Preparation of TiC-TiB<SUB>2</SUB>-SiC Ternary Eutectic Composites by Arc-Melting and Their Characterizations

Abstract

TiC-TiB 2 -SiC composites were synthesized by arc-melting using TiC, TiB 2 and SiC powders as starting materials in Ar atmosphere. TiCTiB 2 -SiC system was a ternary eutectic, whose eutectic composition was 34TiC-22TiB 2 -44SiC (mol%). The TiC-TiB 2 -SiC eutectic composite showed a lamellar texture, where lamellar SiC grains paralleled to lamellar TiC grains. TiB 2 grains had an angle of about 30 to 60 with lamellar SiC and TiC grains. The hardness of TiC-TiB 2 -SiC eutectic composite was 25.5 GPa at the load of 1.96 N and increased with increasing TiC content. The electrical conductivity of the eutectic composite was 2:81 Â 10 3 Sm À1 at the room temperature and decreased with increasing temperature. The thermal conductivity of the eutectic composite was 25 to 60 WK À1 m À1 at the room temperature and decreased with increasing temperature. The electrical conductivity of TiC-TiB 2 -SiC ternary composites decreased with increasing SiC content, and the thermal conductivity decreased with increasing TiC content.

Solidification of welded SiC–ZrB2–ZrC ceramics

“…Based on similarities in the properties of TiB 2 and ZrB 2 as well as TiC and ZrC, it was hypothesized that a SiC–ZrB 2 –ZrC ternary eutectic was present in the system. Furthermore, like the SiC–TiB 2 –TiC system, the ternary invariant temperature would be lower than any of the binary invariant temperatures . Therefore, the initial welding speed was set higher, at 15 cm/min, to reduce the overall linear energy input into SZZ weldments.…”

“…The system selected has three phases, which could prove beneficial during solidification, as observed by King et al through the solidification of ZrB 2 –ZrC–C weld pools. While phase equilibria for the SiC–ZrB 2 –ZrC ternary system is essentially unknown, the similar SiC–TiB 2 –TiC ternary system has been investigated and a ternary eutectic composition of 44 mol% SiC, 22 mol% TiB 2 , and 34 mol% TiC was reported . It has also been reported that the SiC and ZrB 2 system has a binary eutectic (48‐50 vol%; 33‐35 wt%; 58‐60 mol% SiC); the ZrB 2 and ZrC system has binary eutectic (61.2 vol%; 59.2 wt%; 57 mol% ZrB 2 ); and the SiC and ZrC system is expected to have a binary eutectic (67‐68 vol%; 50‐51 wt%; 72‐73 mol% SiC) .…”

“…While phase equilibria for the SiC-ZrB 2 -ZrC ternary system is essentially unknown, the similar SiC-TiB 2 -TiC ternary system has been investigated and a ternary eutectic composition of 44 mol% SiC, 22 mol% TiB 2 , and 34 mol% TiC was reported. 26 It has also been reported that the SiC and ZrB 2 system has a binary eutectic (48-50 vol%; 33-35 wt%; 58-60 mol% SiC) [27][28][29] ; the ZrB 2 and ZrC system has binary eutectic (61.2 vol%; 59.2 wt%; 57 mol% ZrB 2 ) 30 ; and the SiC and ZrC system is expected to have a binary eutectic (67-68 vol%; 50-51 wt%; 72-73 mol% SiC). 31 Therefore, even if a ternary eutectic composition were not present in the SiC-ZrB 2 -ZrC system, the (PM) would still melt through the three binary eutectic invariant reactions, even with a high SiC content.…”

Directionally Solidified Boride and Carbide Eutectic Ceramics

“…1, the vapor pressures of elements in boride and carbide compounds increase dramatically at high temperatures and cannot be ignored during processing. 49 Arc melting is a convenient approach for preliminary studies of new eutectic systems, as the electric arc can provide temperatures exceeding 3000°C 50,51 and the inert atmosphere is particularly well suited for non-oxide DSEs. 48 Furthermore, the generated vapor inside the chamber may induce thermal fluctuations, as reported in the electronbeam-processed LaB 6 -ZrB 2 DSE.…”

“…45,46 The volatilization of materials may generate gas and lead to the formation of pores 47 and difficulty in maintaining the eutectic composition. [50][51][52] Nondirectional eutectic solidification has also been demonstrated in inert-atmosphere plasma spray processes, 53 which may be a potential path for large-scale production of ceramic powders containing a eutectic composite microstructure. 49 Arc melting is a convenient approach for preliminary studies of new eutectic systems, as the electric arc can provide temperatures exceeding 3000°C 50,51 and the inert atmosphere is particularly well suited for non-oxide DSEs.…”