Structural Materials for Aerospace and Defense: Challenges and Prospects: Composites and Nanocomposites
Sponsored by: MS&T Organization
Program Organizers: Roumiana Petrova, New Jersey Institute of Tech

Wednesday 8:00 AM
October 19, 2011
Room: D242/243
Location: Greater Columbus Convention Center

Session Chair: Yellapu Murty, Cellular Materials International, Inc

8:00 AM  Invited
Lightweight, Multifunctional Composite for Aerospace Applications: Tiffany Miller¹; ¹Powdermet, Inc.
    Powdermet has developed a lightweight, high-strength, multifunctional composite material. This composite provides both radiation shielding protection and can be used as structural support. This novel material utilizes a multilayer design consisting of alternating structural layers and radiation shielding layers. The radiation shielding layers utilize low-Z materials to avoid any secondary radiation effects and to minimize the weight of the composite. The structural aspect is gained by integrating lightweight, high-strength materials into the composite. The novel design of this material is due to its multifunctional capabilities because traditionally radiation shielding material has lacked structural capabilities and/or is too heavy to be used in space applications. Our proof-of-concept program (SBIR Phase I NASA grant) demonstrated that our multifunctional composites perform comparably or better than both traditional structural and radiation shielding materials independently.

8:40 AM
Aluminum SComP for Lightweight Structural and Energy Absorbing Applications: Brian Doud¹; ¹Powdermet Inc.
    Aluminum SComPTM is a Metal Matrix Syntactic composite that is created using powder metallurgical techniques combining ultra lightweight hollow ceramic spheres with standard aluminum alloys to decrease the density of the alloys by 30-40% yet retaining up to 90% of the mechanical properties. These powder metal parts are then consolidated to 80% density and can then be extruded or rolled or forged into its final shape and density (1.8-2.0g/cc). The Final parts can be annealed or aged to tempera nd relieve stress and are available in rod, Bar, Plate sheet and some near net, and net shape parts. Although properties vary slightly from various processing routes properties shown here will compare Aluminum SComP in its rolled form to other engineering alloys.

9:00 AM
Unusual Hot Tearing Resistance Enhancement in Cast A206/Al₂O₃ Nanocomposite: Hongseok Choi¹; Yi Sun¹; Hiromi Konishi¹; Xiaochun Li¹; ¹University of Wisconsin-Madison
    It has been well-known that applications of Al-Cu alloys to critical structure components in automotive and aerospace industries are limited due to their high susceptibility to hot tearing although they have high strength and high fracture toughness, both at room and elevated temperatures. The effect of Al₂O₃ nanoparticles on hot tearing resistance of the as-cast Al-Cu alloy (A206) was investigated. A small amount of Al₂O₃ nanoparticles were dispersed into A206 alloy melts through an ultrasonic based dispersion method. The susceptibility of A206 alloy to hot tearing during permanent mold casting was studied using constrained rod casting (CRC) in a steel mold. The hot tearing susceptibility (HTS) of A206 nanocomposite was significantly reduced to be almost same as that of Al-Si alloy (A356). Microstructural analysis was conducted to further understand the enhancement of hot tearing resistance of A206 alloy with Al₂O₃ nanoparticles.

9:20 AM
Cast AZ91D/TiB₂ Nanocomposites with an Automatic Nanoparticle-Feeding System: Hongseok Choi¹; Yi Sun¹; Ben Slater¹; Xiaochun Li¹; ¹University of Wisconsin-Madison
     A small scale automatic nanoparticle-feeding system has been developed to add TiB₂ nanoparticles into AZ91D alloy melt. The developed feeding system allows for a controlled gradual introduction of nanoparticles directly into the cavitation zone of an ultrasonic probe. The nanoparticles in the hopper of the feeding system are protected by an enclosure filled with inert argon gas. TiB₂ nanoparticles with a diameter of 25 nm were successfully fed into the AZ91D melt. The mechanical properties of as-cast AZ91D alloy are significantly improved with the addition of TiB₂ nanoparticles. The microstructural analysis with optical microscope showed that the massive brittle intermetallic phase (β-Mg₁₇Al₁₂) as well as α-Mg grain was significantly refined, which contributes to enhancing both strengths and ductility of cast AZ91D alloy.

9:40 AM Break

10:00 AM  Invited
Ti2AlC-Nanocrystalline Mg-Matrix Composites with Ultrahigh Damping, Stiffnesses and Strengths: Michel Barsoum¹; Babak Anasori¹; ¹Drexel University
    Herein we report on the processing and properties of Ti2AlC-nanocrystalline magnesium, nc-Mg-matrix composites fabricated using a pressureless spontaneous melt infiltration method. These composites are readily machinable, relatively stiff, strong and light, and exhibit ultrahigh damping. Increasing the nc-Mg volume fraction leads to lighter composites with higher damping characteristics at lower stresses (~30% of the mechanical, energy is dissipated at 250 MPa). The sub 100 nm Mg grains are extraordinarily thermally stable (annealing at 500°C for 8h does not lead to coarsening), which renders these composites good candidates for applications at temperatures higher than ambient. When Mg-alloys are used, ultimate tensile stresses of 800 MPa are obtained. The pressureless melt infiltration method is inexpensive and most readily scalable.

10:40 AM
Development of Ti-TiAl₃ Metallic-Intermetallic Laminate Composites for Structural, Defense, and Aerospace Applications: Derrick Stokes¹; Xiu-Ren Bu²; Jennifer Conway¹; Stan Jones¹; Viola Acoff¹; ¹The University of Alabama; ²Clark Atlanta University
    Metallic-Intermetallic Laminate Composites (MLCs) are comprised of alternating layers of elemental metals and intermetallic compounds. By combining in this manner, MLCs exhibit properties that make them ideal for consideration for use in ballistics applications. MLCs composed of elemental titanium (Ti) and the intermetallic compound TiAl₃ are ideal candidates for these applications. In this study, a cost-effective and energy efficient way of producing Ti-TiAl₃ MLCs developed by researchers at The University of Alabama is investigated. This method involves the process of accumulative roll bonding (ARB) of elemental foils followed by annealing to produce Ti-TiAl₃ MLCs. The focus of the results presented here is the as-rolled specimens consisting of alternating layers of elemental titanium and aluminum (Al), prior to annealing. To measure the impact and residual velocities of the Ti-Al multilayered specimens, perforation testing, using a method developed at The University of Alabama was employed.

11:00 AM
Current NDE Studies of Impact Damage in Multi-Layered Transparent Panel Structures: William Green¹; Raymond Brennan¹; ¹U.S. Army Research Laboratory
    Transparent and opaque materials are used by the Army in protective systems for enhancing survivability of ground vehicles, air vehicles, and personnel. Transparent materials are utilized for face shields, riot gear, and vehicle windows, in addition to other applications for sensor protection, including radomes and electromagnetic (EM) windows. Fracture from low velocity impacts limits visibility and impairs continued vehicle operations. For both transparent and opaque protective systems, low velocity impact damage compromises the structural integrity and increases the likelihood of further damage or penetration from a high velocity impact strike. Transparent protective systems typically consist of glass, polymeric and ceramic materials. Impact damage in different multi-layered transparent panel structure types was investigated using nondestructive evaluation (NDE) methods, including phased array ultrasonic testing, x-ray computed tomography, and optical characterization using cross polarization. Results of the structural damage characterization using the different NDE methods will be presented and discussed.

11:20 AM
Thermo-Mechanical Properties of Epoxy Based Shape Memory Polymers: Haluk Karaca¹; Burak Basaran¹; Mohammed Souri¹; Anil Erol¹; ¹UNIVERSITY OF KENTUCKY
    Shape memory polymers (SMP) are emerging in the group of “smart” materials due to their capability to recover extreme deformations, their low costs, relatively simple pretreatment procedures and ease of processing. SMPs possess unique properties which would allow them to be employed in biomedical, aerospace and automotive industries. However, they lack the ability to perform at high temperatures, stress levels and in a reversible manner, hence currently have restricted employment for prospective applications. In this study, the effects of chemical composition, operation temperature and applied stress on the shape memory properties of epoxy-based SMPs are investigated. It will be shown that epoxy-based SMPs can generate very high recovery stresses (> 20 MPa), exhibit two-way shape memory behavior under selected stress levels. Furthermore, it will be revealed that their shape memory behavior depends on the thermo-mechanical loading history where new shape memory cycles can be utilized for various actuation applications.

11:40 AM
Novel Ti₂AlNb-Based Intermetallic Alloys and Composites: Marat Shagiev¹; ¹Institute for Metals Superplasticity Problems
     Optimization of the chemical composition of Ti₂AlNb-based alloy resulted in development of novel high-strength intermetallic with rather low density ρ≈5.1 g/cm³. Mechanical properties of the alloy were considerably improved due to the grain refinement down to the nanometer level. At room temperature, elongations up to 25% were obtained and the ultimate strength reached 1400 MPa. The alloy exhibited superplastic behavior in the temperature range of 850-1000°C. The maximum elongation δ=930% and steady state flow stress σ₅₀≈125 MPa were obtained at 900°C and strain rate of 4.2×10^-3 s^-1. The ultrafine-grained material was used for production of intermetallic sheets and multilayer composite plates consisting of alternating layers of orthorhombic intermetallic and commercial high-temperature titanium alloy. The multilayer composites possessed improved strength and reasonable ductility both at room and elevated temperatures.The present work was supported by the Russian Foundation for Basic Research (RFBR) within the Project No. 11-08-91153-NSFC_a.

12:00 PM
Extreme Anelastic Responses in Zn₈₀Al₂₀ Matrix Composite Materials Containing BaTiO₃ Inclusion: Liang Dong¹; Donald Stone¹; Roderic Lakes¹; ¹University of Wisconsin, Madison
    Classical bounds for composite properties, such as stiffness, damping, thermal expansion, can be exceeded if the composite has a negative stiffness phase. In this work, anelastic properties have been measured on Zn₈₀Al₂₀-BaTiO₃ composite system. In particular, extreme anelastic stiffness exceeding that of diamond and large positive and negative damping by a factor of 10 to -50 vs. temperature have been observed in composite after sufficient aging below the Curie point of BaTiO₃. Enough aging above the Curie point eliminated such anomaly. The extreme responses are attributed to constrained negative stiffness effect of the BaTiO₃ inclusions, and an oxygen vacancy mechanism is considered as a cause. Such a defect mechanism induced negative stiffness effect in ferroelastic materials below Tc can be utilized to fabricate novel composite materials with composite properties far beyond the limits set by the classical composite theory.

12:20 PM  Cancelled
Characterization of TiB₂ and Al₂O₃-TiB₂ Composites on the MISSE-6 Mission: Eric Faierson¹; Kathryn Logan²; Sharon Jefferies³; ¹National Institute of Aerospace - Virginia Tech; ²Virginia Tech; ³NASA Langley Research Center
    Hot-pressed specimens of TiB₂ and Al₂O₃-TiB₂ were flown on the Materials International Space Station Experiment-6 (MISSE-6) mission. The MISSE-6 mission exposed materials to the low earth orbit (LEO) environment outside of the international space station. Atomic oxygen, solar radiation, thermal cycling, vacuum, and micro-meteoroids are all present in LEO. The purpose of this work was to evaluate effects of the LEO environment on TiB₂ and Al₂O₃-TiB₂ composites. TiB₂ has a high melting point (3225° C) and a relatively low density (4.52 g/cm³). Potential applications for TiB₂ and Al₂O₃-TiB₂ include use as leading edges, thermal protection systems, and hot structures. TiB₂ also has potential for use in space mirrors due to its high reflectivity. Microstructural and chemical analyses were performed on the specimens using SEM and EDS techniques. Mass loss, induced by LEO exposure, was determined for each specimen. Reflectance measurements were performed on the mirror-polished TiB₂ specimens using a spectroreflectometer.