Effect of Fe-C alloy additions on properties of Cu-Zr-Ti metallic glasses

Highlights

• The strength and plasticity are drastically increased by Fe-C alloy additions.

• The corrosion potential increases with increasing Fe-C alloy content.

• The corrosion current density decreases with increasing Fe-C alloy content.

• The corrosion behavior switches from the pitting corrosion to the self-passivization.

Abstract

The effect of Fe-C alloy additions on thermal, mechanical and corrosive properties of (Cu₅₀Zr₄₀Ti₁₀)_1-x(Fe-C)_x (x = 0–2.20 at%) alloys were systematically investigated. The results show that the Fe and C additions can enhance glass transition temperature T_g and onset crystallization temperature T_x, but narrow supercooled liquid region ΔT_x. Work-hardening can be clearly observed for the Cu-based bulk metallic glasses (BMGs) containing Fe and C elements. The yield strength (σ_y), fracture strength (σ_f) and plastic strain (ε_p) are drastically increased by Fe-C alloy additions. The corrosion potential E_c increases and the corrosion current density i_c decreases with increasing Fe and C contents. The studied Cu-based BMGs exhibit unique and novel anodic polarization behavior characterized by current platforms plus current serrations. The current serrations are much larger for the Cu-based BMGs with 0 ≤ x ≤ 1.32 at% than for those with 1.76 ≤ x ≤ 2.20 at%. The corrosion surface images are changed from the pits to the passive films by Fe-C alloy additions. The corrosion behavior gradually transforms from the pitting corrosion to the self-passivization with increasing Fe and C contents. The corresponding mechanisms are also discussed.

Introduction

CuZr-based bulk metallic glasses (BMGs) have been extensively investigated because of their excellent mechanical properties, such as work-hardening [1], stress/strain-induced martensitic transformation [2], and room-temperature plasticity [[1], [2], [3], [4], [5], [6], [7], [8], [9], [10]] and even cryogenic temperature plasticity [11], which makes their potential applications as promising structural materials. Increasing efforts have demonstrated that CuZr-based alloys are the alloys system for the formation of bulk metallic glass composites (BMGCs) with large plasticity attributed to the martensitic transformation during deformation [4,[12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22]], which provides an intriguing route for overcoming the room-temperature brittleness of the Cu-based BMGs.

Cu-Zr-Ti ternary alloy system is one of CuZr-based alloys that can be cast into the BMGs with critical glass forming dimension of 5 mm [23,24] and high tensile fracture strength up to 2 GPa [25] as well as large room-temperature plastic strain up to 7.4% [5]. It is generally acknowledged that the microalloying is an effective method for tailoring mechanical and physical properties of the BMGs [4,6,7,10,[26], [27], [28], [29], [30], [31], [32], [33], [34]]. For example, the glass forming ability (GFA) can be enhanced in Cu₅₀Zr₅₀ alloy by Al addition or Al plus Gd addition [27,28]. Yu et al. [27] and Fernández et al. [29] found that the Al addition can remarkably improve the thermal stability of Cu₅₀Zr₅₀-based glass forming alloy. The plasticity of Cu₆₀Zr₃₀Ti₁₀ BMG was drastically improved from 1% up to 23% by Be addition [26]. The GFA and plasticity were simultaneously enhanced in Cu-Zr-Al by the addition of Ti [4], or rare-earth elements [6], or V [10]. Our previous investigations found that the mechanical, thermal, electrical properties as well as the GFA of a Cu-Zr-Ti BMG were simultaneously improved by Ni addition [7]. Zhang et al. [30] found that Fe addition didn't influence the GFA but narrowed the supercooled liquid region (ΔT_x) of Cu₆₀Zr₃₀Ti₁₀ alloy for Fe ≤ 4 at%, while the strength and plasticity were simultaneously increased for Fe ≤ 2.5 at%. The GFA, Young's modulus, and strength of Cu₄₇Ti₃₄Zr₁₁Ni₈ BMG were decreased but its plasticity slightly was increased by 1 at% Fe addition [31,32]. The addition of 1 at% Fe can increase the plasticity [33,34] but decrease the ΔT_x and the strength [34] of CuZrAl BMGs. In addition, the metalloid carbon with small atom can form strong covalent bonds with the metallic constituents and influence the GFA and properties of glass forming alloys [35,36]. The carbon addition can improve the GFA of Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 [35] and a Fe-based alloy [36], and the ΔT_x and the hardness of Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 alloy [35]. On the other hand, Pauly, et al. [37] developed a series of Cu₅₀Zr_50-xTi_x (2.5 ≤ x ≤ 7.5 at%) bulk metallic glass composites (BMGCs) with large plasticity and work-hardening feature. Recently, Song, et al. [38] found that Cu-Zr-Ti ternary BMGs have the martensitic transformation behavior.

As an engineering material, the corrosion resistance of the BMGs/BMGCs is one of the important performances. It has been found that Cu-based metallic glasses are easily subjected to the pitting corrosion in chlorine-ion-containing solution [[39], [40], [41], [42], [43], [44], [45], [46]]. However, the corrosive property of Cu-based metallic glasses can be remarkably improved by microalloying [[43], [44], [45], [46]]. For example, Nie, et al. [46] found that Ti addition greatly improves the corrosion resistance of a Cu-Zr-Ag-Al BMG in both H⁺ and Cl⁻ solutions. Qin et al. [40] developed a (Cu_0.6Hf_0.25Ti_0.15)₉₀Nb₁₀ BMGC with an excellent combination of high corrosion resistance and superior mechanical properties by adding Nb into Cu_0.6Hf_0.25Ti_0.15 glass forming alloy. To our best knowledge, effect of carbon addition or combination of Fe and C additions on properties of Cu-based glass forming alloys has not been reported.

In the present work, the effect of Fe-C alloy additions on the thermal, mechanical, and corrosive properties as well as the GFA of Cu₅₀Zr₄₀Ti₁₀ glass forming alloy was systematically investigated.