Effect of tantalum content on the microstructure and mechanical behavior of cermets based on (TixTa1−x)(C0.5N0.5) solid solutions

Abstract

Titanium-tantalum carbonitride, (Ti,Ta)(C,N), based cermets with different Ti and Ta contents were prepared using a mechanically induced self-sustaining reaction and then densified using a pressureless sintering process. Complete microstructural and mechanical characterizations were performed on the materials, which revealed that the size of the carbonitride ceramic particle was significantly reduced when the Ta content was increased. The flexural strength and fracture toughness were measured using the ball on three balls test and the indentation microfracture test, respectively. The strength profile was analyzed under the framework of Weibull theory. The change in the mechanical properties as a function of the Ta content was correlated with the normalized microstructural parameters, such as the binder mean free path. The decrease in toughness and flexural strength was attributed to the presence of intermetallic compounds in the binder phase, which was also corroborated by the nanoindentation tests.

Hot-pressing of (Ti, Mt)(C, N)–Co–Mo 2 C (Mt = Ta, Nb) powdered cermets synthesized by a mechanically induced self-sustaining reaction

“…However, the reflections of Co, the presumed binder phase, were not observed in figure 1a after the MSR process. Instead, a broad peak centered at ~ 43º 2 was seen in all of the XRD diagrams, which as published previously [31], corresponds to an alloy containing Co and the other transition metals (Ti, Nb and Ta) introduced in the starting powder mixture.…”

“…Concerning the binder phase, it was observed that this phase was always composed of intermetallic compounds after HP sintering, as reported in previous studies of similar cermets sintered by pressureless (PS) methods [13,30,31] or spark plasma sintering (SPS) [29]. Based on the Ti-Co binary phase diagram [41] (table 3).…”

“…The sintering temperatures were selected based on the transition metal composition of the cermets. For higher refractory metals, higher sintering temperatures were used, similar to previous studies [13,30,31]. The dwell time used for each cermet was the minimum time necessary to reach maximum shrinkage (densification) at the sintering temperature.…”

Toughening of complete solid solution cermets by graphite addition

“…Cermets combine the advantages of ceramics and metals [3]; the ceramic phase must mainly provide hardness and wear resistance, whereas the binder phase provides fracture strength and impact resistance [6]. For the hard component, other binary carbides, such as TaC, NbC, Mo 2 C, WC, HfC, VC and ZrC, are added to improve specific properties, for example, thermal shock resistance, hot hardness, chemical stability at high temperature, oxidation resistance and high-temperature creep resistance [7][8][9][10][11]. The binder phase can also contain other minor metallic components (Al, Cr, Mo, Fe, Mn, V or Ce) to support microstructure refinement, particulate dispersion, hardening of the binder and improvement of corrosion resistance [12,13].…”

“…The presence of intermetallics in cermets, which precipitate during cooling, is not a new phenomenon [2,29,30] and has been associated with the excessive dissolution of the ceramic particles in the molten binder, causing Ti enrichment. Although some authors have shown that ductile intermetallic alloys, especially aluminides, are good candidates for binders because the mechanical properties of cermets can be retained at high temperature [31,32], the formation of brittle intermetallics during sintering, such as Ti x Ta 1-x Co 2 , can be extremely harmful for cermets, greatly damaging the fracture strength and toughness [8].…”