Effects of Re addition on phase stability and mechanical properties of hexagonal OsB₂

Abstract

ReB 2 -type hexagonal Osmium diboride (OsB 2 ) has been predicted to exhibit higher hardness than its orthorhombic phase, but hexagonal-orthorhombic phase transformation occurs at temperature higher than 600°C, resulting in the decrease in its hardness. Therefore, ReB 2 -type hexagonal OsB 2 samples with Re addition were produced by a combination of mechanochemical method and pressureless sintering technique, and the effects of Rhenium (Re) addition on phase composition, thermal stability and mechanical properties of OsB 2 were investigated in this study. X-ray diffraction (XRD) analysis of the as-synthesized powders by high-energy ball milling indicates the formation of hexagonal Os 1-x Re x B 2 solid solution with Re concentration of 5 and 10 at.% without forming a second phase. After being sintered at 1700°C, part of the hexagonal phase in OsB 2 transformed to orthorhombic structure, while Os 0.95 Re 0.05 B 2 and Os 0.9 Re 0.1 B 2 maintained their hexagonal structure. This suggests that the thermal stability of the hexagonal OsB 2 was significantly improved with the addition of Re. Scanning electron microscopy (SEM) photographs show that all of the as-sintered samples exhibit a homogeneous microstructure with some pores and cracks formed throughout the samples with the relative density >90%. The measurements of micro-hardness, nano-hardness, and Young's modulus of the OsB 2 increased with Re addition, and these properties of the sample with 5 at.% addition of Re is higher than that with 10 at.% Re. K E Y W O R D Shardness, Os 1-x Re x B 2 , phase composition, thermal stability | INTRODUCTIONSuper-hard materials, due to their high hardness, high bulk modulus and high wear resistance, are widely used in machining, construction, aerospace, processing of new materials, automobile, and other fields.1 Conventional super-hard materials, e.g., diamond and c-BN, have been considered as the best option for fulfilling industrial machining requirements. 2-4 However, diamond cannot effectively machine steel or other ferrous metals due to the tendency to form iron carbide at elevated temperatures. c-BN would cut these ferrous materials, but it must be synthesized under high-pressure and high-temperature conditions, which makes it very expensive. To overcoming these shortcomings, it is highly desirable to develop new class of super-hard materials. 5During the past decade, efforts have been devoted to design and synthesis new super-hard materials for both scientific and practical application purposes. Recent searches on new super-hard materials mainly focus on two classes

Crystal structures and mechanical properties of osmium diboride at high pressure

“…Moreover, oP 6-OsB 2 is located only in a very small region at the lower left corner of phase diagram, and it will transition to hP 6-OsB 2 with a temperature of ~ 1000 K at zero pressure. This is consistent with the previous experimental results of 873 K 12 . Meanwhile, the phase transformation of hP 6-OsB 2 → oI 12-OsB 2 occurs at 374.5 GPa under room temperature of 300 K.

Figure 5 Calculated temperature–pressure phase diagram of OsB 2 based on the QHA.

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“…Therefore, a lot of efforts have been invested to seek new hard materials in the past several decades. So far, one of the design principle of synthetic hard materials is to add light elements B, C, and N to electron-rich transition metals 3 , such as ReB 2 4 – 7 , OsB 2 8 – 12 , WB 4 13 , 14 , PtC 15 , Re 2 C 16 , OsN 2 17 , PtN 2 18 , 19 , etc. Among them, the transition-metal borides have attracted considerable attention because of their excellent physicochemical property 20 , 21 .…”

“…OsB 2 as a potential hard material, its structure and internal physical properties have been extensively studied in resent years [8][9][10][11][12][22][23][24][25][26][27] . To our best knowledge, OsB 2 was first synthesized by Cumberland et al 8 through resistive heating method.…”

Mechanochemical synthesis and annealing of tungsten di‐ and tetra‐boride

“…Recently, Ma et al synthesized WB 4 with relatively high density and improved mechanical properties by powder metallurgic method (reactive hot pressing), which has advantages, including lower costs, higher operation, and productivity. In our previous work, it was found that, a combination of mechanochemical method and the subsequent sintering is an effective way to prepare TMBs . Compared with the TMBs prepared with arc melting, samples produced by powder metallurgic method have fine‐grained microstructure and high‐ingredient uniformity, while no adhesion phenomenon caused by the formation of β‐rhombohedral boron was found.…”

“…In our previous work, it was found that, a combination of mechanochemical method and the subsequent sintering is an effective way to prepare TMBs. [26][27][28] Compared with the TMBs prepared with arc melting, samples produced by powder metallurgic method have fine-grained microstructure and high-ingredient uniformity, while no adhesion phenomenon caused by the formation of β-rhombohedral boron was found.…”