Highly Conductive Al/Al Interfaces in Ultrafine Grained Al Compact Prepared by Low Oxygen Powder Metallurgy Technique.

Dasom Kim,Makoto Kobashi,Zheng Liu,Yusuke Hirayama,Kenta Takagi,Hansang Kwon

doi:10.3390/nano11051182

Abstract

The low oxygen powder metallurgy technique makes it possible to prepare full-dense ultrafine-grained (UFG) Al compacts with an average grain size of 160 nm by local surface bonding at a substantially lower temperature of 423 K from an Al nanopowder prepared by a low oxygen induction thermal plasma process. By atomic level analysis using transmission electron microscopy, it was found that there was almost no oxide layer at the Al/Al interfaces (grain boundaries) in UFG Al compact. The electrical conductivity of the UFG Al compact reached 3.5 × 107 S/m, which is the same level as that of the cast Al bulk. The Vickers hardness of the UFG Al compact of 1078 MPa, which is 8 times that of the cast Al bulk, could be explained by the Hall–Petch law. In addition, fracture behavior was analyzed by conducting a small punch test. The as-sintered UFG Al compact initially fractured before reaching its ultimate strength due to its large number of grain boundaries with a high misorientation angle. Ultimate strength and elongation were enhanced to 175 MPa and 24%, respectively, by reduction of grain boundaries after annealing, indicating that high compatibility of strength and elongation can be realized by appropriate microstructure control.

Highlights

IntroductionBonding is an indispensable technology for establishing and functioning structures ranging from delicate components such as precision parts for home appliances to parts such as used in civil engineering, architecture, and shipbuilding
UFG Al compacts were prepared from an unexposed Al nanopowder with less oxide film and prepared by the low oxygen-induction thermal plasma (LO-ITP) process
Since the Al/Al grain boundaries are thin enough to work as a gate for electrons, the electrical conductivity of the unexposed Al compacts with the highly conductive grain boundary, which reached the same level as in the cast Al bulk

Summary

Introduction

Bonding is an indispensable technology for establishing and functioning structures ranging from delicate components such as precision parts for home appliances to parts such as used in civil engineering, architecture, and shipbuilding. The processes used in metal bonding, such as the solid-state bonding techniques of diffusion bonding [1,2], fusion welding [3], friction welding [4], and brazing [5], require holding at a high temperature for an extended time to achieve an interface without voids. Low-temperature bonding has several merits, including an increased degree of freedom in selecting the bonding target materials, reduced energy consumption, lower thermal strain, and suppressed interfacial reactants, resulting in improved mechanical strength of the bonded body

Methods

Results

Conclusion