Properties of Boron Subcarbide (B13C2) Synthesized by Self-propagating High-temperature Synthesis (SHS)   Lembit Kommel, Raido Metsvahi and Karl Kolju Department of Materials Engineering, Tallinn University of Technology Ehitajate tee 5, 19086 , Tallinn, Estonia Fig.3. Nanoindentation test region for 10 x10 = 100 indents (a) and detected Phases Nanohardness vs. Modulus of elasticity (b). Fig. 4. A composite was produced from mixture of B4C (50, 60, 70 and 80 wt.%) and Al-Cu powders with WC-Co additives (during ball milling) as catalysts for SHS process for B13C2 – phase forming in B4C grains (a). The density of composite depend on milling time and processing temperature (b). Fig. 5. B4C-B13C2 grain after SHS (a). B-11is the major component of natural boron (b). This natural isotope is the best absorber of fast neutrons, and an excellent absorber of slow neutrons. Such B-N based composites will be used as defense material in future. Fig. 6. Protrusions of superhard c-BC2N-phase on diamond grinded surface (a) and on wear track surface (b). Fig.7. Coefficient of friction (a) and volume wear (b) dependence from heat treatment temperature as well as B13C2 content in composite. CONCLUSIONS During SHS process the B4C in composite was transformed into B13C2 up to the amount of ~45 wt. %. As a result, the summarized mean nanohardness increased to HV = 39±2 GPa and hardness of composite increased to 82±2 HRA, respectively. The composite has great hardness and mechanical strength, low mass density, high thermal conductivity and neutrons attenuation factor, chemical inertness, excellent wear resistant and low friction coefficient. REFERENCES [1] Kommel L. USSR Patent 1,836,190 A3 (1991) (in Russian). [2] Guo X. et al., Physical Rev. (2006), B73:104115-1-7. [3] Enyashin A.N. et.al., Physics of the Solid State (2001), 53-8:1569-1574. [4] Kommel L. et al., Key Eng. Mater. (2013), 527:137-142. ACKNOWLEDGEMENTS The authors would like to acknowledge support from Estonian Science Foundation (SF0140062s08) and EU 7FP ERA.Net RUS STProjects-219 and Ph.D. M. Viljus for help with OM and SEM imaging, E. Kimmari for help with nanoindentation and Ph.D. R. Traksmaa for help with XRD investigation of composites. INTRODUCTION Creation of light weight components for defense elements [1] application based on TiC, B4C, etc. and produced via powder metallurgy techniques has seen significant developments in the last decades. At present these military defense components will be have next essential characteristic as light weight, high hardness, etc. The synthesis, characterization and properties (first–principles calculations) of the superhard (Hv = 43-45 GPa) icosahedral boron subcarbide (B13C2) have been previously studied in [2-4]. The aim of this work is to synthesize via SHS and study of the properties of such light weight metallic matrix or ceramic matrix composite. EXPERIMENTAL METHODS The powders of industrial B4C with grain size (GS) average of 15 m in amount of 50, 60, 70 and 80 wt. % and aluminum (Al) PA-4 were used as inlet materials. The Co was inserted before ball milling in quantity of 4 wt.%. The attrition milling time was of 2 h. The B13C2 was synthesized in B4C crystals via solid phase transformation and low costly capsule technique of SHS. For microstructure studies of composites, after each step of processing the light optical (Nikon CX) and scanning electron microscopes (Zeiss EVO MA-15) were used. The X-ray diffraction technique (Bruker AXS, D5005) was used to analyze the B13C2 forming depending on initial powder content and process parameters. The micromechanical properties of B13C2 were characterized by using the nanoindentation device of NanoTest NTX testing centre (Micro Materials Ltd.). Nanoindentation was conducted in diamond polished surface under load of 20, 100 and 500 mN for 100 indents, respectively. The phases and micromechanical properties were identified by EDS in SEM pictures. RESULTS AND DISCUSSION Fig. 1. B13C2 compound was formed via phase transition in boron carbide (B4C) crystals during self-propagating high-temperature synthesis (SHS) of light-weight B4C/Al-based composite. The results of X-ray investigation show that the WC-Co content as catalyst was increased during ball milling and the tungsten aluminum carbide and aluminum cobalt contents were formed in binder phase of composite. During SHS the B13C2 content in quantity of ~45 wt. % was formed on base of B4C. By nanoindentation was established, that the B13C2 has nanohardness within 42-55 GPa. Fig. 2. Load vs. depth curves for micromechanical properties of B13C2 (a) N17, Hv = 47,5 GPa and Er = 412 GPa and c-BC2N (b) N9 Hv = 100,8 GPa and Er = 648 GPa, respectively. F