The Benefit of the Glassy State of Reinforcing Particles for the Densification of Aluminum Matrix Composites

Abstract

In metallic glass-reinforced metal matrix composites, the glassy phase can serve a dual purpose: (i) it can behave as soft binder and porosity remover during consolidation; and (ii) it can act as the hard reinforcing phase after densification. The present work aimed to demonstrate the benefit of the glassy reinforcing particles for the densification of aluminum matrix composites. The consolidation behavior of Al–50 vol.% Fe-based alloy mixtures prepared using a glassy Fe66Cr10Nb5B19 alloy powder (Tg = 521 °C, Tx = 573 °C) or a crystalline Fe62Cr10Nb12B16 alloy powder was studied under spark plasma sintering (SPS) and hot pressing (HP) conditions. The powders were consolidated by heating above the glass transition temperature of the glassy alloy (up to 540 °C in SPS and 570 °C in HP). When the coarse aluminum powder was used, the reinforcing particles formed chains within the microstructure. In composites formed from the fine Al powder, the particles of the Fe-based alloy were separated from each other by the metallic matrix, and the tendency to form agglomerates was reduced. The glassy state of the alloy was shown to be beneficial for densification, as the metallic glass acted as a soft binder. The densification enhancement effect was more pronounced in the case of reinforcing particles forming chains. The hardness of the Al–50 vol.% glassy Fe66Cr10Nb5B19 composites obtained by SPS was twice the hardness of the unreinforced sintered aluminum (110 HV1 versus 45 HV1).

Metallic Glass-Reinforced Metal Matrix Composites: Design, Interfaces and Properties

“…In [ 82 ], the benefit of the glassy reinforcing particles over crystalline particles with a close chemical composition for the densification of Al matrix composites during spark plasma sintering (SPS) was demonstrated. When the Fe-based alloy powders (glassy and crystalline) were heated under pressure, the punch displacement caused by compact shrinkage was observed ( Figure 9 a) in the case of the glassy alloy when the temperature of the sample reached the glass transition temperature of the alloy (521 °C).…”

“…This temperature is in the supercooled liquid region of the metallic glass (T g = 521 °C, T x = 573 °C). The glassy state of the Fe-based alloy was beneficial for densification, as seen by comparing the images in Figure 10 a,c with those shown in Figure 10 b,d [ 82 ]. The metallic glass played the role of a binder; the densification enhancement effect was more pronounced when the Fe-based alloy particles formed chains ( Figure 11 ) [ 82 ].…”

“…Black lines—temperature; red lines—displacement. Reprinted from [ 82 ]. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( ).…”

“…( a , c , d ) Micrographs of the polished cross-sections, SE images; ( b ) micrograph of the fracture surface, BSE image. Reprinted from [ 82 ]. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( ).…”

“… Schematic of the microstructures of aluminum matrix composites formed using a glassy ( a , c ) or a crystalline ( b , d ) alloy reinforcement. Reprinted from [ 82 ]. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( ).…”