–Sc and Al–Ti alloys, e.g., grain sizes and secondary precipitates, leads to their different impact resistance. Furthermore, residual microstructure around the impact crater of TC4 alloy showed that the shear bands varied from deformed shear bands to the white-etching shear bands with increase of shear strain (Li et al., 2005). Properties of different composites under the dynamic loading were also investigated recently (Tennyson and Lamontagne, 2000; Silverman, 1995; Harel et al., 2002; Zee and Hsieh, 1993). The damage of graphite/PEEK laminates composites was characterized by front face spallation, debonding and debris plume (Tennyson and Lamontagne, 2000).

∗ Corresponding author. Tel.: +86 451 86413922; fax: +86 451 86413922. E-mail addresses: [email protected], [email protected] (Q. Guo). 0968-4328/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.micron.2011.07.013

Unfortunately, the damage behavior of aluminium matrix composites, an important candidate for aerospace application, has been rarely reported. It is reported that velocity of the fragment cloud at the cloud center of gravity was decreased 35% than the impact velocity of the projectile by aluminium meshes (Higashide et al., 2006). Since TC4 (Ti–6Al–4V) fibers present low density, high modulus, strength and good ductility, it would be very promising for aluminium matrix composite reinforced with TC4 fiber (TC4f /Al) for shelter application. Therefore, 15 vol.% TC4 meshes reinforced 5A06Al matrix composites (TC4m /5A06Al) were fabricated by pressure infiltration method. The resistance of TC4m /5A06Al composites to hypervelocity impact was tested by a two-stage light gas gun, whereas residual microstructure of the composite was investigated. 2. Experimental TC4 meshes (15 vol.%) were used as reinforcement to obtain isotropic properties in planes in the composites. The fiber diameter was 100 ␮m while the spacing between fibers in mesh was 500 ␮m. 5A06Al alloy was selected as matrix, whose composition was 5.8–6.8 Mg, 0.5–0.8 Mn, 0.4 Fe, 0.4 Si, 0.05 Cu, 0.02–0.10 Ti and the balance was Al. Later the TC4m /5A06Al composites were fabricated by pressure infiltration method (Wu, 2007). Temperatures for melting Al alloy and mould were 750 and 500 ◦ C, respectively. During the infiltration process, a pressure of 5 MPa was applied and maintained for 10 min, and then the composites were solidified in air. Afterward, the TC4m /5A06Al composites for hypervelocity impact testing were annealed at 330 ◦ C for 30 min.

202

Q. Guo et al. / Micron 43 (2012) 201–204

The hypervelocity impact testing was performed on a twostage light gas gun at the Hypervelocity Aerodynamics Institute (China Aerodynamics R&D Center) using 2 mm 2024Al projectile with a speed of 3.5 km/s and normal angle. The thickness of TC4m /5A06Al composite target was 15 mm. Residual microstructure of TC4m /5A06Al composites was observed by ZEISS-40MAT optical microscope, Olympus SZX7 stereomicroscope and S-4700 scanning electron microscopy (SEM) equipped with energy dispersive X-ray (EDX). The further observation was carried out on Philips CM-12 transmission electron microscopy (TEM) equipment with an accelerated voltage of 120 kV and Tecnai G2 F30 high-resolution transmission electron microscopy (HREM) with an accelerated voltage of 300 kV. 3. Results and discussion 3.1. Microstructure of TC4m /5A06Al composite Microstructure of TC4m /5A06Al composite before impact is shown in Fig. 1. TC4 meshes were well infiltrated by the molten Al and no apparent porosity or significant casting defects were observed (Fig. 1a). Moreover, secondary phases ((Fe, Mn)Al6 ) were found in the Al matrix (Fig. 1a). A thin layer was observed at TC4–Al interface, and further TEM observation revealed that the TC4–Al interface was composed of two layers (Fig. 1b). The outer phase closed to Al matrix was confirmed to be TiAl3 by electron diffraction patterns (Fig. 1c). The inner phase closed to TC4 fiber was Ti3 Al by

electron diffraction patterns (Fig. 1d). It was reported that a series of Ti–Al intermetallic compounds, such as Ti3 Al phase, TiAl phase and TiAl3 phase would be formed between Ti fiber and Al above 600 ◦ C (Liu et al., 2009). TiAl3 is the first reactant in Ti/Al system (Xiu et al., in press), and then Al diffuses through TiAl3 layer to react with Ti to form Ti3 Al (Yang et al., 2011). 3.2. Microstructure around the crater in TC4m /5A06Al composite after impact The crater of TC4m /5A06Al composite after impact is shown in Fig. 2. The shape of the crater was hemispheric (Fig. 2a) and flange (Fig. 2b) was formed around crater on the front face of target by surface wave during impact. The diameter and depth of the crater were about 6.3 and 2.8 mm, respectively. Meanwhile, the trace of the melted Al projectile and composite could be found on the surface of the crater in the composite (Fig. 2a). Fig. 3 illustrates the deformation of TC4 fibers and Al matrix in different regions around the crater in TC4m /5A06Al composite impacted by Al projectile with the diameter of 2 mm and the velocity of 3.5 km/s. Near the pithead (region 1 in Fig. 2b), separation of TC4 fibers and Al matrix was occurred along the impact direction due to the lateral compress wave during the impact (Meyers, 1994) (Fig. 3a). Moreover, holes or cracks connected with each other under the effect of surface wave during impact (Meyers, 1994). However, around the middle of the crater (region 2 in Fig. 2b), TC4 fibers were sheared into several sections and separation of TC4 fibers and Al matrix occurred along the

Fig. 1. Microstructure of TC4m /5A06Al composite before impact. (a) SEM microstructure of composite; (b) TEM microstructure of interface between matrix and TC4 fiber; (c) selected area electron diffraction (SAED) patterns of TiAl3 phase; (d) SAED patterns of Ti3 Al phase.

Q. Guo et al. / Micron 43 (2012) 201–204

203

Fig. 2. Macro-morphologies of craters in TC4m /5A06 composite impacted by Al projectile with the diameter of 2 mm and the velocity of 3.5 km/s. (a) Top view; (b) corresponding cross-section view.

Fig. 3. Deformation of TC4 fibers and matrix in different regions around the crater in TC4m /5A06Al composite impacted by Al projectile with the diameter of 2 mm and the velocity of 3.5 km/s. (a) Near the pithead (region 1 of Fig. 2b); (b) near the middle (region 2 of Fig. 2b); (c) near the bottom (region 3 of Fig. 2b).

outline of crater. Furthermore, grains of matrix are elongated along the outline of crater (Fig. 3b). Near the bottom of crater (region 3 in Fig. 2b), ASB occurred in TC4 fiber, while the angle between shear plane and cross section was 45◦ (Fig. 3c). Shear band occurs when the state of plastic instability is reached and the motion of dislocations and the twinning process are unable to accommodate the very high strain (Yang et al., 1996). The accumulation of energy along the shearing plane transforms into heat and leads to temperature raise, which results in the decreased stress and plastic shearing deformation. Thereafter, the localized deformation would be developed and ASB is formed. Moreover, (Fe, Mn)Al6 phases near the crater have been sheared into several parts along the direction of spherical shock wave, as shown in Fig. 4.

3.3. Interfacial structure between TC4 fiber and Al matrix after impact Fig. 5 shows microstructure of TC4–Al interface at bottom of crater in TC4m /5A06Al composite impacted by Al projectile with the diameter of 2 mm and the velocity of 3.5 km/s. It is obvious that the TC4 fiber and Al matrix have been separated after impact. Selected area electron diffraction (SAED) of interface of region 1 revealed the characteristic halo pattern (Fig. 5b), which demonstrates that amorphous phase was formed at the interface close to TC4 fiber. The amorphous phase was further observed by HRTEM (Fig. 5c). It should be noted that nanocrystalline region within the amorphous phase was also observed by HRTEM (Fig. 5c). EDX anal-

Fig. 4. Deformation of the secondary phase in different regions around the crater in TC4m /5A06Al composite impacted by Al projectile with the diameter of 2 mm and the velocity of 3.5 km/s. (a) Near the pithead; (b) near the middle; (c) near the bottom.

204

Q. Guo et al. / Micron 43 (2012) 201–204

Fig. 5. TEM and HREM photos at bottom of crater in composite impacted by Al projectile with the diameter of 2 mm and the velocity of 3.5 km/s. (a) TEM microstructure of interface; (b) SEAD patterns of region 1 in Fig. 5a; (c) HREM microstructure of region 1; (d) EDX analysis of amorphous interface in region 1; (e) SEAD patterns of region 2 in Fig. 5a; (f) SEAD patterns of region 2 in Fig. 5a.

ysis of region 1 is shown in Fig. 5d. The main chemical compositions of region 1 were Ti and Al with atomic ratio of 62:27, which is close to that of Ti3 Al. The phases in region 2 and 3 were Ti3 Al and TiAl3 according to their SEAD patterns (Fig. 5e and f), respectively. Therefore, the crack propagated along TC4–Ti3 Al interface. Severe local shear deformation was occurred at the TC4–Al interface during impact. Both heating and cooling time of interface are on the order of fraction of milliseconds and nucleation-growth processes are inhibited during hypervelocity impact (Meyers et al., 2003, 2004). Moreover, alloy with the chemical composition of stable compound tends to form amorphous structure (Schwarz and Johnson, 1983). Therefore, Ti3 Al phase at the TC4–Al interface (Fig. 1b) transforms to amorphous state with few nanocrystals after hypervelocity impact. 4. Conclusions In this paper, residual microstructure of TC4m /5A06Al composite after hypervelocity impact was observed by SEM, TEM and HRTEM. 1. The TC4–Al interface before impact was composed of two layers. The outer phase closed to Al matrix was TiAl3 and the inner phase closed to TC4 fiber was Ti3 Al. 2. Near the pithead, separation of TC4 fibers and Al matrix occurred along the impact direction. Around the middle of the crater, TC4 fibers were sheared into several sections. Near the bottom of crater, ASB occurred in TC4 fiber, while the angle between shear plane and cross section was 45◦ . 3. The crack propagated along TC4–Ti3 Al interface during impact and some Ti3 Al phase at the TC4–Al interface transformed to amorphous with few nanocrystals after hypervelocity impact.

References Zhen, L., Li, G.A., Zhou, J.S., et al., 2005. Micro-damage behaviors of Al–6Mg alloy impacted by projectiles with velocities of 1–3.2 km/s. Materials Science and Engineering A 391, 354–366. Ye, Y.C., Li, P.J., Novikov, L.S., et al., 2010. Comparison of residual microstructures associated with impact craters in Al–Sc and Al–Ti alloys. Acta Materialia 58, 2520–2526. Li, G.A., Zhen, L., Lin, C., et al., 2005. Deformation localization and recrystallization in TC4 alloy under impact condition. Materials Science and Engineering A 395, 98–101. Tennyson, R.C., Lamontagne, C., 2000. Hypervelocity impact damage to composites. Composites Part A 31, 785–794. Silverman, E.M., 1995. Space Environmental Effects on Spacecraft-LEO Material Selection Guide. NASA Contractor Report No. 4661. Langley Research Center. Harel, H., Marom, G., Kenig, S., 2002. Delamination controlled ballistic resistance of polyethylene/polyethylene composite materials. Applied Composite Materials 9, 33–42. Zee, R.H., Hsieh, C.Y., 1993. Energy-loss partitioning during ballistic impact of polymer composites. Polymer Composites 14, 265–271. Higashide, M., Tanaka, M., Akahoshi, Y., et al., 2006. Hypervelocity impact tests against metallic meshes. International Journal of Impact Engineering 33, 335–342. Wu, G.H., 2007. Patent of the People’s Republic of China: ZL 200710072590.9 (in Chinese). Liu, Y.M., Xiu, Z.Y., Wu, G.H., et al., 2009. Study on Ti fiber reinforced TiAl3 composite by infiltration in situ reaction. Journal of Materials Science 44, 4258–4263. Xiu, Z.Y., Yang, W.S., Wang, X., et al. Materials Science and Technology, in press. Yang, W.S., Xiu, Z.Y., Wang, X., et al., 2011. Microstructure evolution and oxidation behaviour of Tif /TiAl3 composites. Materials and Design 32, 207–216. Meyers, M.A., 1994. Dynamic Behavior of Materials, 1st edn Wiley Interscience New York. Yang, Y., Xinming, Z., Zhenghua, L., et al., 1996. Adiabatic shear band on the titanium side in the Ti/mild steel explosive cladding interface. Acta Metallurgica 44, 561–565. Meyers, M.A., Cao, B.Y., Nesterenko, V.F., et al., 2004. Shear localization–martensitic transformation interactions in Fe–Cr–Ni monocrystal. Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science 35, 2575–2586. Meyers, M.A., Xu, Y.B., Xue, Q., et al., 2003. Microstructural evolution in adiabatic shear localization in stainless steel. Acta Materialia 51, 1307–1325. Schwarz, R.B., Johnson, W.L., 1983. Formation of an amorphous alloy by solid-state reaction of pure polycrystalline metals. Physical Review Letters 51, 415–418.