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Article

Effect of Al2O3 and SiO2 Inert-Fillers on the Microstructural Evolution and High Temperature Oxidation Resistance of B Modified Silicides Coatings Prepared by Pack Cementation Technology

by
Linfen Su
1,2,*,
Guanqun Zhuo
1,2,
Haiwen Song
1,2,
Jianyong Yang
1,2 and
Kaiyong Jiang
1,2
1
College of Mechanical Engineering and Automation, Huaqiao University, Xiamen 361021, China
2
Fujian Key Laboratory of Special Energy Manufacturing, Huaqiao University, Xiamen 361021, China
*
Author to whom correspondence should be addressed.
Coatings 2021, 11(6), 700; https://doi.org/10.3390/coatings11060700
Submission received: 16 April 2021 / Revised: 7 June 2021 / Accepted: 8 June 2021 / Published: 11 June 2021
Browse Figures
Versions Notes

Abstract

:
In this study, B modified silicide coatings were prepared on Nb-Si based alloy with Al2O3 or SiO2 inert-filler by pack cementation technology. Both coatings primarily consisted of a (Nb,X)Si2 with a (Nb,X)B2 + (Nb,X)Si2 outer layer. After oxidation at 1250 °C for 100 h, the coatings showed good oxidation resistance due to the formation of a dense silica. The oxidation products of the coating prepared with Al2O3 inert-filler consisted of SiO2, TiO2 and Cr2O3, while that of the coating prepared with SiO2 inert-filler consisted of SiO2, TiO2, Cr2O3, and HfO2. The different oxidation products may be due to the different oxidation process of these two sample at initial oxidation stage.

1. Introduction

The Nb-Si based alloys have attracted significant research interest as the promising candidate for high temperature structure materials due to their excellent mechanical properties at high temperatures [1,2,3]. However, the widespread use of Nb−Si based alloys is limited as their oxidation resistance is still inadequate, which may be due to the formation of non-protective oxides (Nb2O5, CrNbO4, Ti2Nb10O29, and TiNbO4) at high temperatures [4,5,6,7]. Alloying with elements such as Ti, Al, Cr, Sn, Ta, and Ge could moderately increase their high temperature oxidation resistance [8,9,10,11]. However, further alloying usually leads to deterioration of their mechanical properties [3,12,13]. Consequently, deposition of coatings that can form dense, adherent and slow growing oxide scales is considered an effective way to address the requirement of the enhanced oxidation resistance and high-strength of Nb−Si based alloys [14,15].
Aluminide and silicide coatings, which can produce continuous Al2O3 and SiO2 scales at high temperature, have been widely studied [16,17,18]. In particular, silicide coatings are more attractive due to their higher application temperature. Among various coating preparation techniques, pack cementation is considered an effective way to prepare silicide coatings, owing to its simple process [19]. The substrates are embedded into a powder mixture consisting of depositing elements as a donor, a halide salt as an activator, and an inert-filler. The effects of donor, activator, and prepared condition on the coating microstructure have been widely investigated. Zhou et al. [20] have used the TiB2 as the boron source to form a B-modified silicide coating, which exhibited good oxidation resistance at both high and intermediate temperature. Qiao et al. [21] have investigated the effect of the amount of B powder on the microstructural evolution and oxidation resistance of the coating. Cockeram and Rapp [22] have investigated the effect of different activators (NaF, MgF2, AlF3 and CuF2) on the oxidation resistance of MoSi2 coating, revealing that the NaF-base byproduct layer provided outstanding protection against the catastrophic disintegration of the MoSi2 coatings at low temperature. Although few studies have focused on the effect of the inert-filler on the microstructural evolution and oxidation resistance of the Si−B coating, some investigations are conducted in other refractory alloys. For Ni substrate, the chromizing coating using CeO2 + Al2O3 filler exhibited better oxidation resistance than that prepared with only Al2O3 filler, as the addition of CeO2 in Al2O3 can significantly retard the grain growth of the coating [23]. For Mo substrate, the MoSi2 coating prepared with SiO2 filler showed the best oxidation resistance, while the coating prepared with SiC filler exhibited the thickest MoSi2 layer [24]. In the present work, Si−B coatings were prepared on a Nb-Si based alloy; Si and TiB2 were selected as the donor, NaF was selected as the activator, and the Al2O3 or SiO2 was selected as the inert-filler. The effects of different inert-fillers on the microstructure evolution and high temperature oxidation resistance were investigated. Furthermore, the coating formation and oxidation mechanism of Si-B coatings were discussed.

2. Materials and Methods

2.1. Materials

Substrates (Nb-15Si-24Ti-13Cr-2Al-2Hf (at.%)) were fabricated by non-consumable arc-melting. The ingots were re-melted and inverted at least four times to guarantee the uniformity of the composition. Samples were cut into Ø10 mm × 3 mm by electro-discharge machining. These samples were polished on wet SiC paper to 800 grit, then ultrasonically washed in an alcohol machine and dried for 1 h.

2.2. Coating Preparation

Powder mixtures with 8 wt.% Si (99.9 wt.% purity), 8 wt.% TiB2 (99.9 wt.% purity), 5 wt.% NaF (99.9 wt.% purity), and 79 wt.% Al2O3 (99.9 wt.% purity) or SiO2 (99.9 wt.% purity) were chosen as inert-filler respectively. The average diameters of Al2O3 and SiO2 filler were 5.8 um and 12.4 μm, respectively. Each powder was first ground in a ball miller for 1 h to ensure composition homogeneity. Next, the substrate and mixed pack were put into an alumina retort and the substrate was completely covered by the powder. The retort was heated in a tube furnace at a rate of 5 °C/min and kept at 1300 °C for 10 h. The tube furnace was filled with high-purity argon (99.99 wt.% purity) until the tube furnace was cooled to room temperature.

2.3. Oxidation Test

Prior the oxidation test, the alumina crucible was placed at 1250 °C for 2 h to assure the quality of crucible was stable. Then each sample was put in a separate alumina crucible for isothermal oxidation test of 1250 °C. The samples were removed from the furnace at the intervals of 10, 20, 40, 60, 80, and 100 h and the oxidation weight gain of the samples was recorded, using a precision analytical balance (model CPA225D, Sartorius, Göttingen, Germany) with an accuracy of 0.00001 g.

2.4. Characterization

Phase composition of the as-prepared and oxidized coatings was analyzed by X-ray diffraction (XRD SmartLaSmar, Rigaku, Tokyo, Japan) with Cu radiation. The operating parameters were: K-α target with using Cu, scanning speed was 6°/min, the scanning range was 20–90°, and the working voltage and current were 40 kV and 20 mA, respectively. The surface morphologies, i.e., micrographs of cross-sections of the as-prepared and oxidized coatings were observed by scanning electron microscope with an energy dispersive spectroscopy (JSM-IT500, JEOL Ltd., Tokyo, Japan).

3. Results

3.1. Microstructures of B Modified Coatings

Figure 1 shows the XRD patterns of B modified coatings prepared with Al2O3 and SiO2 inert-fillers. Both samples primarily consisted of (Nb,X)Si2 (JCPD 08-0450) and (Nb,X)B2 (JCPD 35-0742) (X represents Ti, Cr, and Hf elements). In addition, it was found that Al2O3 and SiO2 were also detected in the XRD pattern, indicating that inert-fillers were adhered on the coating surface. Figure 2 demonstrates surface morphologies of Si-B coatings. As shown in Figure 2, surface morphologies of both Si-B coatings were relatively dense, with no significant cracks. For the coating prepared with Al2O3, a small amount of white, particle-like residual inert-filler Al2O3 was adhered to the coating surface. For the coating prepared with SiO2, some plate-like SiO2 was covered on the coating surface, suggesting that the residual inert-filler SiO2 particles melted during the pack cementation process.
Figure 3 shows cross-section microstructures of B modified coatings prepared with Al2O3 and SiO2 inert-fillers. Table 1 presents the element composition of B modified coatings. Both coatings consisted of a (Nb,X)B2 + (Nb,X)Si2 outer layer, a (Nb,X)Si2 intermediate layer, and a (Nb,X)5Si4 inner layer, as confirmed by XRD (Figure 1) and EDS (Table 1), which was in agreement with the study of Zhou et al. [20]. In addition, it was found that white particles and blocks (as shown in Figure 3) dispersed in the intermediate and transitional layers have a higher content of Hf, which were confirmed to be Hf-rich (Nb,X)Si2 and Hf-rich (Nb,X)5Si4, respectively. The thickness of B modified coatings prepared with Al2O3 and SiO2 inert-fillers were 198 ± 3 and 178 ± 2 μm, respectively.

3.2. Oxidation Resistance of B Modified Coatings

Figure 4 demonstrates the oxidation weight gain curves of B modified coatings samples. The weight gains of the samples prepared with Al2O3 and SiO2 after oxidation at 1250 °C for 100 h were 2.77 mg cm−2 and 2.31 mg cm−2, respectively. In our previous study [18], the Nb-Si bases alloy without coating experiences linear oxidation with a weight gain of 87.6 mg/cm2 after oxidation at 1250 °C for 100 h, suggesting that the coatings showed good oxidation resistance protecting the substrate from oxidation. The oxidation mechanism of B modified coating conforms to the parabolic law (Figure 4b) according to Equation (1) [9]:
Δ m A 2 = k t
where ∆m, A, and t are the mass variation, the total surface area of sample and the oxidation time, respectively. The value of k determines the oxidation rate of sample. The parabolic rate constants (g2 cm−4 s−1) of the samples prepared with Al2O3 and SiO2 are calculated to be 2.13 × 10−11 and 1.48 × 10−11, respectively.

3.3. Oxidation Products and Microstructure of Oxide Scale

Figure 5 demonstrates the XRD patterns of B modified coatings after oxidation at 1250 °C for 1, 10, and 100 h. The oxidized coating prepared with Al2O3 inert-filler mainly consisted of TiO2 (JCPD 21-1276), SiO2 (JCPD 39-1425) and Cr2O3 (JCPD 38-1479), while the oxidized coating prepared with SiO2 inert-filler mainly consisted of TiO2, SiO2, Cr2O3, and HfO2 (JCPD 40-1173). Figure 6 shows surface morphologies of oxidized B modified coatings after oxidation at 1250 °C for 1, 10, and 100 h. For the coating prepared with Al2O3 inert-filler, the surface scale mainly consisted of a dark, dense glass-like phase, distributed with a rod-like phase. EDS analysis demonstrated that the glass-like phase had a composition of 61.4O-33.3Si-1.4Ti-0.4Cr-1.3Nb (at.%), which indicated that it was SiO2, while the rod-like phase had a composition of 54.4O-38.5Ti-2.94Cr at.%), which indicated that it was TiO2. For the coating prepared with SiO2 inert-filler, the surface scale mainly consisted with a dark, dense glass-like phase, distributed with a rod-like phase and a particle-like phase. According to EDS analysis the glass-like phase and the rod-like phase were also the SiO2 and TiO2, respectively. The particle-like phase had a composition of 74.9O-1.8Ti-23.3Hf (at.%), which indicates that it is HfO2. It could be concluded that the HfO2 phase appeared in the sample prepared with SiO2 inert-filler.
Figure 7 demonstrates the cross-section microstructures of oxidized B modified coatings after oxidation at 1250 °C for 1, 10, and 100 h. Table 2 presents the element composition of oxidized B modified coatings. As shown in Figure 7, the uniform and continuous SiO2 oxide scales were formed and adhered tightly on the coatings. For the coating prepared with Al2O3 inert-filler, the dark matrix and rod-like phase were confirmed to be SiO2 and TiO2, respectively, according to EDS analysis. For the oxide scales formed after oxidation for 1 and 10 h, the upper layer of the oxide scale consisted of SiO2 and TiO2, while the lower layer of the oxide scale consisted of SiO2, TiO2, and Cr2O3 according to the BSE and EDS results (Figure 5 and Figure 7, Table 2). To further increase the oxidation time to 100 h, the lower layer of the oxide scale was changed to a continuous Cr2O3 layer (as shown in Figure 7c).
For the coating prepared with SiO2 inert-filler, a thick SiO2 was formed after oxidation for 1 h, and the TiO2 and Cr2O3 were mainly distributed at the interface of silica and coating (Figure 7d). Unlike the glass scale of the coating prepared with Al2O3 inert-filler, with the oxidation time increasing to 100 h, the lower layer of the oxide scale did not change to a continuous Cr2O3, but consisted of SiO2 and Cr2O3 (Figure 7f). HfO2 was not observed in the cross-sectional microstructures of the scale, suggesting that the HfO2 was mainly distributed on the surface of the scale.
Remarkably, the thickness of the coating prepared with Al2O3 and SiO2 decreased by 29 ± 1 and 30 ± 2 μm, respectively, compared to that of as-prepared samples after oxidation for 100 h, suggesting that the consumption of both two coating was similar.

4. Discussion

4.1. Formation Mechanism of the Coatings

In this study, B modified coatings were prepared on a Nb-Si based alloy, Si and TiB2 were selected as the donor material, NaF was selected as the activor, and Al2O3 or SiO2 was selected as the inert-filler. As discussed above, the coatings prepared with Al2O3 and SiO2 inert-filler showed similar coating structures, mainly consisting of (Nb,X)Si2 with a (Nb,X)B2 + (Nb,X)Si2 outer layer. At elevated temperatures, the activator NaF would react with Si and B to form a series of their own halide vapor species, such as SiFx (x = 1–4), BFy (y = 1–3) and B2F4 [25,26]. The existence of chemical gradient made fluorides diffused to the substrate surface, resulting in the formation of active atoms Si and B [25], which were deposited together on the substrate surface. In addition, the quantity of deposited Si atoms was significantly more than that of the deposited B atoms, as the partial pressure of Si fluoride was higher than that of B fluoride at 1300 °C [20]. Therefore, the B modified coatings mainly consisted of (Nb,X)Si2 with a (Nb,X)B2 + (Nb,X)Si2 outer layer.
The role of inert-filler in the pack was providing the medium surrounding reaction environment. In addition, it was found that the inert filler resided on the coating surface in this study. The theoretical melting point of Al2O3 and SiO2 were 2054 °C and 1723 °C, respectively [23]. However, SiO2 particles might melt partially on the surface during the pack cementation process, which was in agreement with the study of Sun et al. [23]. Al2O3 had much higher melting point than that of SiO2, thus only a few particles could be found on the coating surface.

4.2. Oxidation Mechanism of the Coatings

As shown in Figure 7, the B modified coatings prepared with Al2O3 or SiO2 inner-filler both showed good oxidation resistance due to the formation of a dense and continuous SiO2 glass with self-healing ability. Figure 8 shows the oxidation process of the sample prepared with inert-filler Al2O3 or SiO2 are sketched in Figure 8. On the basis of above results, the oxidation products were different in two samples. The oxidized coating prepared with Al2O3 inert-filler mainly consisted of TiO2, SiO2, and Cr2O3, while the oxidized coating prepared with SiO2 inert-filler mainly consisted of TiO2, SiO2, Cr2O3, and HfO2. The integrity of the oxide scale depends on the Pilling Bedworth Ratio (PBR) of oxide, i.e., the ratio of oxide volume produced to metal volume consumed [27]. The PBR values of Nb2O5, SiO2, Cr2O3, TiO2, and HfO2 were reported to be 2.74, 1.72, 2.02, 1.73, and 1.17, respectively [28]. Typically, a PBR value ranging from 1 to 2 can protect the metal from oxidation, while an excessive PBR value would result in the fracture of the oxide scale [29]. As the oxidation products of the sample prepared with Al2O3 or SiO2 were TiO2, SiO2, Cr2O3, and HfO2, their PBR values ranging from 1 to 2, it could produce the dense oxide scale with good oxidation resistance.
According to the ΔG0-T plots of various oxides [20,30], the ascending order of ΔG0 at all temperatures were:
ΔG0 HfO2 < ΔG0 TiO2 < ΔG0 SiO2 < ΔG0 B2O3 < ΔG0 Cr2O3< ΔG0 Nb2O5
Therefore, the descending order of stability was HfO2 > TiO2 > SiO2 > B2O3 > Cr2O3> Nb2O5. For the sample prepared with Al2O3, the residual inert-filler Al2O3 remain particle-like after pack cementation at 1300 °C. As suggested by Qiao et al. [21], the inert-filler Al2O3 could enhance the oxidation resistance to some extent. However, Al2O3 particles did not melt to cover the coating and protect it from oxidation. Therefore, at the initial oxidation, the coating was exposed to the oxidation environment. Titanium would oxidize primarily to form TiO2 rods. As the oxidation processed, silicon would oxidize to form SiO2. Additionally, B2O3 can be formed by the outward diffusion of B. The dissolving of B2O3 in the SiO2 could reduce the viscosity of the glass scale, and increase the coefficients of thermal expansion (CTE) [31]. Thus, the oxide scale has better self-healing ability and a much better match in CTE with the B modified coating, minimizing spallation and cracks of the oxide scale [31]. HfO2 was not formed in this sample, due to the lower content (2.0 at.%, as shown in Table 1). Then, the outward diffused Cr3+ reacted with oxygen and Cr2O3 was formed distributed in the interface of the oxide scale and coating. After a certain time of exposure, the upper layer of the oxide scale consisted of aSiO2 + TiO2, while the lower layer of the oxide scale consisted of SiO2 + TiO2 + Cr2O3 (1 h and 10 h, Figure 8a). With the exposure time increasing to 100 h, the lower layer transformed to a continuous Cr2O3 layer (Figure 8a) owing to the outward diffusion of Ti4+ from the oxide/alloy interface to the oxide/air interface [20,21].
For the sample prepared with SiO2, the residual inert-filler SiO2 transformed to plate-like after pack cementation at 1300 °C. During high temperature oxidation, the plate-like residual pack agent SiO2 would melt into fluid SiO2 to cover the coating surface, resulting in the rapid formation of a dense SiO2 layer, thus this sample showed a lower parabolic rate constant as compared to that prepared with Al2O3. It was found that the thick SiO2 layer was formed only after oxidation for 1 h, and the TiO2 and Cr2O3 were mainly distributed at the interface of silica and coating, suggesting that the oxidation process was governed by the inward diffusion of O (Figure 8b). Therefore, HfO2 was formed due to its lower ΔG value and higher oxygen affinity. The formation mechanism of HfO2 was similar to the internal oxidation of Nb-Si based alloys, the oxidation process of which was also governed by the inward diffusion of O [9]. HfO2 has higher melting point (2800 °C) than that of pure SiO2 [32]. Thus, the dispersion of HfO2 in SiO2 glass could increase the melting temperature of the silica. In this sample, TiO2 and Cr2O3 were also formed due to the outward diffusion of Ti4+ and Cr3+, as well as the inward diffusion of O. However, the continuous Cr2O3 was not formed in this sample, which may be due to the lower parabolic rate constant.

5. Conclusions

  • First item; The B modified coatings prepared with Al2O3 and SiO2 inert-filler mainly consisted of (Nb,X)Si2 with a (Nb,X)B2 + (Nb,X)Si2 outer layer. The Al2O3 and SiO2 inert-fillers were tightly adhered on the coating surface after pack cementation;
  • Second item; After oxidation at 1250 °C for 100 h, the coatings prepared with Al2O3 or SiO2 inert-fillers showed good oxidation resistance due to the formation of a dense silica. The oxidized coating prepared with Al2O3 inert-filler consisted of TiO2, SiO2, and Cr2O3, while the oxidized coating prepared with SiO2 inert-filler consisted of TiO2, SiO2, Cr2O3, and HfO2;
  • For the coating prepared with SiO2 inert-fillers, the adherent SiO2 on the coating would melt partially, resulting in the rapid formation of a dense silica scale during high temperatures. Thus, the oxidation process of this sample was governed by the inward diffusion of O at the initial oxidation stage, leading to a lower parabolic rate constant.

Author Contributions

Conceptualization, L.S. and K.J.; methodology, G.Z. and H.S.; investigation, G.Z. and J.Y.; writing—review and editing, L.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by National Nature Science Foundation of P.R. China, grant number 51701077, Fujian Nature Science Foundation, grant number 2017J05082 and Promotion Program for Young and Middle-aged Teacher in Science and Technology Research of Huaqiao University, grant number ZQN-PY505.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.

Acknowledgments

The support given are covered by the author contribution and funding sections.

Conflicts of Interest

The authors declare no conflict of interest.

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Coatings 11 00700 g001 550
Figure 1. X-ray patterns of B modified silicides coatings prepared with Al2O3 (a) and SiO2 (b).
Figure 1. X-ray patterns of B modified silicides coatings prepared with Al2O3 (a) and SiO2 (b).
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Figure 2. SE image of surface morphologies of B modified silicides coatings prepared with Al2O3 (a) and SiO2 (b).
Figure 2. SE image of surface morphologies of B modified silicides coatings prepared with Al2O3 (a) and SiO2 (b).
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Figure 3. BSE image of cross-section morphologies of B modified silicides coatings prepared with Al2O3 (a) and SiO2 (b); (a’) and (b’): enlarge BSE images of the outer layer of the coatings.
Figure 3. BSE image of cross-section morphologies of B modified silicides coatings prepared with Al2O3 (a) and SiO2 (b); (a’) and (b’): enlarge BSE images of the outer layer of the coatings.
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Figure 4. (a) Oxidation curve of B modified silicides coatings prepared with Al2O3 and SiO2 inert-filler at 1250 °C for 100 h; (b) representation of the weight gain versus the square root of time for the B modified coatings.
Figure 4. (a) Oxidation curve of B modified silicides coatings prepared with Al2O3 and SiO2 inert-filler at 1250 °C for 100 h; (b) representation of the weight gain versus the square root of time for the B modified coatings.
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Figure 5. X-ray patterns of B modified silicides coatings prepared with Al2O3 (a) and SiO2 (b) after oxidation at 1250 °C.
Figure 5. X-ray patterns of B modified silicides coatings prepared with Al2O3 (a) and SiO2 (b) after oxidation at 1250 °C.
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Figure 6. SE image of surface morphologies of oxidized B modified silicides coatings prepared with Al2O3 (a–c) and SiO2 (d–f) after oxidation at 1250 °C for 1 h (a,d), 10 h (b,e), and 100 h (c,f).
Figure 6. SE image of surface morphologies of oxidized B modified silicides coatings prepared with Al2O3 (a–c) and SiO2 (d–f) after oxidation at 1250 °C for 1 h (a,d), 10 h (b,e), and 100 h (c,f).
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Figure 7. BSE image of cross-section morphologies of oxidized B modified silicides coatings prepared with Al2O3 (a–c) and SiO2 (d–f) after oxidation at 1250 °C for 1 h (a,d), 10 h (b,e), and 100 h (c,f).
Figure 7. BSE image of cross-section morphologies of oxidized B modified silicides coatings prepared with Al2O3 (a–c) and SiO2 (d–f) after oxidation at 1250 °C for 1 h (a,d), 10 h (b,e), and 100 h (c,f).
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Figure 8. Schematic drawing of oxidation process of B modified silicides coatings at 1250 °C prepared with Al2O3 (a) and SiO2 (b).
Figure 8. Schematic drawing of oxidation process of B modified silicides coatings at 1250 °C prepared with Al2O3 (a) and SiO2 (b).
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Table
Table 1. Element composition (at.%) of B modified silicides coatings prepared with Al2O3 and SiO2 filler.
Table 1. Element composition (at.%) of B modified silicides coatings prepared with Al2O3 and SiO2 filler.
SamplePhaseComposition
BSiTiCrNbHf
Sample prepared with Al2O3(Nb,X)B245.4 ± 0.923.4 ± 0.117.8 ± 0.40.8 ± 0.111.6 ± 0.70.9 ± 0.2
(Nb,X)Si2-65.2 ± 0.29.5 ± 0.76.0 ± 0.118.2 ± 0.61.1 ± 0.1
Hf-rich (Nb,X)Si2-44.0 ± 0.525.0 ± 0.95.7 ± 0.821.3 ± 0.54.1 ± 0.3
(Nb,Ti)5Si4-43.1 ± 0.524.6 ± 0.24.8 ± 0.626.4 ± 0.71.2 ± 0.2
Hf-rich (Nb,X)5Si4-41.7 ± 0.425.7 ± 0.93.4 ± 0.625.2 ± 0.54.1 ± 0.5
Sample prepared with SiO2(Nb,X)B246.2 ± 0.321.5 ± 0.115.8 ± 0.81.8 ± 0.313.5 ± 0.11.3 ± 0.2
(Nb,X)Si2-59.8 ± 0.910.0 ± 0.43.5 ± 0.925.7 ± 0.41.0 ± 0.1
Hf-rich (Nb,X)Si2-50.6 ± 0.816.8 ± 0.22.9 ± 0.424.0 ± 0.55.7 ± 0.2
(Nb,Ti)5Si4-45.1 ± 0.318.9 ± 0.111.2 ± 0.123.4 ± 0.71.4 ± 0.3
Hf-rich (Nb,X)5Si4-42.9 ± 0.122.6 ± 0.99.0 ± 0.621.3 ± 0.14.3 ± 0.7
Table
Table 2. Element composition (at.%) of B modified silicides coatings prepared with Al2O3 and SiO2 filler after oxidation at 1250 °C for 100 h.
Table 2. Element composition (at.%) of B modified silicides coatings prepared with Al2O3 and SiO2 filler after oxidation at 1250 °C for 100 h.
SamplePhaseComposition
BSiTiCrNbHfO
Sample prepared with Al2O3(Nb,X)B253.6 ± 0.917.6 ± 0.617.7 ± 0.21.4 ± 0.27.7 ± 0.42.0 ± 0.9-
(Nb,X)Si2-63.5 ± 0.510.7 ± 0.52.4 ± 0.622.7 ± 0.70.7 ± 0.1-
Hf-rich (Nb,X)Si2-57.7 ± 0.411.7 ± 0.11.5 ± 0.225.9 ± 0.43.1 ± 0.6-
(Nb,Ti)5Si4-43.0 ± 0.417.6 ± 0.59.1 ± 0.128.9 ± 0.81.5 ± 0.1-
Hf-rich (Nb,X)5Si4-41.0 ± 0.726.0 ± 0.33.5 ± 0.225.4 ± 0.24.1 ± 0.1-
SiO2-32.4 ± 0.91.4 ± 0.1002.1 ± 0.162.3 ± 0.8
TiO2-026.1 ± 0.26.8 ± 0.10057.2 ± 0.4
Cr2O3-00.4 ± 0.146.5 ± 0.90052.9 ± 0.9
Sample prepared with SiO2(Nb,X)B246.9 ± 0.917.6 ± 0.722.4 ± 0.70.8 ± 0.110.9 ± 0.11.3 ± 0.1-
(Nb,X)Si2-60.8 ± 0.58.3 ± 0.13.9 ± 0.226.2 ± 0.10.9 ± 0.3-
Hf-rich (Nb,X)Si2-51.5 ± 0.116.3 ± 0.51.9 ± 0.227.0 ± 0.23.3 ± 0.1-
(Nb,Ti)5Si4-42.7 ± 0.419.9 ± 0.78.2 ± 0.827.6 ± 0.81.7 ± 0.1-
Hf-rich (Nb,X)5Si4-41.7 ± 0.513.6 ± 0.21.4 ± 0.541.0 ± 0.12.4 ± 0.1-
SiO2-32.3 ± 0.31.6 ± 0.6000.3 ± 0.165.1 ± 0.7
TiO2-035.8 ± 0.800064.3 ± 0.9
Cr2O3-00.8 ± 0.143.4 ± 0.80055.6 ± 0.1
HfO2-26.5 ± 0.51.1 ± 0.201.7 ± 0.110.3 ± 0.360.1 ± 0.8
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Su, L.; Zhuo, G.; Song, H.; Yang, J.; Jiang, K. Effect of Al2O3 and SiO2 Inert-Fillers on the Microstructural Evolution and High Temperature Oxidation Resistance of B Modified Silicides Coatings Prepared by Pack Cementation Technology. Coatings 2021, 11, 700. https://doi.org/10.3390/coatings11060700

AMA Style

Su L, Zhuo G, Song H, Yang J, Jiang K. Effect of Al2O3 and SiO2 Inert-Fillers on the Microstructural Evolution and High Temperature Oxidation Resistance of B Modified Silicides Coatings Prepared by Pack Cementation Technology. Coatings. 2021; 11(6):700. https://doi.org/10.3390/coatings11060700

Chicago/Turabian Style

Su, Linfen, Guanqun Zhuo, Haiwen Song, Jianyong Yang, and Kaiyong Jiang. 2021. "Effect of Al2O3 and SiO2 Inert-Fillers on the Microstructural Evolution and High Temperature Oxidation Resistance of B Modified Silicides Coatings Prepared by Pack Cementation Technology" Coatings 11, no. 6: 700. https://doi.org/10.3390/coatings11060700

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