An ultrastrong niobium alloy enabled by refractory carbide and eutectic structure

Figures & data

Figure 1. Microstructure of the as-cast Nb₂MoWC_0.96 alloy. (a) XRD pattern and (b) SEM-BSE images show a fully eutectic microstructure. (c) HAADF-STEM image and the corresponding EDS maps show element distribution. (d) HADDF-STEM image of the eutectic structure. (e) HRTEM image of the BCC/NbC interface and the corresponding FFT patterns

Table 1. Chemical composition of the phases measured by TEM-EDS.

	Chemical composition (at%)
Phase	Nb	Mo	W	C
BCC	32.5 ± 0.6	30.2 ± 0.6	33.1 ± 0.6	4.2 ± 1.7
NbC	53.4 ± 0.7	5.5 ± 0.1	5.5 ± 0.1	35.6 ± 1.2

Figure 2. (a) Calculated pseudo-binary phase diagram of Nb₂MoWC_x alloys. (b) XRD patterns of the as-cast and annealed Nb₂MoWC_0.96 samples. (c) SEM-BSE images of the as-cast and annealed Nb₂MoWC_0.96 samples.

Figure 3. (a, b) Engineering and true stress-strain curves of the as-cast Nb₂MoWC_0.96 alloy at varying compression temperatures. (c-d) A comparison of specific strength and specific ultimate strength of the Nb₂MoWC_0.96 alloy with reported Nb and Nb-containing alloys [13,19-24].

Table 2. Compressive properties of the as-cast Nb₂MoWC_0.96 alloy at varying temperatures.

	Engineering True
Temperature/K	YS/MPa	CS/MPa	ϵ/%	CS/Mpa	ϵ/%
1073	1267	1813	18.0	1145	21.2
1273	1087	1571	24.5	998	31.0
1473	875	1416	34.5	806	45.1
1673	808	1007	37.5	752	49.4

YS: yield strength, CS: compressive strength, ϵ: fracture strain.

Table 3. Calculated theoretical densities of various Nb and Nb-containing alloys.

Alloy	Density/(g·cm^−3)	Alloy	Density/(g·cm^−3)
Nb-1Zr	8.57	NbMoTaW	13.71
C-103	8.85	NbMoTaWV	12.08
FS-85	10.60	NbMoHfZrTi	8.68
F-50	8.92	NbCrMo0.5Ta0.5TiZr	8.22
WC-3009	10.10	NbAlMo0.5Ta0.5TiZr	7.40
NbC0.25Hf0.25TaW0.5	13.12	NbSi0.14Ti0.35Hf0.11Cr0.18	7.46
NbHfMo0.5TiV0.5Si0.7	7.89	Nb2MoWC0.96 (This work)	10.46

Figure 4. EBSD maps of the as-cast and compressed Nb₂MoWC_0.96 alloy reveal the changes in the density of GNDs and orientation relationships between the BCC and NbC phases. (a) Phase maps, (b) IPF maps, (c) GND maps.

Table 4. GNDs of Nb and NbC in the as-cast and high compression temperatures.

	Nb/(10^14/m^2)	NbC/(10^14/m^2)
As-cast	8.127	2.735
1073K	15.319	3.974
1273K	19.555	11.971
1473K	26.769	17.175
1673K	23.028	8.521

Figure 5. EBSD pole figures of BCC and NbC phases from (a) whole area, (b) area 1 (black square), (c) area 2 (black square) of Figure 4(b).

Figure 6. (a-d) HAADF-STEM images of the compressed Nb₂MoWC_0.96 alloy at varying temperatures. (e) atomic structure of stacking fault ribbons in the NbC phase. (f) HRTEM and the corresponding FFT patterns of the BCC/NbC phase interface.

Kim WY, Tanaka H, Kasama A, et al. Microstructure and room temperature fracture toughness of Nbss/Nb5Si3 in situ composites. Intermetallics. 2001;9:827–834.

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