- Email: [email protected]
The effect of (ZrB2-SiC) addition on microstructure and mechanical properties of NbMo-matrix composites fabricated by hot-pressing
Journal Pre-proof The effect of (ZrB2-SiC) addition on microstructure and mechanical properties of NbMo-matrix composites fabricated by hot-pressing
Qi Wang, Zongde Liu, Yongtian Wang, Xinyu Wang PII:
S0263-4368(19)30508-6
DOI:
https://doi.org/10.1016/j.ijrmhm.2019.105098
Reference:
RMHM 105098
To appear in:
International Journal of Refractory Metals and Hard Materials
Received date:
28 June 2019
Revised date:
27 August 2019
Accepted date:
16 September 2019
Please cite this article as: Q. Wang, Z. Liu, Y. Wang, et al., The effect of (ZrB2-SiC) addition on microstructure and mechanical properties of NbMo-matrix composites fabricated by hot-pressing, International Journal of Refractory Metals and Hard Materials(2019), https://doi.org/10.1016/j.ijrmhm.2019.105098
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2019 Published by Elsevier.
Journal Pre-proof
The effect of (ZrB2-SiC) addition on microstructure and mechanical properties of NbMo-matrix composites fabricated by hot-pressing
Qi Wang 1, a, Zongde Liu 1,b, * , Yongtian Wang1,c, Xinyu Wang1,d 1
Key Laboratory of Condition Monitoring and Control for Power Plant Equipment of Ministry of
Education, North China Electric Power University, Beijing 102206, China [email protected]
b
email:
[email protected]
c
of
email:
email :[email protected]
d
email :
ro
a
[email protected]
-p
*Corresponding author: Zongde Liu
re
Abstract
lP
The effects of (0-60%) vol% (70 vol% ZrB2 + 30 vol% SiC) additions on
na
microstructure and properties of NbMo substrate fabricated by hot-pressing were studied at room temperature. Types of formed phase were decided by the amount of
Jo ur
ZrB2 and SiC additives. The effective eutectic phase was observed in 15 vol% (70 vol% ZrB2 + 30 vol% SiC)-NbMo, which was attributed to the addition of SiC. 30 vol% (70 vol% ZrB2 + 30 vol% SiC)-NbMo had the highest relative density of 98.69%. Compared with x ZrB2-NbMo composites, the addition of SiC could further improve the hardness of NbMoss in x (70% ZrB2 + 30% SiC)-NbMo when the value of x was same, and NbMoss in 60 vol% (70 vol% ZrB2 + 30 vol% SiC)-NbMo had the highest hardness of 6.82 GPa. Only the 15 vol% (70 vol% ZrB2 + 30 vol% SiC) addition could improve the compressive strength of NbMo matrix. The reasons for the low strength of 30, 45, 60 vol% (70% ZrB2 + 30% SiC)-NbMo were the lack of ductile
Journal Pre-proof
phase and the large amount of hard phase production. Keywords: Mechanical properties; NbMo; ZrB2; SiC; Hot-pressing
1. Introduction Niobium-based alloys are promising candidate for high temperature structural
of
materials because they have low density, high melting points, good ductility and high resistance to corrosion [1]. However, the strength declines rapidly when the
ro
temperature is above 1200 K [2]. The addition of refractory metal Molybdenum (Mo)
-p
to Nb could make up for this shortcoming of Nb at high temperature by solution
re
strengthening, and the degree of strengthening reaches its maximum extent when
lP
Nb/Mo volume ratio is approximately 1 [3]. Zirconium diboride (ZrB2) has excellent
na
performance at ultra-high temperature because of its ultra-high melting point (3246 ℃), high hardness and other desirable mechanical properties [4,5]. In our early
Jo ur
research, (0–60) vol% ZrB2-NbMo composites were fabricated by hot-pressing at the temperature of 2400 °C with a pressure of 50 MPa for 10 min in Argon, and the volume fraction of additive Nb and Mo is same (Nb/Mo=1). The properties of (0–60) vol% ZrB2-NbMo composites at room temperature and the temperature range of 800 ℃ to 1300 ℃ were tested and analyzed. The results show ZrB2 addtion to NbMo can greatly improve the compressive strength of the composites at all tested temperature compared to NbMo solid solution, and the compressive strength of 60 vol% ZrB2-NbMo is 700.46 MPa even at 1300 ℃ [6,7]. Previous study reported the addition of silicon carbide (SiC) to ZrB2-based composites could improve properties
Journal Pre-proof
and ZrB2-SiC composites had high room temperature strengths, high fracture toughness and high hardness values, in which SiC additive could limit the grain growth [8-10]. Jayaseelan et al. reported the oxide impurities in the ZrB2-10 vol% SiC [11], and Liang et al. observed a lot of edge dislocations in ZrB2-20 vol% SiC [12]. Fahrenholtz et al. found that ZrB2 with 30 vol% SiC has excellent strength and
of
fracture toughness [13]. Neuman et al. reported the strength of ZrB2-30 vol% SiC up to 1600 MPa in air condition [14-15].
ro
In this study, mixture powder of 70 vol% ZrB2 and 30 vol% SiC is added to NbMo,
-p
and the volume ratio of Nb/Mo is 1. The aim of this present work is to investigate
re
the room temperature properties of the 15, 30, 45, 60 vol% (70 vol% ZrB2 + 30 vol%
lP
SiC)-NbMo composites fabricated by the method reported in our early literature [6].
na
The effects of composite additive on the microstructure and mechanical properties of the x (70% ZrB2 + 30% SiC) -NbMo were discussed.
Jo ur
2. Experimental Procedure 2.1 Processing
Five compositions were selected (amounts in vol%): NM-0: 50%Nb + 50%Mo NM-15ZS: 42.5%Nb + 42.5%Mo + 10.5%ZrB2 + 4.5%SiC NM-30ZS: 35%Nb + 35%Mo + 21%ZrB2 + 9%SiC NM-45ZS: 27.5%Nb + 27.5%Mo + 31.5%ZrB2 + 13.5%SiC NM-60ZS: 20%Nb + 20%Mo + 42%ZrB2 + 18%SiC The starting materials were high purity Nb (N, for short) and Mo (M, for short)
Journal Pre-proof powders (purity > 99.95%, mean particle size 18-25 μm) and ZrB2 (Z, for short) powders (purity > 99.95%, mean particle size 23 μm) and SiC (S, for short) powders (purity > 99.9%, mean particle size 45 μm) supplied by Beijing Gold Crown for the New Material Technology Co. Ltd. China. The powders were dried at the temperature of 110℃ for 3 hours, then mixed in the planetary ball mill at 200 rpm for up to 10
under 50 MPa using pure Argon as a shielding gas.
ro
2.2 Characterization
of
hours for the purpose of thorough blend, and finally hot-pressed at 2400℃ for 10 min
-p
The cylindrical samples with dimensions of 14 mm in diameter and 70 mm in height
re
were cut into 10mm*10mm*8mm specimens for microstructure observation and XRD
lP
test by wire cut electrical discharge machining (WEDM). Ultrasonic cleaner was used
na
to clean the specimens. Phase composition was detected by X-ray diffraction analysis. Microstructure and element distribution were detected by scanning electron
Jo ur
microscopes (FEI Quanta 200F and SU8010) equipped with energy dispersive spectroscopy. Densimeter (FA1104J) device was employed to measure the density, and the average density value was from at least three measurements. The Vickers hardness test (FM-300) was conducted with 300g load applied for 10 s with diamond indenter on polished section. At least three points were tested for calculating the average hardness for each phase. The compression experiment was performed on the hydraulic universal tester (SHT 4305) at room temperature, with the loading rate of 600N/m. Young’s modulus was determined by dynamic Young’s modulus tester (RFDA system 23). The crack for observing propagation path was conducted on the
Journal Pre-proof
Vickers hardness tester (HVS-50P) under the load of 98 N with a dwell of 15 s in air condition. The fracture toughness value was measured by a three-point bending test (Electromechanical
Universal
Testing
Machine
C45.105)
using
the
single-edge-notched beam (SENB) specimens with the dimension of 3 mm * 4mm cross-section and 36 mm span, and the notch was 1.5 mm in depth and 0.15 mm in
of
width. 3. Results and Discussion
ro
3.1. Phase Composition
-p
Fig. 1 shows the XRD patterns of five samples. NbMo solid solution and ZrC exist in
re
all the four samples with additives, and SiC are decomposed in these four. There are
lP
no residual ZrB or ZrB2 in NM-15ZS, which indicating the ZrB2 are totally
na
decomposed to form ZrC and NbB2 in it. There are two stable niobium borides phase formed in the x (70% ZrB2 + 30% SiC)-NbMo composites: NbB2 and Nb3B4, which is
Jo ur
easily explained by Nb-B phase diagram [16]. Nb5Si3 are found in all the four composites. Mo3Si (A15) and Mo5SiB2 (T2) exist in NM-30ZS, NM-45ZS and NM-60ZS, and MoSi2 are found in NM-45ZS and NM-60ZS. Mo2C is only detected in NM-60ZS. The details are listed in Table 1. Fig. 1 X-ray diffraction (XRD) patterns of the five samples.
Table 1 The compounds in five samples after hot-pressing
NM-15ZS
√
NM-30ZS
√
NM-45ZS
√
NM-60ZS
√
ZrC
NbB2
Nb3B4
Nb5Si3
√
√
√
√
√
√
√
√
√
√
√
3.2. Densification
√
ro
√
ZrB2
-p
NM-0
ZrB
Mo3Si
Mo5SiB2
MoSi2
√
√
√
√
√
√
√
√
√
√
√
√
√
√
re
NbMoss
lP
Samples
of
Journal Pre-proof
na
The curve of relative density is shown in Fig.2. The theoretical density is calculated
Jo ur
according to the rule of mixtures, based on the original ingredient before hot-pressing, and the densities are 8.57 g/cm3, 10.2 g/cm3, 6.085 g/cm3 and 3.2 g/cm3 for Nb, Mo, ZrB2 and SiC, respectively. NM-30ZS has the highest relative density of 98.69%, and reason could be found in Fig. 3. Fig. 3 (a) and (b) are in the same magnification of 2000, and (c) and (d) are in the same magnification of 5000. From NM-15ZS to NM-60ZS, the sizes of zirconium compound are around 4 μm, 2 μm, 1 μm and 5 μm, respectively, which are much smaller than the size of starting ZrB2 powder. This change of size supplies evidence for particles fragmentation. NM-30ZS has the smallest size of spherical particles of zirconium compound among the four samples. Besides, the distribution of zirconium compound is relatively homogeneous in
Mo2C
√
Journal Pre-proof
NM-30ZS and NM-60ZS. In addition, with the increasing amounts of additives, the amounts of ductile Nb and Mo decrease, resulting in the decrease of phase fluidity in the process of solidification. It seems that the densification of the composites is affected by the size of productive zirconium compound, the even degree of phase distribution and the phase fluidity.
of
Except for NM-45ZS, the relative density of x (70% ZrB2 + 30% SiC)-NbMo composites is lower than the x ZrB2-NbMo composites in our early study [6] when the
ro
value of x is same. The possible reason is the pores caused by the difference of
-p
thermal expansivity of ZrB2 and SiC (5.9×10-6-6.8×10-6 for ZrB2 and 4×10-6-4.7×
re
10-6 for SiC) [17-18] in the initial stage of solidification. The relative density of
lP
NM-45ZS is higher than 45% ZrB2 -NbMo, and the reason for this may be the
na
particularly poor property of 45% ZrB2 -NbMo such as the large particles, irregular grain shape and uneven phase distribution.
Jo ur
Fig. 2. Effect of (70% ZrB2+30% SiC) content on the relative density.
Table 2 Compositions, relative densities of the hot-pressed composites.
Journal Pre-proof
Samples
Compositions (vol.%)
Test
Theoretical 3
Relative density
3
Mo
ZrB2
SiC
density(g/cm )
density(g/cm )
（%）
NM-0
50
50
0
0
8.857 0.072
9.330
94.93 0.77
NM-15ZS
42.5
42.5
10.5
4.5
8.309 0.015
8.710
95.39 0.17
NM-30ZS
35
35
21
9
7.989 0.027
8.095
98.69 0.34
NM-45ZS
27.5
27.5
31.5
13.5
7.232 0.082
7.479
96.70 1.10
NM-60ZS
20
20
42
18
6.185 0.031
6.863
90.12 0.45
-p
ro
of
Nb
re
3.3. Hardness
lP
The hardness of NbMoss in NM-15ZS, NM-30ZS, NM-45ZS and NM-60ZS are 4.37
na
GPa, 4.41 GPa, 5.15 GPa and 6.82 GPa, respectively. The hardness of NbMoss increases with the additive amounts, which could be attributed to the solid solution of
Jo ur
increasing Zr, B, Si and B atoms that could strengthen the NbMoss. The hardness of eutectic phase in NM-15ZS is 7.87 GPa, and that of continuous phase (Nb5Si3+Niobium borides+A15+T2) in NM-30ZS is 12.17 GPa. The hardness of A15+T2+MoSi2 phase in NM-45ZS is 13.89 GPa, and that in NM-60ZS is 14.65 GPa. The size of zirconium compound particles in NM-30ZS is too small to be detected accurately. The hardness of the zirconium compound with surrounding niobium borides area in NM-45ZS is detected to be 18.36 GPa, and the hardness of that area in NM-60ZS is 20.67 GPa. In addition, the hardness of NbMoss in x (70% ZrB2 + 30% SiC)-NbMo composites is
Journal Pre-proof
higher than that in x ZrB2-NbMo composites when the value of x is same, which indicating the addition of SiC could further improve the hardness of NbMoss. 3.4. Microstructure Typical microstructure of the composites was observed and shown in Fig. 3. Zirconium compounds exist as spherical particle in all the four samples.
of
It is worth mentioning that eutectic phase is found in NM-15ZS. By combining the XRD (Fig. 1), SEM (Fig. 3) and EDS (Fig. 4 and Table 3) results, it is confirmed the
ro
continuous phase in NM-15ZS is NbMo solid solution with C, Si and a little Zr atoms
-p
dissolved, and ZrC particles distributed as reinforcing phase. Detection of boron with
re
EDS is not shown in this study because boron element is too light to be detected
lP
accurately.
Jo ur
(d) NM-60ZS (5000X).
na
Fig. 3. Polished surface of (a) NM-15ZS (2000X), (b) NM-30ZS (2000X), (c) NM-45ZS (5000X) and
re
-p
ro
of
Journal Pre-proof
Jo ur
na
lP
Fig. 4. High magnification SEM images of NM-15ZS.
Table 3 Atom fraction (%) of the phases in Fig. 4. Element
Nb
Mo
Zr
Si
Point 1
34.08
5.80
32.29
Point 2
47.53
24.14
2.86
13.31
Point 3
40.01
58.56
0.53
0.90
Point 4
54.30
2.16
18.65
Point 5
36.27
53.09
0.12
C
O
24.65
3.17
12.16 19.66
0.64
9.88
5.22
Journal Pre-proof
The microstructure and elements distribution map of NM-30ZS are shown in Fig. 3 (b) and Fig. 5, respectively. There are no big holes observed in this sample. ZrB is found to be the production of ZrB2 decomposition. Reinforcing phase zirconium compound particles are found small and distribute between NbMoss and continuous phase (Nb5Si3+Niobium borides+A15+T2). Nb5Si3, niobium borides and A15+T2 phase
of
distribute together and are not easy to be distinguished by SEM image. But the A15+T2 phase could be identified more clearly by the marked circle in the
ro
multi-phase area of Fig. 5. The area of NbMoss in NM-30ZS is not as big as that in
-p
NM-15ZS, indicating more Nb and Mo atoms react with added B and Si atoms to
re
form high hardness phases.
Jo ur
na
lP
Fig. 5 BSE images and EDS maps of NM-30ZS.
The microstructure of NM-45ZS is displayed in Fig. 3 (c), and Fig. 6 shows the elements distribution map of it. The shape of Nb5Si3 is found to be oval and the shape of niobium borides phase in this sample is different from that in NM-30ZS. A15+T2+MoSi2 phase locate in NbMoss and is observed to be light grey closed to white. A15+T2+MoSi2 phase is more obvious in NM-45ZS and the area of it is bigger
Journal Pre-proof
than that in NM-30ZS. The amount of NbMoss phase in NM-45ZS is more less than that in NM-30ZS as shown.
re
-p
ro
of
Fig. 6 BSE images and EDS maps of NM-45ZS.
lP
Figure 3 (d) shows the microstructure of NM-60ZS and Fig.7 displays the elements distribution map. There are residual undecomposed ZrB2 particles and their size is
na
much larger than the other three composites. Zirconium compound phase is
Jo ur
surrounded by Nb3B4 phase. There are more A15+T2+MoSi2 phase in NM-60ZS than other three. NbMoss is found in XRD pattern, however, it’s not easy to find it in Fig. 3 (d), due to the small amount of it. The reason for the decrease of NbMoss is that more Nb and Mo atoms are reacted with additives Fig. 7 BSE images and EDS maps of NM-60ZS.
of
Journal Pre-proof
ro
Addition of (70% ZrB2 + 30% SiC) could affect the phase formation. In addition, the
of 45 to 60 vol%.
lP
3.4. Compression and fracture surface
re
-p
highest (70% ZrB2 + 30% SiC) concentration reacting with Nb and Mo is at the range
Figure 8 and Table 4 show compression experiment results. All the x (70% ZrB2 + 30%
na
SiC)-NbMo exhibit brittleness. The highest compressive strength of x (70% ZrB2 + 30%
Jo ur
SiC)-NbMo belongs to NM-15ZS, though its relative density is only 95.39%. Although there are more hard reinforcing phases in NM-30ZS, NM-45ZS and NM-60ZS , and the degree of solution strengthening in NM-30ZS, NM-45ZS and NM-60ZS is higher than that in NM-15ZS, the compressive strengths of these three composites are not as high as NM-15ZS, and the reasons for the this phenomenon are the lack of ductile phase. Since the the energy of crack initiation and propagation could be dissipated by ductile phase (NbMoss in this study) in the form of plastic deformation and crack bridging [19-22]. However, there is no enough ductile phase in NM-30ZS, NM-45ZS and NM-60ZS to absorb and dissipate the crack energy and release stress concentration, though there is much hard phase in them. The
Journal Pre-proof
compressive strength of NM-0 is not as high as NM-15ZS. The reasons for that relatively high compressive strength of NM-15ZS are the dispersion strengthening of high hardness particles and solid solution strengthening of Si, C, B and a little Zr atoms to NbMo solid solution. Compared with x ZrB2-NbMo composite, this phenomenon indicates that not all
of
addition of SiC is effective for the improvement of room temperature compression property of the x (70% ZrB2 + 30% SiC)-NbMo composites. Only when x=15% is the
ro
compressive strength of x (70% ZrB2 + 30% SiC)-NbMo higher than x ZrB2-NbMo.
Compressive strength （MPa）
Young’s modulus E
re
Samples
-p
Table 4 Compressive strength, Young’s modulus and fracture toughness of the five composites.
（MPa）
KIC (MPa m 1/2)
226.56 0.50
6.12 0.30
189.55 0.29
5.63 0.34
281.02 0.81
4.70 0.30
355.69
279.71 0.57
2.96 0.15
401.55
227.21 6.27
2.93 0.24
931.69 1053.30
NM-30Z
426.70
NM-45Z NM-60Z
Jo ur
na
lP
NM-0 NM-15Z
Fig. 8. Stress-strain curves at room temperature.
Fracture toughness results are displayed in Table 4, which indicates that the fracture
Journal Pre-proof
toughness value decreases with the increasing amounts of additives. Compared with the fracture toughness value of x ZrB2-NbMo composite, that value of x (70 % ZrB2 + 30 % SiC)-NbMo composites is lower when the value of x is fixed. In other words, the introduction of SiC decrease the toughness property, which could also be verified by the following analysis of crack propagation. Fig.9 shows the crack propagation
of
behavior of these four composites. The crack bridging is observed in NbMoss of NM-15ZS, which could enhance fracture toughness by dissipating energy. In
ro
NM-30ZS, crack bridging is observed in continuous phase as displayed in NM-30ZS.
-p
In NM-45ZS and NM-60ZS, the crack deflection is only found in the boundary of
re
zirconium compound and other phases at the end of crack. There is no effective
lP
resistance at the beginning of the crack in NM-45ZS and NM-60ZS, and the crack go
na
straightly through the zirconium compound particles.
Jo ur
Fig. 9. Typical crack propagation of (a) NM-15ZS, (b) NM-30ZS, (c) NM-45ZS and (d) NM-60ZS.
re
-p
ro
of
Journal Pre-proof
lP
Figure 10 shows fracture surface after compression. Both intergranular fracture and
na
transgranular fracture are observed in the four composites. The transgranular fracture is observed in NbMoss, niobium borides, Nb5Si3 and A15+T2 phase. It is worth
Jo ur
mentioning that there are intergranular zirconium compound particles found inside or between other phases in all the four composites, and the micro crack surrounding zirconium compound particles could be a possible reason for the initial cracks. Decohesion is found in NM-15ZS, which effectively enhance fracture toughness according to Ashby et al. [23]. Therefore, the NbMoss and eutectic phase in NM-15ZS play a role in enhancing fracture toughness. Fig. 10. Fracture surface of (a) NM-15ZS, (b) NM-30ZS, (c) NMs-45ZS and (d) NM-60ZS.
re
-p
ro
of
Journal Pre-proof
lP
4. Conclusions
na
x (70 vol% ZrB2 + 30 vol% SiC)-NbMo composites (x=15 vol%, 30 vol%, 45 vol%, 60 vol%) were hot-pressed at 2400 °C with the pressure of 50 MPa for 10 min in Ar
Jo ur
gas condition. The object is to investigate the effects of effect of (ZrB2-SiC) addition on phase composition, relative density, hardness and compressive strength at room temperature. The main conclusions are: (1) The types of formed phase were decided by the amount of ZrB2 and SiC addition. The eutectic phase in 15% (70 % ZrB2 + 30 % SiC)-NbMo was attributed to the addition of SiC. (2) 30 % (70 % ZrB2 + 30 % SiC)-NbMo had the highest relative density of 98.69%. In general, compared with x ZrB2-NbMo, the addition of SiC had negative effects on the densification of x (70 % ZrB2 + 30 % SiC)-NbMo composites.
Journal Pre-proof
(3) The addition of SiC improved the hardness of x (70 % ZrB2 + 30 % SiC)-NbMo composites, which is directly proportional to the fraction of (70 % ZrB2 + 30 % SiC) additives. (4) The addition of (70 % ZrB2 + 30% SiC) improved the compressive strength of x (70 % ZrB2 + 30% SiC)-NbMo only when x=15%, and the reasons for the low
of
strength of 30%, 45%, 60% (70% ZrB2 + 30% SiC)-NbMo were the lack of ductile phase and the large amount of hard phase production.
ro
The high temperature properties and oxidation resistance of x (70% ZrB2 + 30%
-p
SiC)-NbMo composites will be investigated in our future work.
re
Acknowledgement
lP
The authors would like to thank the financial support from the National Natural
na
Science Foundation of China (No. 11372110) and the Fundamental Research Funds
Reference 1.
Jo ur
for the Central Universities (No. 2017XS053).
Nico, Monteiro, Graça, Niobium oxides and niobates physical properties: Review and prospects, Prog. Mater. Sci. 80 (2016) 1-37.
2.
Tan, Ma, Kasama, Tanaka, Mishima, Hanada, Yang, Effect of alloy composition on microstructure and high temperature properties of Nb-Zr-C ternary alloys, Mater. Sci. Eng. A. 341 (2003) 282-288.
3.
Tan, Ma, Kasama, Anaka, Yang, High temperature mechanical behavior of Nb-Mo-ZrC alloys, Mater. Sci. Eng. A. 355 (2003) 260-266.
4.
Neuman, Hilmas, Fahrenholtz, Processing, microstructure, and mechanical properties of
Journal Pre-proof
large-grained zirconium diboride ceramics, Mater. Sci. Eng. A. 670 (2016) 196-204. 5.
Zhang, Ni, Zou, et al., Inherent anisotropy in transition metal diborides and microstructure/property tailoring in ultra-high temperature ceramics-a review, J. Eur. Ceram. Soc. 38 (2018) 371-389.
6.
Liu, Wang, Gao, Wang, Sun, Gong, Preparation and properties of hot-pressed NbMo matrix
Wang, Liu, Wang, Sun, Gong, High temperature compression properties of hot-pressed
ro
7.
of
composites reinforced with ZrB2 particles, Int. J. Refract. Met. Hard Mater. 68 (2017) 104-112.
NbMo-matrix composites reinforced with ZrB2 particles, Int. J. Refract. Met. Hard Mater. 77
Chamberlain, Fahrenholtz, Hilmas, High-strength zirconium diboride-based ceramics, J. Am.
Watts, Hilmas, Fahrenholtz, Mechanical characterization of ZrB2-SiC composites with varying
na
9.
lP
Ceram. Soc. 87 (2004) 1170-1172.
re
8.
-p
(2018) 132-140.
SiC particle sizes, J. Am. Ceram. Soc. 94 (2011) 4410-4418.
Jo ur
10. Nayebi, Asl, Kakroudi, Shokouhimehr, Temperature dependence of microstructure evolution during hot pressing of ZrB2-30vol.% SiC composites, Int. J. Refract. Met. Hard Mater. 54 (2016) 7-13.
11. Jayaseelan, Wang, Hilmas, Fahrenholtz, Brown, Lee, TEM investigation of hot pressed-10 vol.% SiC-ZrB2 composite, Adv. Appl. Ceram. 110 (2011) 1-7. 12. Liang, Wang, Meng, Interface and defect characterization in hot-pressed ZrB2-SiC ceramics, Int. J. Refract. Met. Hard Mater. 29 (2011) 341-343. 13. Fahrenholtz, Hilmas, Chamberlain, A. L. and Zimmermann, Processing and characterization of ZrB2-based ultra-high temperature monolithic and fibrous monolithic ceramics, J. Mater. Sci, 39
Journal Pre-proof
(2004), 5951–5957. 14. Neuman, Hilmas, Fahrenholtz, Mechanical behavior of zirconium diboride-silicon Carbide ceramics at elevated temperature in air, J. Eur. Ceram. Soc. 35 (2013) 2889-2899. 15. Neuman, Hilmas, Fahrenholtz, Elevated temperature strength enhancement of ZrB2-30 vol% SiC ceramics by postsintering thermal annealing, J. Am. Ceram. Soc. 99 (2016) 962-970.
of
16. Rudy, Windisch, Related binary systems. Part I, systems V-B, Nb-B and Ta-B, Ternary Phase
ro
Equilibria in Transition Metal-Boron-Carbon-Silicon Systems, vol. X, Air Force Materials Laboratory, Wright-Patterson Air Force Base, 1966, 1–104.
-p
17. Solvas, Jayaseelan, Lin, Brown, Lee, Mechanical properties of ZrB2- and HfB2-based ultra-high
re
temperature ceramics fabricated by spark plasma sintering, J EUR CERAM SOC, 33 (2013),
lP
1373-1386.
na
18. James. Zimmermann, Hilmas, Fahrenholtz, Thermal shock resistance of ZrB2 and ZrB2–30% SiC, MATER CHEM PHY, 112 (2008) 140-145.
Jo ur
19. Xu, Hu, Yan, Lu, Munroe, Xie, Microstructure and mechanical properties of a Mo-toughened Mo3Si-based in situ nanocomposite, Vaccum. 109 (2014) 112-119. 20. Zhu, Luo, Li, Wu, The influence of powder characteristics on mechanical properties of Al2O3-TiC-Co ceramic materials prepared by co-coated Al2O3/TiC powders. Int J Refract Met Hard Mater. 34 (2012) 61-65. 21. Gu, Huang, Zou, Liu, Effect of (Ni,Mo) and TiN on the microstructure and mechanical properties of TiB2 ceramic tool materials, Mater Sci Eng A. 433 (2006) 39-44. 22. Choe, Chen, Schneibel, Ritchie, Ambient to high temperature fracture toughness and fatigue-crack propagation behavior in a Mo-12Si-8.5B (at.%) intermetallic, Intermetallics. 9
Journal Pre-proof
(2001) 319-329. 23. Ashby, Blunt, Bannister, Flow characteristics of highly constrained metal wires, Met. Mater. 37
Jo ur
na
lP
re
-p
ro
of
(1989) 1847.
Journal Pre-proof
Highlight
na
lP
re
-p
ro
of
High dense 30 % (70 % ZrB2 + 30 % SiC)-NbMo composites (98.69%) were hot-pressed. The eutectic phase in 15% (ZrB2 + SiC)-NbMo is attributed to the addition of SiC. The addition of SiC improves the hardness of NbMoss in x (ZrB2 + SiC)-NbMo. The addition of SiC improves the compressive strength of 15% (ZrB2 + SiC)-NbMo.
Jo ur
Qi Wang, Zongde Liu, Yongtian Wang, Xinyu Wang PII:
S0263-4368(19)30508-6
DOI:
https://doi.org/10.1016/j.ijrmhm.2019.105098
Reference:
RMHM 105098
To appear in:
International Journal of Refractory Metals and Hard Materials
Received date:
28 June 2019
Revised date:
27 August 2019
Accepted date:
16 September 2019
Please cite this article as: Q. Wang, Z. Liu, Y. Wang, et al., The effect of (ZrB2-SiC) addition on microstructure and mechanical properties of NbMo-matrix composites fabricated by hot-pressing, International Journal of Refractory Metals and Hard Materials(2019), https://doi.org/10.1016/j.ijrmhm.2019.105098
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2019 Published by Elsevier.
Journal Pre-proof
The effect of (ZrB2-SiC) addition on microstructure and mechanical properties of NbMo-matrix composites fabricated by hot-pressing
Qi Wang 1, a, Zongde Liu 1,b, * , Yongtian Wang1,c, Xinyu Wang1,d 1
Key Laboratory of Condition Monitoring and Control for Power Plant Equipment of Ministry of
Education, North China Electric Power University, Beijing 102206, China [email protected]
b
email:
[email protected]
c
of
email:
email :[email protected]
d
email :
ro
a
[email protected]
-p
*Corresponding author: Zongde Liu
re
Abstract
lP
The effects of (0-60%) vol% (70 vol% ZrB2 + 30 vol% SiC) additions on
na
microstructure and properties of NbMo substrate fabricated by hot-pressing were studied at room temperature. Types of formed phase were decided by the amount of
Jo ur
ZrB2 and SiC additives. The effective eutectic phase was observed in 15 vol% (70 vol% ZrB2 + 30 vol% SiC)-NbMo, which was attributed to the addition of SiC. 30 vol% (70 vol% ZrB2 + 30 vol% SiC)-NbMo had the highest relative density of 98.69%. Compared with x ZrB2-NbMo composites, the addition of SiC could further improve the hardness of NbMoss in x (70% ZrB2 + 30% SiC)-NbMo when the value of x was same, and NbMoss in 60 vol% (70 vol% ZrB2 + 30 vol% SiC)-NbMo had the highest hardness of 6.82 GPa. Only the 15 vol% (70 vol% ZrB2 + 30 vol% SiC) addition could improve the compressive strength of NbMo matrix. The reasons for the low strength of 30, 45, 60 vol% (70% ZrB2 + 30% SiC)-NbMo were the lack of ductile
Journal Pre-proof
phase and the large amount of hard phase production. Keywords: Mechanical properties; NbMo; ZrB2; SiC; Hot-pressing
1. Introduction Niobium-based alloys are promising candidate for high temperature structural
of
materials because they have low density, high melting points, good ductility and high resistance to corrosion [1]. However, the strength declines rapidly when the
ro
temperature is above 1200 K [2]. The addition of refractory metal Molybdenum (Mo)
-p
to Nb could make up for this shortcoming of Nb at high temperature by solution
re
strengthening, and the degree of strengthening reaches its maximum extent when
lP
Nb/Mo volume ratio is approximately 1 [3]. Zirconium diboride (ZrB2) has excellent
na
performance at ultra-high temperature because of its ultra-high melting point (3246 ℃), high hardness and other desirable mechanical properties [4,5]. In our early
Jo ur
research, (0–60) vol% ZrB2-NbMo composites were fabricated by hot-pressing at the temperature of 2400 °C with a pressure of 50 MPa for 10 min in Argon, and the volume fraction of additive Nb and Mo is same (Nb/Mo=1). The properties of (0–60) vol% ZrB2-NbMo composites at room temperature and the temperature range of 800 ℃ to 1300 ℃ were tested and analyzed. The results show ZrB2 addtion to NbMo can greatly improve the compressive strength of the composites at all tested temperature compared to NbMo solid solution, and the compressive strength of 60 vol% ZrB2-NbMo is 700.46 MPa even at 1300 ℃ [6,7]. Previous study reported the addition of silicon carbide (SiC) to ZrB2-based composites could improve properties
Journal Pre-proof
and ZrB2-SiC composites had high room temperature strengths, high fracture toughness and high hardness values, in which SiC additive could limit the grain growth [8-10]. Jayaseelan et al. reported the oxide impurities in the ZrB2-10 vol% SiC [11], and Liang et al. observed a lot of edge dislocations in ZrB2-20 vol% SiC [12]. Fahrenholtz et al. found that ZrB2 with 30 vol% SiC has excellent strength and
of
fracture toughness [13]. Neuman et al. reported the strength of ZrB2-30 vol% SiC up to 1600 MPa in air condition [14-15].
ro
In this study, mixture powder of 70 vol% ZrB2 and 30 vol% SiC is added to NbMo,
-p
and the volume ratio of Nb/Mo is 1. The aim of this present work is to investigate
re
the room temperature properties of the 15, 30, 45, 60 vol% (70 vol% ZrB2 + 30 vol%
lP
SiC)-NbMo composites fabricated by the method reported in our early literature [6].
na
The effects of composite additive on the microstructure and mechanical properties of the x (70% ZrB2 + 30% SiC) -NbMo were discussed.
Jo ur
2. Experimental Procedure 2.1 Processing
Five compositions were selected (amounts in vol%): NM-0: 50%Nb + 50%Mo NM-15ZS: 42.5%Nb + 42.5%Mo + 10.5%ZrB2 + 4.5%SiC NM-30ZS: 35%Nb + 35%Mo + 21%ZrB2 + 9%SiC NM-45ZS: 27.5%Nb + 27.5%Mo + 31.5%ZrB2 + 13.5%SiC NM-60ZS: 20%Nb + 20%Mo + 42%ZrB2 + 18%SiC The starting materials were high purity Nb (N, for short) and Mo (M, for short)
Journal Pre-proof powders (purity > 99.95%, mean particle size 18-25 μm) and ZrB2 (Z, for short) powders (purity > 99.95%, mean particle size 23 μm) and SiC (S, for short) powders (purity > 99.9%, mean particle size 45 μm) supplied by Beijing Gold Crown for the New Material Technology Co. Ltd. China. The powders were dried at the temperature of 110℃ for 3 hours, then mixed in the planetary ball mill at 200 rpm for up to 10
under 50 MPa using pure Argon as a shielding gas.
ro
2.2 Characterization
of
hours for the purpose of thorough blend, and finally hot-pressed at 2400℃ for 10 min
-p
The cylindrical samples with dimensions of 14 mm in diameter and 70 mm in height
re
were cut into 10mm*10mm*8mm specimens for microstructure observation and XRD
lP
test by wire cut electrical discharge machining (WEDM). Ultrasonic cleaner was used
na
to clean the specimens. Phase composition was detected by X-ray diffraction analysis. Microstructure and element distribution were detected by scanning electron
Jo ur
microscopes (FEI Quanta 200F and SU8010) equipped with energy dispersive spectroscopy. Densimeter (FA1104J) device was employed to measure the density, and the average density value was from at least three measurements. The Vickers hardness test (FM-300) was conducted with 300g load applied for 10 s with diamond indenter on polished section. At least three points were tested for calculating the average hardness for each phase. The compression experiment was performed on the hydraulic universal tester (SHT 4305) at room temperature, with the loading rate of 600N/m. Young’s modulus was determined by dynamic Young’s modulus tester (RFDA system 23). The crack for observing propagation path was conducted on the
Journal Pre-proof
Vickers hardness tester (HVS-50P) under the load of 98 N with a dwell of 15 s in air condition. The fracture toughness value was measured by a three-point bending test (Electromechanical
Universal
Testing
Machine
C45.105)
using
the
single-edge-notched beam (SENB) specimens with the dimension of 3 mm * 4mm cross-section and 36 mm span, and the notch was 1.5 mm in depth and 0.15 mm in
of
width. 3. Results and Discussion
ro
3.1. Phase Composition
-p
Fig. 1 shows the XRD patterns of five samples. NbMo solid solution and ZrC exist in
re
all the four samples with additives, and SiC are decomposed in these four. There are
lP
no residual ZrB or ZrB2 in NM-15ZS, which indicating the ZrB2 are totally
na
decomposed to form ZrC and NbB2 in it. There are two stable niobium borides phase formed in the x (70% ZrB2 + 30% SiC)-NbMo composites: NbB2 and Nb3B4, which is
Jo ur
easily explained by Nb-B phase diagram [16]. Nb5Si3 are found in all the four composites. Mo3Si (A15) and Mo5SiB2 (T2) exist in NM-30ZS, NM-45ZS and NM-60ZS, and MoSi2 are found in NM-45ZS and NM-60ZS. Mo2C is only detected in NM-60ZS. The details are listed in Table 1. Fig. 1 X-ray diffraction (XRD) patterns of the five samples.
Table 1 The compounds in five samples after hot-pressing
NM-15ZS
√
NM-30ZS
√
NM-45ZS
√
NM-60ZS
√
ZrC
NbB2
Nb3B4
Nb5Si3
√
√
√
√
√
√
√
√
√
√
√
3.2. Densification
√
ro
√
ZrB2
-p
NM-0
ZrB
Mo3Si
Mo5SiB2
MoSi2
√
√
√
√
√
√
√
√
√
√
√
√
√
√
re
NbMoss
lP
Samples
of
Journal Pre-proof
na
The curve of relative density is shown in Fig.2. The theoretical density is calculated
Jo ur
according to the rule of mixtures, based on the original ingredient before hot-pressing, and the densities are 8.57 g/cm3, 10.2 g/cm3, 6.085 g/cm3 and 3.2 g/cm3 for Nb, Mo, ZrB2 and SiC, respectively. NM-30ZS has the highest relative density of 98.69%, and reason could be found in Fig. 3. Fig. 3 (a) and (b) are in the same magnification of 2000, and (c) and (d) are in the same magnification of 5000. From NM-15ZS to NM-60ZS, the sizes of zirconium compound are around 4 μm, 2 μm, 1 μm and 5 μm, respectively, which are much smaller than the size of starting ZrB2 powder. This change of size supplies evidence for particles fragmentation. NM-30ZS has the smallest size of spherical particles of zirconium compound among the four samples. Besides, the distribution of zirconium compound is relatively homogeneous in
Mo2C
√
Journal Pre-proof
NM-30ZS and NM-60ZS. In addition, with the increasing amounts of additives, the amounts of ductile Nb and Mo decrease, resulting in the decrease of phase fluidity in the process of solidification. It seems that the densification of the composites is affected by the size of productive zirconium compound, the even degree of phase distribution and the phase fluidity.
of
Except for NM-45ZS, the relative density of x (70% ZrB2 + 30% SiC)-NbMo composites is lower than the x ZrB2-NbMo composites in our early study [6] when the
ro
value of x is same. The possible reason is the pores caused by the difference of
-p
thermal expansivity of ZrB2 and SiC (5.9×10-6-6.8×10-6 for ZrB2 and 4×10-6-4.7×
re
10-6 for SiC) [17-18] in the initial stage of solidification. The relative density of
lP
NM-45ZS is higher than 45% ZrB2 -NbMo, and the reason for this may be the
na
particularly poor property of 45% ZrB2 -NbMo such as the large particles, irregular grain shape and uneven phase distribution.
Jo ur
Fig. 2. Effect of (70% ZrB2+30% SiC) content on the relative density.
Table 2 Compositions, relative densities of the hot-pressed composites.
Journal Pre-proof
Samples
Compositions (vol.%)
Test
Theoretical 3
Relative density
3
Mo
ZrB2
SiC
density(g/cm )
density(g/cm )
（%）
NM-0
50
50
0
0
8.857 0.072
9.330
94.93 0.77
NM-15ZS
42.5
42.5
10.5
4.5
8.309 0.015
8.710
95.39 0.17
NM-30ZS
35
35
21
9
7.989 0.027
8.095
98.69 0.34
NM-45ZS
27.5
27.5
31.5
13.5
7.232 0.082
7.479
96.70 1.10
NM-60ZS
20
20
42
18
6.185 0.031
6.863
90.12 0.45
-p
ro
of
Nb
re
3.3. Hardness
lP
The hardness of NbMoss in NM-15ZS, NM-30ZS, NM-45ZS and NM-60ZS are 4.37
na
GPa, 4.41 GPa, 5.15 GPa and 6.82 GPa, respectively. The hardness of NbMoss increases with the additive amounts, which could be attributed to the solid solution of
Jo ur
increasing Zr, B, Si and B atoms that could strengthen the NbMoss. The hardness of eutectic phase in NM-15ZS is 7.87 GPa, and that of continuous phase (Nb5Si3+Niobium borides+A15+T2) in NM-30ZS is 12.17 GPa. The hardness of A15+T2+MoSi2 phase in NM-45ZS is 13.89 GPa, and that in NM-60ZS is 14.65 GPa. The size of zirconium compound particles in NM-30ZS is too small to be detected accurately. The hardness of the zirconium compound with surrounding niobium borides area in NM-45ZS is detected to be 18.36 GPa, and the hardness of that area in NM-60ZS is 20.67 GPa. In addition, the hardness of NbMoss in x (70% ZrB2 + 30% SiC)-NbMo composites is
Journal Pre-proof
higher than that in x ZrB2-NbMo composites when the value of x is same, which indicating the addition of SiC could further improve the hardness of NbMoss. 3.4. Microstructure Typical microstructure of the composites was observed and shown in Fig. 3. Zirconium compounds exist as spherical particle in all the four samples.
of
It is worth mentioning that eutectic phase is found in NM-15ZS. By combining the XRD (Fig. 1), SEM (Fig. 3) and EDS (Fig. 4 and Table 3) results, it is confirmed the
ro
continuous phase in NM-15ZS is NbMo solid solution with C, Si and a little Zr atoms
-p
dissolved, and ZrC particles distributed as reinforcing phase. Detection of boron with
re
EDS is not shown in this study because boron element is too light to be detected
lP
accurately.
Jo ur
(d) NM-60ZS (5000X).
na
Fig. 3. Polished surface of (a) NM-15ZS (2000X), (b) NM-30ZS (2000X), (c) NM-45ZS (5000X) and
re
-p
ro
of
Journal Pre-proof
Jo ur
na
lP
Fig. 4. High magnification SEM images of NM-15ZS.
Table 3 Atom fraction (%) of the phases in Fig. 4. Element
Nb
Mo
Zr
Si
Point 1
34.08
5.80
32.29
Point 2
47.53
24.14
2.86
13.31
Point 3
40.01
58.56
0.53
0.90
Point 4
54.30
2.16
18.65
Point 5
36.27
53.09
0.12
C
O
24.65
3.17
12.16 19.66
0.64
9.88
5.22
Journal Pre-proof
The microstructure and elements distribution map of NM-30ZS are shown in Fig. 3 (b) and Fig. 5, respectively. There are no big holes observed in this sample. ZrB is found to be the production of ZrB2 decomposition. Reinforcing phase zirconium compound particles are found small and distribute between NbMoss and continuous phase (Nb5Si3+Niobium borides+A15+T2). Nb5Si3, niobium borides and A15+T2 phase
of
distribute together and are not easy to be distinguished by SEM image. But the A15+T2 phase could be identified more clearly by the marked circle in the
ro
multi-phase area of Fig. 5. The area of NbMoss in NM-30ZS is not as big as that in
-p
NM-15ZS, indicating more Nb and Mo atoms react with added B and Si atoms to
re
form high hardness phases.
Jo ur
na
lP
Fig. 5 BSE images and EDS maps of NM-30ZS.
The microstructure of NM-45ZS is displayed in Fig. 3 (c), and Fig. 6 shows the elements distribution map of it. The shape of Nb5Si3 is found to be oval and the shape of niobium borides phase in this sample is different from that in NM-30ZS. A15+T2+MoSi2 phase locate in NbMoss and is observed to be light grey closed to white. A15+T2+MoSi2 phase is more obvious in NM-45ZS and the area of it is bigger
Journal Pre-proof
than that in NM-30ZS. The amount of NbMoss phase in NM-45ZS is more less than that in NM-30ZS as shown.
re
-p
ro
of
Fig. 6 BSE images and EDS maps of NM-45ZS.
lP
Figure 3 (d) shows the microstructure of NM-60ZS and Fig.7 displays the elements distribution map. There are residual undecomposed ZrB2 particles and their size is
na
much larger than the other three composites. Zirconium compound phase is
Jo ur
surrounded by Nb3B4 phase. There are more A15+T2+MoSi2 phase in NM-60ZS than other three. NbMoss is found in XRD pattern, however, it’s not easy to find it in Fig. 3 (d), due to the small amount of it. The reason for the decrease of NbMoss is that more Nb and Mo atoms are reacted with additives Fig. 7 BSE images and EDS maps of NM-60ZS.
of
Journal Pre-proof
ro
Addition of (70% ZrB2 + 30% SiC) could affect the phase formation. In addition, the
of 45 to 60 vol%.
lP
3.4. Compression and fracture surface
re
-p
highest (70% ZrB2 + 30% SiC) concentration reacting with Nb and Mo is at the range
Figure 8 and Table 4 show compression experiment results. All the x (70% ZrB2 + 30%
na
SiC)-NbMo exhibit brittleness. The highest compressive strength of x (70% ZrB2 + 30%
Jo ur
SiC)-NbMo belongs to NM-15ZS, though its relative density is only 95.39%. Although there are more hard reinforcing phases in NM-30ZS, NM-45ZS and NM-60ZS , and the degree of solution strengthening in NM-30ZS, NM-45ZS and NM-60ZS is higher than that in NM-15ZS, the compressive strengths of these three composites are not as high as NM-15ZS, and the reasons for the this phenomenon are the lack of ductile phase. Since the the energy of crack initiation and propagation could be dissipated by ductile phase (NbMoss in this study) in the form of plastic deformation and crack bridging [19-22]. However, there is no enough ductile phase in NM-30ZS, NM-45ZS and NM-60ZS to absorb and dissipate the crack energy and release stress concentration, though there is much hard phase in them. The
Journal Pre-proof
compressive strength of NM-0 is not as high as NM-15ZS. The reasons for that relatively high compressive strength of NM-15ZS are the dispersion strengthening of high hardness particles and solid solution strengthening of Si, C, B and a little Zr atoms to NbMo solid solution. Compared with x ZrB2-NbMo composite, this phenomenon indicates that not all
of
addition of SiC is effective for the improvement of room temperature compression property of the x (70% ZrB2 + 30% SiC)-NbMo composites. Only when x=15% is the
ro
compressive strength of x (70% ZrB2 + 30% SiC)-NbMo higher than x ZrB2-NbMo.
Compressive strength （MPa）
Young’s modulus E
re
Samples
-p
Table 4 Compressive strength, Young’s modulus and fracture toughness of the five composites.
（MPa）
KIC (MPa m 1/2)
226.56 0.50
6.12 0.30
189.55 0.29
5.63 0.34
281.02 0.81
4.70 0.30
355.69
279.71 0.57
2.96 0.15
401.55
227.21 6.27
2.93 0.24
931.69 1053.30
NM-30Z
426.70
NM-45Z NM-60Z
Jo ur
na
lP
NM-0 NM-15Z
Fig. 8. Stress-strain curves at room temperature.
Fracture toughness results are displayed in Table 4, which indicates that the fracture
Journal Pre-proof
toughness value decreases with the increasing amounts of additives. Compared with the fracture toughness value of x ZrB2-NbMo composite, that value of x (70 % ZrB2 + 30 % SiC)-NbMo composites is lower when the value of x is fixed. In other words, the introduction of SiC decrease the toughness property, which could also be verified by the following analysis of crack propagation. Fig.9 shows the crack propagation
of
behavior of these four composites. The crack bridging is observed in NbMoss of NM-15ZS, which could enhance fracture toughness by dissipating energy. In
ro
NM-30ZS, crack bridging is observed in continuous phase as displayed in NM-30ZS.
-p
In NM-45ZS and NM-60ZS, the crack deflection is only found in the boundary of
re
zirconium compound and other phases at the end of crack. There is no effective
lP
resistance at the beginning of the crack in NM-45ZS and NM-60ZS, and the crack go
na
straightly through the zirconium compound particles.
Jo ur
Fig. 9. Typical crack propagation of (a) NM-15ZS, (b) NM-30ZS, (c) NM-45ZS and (d) NM-60ZS.
re
-p
ro
of
Journal Pre-proof
lP
Figure 10 shows fracture surface after compression. Both intergranular fracture and
na
transgranular fracture are observed in the four composites. The transgranular fracture is observed in NbMoss, niobium borides, Nb5Si3 and A15+T2 phase. It is worth
Jo ur
mentioning that there are intergranular zirconium compound particles found inside or between other phases in all the four composites, and the micro crack surrounding zirconium compound particles could be a possible reason for the initial cracks. Decohesion is found in NM-15ZS, which effectively enhance fracture toughness according to Ashby et al. [23]. Therefore, the NbMoss and eutectic phase in NM-15ZS play a role in enhancing fracture toughness. Fig. 10. Fracture surface of (a) NM-15ZS, (b) NM-30ZS, (c) NMs-45ZS and (d) NM-60ZS.
re
-p
ro
of
Journal Pre-proof
lP
4. Conclusions
na
x (70 vol% ZrB2 + 30 vol% SiC)-NbMo composites (x=15 vol%, 30 vol%, 45 vol%, 60 vol%) were hot-pressed at 2400 °C with the pressure of 50 MPa for 10 min in Ar
Jo ur
gas condition. The object is to investigate the effects of effect of (ZrB2-SiC) addition on phase composition, relative density, hardness and compressive strength at room temperature. The main conclusions are: (1) The types of formed phase were decided by the amount of ZrB2 and SiC addition. The eutectic phase in 15% (70 % ZrB2 + 30 % SiC)-NbMo was attributed to the addition of SiC. (2) 30 % (70 % ZrB2 + 30 % SiC)-NbMo had the highest relative density of 98.69%. In general, compared with x ZrB2-NbMo, the addition of SiC had negative effects on the densification of x (70 % ZrB2 + 30 % SiC)-NbMo composites.
Journal Pre-proof
(3) The addition of SiC improved the hardness of x (70 % ZrB2 + 30 % SiC)-NbMo composites, which is directly proportional to the fraction of (70 % ZrB2 + 30 % SiC) additives. (4) The addition of (70 % ZrB2 + 30% SiC) improved the compressive strength of x (70 % ZrB2 + 30% SiC)-NbMo only when x=15%, and the reasons for the low
of
strength of 30%, 45%, 60% (70% ZrB2 + 30% SiC)-NbMo were the lack of ductile phase and the large amount of hard phase production.
ro
The high temperature properties and oxidation resistance of x (70% ZrB2 + 30%
-p
SiC)-NbMo composites will be investigated in our future work.
re
Acknowledgement
lP
The authors would like to thank the financial support from the National Natural
na
Science Foundation of China (No. 11372110) and the Fundamental Research Funds
Reference 1.
Jo ur
for the Central Universities (No. 2017XS053).
Nico, Monteiro, Graça, Niobium oxides and niobates physical properties: Review and prospects, Prog. Mater. Sci. 80 (2016) 1-37.
2.
Tan, Ma, Kasama, Tanaka, Mishima, Hanada, Yang, Effect of alloy composition on microstructure and high temperature properties of Nb-Zr-C ternary alloys, Mater. Sci. Eng. A. 341 (2003) 282-288.
3.
Tan, Ma, Kasama, Anaka, Yang, High temperature mechanical behavior of Nb-Mo-ZrC alloys, Mater. Sci. Eng. A. 355 (2003) 260-266.
4.
Neuman, Hilmas, Fahrenholtz, Processing, microstructure, and mechanical properties of
Journal Pre-proof
large-grained zirconium diboride ceramics, Mater. Sci. Eng. A. 670 (2016) 196-204. 5.
Zhang, Ni, Zou, et al., Inherent anisotropy in transition metal diborides and microstructure/property tailoring in ultra-high temperature ceramics-a review, J. Eur. Ceram. Soc. 38 (2018) 371-389.
6.
Liu, Wang, Gao, Wang, Sun, Gong, Preparation and properties of hot-pressed NbMo matrix
Wang, Liu, Wang, Sun, Gong, High temperature compression properties of hot-pressed
ro
7.
of
composites reinforced with ZrB2 particles, Int. J. Refract. Met. Hard Mater. 68 (2017) 104-112.
NbMo-matrix composites reinforced with ZrB2 particles, Int. J. Refract. Met. Hard Mater. 77
Chamberlain, Fahrenholtz, Hilmas, High-strength zirconium diboride-based ceramics, J. Am.
Watts, Hilmas, Fahrenholtz, Mechanical characterization of ZrB2-SiC composites with varying
na
9.
lP
Ceram. Soc. 87 (2004) 1170-1172.
re
8.
-p
(2018) 132-140.
SiC particle sizes, J. Am. Ceram. Soc. 94 (2011) 4410-4418.
Jo ur
10. Nayebi, Asl, Kakroudi, Shokouhimehr, Temperature dependence of microstructure evolution during hot pressing of ZrB2-30vol.% SiC composites, Int. J. Refract. Met. Hard Mater. 54 (2016) 7-13.
11. Jayaseelan, Wang, Hilmas, Fahrenholtz, Brown, Lee, TEM investigation of hot pressed-10 vol.% SiC-ZrB2 composite, Adv. Appl. Ceram. 110 (2011) 1-7. 12. Liang, Wang, Meng, Interface and defect characterization in hot-pressed ZrB2-SiC ceramics, Int. J. Refract. Met. Hard Mater. 29 (2011) 341-343. 13. Fahrenholtz, Hilmas, Chamberlain, A. L. and Zimmermann, Processing and characterization of ZrB2-based ultra-high temperature monolithic and fibrous monolithic ceramics, J. Mater. Sci, 39
Journal Pre-proof
(2004), 5951–5957. 14. Neuman, Hilmas, Fahrenholtz, Mechanical behavior of zirconium diboride-silicon Carbide ceramics at elevated temperature in air, J. Eur. Ceram. Soc. 35 (2013) 2889-2899. 15. Neuman, Hilmas, Fahrenholtz, Elevated temperature strength enhancement of ZrB2-30 vol% SiC ceramics by postsintering thermal annealing, J. Am. Ceram. Soc. 99 (2016) 962-970.
of
16. Rudy, Windisch, Related binary systems. Part I, systems V-B, Nb-B and Ta-B, Ternary Phase
ro
Equilibria in Transition Metal-Boron-Carbon-Silicon Systems, vol. X, Air Force Materials Laboratory, Wright-Patterson Air Force Base, 1966, 1–104.
-p
17. Solvas, Jayaseelan, Lin, Brown, Lee, Mechanical properties of ZrB2- and HfB2-based ultra-high
re
temperature ceramics fabricated by spark plasma sintering, J EUR CERAM SOC, 33 (2013),
lP
1373-1386.
na
18. James. Zimmermann, Hilmas, Fahrenholtz, Thermal shock resistance of ZrB2 and ZrB2–30% SiC, MATER CHEM PHY, 112 (2008) 140-145.
Jo ur
19. Xu, Hu, Yan, Lu, Munroe, Xie, Microstructure and mechanical properties of a Mo-toughened Mo3Si-based in situ nanocomposite, Vaccum. 109 (2014) 112-119. 20. Zhu, Luo, Li, Wu, The influence of powder characteristics on mechanical properties of Al2O3-TiC-Co ceramic materials prepared by co-coated Al2O3/TiC powders. Int J Refract Met Hard Mater. 34 (2012) 61-65. 21. Gu, Huang, Zou, Liu, Effect of (Ni,Mo) and TiN on the microstructure and mechanical properties of TiB2 ceramic tool materials, Mater Sci Eng A. 433 (2006) 39-44. 22. Choe, Chen, Schneibel, Ritchie, Ambient to high temperature fracture toughness and fatigue-crack propagation behavior in a Mo-12Si-8.5B (at.%) intermetallic, Intermetallics. 9
Journal Pre-proof
(2001) 319-329. 23. Ashby, Blunt, Bannister, Flow characteristics of highly constrained metal wires, Met. Mater. 37
Jo ur
na
lP
re
-p
ro
of
(1989) 1847.
Journal Pre-proof
Highlight
na
lP
re
-p
ro
of
High dense 30 % (70 % ZrB2 + 30 % SiC)-NbMo composites (98.69%) were hot-pressed. The eutectic phase in 15% (ZrB2 + SiC)-NbMo is attributed to the addition of SiC. The addition of SiC improves the hardness of NbMoss in x (ZrB2 + SiC)-NbMo. The addition of SiC improves the compressive strength of 15% (ZrB2 + SiC)-NbMo.
Jo ur