Electronic structure based design of thin film metallic glasses with superior fracture toughness

Simon Evertz,Ines Kirchlechner,Rafael Soler,Christoph Kirchlechner,Paraskevas Kontis,Jozef Bednarcik,Baptiste Gault,Gerhard Dehm,Dierk Raabe,Jochen M Schneider

doi:10.1016/j.matdes.2019.108327

Abstract

High fracture toughness is crucial for the application of metallic glasses as structural materials to avoid catastrophic failure of the material in a brittle manner. One fingerprint for fracture toughness in metallic glasses is the fraction of hybridized bonds, which is affected by alloying Pd57.4Al23.5Y7.8M11.3 with M = Fe, Ni, Co, Cu, Os, Ir, Pt, and Au. It is shown that experimental fracture toughness data is correlated to the fraction of hybridized bonds which scale with the localized bonds at the Fermi level. Thus, the localized bonds at the Fermi level are utilized quantitatively as a measure for fracture toughness. Based on ab initio calculations, the minimum fraction of hybridized bonds was identified for Pd57.4Al23.5Y7.8Ni11.3. According to the ansatz that the crystal orbital overlap population at the Fermi level scales with fracture toughness, for Pd57.4Al23.5Y7.8Ni11.3 a value of around 95 ± 20 MPa·m0.5 is predicted quantitatively for the first time. Consistent with this prediction, in micro-mechanical beam bending experiments Pd57.4Al23.5Y7.8Ni11.3 thin films show pronounced plasticity and absence of crack growth.

Highlights

Some metallic glasses envisaged for mechanical applications have a high strength [1,2,3] and show the capability of plastic deformation, S
Due to its fracture toughness of 49.0 MPa·m0.5 reported by Schnabel et al [12], the Pd57.0Al23.9Y7.7Cu11.4 metallic glass is chosen as a reference and Pd57.0Al23.9Y7.7M11.4 (M = Fe, Ni, Os, Ir, Pt, and Au) as the model system with the aim to understand the relationship between electronic structure and fracture toughness by quantification of the fraction of hybridized bonds
Inspired by the qualitative notion of Schnabel et al [12] that the fraction of bonds stemming from hybridized states compared to the overall bonding can be associated with damage tolerance in thin film metallic glasses, a correlation between the fraction of localized and anti-bonding bonds scaling with the crystal orbital overlap population at the Fermi level and experimental fracture toughness data is identified

Summary

Introduction

Some metallic glasses envisaged for mechanical applications have a high strength [1,2,3] and show the capability of plastic deformation, S. Decreasing the fraction of hybridized bonds [12] is proposed to serve as a guideline for increasing fracture toughness Based on this approach the high fracture toughness of 49.0 MPa·m0.5 reported for a Pd57.0Al23.9Y7.7Cu11.4 glass can be rationalized by a comparative analysis of densities of states and bonding with brittle metallic glass systems such as Cu69.6Zr30.4 [12]. For the design of though metallic glasses, Schnabel's proposal lacks, predictive capability since a quantitative relationship between fracture toughness and electronic structure has not been established so far. The quantitative model to predict the fracture toughness of metallic glasses based on the fraction of hybridized bonds presented here enables the quantitative prediction of fracture toughness of metallic glasses for the first time In this model, the crystal orbital overlap population [15] at the Fermi level is utilized as a measure to quantify localized bonds.

Methods

Results

Conclusion