A Lamellar Shape Memory Alloy in Composite Structure

Advanced Composites for Aerospace, Marine, and Land Applications II Edited by: T. Sano and T.S. Srivatsan TMS (The Minerais, Metals & Materials Society),

2015

THE SYNTHESIS AND PROCESSING OF SELF-HEALING MATERIALS: A LAMELLAR SHAPE MEMORY ALLOY IN COMPOSITE STRUCTURE

Bakr Mohamed Rabeeh 1 and Yasser Fouad 2 1 Professor Engineering and Materials Science German University in Cairo, GUC. 2 Associate Professor Engineering and Materials Science German University in Cairo, GUC.

Keywords:

Composite, HIPing; Hybrid; interface, interphase; fibrous, laminated, LMP, Self-healing. Abstract

Nontraditional self-healing alloy composite has been introduced to address the need for selfrepairable high-strength structural materials. Cu-Zn/Al laminates are uniaxial hot pressed for either lamellar or particulate composite. A new bridging and stitching technique is introduced with crack mitigation via the synergetic effect of interfacial alloying elements. Low melting phase (LMP) induced structures of Al phase, Cr-Fe phase, and Al-Cu-Zn phase via alloy segregation. Microstructural and mechanical characterization is also established via scanning electron microscopy, energy dispersive x-ray spectroscopy and tensile testing. The interphase kinetic established with micro plasticity, metal flow, low melting phase, LMP and delocalized Al enriched zone and Cu enriched zone. The improvements in performance of self-healing interphase with SMA composite structure are due to heating of low melting phase induce crack closure, and crack mitigation via stitching and bridging mechanisms. Engineering material can be designed with multifunctionalities ranging from the macro- to Nano-scale to optimize performance while minimizing time and the need for extensive repair.

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1.

Introduction

Aluminum based metal matrix composites are used in aerospace, defense and selected automotive applications such as high performance racing applications [1], The most commonly used materials as reinforcement are SiC, A1203 or B4C into the aluminum matrix. These materials are used to improve elastic modulus, enhanced heat and wear resistance [2], However, the addition of copper and/or brass in a lamellar structure to aluminum based composite is an objective. A solid state processing, unidirectional pressing, is selected at different parametric study; pressure, temperature and holding time. The most important concept in this technique is that the synergetic effects of parametric study [3], While applying this technique for lamellar composite distribution, the kinetic of interface/interphase is being considered for mechanical alloying (MA). Though, it is not really „alloying" due to insolubility of the dispersoids in the matrix [4], Mechanical alloying, as originally developed by Benjamin, was used to produce a combined oxide dispersion strengthening with gamma prime precipitation hardening in a nickel- based super alloy [5], The purpose of the present studies is to investigate the influence of engineered interface on SMA processing of composite [8-9], Interface/interphase size, shape and microstructural changes is being controlled and engineered for producing new delocalized constituents of composite reinforcement and their corresponding properties. A shape memory composite which is made of two types of shape memory materials, namely shape memory alloy (SMA) and shape memory hybrid. This composite has repeated instant self-healing function by means of not only shape recovery but also strength recovery (over 80%). The activation of the self-healing function is triggered by joule heating the embedded SMA [10], 2.

Methodology

2024 Al alloy foils is introduced with brass foils at 0.5 mm thickness each and a solid state processing technique uniaxial pressing is applied at different temperatures 450, 500, 540 °C for different holding time (10, 20, and 90 minutes) and press level of 100 Ton. Design architectures as well as ply numbers are being considered for composite processing. The chemical composition of the 2024A1 powder is shown in Table 1. As-received 2024 Al foils was arranged in a foil-foil technique and at different architectures 3 plies, 5 plies and seven plies. The constituent's weight fraction is being considered as 2:1, and 3:2 for 3, 5 and 7 plies symmetry arranged lamellar structural composite materials. Chemical and mechanical interfacial bond is established and is controlled via the synergetic effect of interfacial alloying elements Zn [LMP], Fe and Cr. Table 1. The Chemical Composition of 2024A1 foil (Wt. %) Component Weight %

Al balance

Cr Max. 0.1

Fe Max. 0.5

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Cu 3.8-4.9

Zn Max. 0.25

others Max. 0.05

3.

Results and Discussion

A self-healing, metal matrix composite along with shape memory alloy is introduced via the engineering of lamellar structure composite materials. Engineering of Brass-Al-Brass foils layup, stacked in a symmetrical 3 plies, and then hot isostatic pressed, in a unidirectional press. Figure 1 presents scanning electron microscopy of 3-ply brass/Al at 560 C and 10 minutes holding time with 50 MPa pressure. After 30 minutes with the same parametric study, brass (Cu-Zn) layer is completely consumed and diffused within Al layers producing delocalized particulates (Cu-enriched) in Al-matrix composite (Fig. 2). Figure 3 presents 5 plies symmetrically unidirectional hipped [Brass/Al/brass] at 520°C for 20 minutes holding time and 50 MPa pressure and produced lamellar metal matrix composite with clear and bonded interface. Figure 4 presents high magnification of interface/interphase in scanning electron microscopy of 5-ply brass/Al/brass at 520 C and 20 minutes holding time with 50 MPa pressure. However, the macrostructures of Brass/Al/Brass are completely different from the parent material structure in the as bonded condition; the results are completely different if we switch the arrangement [Al/brass/Al]. The diffusion kinetics as well as the architecture is different in its sequential and directional form. Figure 5 presents scanning electron microscopy of 5 ply of Brass/Al/Brass symmetrically arranged at 540 C and 20 minutes holding time with 50 MPa pressure. The commencement of LMP diffusion along interface may produce minor delamination. Figure 6 presents effect of temperature as well as holding time on crack closure with bulk interphase diffusion at 540 C, 30 minute holding time and 50 MPa. Lateral and transverse bulk interphase flows induced by inter diffusion mechanism and LMP that proceed at 45 minute [Figure 7] and after 60 minutes it completely transform the final microstructure and macrostructure into new emerging materials symmetrically arranged [Figure 8], The diffusion kinetic of alloying elements established with energy dispersive X-ray spectroscopy, EDX, at high magnification of the newly developed structure, Figure 8. It reveals that the outer lamellar composite structure, shape memory alloy, with 75.24 wt. % Cu, 18.74 wt. % Zn and 6.02 wt. % Al. A newly developed shape memory hybrid composite structure is intrinsically and extrinsically processed. Alloy segregation along with low melting phase [Zn] induces fibrous structure [Fe, Cr] in ductile aluminum enriched matrix [Al, Cu and Zn] as a leading interphase [Figure 10], EDX of leading interphase is presented in Figure lla,b,c and d. Trailing interphase [Figure 12] produces delocalized bulk and fibrous structure [Fe, Cr] in aluminum enriched matric [AI, Fe, Cu, Zn], EDX of trailing interphase is established and presented in Figure 13a, b, and c. Heat flow and alloying elements segregation direction and low melting phase that produce aluminum metal matrix composite reinforced with delocalized particulates of copper alloy [Figure 1, and 2], Architectural design and ply number produced either lamellar composite structure [Figure 3] and/or new nontraditional composite structure [Figure 8], However, delamination is a lamellar structure limitation [Figure 5], the control of heat flow, holding time and pressure is dominant for the commencement of bulk interphase [Figure6], Transient liquid phase bonding (TLP) and diffusion kinetics produce transverse and lateral material flow [Figure 7], A lamellar composite structure (outer ply), symmetrically synthesis with micro fibrous interphase and central bulk particulate composite structure is established [Figure 8, and 9], EDX reveals micro fibrous composite interphase with Fe-Cr fibrous structure in aluminum enriched matrix [Al-Cu-Zn] that

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Figure 1.

Scanning electron microscopy of 3-ply brass/Al at 560°C and 10 minutes holding time with 50 MPa pressure.

Figure 2.

Scanning electron microscopy of 3-ply brass/Al at 560°C and 30 minutes holding time with 50 MPa pressure.

Figure 3.

Scanning electron microscopy of 5-ply brass/Al at 520°C and 20 minutes holding time with 50 MPa pressure.

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Figure 4.

Interface/Interphase in scanning electron microscopy of 5-ply brass/Al/brass at 520°C and 20 minutes holding time with 50 MPa pressure. [High mag.]

Figure 5.

Scanning electron microscopy of 5 ply of Brass/Al/Brass symmetrically arranged at 540°C and 20 minutes holding time with 50 MPa pressure.

Figure 6.

Scanning electron microscopy of inter ply diffusion in Al/Brass interface at 540°C and 30 minutes holding time with 50 MPa pressure.

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Figure 7.

Scanning electron microscopy of inner 3 ply inter diffusion Brass/Al/brass at 540°C and 45 minutes holding time with 50 MPa pressure.

Figure 8.

Scanning electron microscopy of final inter ply diffusion in Brass/Al/Brass 5 ply at 540°C and 60 minutes holding time with 50 MPa pressure.

Figure 9.

Scanning electron microscopy of one half 5 ply brass/Al/brass at 540°C and 60 minutes holding time with 50 MPa pressure. [ High mag.]

290

(a)

(b)

1.00 2.11 3.00 4.18 5.00 6.18 7.00 8.88 9.0118.8811.8812.8013.81

(d)

(b) Figure 11.

Figure 12.

Energy dispersive X-ray spectroscopy of aluminum foil along interphase fiber (dark).

Scanning electron microscopy of trailing interface/Interphase in of 5-ply brass/Al/brass at 540°C and 60 minutes holding time with 50 MPa pressure

291

(a)

(b)

(c) Figure 13.

Energy dispersive X-ray spectroscopy of aluminum foil along interphase fiber (white).

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Figure 14.

Stress-strain diagram of [Brass/Aluminum/Brass] 5 plies.

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Figure 15.

Stress-strain diagram of [Brass/Aluminum/Brass] in SMA with self-healing interphase.

presented in Figure 10. The central composite is dominated by aluminum enriched matrix reinforced by fibrous structure, Fe-Cr, and Cu-Zn enriched delocalized shape. Mechanical characterization is applied for the two types of composite in a lamellar and in SMA outer lamellar composite structure with self-healing interphase composite. Stress-strain diagram of [Brass/Aluminum/Brass] 5 plies is conducted and presented in Figure 14, with stepped delamination induced fracture. No clear fracture obtained in stress-strain diagram of [Brass/Aluminum/Brass] in SMA hybrid composite structure with self-healing interphase is presented in Figure 15. When load is applied to the composite after damage, the outer ply SMA apply a compressive force which produces crack closure and clamping. Interfacial delamination is become hindered by the stitching and bridging effect of fibrous reinforcement that produce crack mitigation and shielding. The matrix alloy is now become partially molten at the healing temperature to reverse damage induced plasticity and provide crack welding via LMP. 4.

Conclusions

Engineering of interface/interphase in copper zinc/aluminum lamellar composite structure is established through unidirectional pressing. Lamellar composite structure is obtained in 3, 5 plies symmetrical arrangements. The way these foils stacked as well as hipping parameters induce macroscopic aspects as well as microscopic aspects. Transient liquid phase bonding (TLP) implies that equilibrium state of the joint region is solid. The route, by which solidification can be achieved, can involve up to five related phenomena. These are the diffusion kinetics of alloying elements, materials flow, Transient liquid phase bonding (TLP), shape memory alloy and self-healing kinetic of micro fibrous interphase. The diffusion into the joint metals is mainly temperature, pressure and time dependent. Brass-Aluminum system can be TLP bonded at 540°C produces new emerging shape memory alloy and hybrid composite. The possibility of hybridization introduced with new emerging Cu-Zn-Al shape memory ally (outer ply), controlled micro fibrous interphase and delocalized central Cuenriched whiskers and particulate in aluminum enriched matrix. Crack mitigation, and

toughening mechanism established by stitching and bridging effect of micro Fe-Cr fibrous within aluminum matrix interphase. New nontraditional self-healing interphase with shape memory alloy hybrid composites have been designed to address the need for self-repairable high-strength structural materials. References 1.

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