Metal/ceramic Interface Structures and Segregation Behavior in Aluminum-based Composites

Abstract

Trimodal Al alloy (AA) matrix composites consisting of ultrafine-grained (UFG) and coarse-grained (CG) Al phases and micron-sized B 4 C ceramic reinforcement particles exhibit combinations of strength and ductility that render them useful for potential applications in the aerospace, defense and automotive industries. A critical requirement for the application of trimodal composites is the creation of a strong interfacial bond between ceramic reinforcement and metal matrix to allow for effective load transfer. Different interfacial structures, including presence of amorphous layers between B 4 C and the UFG Al phase [1][2][3], formation of nanocrystalline grains with diameters of 30-50 nm at the Al/B 4 C interface [1,2] and segregation of Mg to Al/B 4 C interfaces [3,4], have been reported in separate literatures. However information on the relationship between different interface morphologies (e.g., amorphous layers, nanocrystalline grains, etc.) and their chemical composition profiles remains absent in the literature.The composite powder was fabricated via mixing cryomilling [5] and unmilled powder together and consists of 10 wt.% B 4 C, 30 wt.% CG 5083 AA, and the balance of UFG 5083 AA. The consolidation of mixed powder was achieved via hot isostatic pressing. Electron-transparent TEM samples were prepared by focused ion beam (FIB) sectioning. TEM imaging was performed with either a JEOL 2500 or a FEI F20 UT Tecnai. Electron Energy Loss Spectroscopy (EELS) was done with either a JEOL 2100 or a F20 UT Tecnai. Elemental distribution maps were acquired using an FEI Super-X windowless EDXS detector (FEI Company, Hillsboro, OR) installed on the Titan G2 80-200 instrument. All microscopes are operated at 200 kV. Figure 1a is a bright field TEM image demonstrating a layered structure between a B 4 C particle and the CG Al phase. Figure 1b is a HRTEM image of the same interface that reveals a double-layered interface consisting of an amorphous layer and a Mg-rich layer. Figure 2 shows integrated EELS intensity line profiles across the Al/B 4 C interfaces as a function of relative distance. Chemical composition profiling suggests the existence of Al oxide in conjunction with B 4 C, while single or multiple layers of Mg-rich oxide are observed in between Al oxide and the alloy matrix. HRTEM and EELS experiments revealed an ultra-thin amorphous aluminum oxide layer separating a poly-crystalline MgO layer from the B 4 C dispersoids. Precession assisted electron diffraction mapping was performed for the UFG Al/B 4 C interface and revealed no preferred orientation of the grains in the UFG region with respect to the B 4 C particle. Hence, grain orientation or texturing did not associate with the segregation of Mg at these interfaces.

Atomic structures of a liquid-phase bonded metal/nitride heterointerface

“…Their X-ray pole figure analysis showed some particular crystallographic orientation between MgO and α-Al 2 O 3 as a result of incongruent reduction; Al 2 O 3 is decomposed into Al metal and O and thus Mg is finally incorporated as MgO. Similar reactions have been also suggested in recent literature, exhibiting the structure of double layer of MgO crystallite/amorphous Al x O y found in the Al-Mg alloy/ceramics composite material 26 . Although these reactions require the presence of Al 2 O 3 surface film on the AlN surface, our preliminary observation confirmed the presence of oxygen on surface of the AlN substrate used in this study.…”

Correlations of grain boundary segregation to sintering techniques in a three-phase ceramic

“…On the other hand, YSZ-spinel and YSZ-alumina heterointerfaces do not show any segregation. This is an interesting observation because segregation is known to occur at other heterointerfaces, such as metal-ceramic systems like Cr-doped Ni/YSZ [46] , MgO/Cu(Ag) [47] , Al alloy-B 4 C [48] . In most of such interfacial segregation stud- ies based on dissimilar phases, a dopant/alloying element added to the metal segregates to lower the total grain boundary energy.…”

Effect of multiple laser shock processing on nano-scale microstructure of an aluminum alloy

“…Comparing with un-treated alloy, it is obvious that the dislocation arrangements in the networks become more the variations in dynamical diffracting conditions [31,40].…”