Tuning glass formation and brittle behaviors by similar solvent element substitution in (Mn,Fe)-based bulk metallic glasses Tao Xu a , Ran Li a,n , Ruijuan Xiao b , Gang Liu c , Jianfeng Wang d , Tao Zhang a,n a Key Laboratory of Aerospace Materials and Performance (Ministry of Education), School of Materials Science and Engineering, Beihang University, Beijing 100191, China b Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China c State Key Laboratory for Mechanical Behavior of Materials, School of Materials Science and Engineering, Xi'an Jiaotong University, Xi'an 710049, China d School of Materials Science and Engineering, Zhengzhou University, Zhengzhou 450001, China article info Article history: Received 1 October 2014 Received in revised form 9 December 2014 Accepted 12 December 2014 Available online 19 December 2014 Keywords: Similar element substitution Bulk metallic glass Glass-forming ability Mechanical properties Fracture toughness abstract A family of Mn-rich bulk metallic glasses (BMGs) was developed through the similar solvent elements (SSE) substitution of Mn for Fe in (Mn x Fe 80 x )P 10 B 7 C 3 alloys. The effect of the SSE substitution on glass formation, thermal stability, elastic constants, mechanical properties, fracture morphologies, Weibull modulus and indentation fracture toughness was discussed. A thermodynamics analysis provided by Battezzati et al. (L. Battezzati, E. Garrone, Z. Metallkd. 75 (1984) 305–310) was adopted to explain the compositional dependence of the glass-forming ability (GFA). The elastic moduli follow roughly linear correlations with the substitution concentration of Mn in (Mn x Fe 80 x )P 10 B 7 C 3 BMGs. The introduction of Mn to replace Fe significantly decreases the plasticity of the resulting BMGs and the Weibull modulus of the fracture strength. A super-brittle Mn-based BMGs of (Mn 55 Fe 25 )P 10 B 7 C 3 BMGs were found with the indentation fracture toughness (K c ) of 1.91 70.04 MPa m 1/2 , the lowest value among all kinds of BMGs so far. The atomic and electronic structure of the selected BMGs were simulated by the first principles molecular dynamics calculations based on density functional theory, which provided a possible understanding of the brittleness caused by the similar chemical element replacement of Mn for Fe. & 2014 Elsevier B.V. All rights reserved. 1. Introduction Bulk metallic glasses (BMGs) with long-range disorder struc- ture exhibit novel physical and chemical properties, e.g. ultrahigh strength and hardness, large elastic limitation, excellent soft magnetic properties, uniform chemical homogeneity and good micro-/nano-formability in supercooled liquid region, which pro- mote them as advanced functional and structural materials for both scientific research and industrial application [1–6]. Thousands of BMGs based on the most of common metallic elements in the periodic table have been reported so far including [1,4]: Mg, Ca, and Sr in s-block; Al in p-block; Sc, Y, Ti, Zr, Hf, Fe, Co, Ni, Pd, Pt, Cu, Ag, and Au in d-block; lanthanide except radioactive one in f-block. However, it should be noticed that there do exist several kinds of transition metals, like V, Cr, Mn, etc., in the middle position of d-block, which cannot be disordered through multi- component alloying to form BMGs. The development of these new families of BMGs is significant for the revelation of novel properties and the enlargement of some potential applications for this kind of amorphous materials. Because the development of new BMGs through trial and errors is a really time-consuming job, a lot of theoretical and empirical methods to design and evaluate glass-forming ability (GFA) for a certain alloy have been proposed to accelerate the processes [7–15]. One of the most well-known criteria is the “confusion” principle [11–14], which refers to a design method of main constituent elements for BMGs by choosing dissimilar elements with different atomic sizes (more than 12%) and negative heats of mixing in a multicomponent alloy. This principle provided an effective way to construct an alloy component with high GFA at the beginning. Furthermore, the improved method through the substitution of similar elements with similar atomic sizes and valence electronic structures to enhance the GFA of an alloy consisting of dissimilar elements was provided [16–18]. The coexistence of similar and dissimilar element pairs can be beneficial for the improvement of the thermodynamic stability of amorphous structure by increasing chemical disorder and the frustration of kinetic crystallization by complicating competitive crystalline phases so as to increase the GFA significantly. For examples, the GFA can be significantly increased by partial similar element substitution of Cu for solute Ni in Zr–Al–(Ni– Cu), Pd–(Ni–Cu)–P, Pt–(Ni–Cu)–P and La–Al–(Ni–Cu) [19–22], Co for Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/msea Materials Science & Engineering A http://dx.doi.org/10.1016/j.msea.2014.12.048 0921-5093/& 2014 Elsevier B.V. All rights reserved. n Corresponding authors. Tel.: þ86 10 82316192; fax: þ86 10 82339705. E-mail addresses: liran@buaa.edu.cn (R. Li), zhangtao@buaa.edu.cn (T. Zhang). Materials Science & Engineering A 626 (2015) 16–26