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Effect of Cr and Al alloying on the oxidation resistance of a Ti5Si3-incorporated MoSiBTiC alloy

  • Xi Nan , Tomotaka Hatakeyama , Shuntaro Ida , Nobuaki Sekido and Kyosuke Yoshimi EMAIL logo
Published/Copyright: June 28, 2021
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High Temperature Materials and Processes
From the journal High Temperature Materials and Processes Volume 40 Issue 1

Abstract

The effects of adding Cr and Al on the oxidation behavior of a Ti5Si3-incorporated MoSiBTiC alloy (46Mo–28Ti–14Si–6C–6B, at%) were investigated at 800 and 1,100°C. The addition of Cr and Al largely improved the oxidation resistance of the MoSiBTiC alloy at 800°C due to the formation of Cr2(MoO4)3 and Al2(MoO4)3 in the oxide scales. These protective molybdates mainly formed on the molybdenum solid solution (Moss) and Mo3Si phases that show poor oxidation resistance in the Cr- and Al-free alloy and consequently increased the oxidation resistance of the alloys. However, accelerated oxidation occurred on the 10Al alloy after the long-term oxidation test, suggesting that the formed oxide scale has limited protection ability. At 1,100°C, the addition of Cr and Al also enhanced the oxidation resistance to some extent by forming Cr2O3 and Al2O3 in the oxide scales.

Keywords: molybdenum; oxidation resistance; high-temperature materials; chromium addition; aluminum addition

1 Introduction

Molybdenum–silicon–boron (Mo–Si–B) alloys are promising ultra-high temperature structural materials for heat engines because of their high melting point and impressive creep strength above 1,150°C [1,2,3,4,5]. Nevertheless, the poor room-temperature fracture toughness and inadequate oxidation resistance of Mo–Si–B alloys prevent their practical use [5,6,7]. Recently, Moriyama et al. found that a TiC-added Mo–Si–B alloy with a typical composition of 65Mo–10Ti–5Si–10C–10B (at%, so-called first-generation MoSiBTiC alloy) showed improved room-temperature fracture toughness compared with conventional Mo–Si–B ternary alloys [8]. The density of this alloy has also been reduced by TiC addition to 8.9 g/cm3 [9], which is within the range of nickel-based single-crystal superalloys. Kamata et al. further revealed that this alloy possessed excellent creep strength (a rupture time of ∼400 h at 1,400°C under 137 MPa) [10]. However, the oxidation resistance of the first-generation MoSiBTiC alloy is very poor, mainly due to the relatively low concentration of Si and the large volume fraction of the molybdenum solid solution (Moss) phase [11]. Experimental efforts to solve this problem by incorporating Ti5Si3, an oxidation-resistant intermetallic phase, into MoSiBTiC alloy have been attempted. The composition modified as a Ti5Si3-incorporated MoSiBTiC alloy is 46Mo–28Ti–14Si–6C–6B (at%), which exhibited better oxidation performance than the first-generation MoSiBTiC alloy at 1,100°C [12]. Unfortunately, due to the low protection from the boron-containing silicate formed at intermediate temperature, a remarkable weight loss of the 46Mo–28Ti–14Si–6C–6B alloy upon exposure to oxygen was observed at 800°C [12,13].

It is well known that Cr and Al are beneficial alloying elements for improving oxidation resistance by forming protective Cr2O3 and Al2O3 layers. The effects of Cr in Mo–Si–B alloys were investigated by Burk et al. [14]. The Mo–Si–B–Cr alloys showed increased oxidation resistance with the increasing Cr content from 5 to 25 at%. A fully passivated Cr2(MoO4)3 layer was formed on the Mo–9Si–8B–25Cr alloy oxidized at 750°C for 10 h. Ström et al. also reported the formation of Cr2(MoO4)3 on the Cr-alloyed MoSi2 at 450°C [15]. Alloying with Al was proved to be able to suppress the pest phenomenon and thus enhanced the oxidation behavior of Mo–Si alloys due to the presence of the Al2O3 scale on the surface at high temperature [16,17,18,19]. Zhao et al. also reported that adding Al or Cr into Mo–Ti–Si–B alloy (35Mo–35Ti–20Si–10B) yielded better intermediate-temperature oxidation resistance [20].

Therefore, in the present study, varying amounts of Cr and Al were added to the Ti5Si3-incorporated MoSiBTiC alloy, and the oxidation performance was evaluated by analyzing oxidation kinetic curves and oxide scales formed at different temperatures, aiming to provide insights for the alloy design of advanced MoSiBTiC alloys for ultra-high temperature applications.

2 Experimental procedures

The Cr- and Al-added Ti5Si3-incorporated MoSiBTiC alloys investigated in this study have the compositions of 36Mo–28Ti–14Si–6C–6B–(10−x)Cr–xAl (x = 0, 5 and 10, at%). For simplicity, they are denoted as base (46Mo and no Cr and Al), 10Cr, 5Cr5Al and 10Al alloys, respectively. These alloys were prepared by conventional arc-melting with a water-cooled copper crucible from high-purity Mo (99.9%), Ti (99.995%), Si (99.99%), Cr (99.9%), Al (99.99%), MoB (99%) and cold-pressed TiC powder (99 wt%, 2–5 µm in diameter) under an argon atmosphere. The button ingots were flipped over and remelted five times to ensure compositional homogenization. Heat treatment was performed at 1,600°C for 10 h under an argon atmosphere. There was no noticeable weight change of the ingots before and after heat treatment. The chemical compositions of the investigated Ti5Si3-incorporated MoSiBTiC alloys are summarized in Table 1. In particular, boron was measured using inductively coupled plasma analysis.

Table 1

Chemical compositions of the investigated Ti5Si3-incorporated MoSiBTiC alloys (at%)

Alloy Mo Ti Si C B Cr Al
Base 46.4 ± 1.1 28.4 ± 0.6 13.0 ± 1.2 5.9 ± 0.6 6.1 ± 0.3 <0.1 <0.1
10Cr 37.1 ± 1.4 28.8 ± 1.1 13.1 ± 1.9 6.3 ± 0.8 5.6 ± 0.5 9.0 ± 1.2 <0.1
5Cr5Al 37.2 ± 1.5 29.1 ± 2.0 13.1 ± 0.9 6.2 ± 0.5 5.5 ± 0.7 4.6 ± 0.9 4.3 ± 1.0
10Al 37.0 ± 1.2 28.8 ± 1.5 13.3 ± 1.3 6.1 ± 0.4 5.7 ± 0.60 <0.1 9.0 ± 1.4

A Bruker D8 Advance X-ray diffractometer (XRD) with Cu-Kα radiation was used for phase identification. The data were collected over a 2θ range of 20–80° with a step size of 0.02° and a count time of 0.5 s/step. Microstructure characterization was conducted using a JEOL JSM-7800F scanning electron microscope (SEM) in a backscattered electron imaging mode. Chemical analysis of constituent phases for Mo, Ti, Si, Cr and Al were carried out using energy-dispersive X-ray spectroscopy (EDX) and electron probe micro analyzer (EPMA) on a JEOL JCM 6000PLUS microscope. B and C were neglected during the measurements due to the serious interference problem between the characteristic lines of Mo and B as well as the low quantitative capability of EDX for these light elements.

For oxidation studies, coupon specimens were sliced from the heat-treated ingots by electron-discharge machining. These specimens were carefully polished using 2000-grit SiC paper to fully remove the heat-damaged layers and given final dimensions of approximately 4 × 3 × 0.5 mm3. They were then cleaned ultrasonically in ethanol for 30 min and dried in air. Oxidation tests were performed isothermally at 800°C for 50 h and 1,100°C for 12 h under an Ar–21% O2 gas flow using a Shimadzu TGA-50H thermo-gravimetric analyzer. The weight change of the specimens was continuously recorded against time to acquire oxidation kinetic curves. The oxidized specimens were also carefully examined by XRD, SEM, EDX and EPMA.

3 Results and discussion

3.1 Microstructure

Figure 1 shows the microstructures of the (a) base, (b) 10Cr, (c) 5Cr5Al and (d) 10Al alloys after 1,600°C/10 h heat treatment. As shown in Figure 1(a) and (b), the base and 10Cr alloys had the same phase constitution, that is, Moss, Ti5Si3, Mo5SiB2 (T2) and TiC. It is suggested that the addition of Cr did not change the phase equilibrium of the base alloy. However, the microstructure of the 10Cr alloys was much coarser than that of the base alloy. Mo3Si was detected in the 5Cr5Al and 10Al alloys, accompanying the decreased volume fraction of Moss (see Figure 1(c) and (d)). In the 10Al alloy, only the polygonal prism-shaped Ti5Si3 rods elongating along the solidification direction can be seen, and the fine secondary Ti5Si3 as observed in the eutectic regions of the base alloy almost disappeared. Some spheroidized Mo3Si particles precipitated in the polygonal prism-shaped Ti5Si3 of the Al-added alloys during annealing. The compositions of each constituent phase measured by SEM-EDX for the heat-treated alloys are presented in Table 2. A large amount of Ti was dissolved in Moss (∼20 at%), Mo3Si (∼23 at%) and T2 (∼31 at%), while a large amount of Mo was dissolved in Ti5Si3 (∼20 at%) and TiC (∼9 at%). In the Cr-added alloys, Cr mainly dissolved in Moss and Mo3Si phases. The previous work by Hatakeyama et al. revealed that Cr can substitute at Mo sites in the Moss and T2 phases and barely change the constituent phases of the alloy [12]. Al mainly dissolved in the Mo3Si phases in Al-added alloys because Al is a Mo3(Si,Al)-forming element [16,21]. In addition, the concentrations of both Cr and Al in TiC phase are negligible (less than 1%). Figure 2 presents the volume fractions of phase constituents in the heat-treated alloys. The volume fraction of T2 and TiC phases also showed insignificant changes with the addition of Cr and Al.

Figure 1 Microstructures of the heat-treated (a) base, (b) 10Cr, (c) 5Cr5Al and (d) 10Al alloys.
Figure 1

Microstructures of the heat-treated (a) base, (b) 10Cr, (c) 5Cr5Al and (d) 10Al alloys.

Table 2

Compositions of each constituent phase as measured by SEM-EDX for the heat-treated alloys (at%)

10Cr alloy 5Cr5Al alloy 10Al alloy
Moss Ti5Si3 T2 TiC Moss Mo3Si Ti5Si3 T2 TiC Mo3Si Ti5Si3 T2 TiC
Mo 61.2 ± 2.2 18.6 ± 1.5 47.0 ± 3.6 8.6 ± 2.1 63.5 ± 3.4 50.2 ± 1.1 18.8 ± 2.2 50.6 ± 1.6 8.4 ± 1.1 56.9 ± 2.3 23.1 ± 0.9 54.5 ± 2.8 9.7 ± 0.4
Si 2.4 ± 0.8 31.7 ± 0.9 14.0 ± 1.1 0.4 ± 0.1 1.6 ± 0.6 12.7 ± 0.4 30.2 ± 1.2 14.1 ± 0.4 0.2 ± 0.1 9.8 ± 0.7 27.3 ± 0.6 13.8 ± 0.3 0.2 ± 0.1
Ti 19.2 ± 1.1 44.0 ± 1.9 32.6 ± 2.6 90.8 ± 2.7 21.4 ± 1.1 23.5 ± 0.5 44.7 ± 2.0 31.7 ± 1.7 90.5 ± 1.0 22.0 ± 1.4 44.5 ± 1.5 30.5 ± 2.7 89.3 ± 0.9
Cr 17.2 ± 1.0 5.7 ± 0.6 6.4 ± 0.4 0.2 ± 0.2 8.7 ± 0.7 6.9 ± 0.5 3.0 ± 0.3 2.6 ± 0.4 0.3 ± 0.1 — — — —
Al — — — — 4.8 ± 0.4 6.7 ± 0.6 3.3 ± 0.2 1.0 ± 0.2 0.6 ± 0.1 11.3 ± 0.3 5.1 ± 1.1 1.2 ± 0.2 0.8 ± 0.2
Figure 2 Volume fractions of constituent phases of the heat-treated alloys.
Figure 2

Volume fractions of constituent phases of the heat-treated alloys.

3.2 Oxidation behavior at 800°C

Figure 3(a) illustrates the isothermal oxidation curves of the alloys obtained at 800°C. The base alloy showed a rapid weight loss (−60 mg/cm2 for 5 h) correlating with the evaporation of MoO3, B2O3 and CO2 from the oxidized surfaces [22,23,24]. In contrast, the 10Cr, 5Cr5Al and 10Al alloys exhibited dramatically reduced weight losses upon oxidation exposure. The weight changes of the 10Cr and 5Cr5Al alloys after 50 h oxidation were less than −1 mg/cm2. This indicates that the weight loss of the base alloy at 800°C can be suppressed by adding Cr and/or Al. It is noteworthy that the weight loss rate of the 10Al alloy suddenly increased from ∼22 h of oxidation. The appearances of the specimens oxidized for 50 h are shown in Figure 3(b)–(e). After the 12 h oxidation test, the base alloy did not change in shape and appeared intact (Figure 3(b)). The 10Cr and 5Cr5Al specimens showed no spalling or cracking after the 50 h oxidation tests, as shown in Figure 3(c) and (d). Nevertheless, the edges of the 10Al coupon became distorted after the oxidation test (Figure 3(e)). This may be related to the suddenly accelerated oxidation as seen in the kinetic curve.

Figure 3 (a) Isothermal oxidation curves of the alloys obtained at 800°C and appearances of the specimens of the (b) base, (c) 10Cr, (d) 5Cr5Al and (e) 10Al alloys oxidized for 50 h.
Figure 3

(a) Isothermal oxidation curves of the alloys obtained at 800°C and appearances of the specimens of the (b) base, (c) 10Cr, (d) 5Cr5Al and (e) 10Al alloys oxidized for 50 h.

Figure 4 shows the XRD spectra of the base and Cr/Al-added alloy samples after 50 h oxidation at 800°C. TiO2 reflections were detected in all samples. Characteristic reflections of chromium and aluminum molybdates (X 2(MoO4)3, X = Cr or/and Al) were observed in the Cr/Al-added alloys. In addition, some weak Al2O3 reflections were also detected in the 10Al alloy. Noteworthy is that signals from MoO3, which should have evaporated during oxidation are also present in the XRD spectra. It might be related to the desublimation of MoO3 during cooling. The cross-section microstructures of all the alloys oxidized at 800°C for 50 h are shown in Figure 5, with the oxide scales identified by XRD and EPMA analyses as described in this article. As shown in Figure 5(a), the base alloy specimen was completely oxidized, and its oxide scale was composed of TiO2, SiO2 and unoxidized Ti5Si3. Even though no SiO2 signals were detected by XRD, high Si and O concentrations measured by EPMA from the oxide scale (15.5Ti–17.2Si–67.3O, at%) could prove the formation of SiO2. The poor oxidation resistance of the base alloy at 800°C is mainly attributed to the rapid oxidation of the Moss phase and the resultant sublimation of MoO3. Although the Ti5Si3 phase possesses good oxidation resistance and barely oxidizes at 800°C [25,26], it cannot form a protective scale covering the entire specimen due to the small amount of oxidation products. Therefore, the oxidation proceeded along the continuous Moss phase to form a microporous TiO2/SiO2 scale. Detailed analyses of the oxidation behavior of the base alloy have been reported elsewhere [13,27]. The oxide scales formed on the 10Cr, 5Cr5Al and 10Al specimens after oxidation for 50 h were very thin (average thickness less than 15 μm). The Ti5Si3 phase in each alloy also barely oxidized and exhibited significant oxidation resistance among constituent phases. Particularly, the recession depths of Moss and Mo3Si phases reduced to less than 6 μm in contrast to the preferentially oxidized Moss phase in the base alloy. For the 10Cr alloy, the oxide scale was composed of TiO2, SiO2 and Cr2(MoO4)3 (see Figure 5(b)). The molybdate was mainly distributed on the Moss phase due to the high amount of Cr dissolved in Moss (∼15 at%) and acted as a protective barrier, which prevented further oxidation. This agrees with the result reported by Burk et al. that the Cr2(MoO4)3 layer formed on the Mo–9Si–8B–25Cr alloy oxidized at 750°C is fully passivated [14]. In the scale formed on the 5Cr5Al specimen, the molybdate (Cr,Al)2(MoO4)3 was also detected.

Figure 4 XRD spectra of the (a) base, (b) 10Cr, (c) 5Cr5Al and (d) 10Al alloys after 50 h oxidation at 800°C.
Figure 4

XRD spectra of the (a) base, (b) 10Cr, (c) 5Cr5Al and (d) 10Al alloys after 50 h oxidation at 800°C.

Figure 5 Cross-section microstructures of the (a) base, (b) 10Cr, (c) 5Cr5Al and (d) 10Al alloys oxidized at 800°C for 50 h.
Figure 5

Cross-section microstructures of the (a) base, (b) 10Cr, (c) 5Cr5Al and (d) 10Al alloys oxidized at 800°C for 50 h.

Figure 6 shows EPMA elemental maps of the oxidized 5Cr5Al alloy specimen. It was found that Ti spread over the whole oxide scale, and Si was mainly distributed in the scale upon the silicide phases. An internal oxidation region, which formed on the top of the T2 phase (indicated by a thick arrow), was Ti and Si deficient, containing a detectable concentration of Mo and O (see Figure 6(f) and (g)). This internal oxidation region formed on the T2 phase was reported elsewhere [6]. The distributions of Cr and Mo were quite uniform (indicated by thin arrows in Figure 6(d)–(f)), and Al also existed in these Cr/Mo-rich regions, coinciding with the molybdate mainly formed on the Moss and Mo3Si. This agrees with the portioning behavior of Cr and Al in each constituent phase as presented in Table 2. Moreover, a high Al content was observed at the outermost layer of the oxide scale, indicating the formation of Al2O3. Similar outward diffusion of Al had been reported for Ti–Al–Si alloys [28,29]. The oxide scale formed on the 10Al specimen had similar oxide scales to that of the 5Cr5Al alloy (see Figure 5(d)). However, the discontinuous Al2O3 layer formed on the outermost scale could not provide sufficient protection for the substrate. It can be concluded that the addition of Cr and Al to the base alloy contributed to the formation of protective molybdates upon Moss and Mo3Si phases, which suppressed the inward diffusion of oxygen and consequently increased the oxidation resistance of the entire alloy.

Figure 6 (a) Cross-section BSE image and (b)–(g) the corresponding EPMA elemental maps of the 5Cr5Al alloy oxidized at 800°C for 50 h.
Figure 6

(a) Cross-section BSE image and (b)–(g) the corresponding EPMA elemental maps of the 5Cr5Al alloy oxidized at 800°C for 50 h.

Even though these chromium and aluminum molybdates, which formed at and below 800°C on the MoSiBTiC alloys, acted as protective oxide, Cr2(MoO4)3 and Al2(MoO4)3 decompose with MoO3 vaporization at temperatures starting from 810 and 800°C, respectively [30,31]. Since the decomposition temperature of Al2(MoO4)3 is the same as the oxidation temperature in this study, the formation and decomposition of Al2(MoO4)3 may progress simultaneously during the oxidation process. This agrees with the SEM results that both Al2(MoO4)3 and Al2O3 were observed in the Al-added alloys (see Figure 5(d)). Therefore, for the 10Al alloy that showed good oxidation resistance in the first several hours (shown in Figure 3(a)), the accelerated oxidation from ∼22 h and the distorted sample edges (see Figure 3(e)) were presumably due to the decomposition of Al2(MoO4)3 to Al2O3 and volatile MoO3 after the long-term oxidation test.

3.3 Oxidation behavior at 1,100°C

Figure 7 shows the isothermal oxidation curves of the alloys at 1,100°C and the appearance of the specimens after 12 h of oxidation. The weight loss corresponds to the evaporation of MoO3, B2O3 and CO2 during oxidation. As shown in Figure 7(a), all of the alloys experienced a rapid weight loss at the beginning of the oxidation (called the “initial stage”), followed by a gradual slowing down of the oxidation rate. Compared with the base alloy for which the initial stage ended around 1 h, the 10Cr, 5Cr5Al and 10Al alloys exhibited a shorter initial stage with the ending time around 10 min. The weight loss in the initial stages of the 10Cr, 5Cr5Al and 10Al alloys was much smaller than that of the base alloy. However, all the alloys showed a continuous weight loss in a linear manner after the initial stage. This means that the oxide scales, which formed on the substrates did not completely passivate them, and thus, the sublimation of MoO3 could not be fully suppressed. Figure 7(b)–(e) show the appearance of the alloys oxidized at 1,100°C for 12 h. It can be seen that the base alloy contained some protruded oxides along the specimen edges (see Figure 7(b)). In contrast, the Cr/Al-added alloys had neat surface morphology as shown in Figure 7(c)–(e). Figure 8 shows the XRD patterns obtained from the surface of the base and Cr/Al-added alloys oxidized at 1,100°C for 12 h. Strong TiO2 reflections were detected, indicating that the main component of the oxide scale was rutile TiO2. The 10Cr alloy had a similar XRD pattern with the base alloy, with only TiO2 being detected. For the Al-added alloys, Al2O3 formed in the scales during the oxidation test, coinciding with the color change of the sample surfaces shown in Figure 7(c) and (d).

Figure 7 (a) Isothermal oxidation curves of the alloys obtained at 1,100°C and the appearance of the (b) base, (c) 10Cr, (d) 5Cr5Al and (e) 10Al specimens oxidized for 12 h.
Figure 7

(a) Isothermal oxidation curves of the alloys obtained at 1,100°C and the appearance of the (b) base, (c) 10Cr, (d) 5Cr5Al and (e) 10Al specimens oxidized for 12 h.

Figure 8 XRD spectra of the specimen surface of the base, 10Cr, 5Cr5Al and 10Al alloys oxidized at 1,100°C for 12 h.
Figure 8

XRD spectra of the specimen surface of the base, 10Cr, 5Cr5Al and 10Al alloys oxidized at 1,100°C for 12 h.

The cross-section microstructures of the base, 10Cr, 5Cr5Al and 10Al alloys oxidized at 1,100°C for 12 h are shown in Figure 9(a)–(e). The average scale thickness of the base, 10Cr, 5Cr5Al and 10Al alloys was 40, 30, 30 and 32 μm, respectively. SiO2 was detected in the oxide layers by EPMA analysis even though there were no silicate peaks in the XRD patterns. The oxide scale formed in the 10Cr alloy was mainly composed of TiO2 and SiO2 as shown in Figure 9(b). Meanwhile, as shown in Figure 9(c), some light gray particles mainly distributed near the scale/substrate interface can be seen for the 10Cr alloy. The results of EPMA analysis listed in Table 3 show that the light gray particles should be Cr2O3. Figure 10 shows an (a) cross-section BSE image with the corresponding EDX elemental maps illustrated the 10Cr alloy oxidized at 1,100°C for 12 h in (b)–(f). High Ti and Si contents were observed in the oxide scale. Cr tended to concentrate on the inner side of the scale (see Figure 10(e)), coinciding with the Cr2O3 particles that are shown in Figure 9(c). The formation of Cr2O3 suppressed the inward diffusion of oxygen at some depth, thereby increasing the oxidation resistance at high temperature. No Cr2O3 particles were detected in the scale near the surface from the XRD or SEM results, where a detectable Cr concentration was found. The absence of Cr2O3 particles near the scale/gas interface may be due to the lower oxygen affinity of Cr than Ti, which suppressed the Cr2O3 formation at the beginning of oxidation or by the sublimation of volatile CrO3 from the scale surface [32]. The oxide scale formed on the 5Cr5Al and 10Al specimens was composed of a TiO2/Al2O3 outermost layer and a TiO2/SiO2 inner layer. Cr2O3 particles were also observed in the scale of the oxidized 5Cr5Al specimen. Since Al has a high affinity with oxygen, Al2O3 would form preferentially at the very beginning of oxidation. However, the Al concentration in the 5Cr5Al and 10Al alloys was relatively low compared with the Ti concentration. Once Al diffused to the surface, the lean-Al region underneath allowed Ti to oxidize to TiO2, giving rise to a mixed outermost layer composed of TiO2 and Al2O3 instead of the continuous alumina layer. This oxide scale structure was similar to the scale formed on the Ti–Al-based alloys with relatively low Al content [28,33,34]. In contrast to the oxide scale of the 10Cr alloy, which consisted of coarse TiO2 grains, these Al2O3-containing scales showed very fine oxide grains. Together with voids as shown in Figure 9(e), these Al2O3-containing scales likely offer only limited protection even though Al2O3 is considered to be an oxidation-resistant phase in many alloy systems.

Figure 9 Cross-section microstructures of the (a) base, (b) 10Cr, (d) 5Cr5Al and (e) 10Al alloys oxidized at 1,100°C for 12 h, (c) high magnification image of the squared area in (b).
Figure 9

Cross-section microstructures of the (a) base, (b) 10Cr, (d) 5Cr5Al and (e) 10Al alloys oxidized at 1,100°C for 12 h, (c) high magnification image of the squared area in (b).

Table 3

Composition of the light gray phase in the oxide scale in Figure 9(c) (at%)

Element Content
Mo 1.2 ± 0.3
Ti 5.4 ± 1.3
Si 1.9 ± 0.1
Cr 29.5 ± 2.7
O 62.0 ± 7.2
Figure 10 (a) Cross-section BSE image and (b)–(f) the corresponding EDX elemental maps of the 10Cr alloy oxidized at 1,100°C for 12 h.
Figure 10

(a) Cross-section BSE image and (b)–(f) the corresponding EDX elemental maps of the 10Cr alloy oxidized at 1,100°C for 12 h.

4 Conclusion

The effects of adding Cr and Al on the oxidation behavior of a Ti5Si3-incorporated MoSiBTiC alloy were investigated. The addition of Cr did not change the constituent phases of the base alloy but coarsened the microstructure, while Mo3Si phases formed by Al alloying. Compared with the base alloy, the alloys added with Cr and Al exhibited largely improved oxidation resistance at 800°C due to the formation of protective Cr2(MoO4)3 and Al2(MoO4)3. These molybdates mainly formed upon Moss and Mo3Si phases that showed poor oxidation resistance in the base alloy and consequently increased the oxidation resistance of the alloys. However, accelerated oxidation occurred on the 10Al alloys after the long-term oxidation test, indicating that the formed oxide scale has limited protection ability. At 1,100°C, the addition of Cr and Al also enhanced the oxidation resistance to some extent by forming Cr2O3 and Al2O3 in the oxide scales.

Acknowledgments

This research was partly supported by the Japan Science and Technology (JST)–Mirai Program (Grant Number JPMJMI17E7).

  1. Funding information: This research was partly supported by the Japan Science and Technology (JST)–Mirai Program (Grant Number JPMJMI17E7).

  2. Author contributions: Xi Nan: writing – original draft, conceptualization, methodology, investigation; Tomotaka Hatakeyama: conceptualization; Shuntaro Ida: writing – review and editing; Nobuaki Sekido: writing – review and editing; Kyosuke Yoshimi: resource, supervision, project administration.

  3. Conflict of interest: The authors state no conflict of interest.

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Received: 2021-01-05
Revised: 2021-04-09
Accepted: 2021-04-14
Published Online: 2021-06-28

© 2021 Xi Nan et al., published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

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https://doi.org/10.1515/htmp-2021-0024
Keywords for this article
molybdenum; oxidation resistance; high-temperature materials; chromium addition; aluminum addition
Creative Commons
BY 4.0

Articles in the same Issue

  1. Research Articles
  2. Fused deposition modeling of poly(ether ether ketone) scaffolds
  3. Investigation of the microstructure evolution in TP347HFG austenitic steel at 700°C and its characterization method
  4. Hot deformation behavior and processing maps of 9Cr3W3Co oxide dispersion-strengthened steel
  5. Evolution of physicochemical properties of quick lime at converter-smelting temperature
  6. Influence of phase distribution of converter slag microzones on the occurrence of P
  7. Investigation on ultrasonic assisted friction stir welding of aluminum/steel dissimilar alloys
  8. Analysis of oxide scale thickness and pores position of HCM12A steel in supercritical water
  9. Behavior of MnS inclusions during homogenization process in low-alloyed steel FAS3420H
  10. Preparation and cutting performance of nano-scaled Al2O3-coated micro-textured cutting tool prepared by atomic layer deposition
  11. Prediction of hot metal temperature based on data mining
  12. Effect of TiO2 content in slag on Ti content in molten steel
  13. Performance evaluation of titanium-based metal nitride coatings and die lifetime prediction in a cold extrusion process
  14. Effect of different drilling techniques on high-cycle fatigue behavior of nickel-based single-crystal superalloy with film cooling hole
  15. Effect of CO2 injection into blast furnace tuyeres on the pulverized coal combustion
  16. Microstructure and properties of Co–Al porous intermetallics fabricated by thermal explosion reaction
  17. Evolution regularity of temperature field of active heat insulation roadway considering thermal insulation spraying and grouting: A case study of Zhujidong Coal Mine, China
  18. Evolution of reduction process from tungsten oxide to ultrafine tungsten powder via hydrogen
  19. A thermodynamic assessment of precipitation, growth, and control of MnS inclusion in U75V heavy rail steel
  20. Effect of basicity on the reduction swelling properties of iron ore briquettes
  21. Effect of Cr and Al alloying on the oxidation resistance of a Ti5Si3-incorporated MoSiBTiC alloy
  22. Microstructure and mechanical properties of 2060 Al–Li alloy welded by alternating current cold metal transfer with high-frequency pulse current
  23. Effects of composition and strain rate on hot ductility of Cr–Mo-alloy steel in the two-phase region
  24. Effect of K and Na on reduction swelling performance of oxidized roasted briquettes
  25. Dephosphorization mechanism and phase change in the reduction of converter slag
  26. Parametric investigation and optimization for CO2 laser cladding of AlFeCoCrNiCu powder on AISI 316
  27. Optimization of heat transfer and pressure drop of the channel flow with baffle
  28. Quantitative analysis of microstructure and mechanical properties of Nb–V microalloyed high-strength seismic reinforcement with different Nb additions
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  30. Research on high-temperature mechanical properties of wellhead and downhole tool steel in offshore multi-round thermal recovery
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  39. Reactions at the molten flux-weld pool interface in submerged arc welding
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  41. Study on manganese volatilization behavior of Fe–Mn–C–Al twinning-induced plasticity steel
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  47. Copper-based kesterite thin films for photoelectrochemical water splitting
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