Solidification pathways and phase equilibria in the Mo–Ti–C ternary system

Abstract

<jats:title>Abstract</jats:title><jats:p>The liquidus surface projection and isothermal section at 1,800°C in the Mo–Ti–C ternary system are examined using arc-melted alloys. A ternary transition peritectic reaction (L + Mo<jats:sub>2</jats:sub>C → Mo + TiC) takes place during solidification, which is apparently different from the ternary eutectic reaction (L → Mo + TiC + Mo<jats:sub>2</jats:sub>C) observed in a previous report. Since the composition of the eutectic reaction (L → Mo + TiC) shifts toward the Mo–Ti binary line with increasing Ti concentration, the volume fraction of the Mo phase and the interlamellar spacing of the Mo and TiC phases increase in the eutectic microstructure. At 1,800°C, the TiC phase in equilibrium with the Mo phase can contain more than 28 at% Mo and a Mo/TiC/Mo<jats:sub>2</jats:sub>C three-phase region exists at around Mo–15Ti–10C.</jats:p>

Additive Manufacturing of Pure Mo and Mo + TiC MMC Alloy by Electron Beam Powder Bed Fusion

“…A study by Ida et al used arc melting to produce ingots with varying Mo-Ti-C compositions and heat-treated them to produce different phase mixtures. 29 While the compositions used in the report 29 were significantly different from that used herein, similar structures were observed in the as-cast and heattreated microstructures, including primary Mo, Mo + TiC, and Mo + Mo 2 C, the latter two phases both existing as eutectics. 29 Umuera and Fukuyama reported eutectic phases present in a Mo-Si-B-TiC alloy by fully melting the system and observing microstructures under a variety of solidification conditions.…”

“…29 While the compositions used in the report 29 were significantly different from that used herein, similar structures were observed in the as-cast and heattreated microstructures, including primary Mo, Mo + TiC, and Mo + Mo 2 C, the latter two phases both existing as eutectics. 29 Umuera and Fukuyama reported eutectic phases present in a Mo-Si-B-TiC alloy by fully melting the system and observing microstructures under a variety of solidification conditions. 30,31 For the composition shown in this study, even if the predicted phases are not highly accurate, it does corroborate the observed structures and the propensity for a variety of phase formation with moderate changes in local chemistry and temperatures, including the presence of eutectics and dendrites, which are observed as mixed microstructure in MMC layers fabricated by EB-PBF.…”

Oxidation Resistance, Creep Strength and Room-Temperature Fracture Toughness of Mo–28Ti–14Si–6C–6B Alloy

“…The experimentally obtained compositions of TiC and Moss are rather close to the predicted value at the liquidus and solvus temperatures, but not at the heat treatment temperature, suggesting sluggish diffusion of these elements or the existence of nanosized precipitates of TiC in the Moss phase and of Moss in the TiC phase, as previously reported for Mo-Si-B-Ti-C systems [15,16]. Another possibility on this underestimation is the insufficient accuracy of the calculation, because the calculated equilibria do not follow the tie line in experimentally determined Mo-Ti-C ternary phase diagram [30].…”

“…For comparison, the composition of the TiC phase in 1 st generation Mo-Si-B-TiC alloy was reported to be 23.5Mo-31.0Ti-45.5C (atom %) [11], which correspondingly contains a much higher proportion of Mo. These differences in the Mo/Ti ratio in TiC phase can be understood by the phase equilibria between Moss and TiC in Mo-Ti-C ternary system [30]. As a positive effect of the off-stoichiometry and Mo substitution in TiC on the fracture toughness was presented by Moriyama [15], the off-stoichiometry and Mo substitution in TiC in the present alloy might also be non-negligible in relation to its mechanical properties.…”

Solidification Microstructure and Mechanical Properties of B1-type TiC in Fe-Ti-C Ternary Alloys

“…B1 型 MX セラミックスは，NaCl 構造を有し，M が遷移金 属，X が非金属元素を主な構成元素とする。その一つであ る TiC は，高融点(3067℃) ，低密度(4.93 g/cm 3 ) ，硬い性質 を有し，高温材料の強化相として有望である 1,2) 。一方で， TiC の課題は靭性である。化学量論組成の TiC の室温破壊 靭性値は 3 MPa √m 程度である 3) 4,13,14) 。溶解鋳造法で作製された，非常に微 細な Mo 相と TiC からなる共晶ラメラ組織を有する合金は， 高温での強度と延性に優れることが報告されている 13,14) 。 同様の挙動は Mo-ZrC 共晶合金でも報告されている 15) 。 TiC の凝固形態に関しては，いくつかの報告がある。例 えば，L → Fe(BCC 構造)＋ TiC の共晶反応によって形成 された Fe 基合金の TiC は晶癖面を有する [16][17][18] 。同様の晶癖 面を持った TiC は，FeAl 基複合材料 19,20) ，TiAl 合金 21,22) ，Al 複合材料 23) でも観察されている。しかし，L → Mo(BCC 構 造)＋ TiC の共晶反応によって形成される Mo 基合金中の TiC は，そのような晶癖面の生成は報告されていない 24,25) 24,26) 。一方，後者の例と して，Fe-Ti-C や Ni-Ti-C などが挙げられる 27,28)…”