Phase Evolution, Microstructure and Hardness of TiB2-based Co-containing Composite by SHS under Pseudo-isostatic Pressure

Abstract

TiB2-based cermets with various Co contents were fabricated from elemental powders "in situ" by means of the Self-propagating High-temperature Synthesis, SHS, and Pseudo-Hot Isostatic Pressing, P-HIP method. The sample pressed into a cylindrical compact was ignited in a steel can by an external heating element coiling the can. After SHS initiation, which was detected by rapid temperature increase, the samples were quickly pressed pseudo-isostatically under a pressure of 192 MPa and held for 5 min. Samples with predominant concentration of TiB2, which varied from 70 to 85 vol.% with the addition of 5 vol% of Ti, were investigated in this study. Appreciable differences in terms of microstructure, density and hardness were observed depending on the composition. The average TiB2 grain size increased while porosity decreased with rising concentration of TiB2. The material synthesized with increased to 85% concentration of superhard TiB2 grains and minimized concentration of Co exhibited greatest densification, highest hardness of about 2 400 HV, and the most homogenous microstructure. The reaction mechanism was reportedly proposed, based on temperature monitoring during combustion and previously reported references.

The Cu matrix cermets remarkably strengthened by TiB2 “in situ” synthesized via self-propagating high temperature synthesis

“…The steel can containing compact was coiled with heating element and then inserted into a steel die. The scheme of device installed in the press mould was described in the previous paper [19]. Dried sand was used as both a pressing medium and electrical insulator.…”

“…Development of such composites with high conductivity and also high strength can be achieved by uniformly distributed ceramic materials such as oxides, borides, carbides and nitrides [2,4,5,[11][12][13] or silicides [14]. Especially TiB 2 , due to extremely high stiffness and hardness (3400HV) [3,10,15,16], ultra-high melting point (3225 o C) [3,17] and the best among borides and carbides both thermal and electrical conductivity (66W/mK) [3,18] is suitable candidate for Cu-matrix composite [7,11,12,[19][20][21]. Indeed, TiB 2 -Cu cermets formed by dispersion strengthening or precipitation hardening are leading candidates for such applications where an excellent combination of high thermal and electrical conductivity and high-temperature mechanical strength is required [1,15,22].…”

“…Such elements as Co or Ni which are commercially used in WC sintered carbides technology, are unsuitable as matrix phase for TiB 2 -based cermets, because it was already proven that both nickel and cobalt are unstable in contact with TiB 2 [19,20]. Contrary to those systems, both high-strength and high-thermal conductivity TiB 2 -reinforced Cu-matrix composites were successfully fabricated [1,3].…”

Vaporization and Poor Wettability as the Main Challenges in Fabrication of TiB2-Cu Cermets Studied by SPS

“…Such metal-like compound also has a very high melting point of 3225 °C [7,8]. The combination of the above-mentioned properties makes TiB2-Cu cermets potentially great candidates for applications where good electrical and/or thermal conductivity is needed [4,5].…”

“…Due to the application of very hard TiB2, hardness, strength, as well as wear and erosion resistance can be significantly improved. By using high volume fraction of TiB2 even the application in cutting tools technology is possible [3,10,11] because remarkably hard cermets can be obtained [7][8][9][10][11].…”