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Formation and Properties of the Ta-[Y.sub.2][O.sub.3], Ta-Zr[O.sub.2], and Ta-TaC Nanocomposites.

1. Introduction

Refractory materials of the melting point higher than 3000[degrees]C are the most desired in design and manufacturing of heavy load-bearing components where resistance to high temperature and wear plays a crucial role. Additionally, these materials usually have high corrosion resistance in very aggressive environments as well as high mechanical properties [1]. The examples of refractory materials are pure metals such as Ta, W, or Mo and theirs alloys [2]. Other most commonly used refractory materials are ceramics such as oxides (Zr[O.sub.2] and [Y.sub.2][O.sub.3]), carbides (TaC, ZrC, and WC), or nitrides (TiN and Si3N4) [3-5]. Both types of refractory materials, that is, metals and ceramics have found applications in the design of bulk parts or coatings. Due to their high hardness, refractory materials (particularly ceramics) are brittle. Both materials can be joined together in the form of composites, which usually constitutes a combination of the best properties of both the metals and the ceramics [6-8]. Particularly, the high brittleness of ceramics can be limited by the addition of a metallic phase and vice versa, and the addition of ceramic phase into the metallic matrix leads to the improvement of the hardness and wear resistance of refractory metals. Refractory materials require high temperature processes for the formation of materials and products. For example, powder metallurgy requires the sintering temperature of at least 1500[degrees]C (usually above 2000[degrees]C) for proper microcrystalline powder consolidation [9]. Conventional high temperature and longtime sintering processes can be applicable for coarse-grained materials of micrometer size grains. Nanomaterials, compared to microcrystalline ones, can be consolidated for a shorter time and at significantly lower temperatures to achieve optimum properties. The consolidation processes used for nanocrystalline powders are usually different than conventional powder metallurgy used for microcrystalline powders. For example, for the consolidation of nanomaterials, the hot pressing working in the heating mode of the spark plasma sintering (SPS) or pulse plasma sintering (PPS) gives the best results [10, 11]. In these processes of consolidation, both the pressure and the temperature increase simultaneously, which results in a shortening of the time for which the material is kept at a given high sintering temperature, and this process can be done at a significantly lower consolidation temperature compared to conventional pressureless sintering [12]. Both factors (temperature and time) are crucial for the reduction of the grain growth and the maintenance of the nanostructure or ultrafine structure [13]. Differences in the absence of wetting and the densities of the melted metal and ceramic components result in their segregation, which requires special casting techniques [14]. Therefore, powder metallurgy is very useful for the formation of homogeneous composites [15]. In the process of preparation of the refractory composites, the powders of metallic and ceramic components of the designed chemical composition are mixed together and then consolidated using hot pressing, SPS, PPS, or other relevant techniques [16-18]. For the formation of nanocomposite powders, the mechanical alloying process can be applied, in which the reduction of microcrystalline into nanocrystalline grains is provided by high-energy impacts of the balls in the milling vial [19]. In the mechanical alloying process, the final powders' mixture comes in the form of agglomerates of the micrometer or submicrometer size composed of nanometer size grains of metallic as well as ceramic phases uniformly distributed in the entire volume of the material [20].

New prospects for refractory nanomaterials are related to their outstanding mechanical properties [21], whereas high-temperature applications are limited due to excess grain growth at elevated temperatures [22]. At high temperatures, the nanostructure is unstable and grows up, which leads to deterioration of the mechanical properties.

In this work, the authors focus on the preparation and properties of tantalum-based nanocomposites, reinforced by ceramic [Y.sub.2][O.sub.3], Zr[O.sub.2], and TaC. Ta has the melting point of 3017[degrees]C and the density of 16.4 g/[cm.sup.3]. The ceramics have the melting point of 2690, 2715, and 3985[degrees]C for [Y.sub.2][O.sub.3], Zr[O.sub.2], and TaC, respectively. The density of ceramics is 5.03, 5.68, and 14.5 g/[cm.sup.3] for [Y.sub.2][O.sub.3], Zr[O.sub.2], and TaC, respectively. The nanocomposites having 5, 10, 20, and 40 wt.% of the ceramic phase were formed using mechanical alloying and PPS. The paper studies the formation of nanocomposites and their structure, microstructure, and mechanical properties.

2. Materials and Methods

In this work, nanocrystalline Ta-x[Y.sub.2][O.sub.3], Ta-xZr[O.sub.2], and TaxTaC composites (x = 5, 10, 20, and 40 wt.% of the ceramic phase) were synthesized using mechanical alloying (MA) followed by hot pressing in the mode of pulse plasma sintering (PPS). In the MA process, the tantalum powder (<44 [micro]m, purity > 99.97%; Alfa Aesar) was intensely mixed and milled with the [Y.sub.2][O.sub.3] powder (<50nm, purity>99.9%; Sigma-Aldrich) as well as the Zr[O.sub.2] powder (0.1-2 [micro]m, stabilized with 5.4% of [Y.sub.2][O.sub.3]; Goodfellow) and TaC (<45 [micro]m, purity >99.5%; Goodfellow). The mixture of a total of 5.5 g of the metallic and ceramic powders was loaded and reloaded into the milling vial in the Unilab glove box (MBraun) providing a high purity Ar 5.0 atmosphere. For each composite composition, several syntheses were performed to provide material for 5 consolidated samples with 8 mm in diameter and 4 mm in height. In the mechanical alloying process (SPEX 8000M Mixer/Mill; SpexSamplePrep), the two types of powders (Ta + selected ceramic one) were high-energy mixed and milled for 48 h at the room temperature in the Ar 5.0 atmosphere. The steel-hardened vial with ball bearings (>62 HRC) was used for proper mixing. Due to the milling of the ceramic phase, the Fe impurity was introduced to the nanocomposites, but, its content did not exceed 2 wt.%. The as-milled powders were axially hot-pressed (Elbit) at 4 Pa vacuum. The graphite die and the graphite movable punches were coated by boron-nitride lubricant spray (HeBoCoat) during the process. The pressure of the punches directed at the powder was 50 MPa. The pulse plasma sintering mode (PPS) was used for the heating. The heating rate, sintering temperature, and time were set at 650[degrees]C/min, 1300[degrees]C, and 5 s. The other setup parameters for the PPS process were automatically selected to maintain proper heating rate and sintering temperature.

For comparison, the nanocrystalline pure tantalum was made using high-energy ball-milling (HEBM) and PPS. In the MA process, at least two different powders (Ta and ceramic powders) are mixed and milled together, whereas in HEBM, only the one component (Ta powder) is mixed and milled. Both processes were conducted in SPEX mill at the same conditions.

The structure and microstructure were investigated using Empyrean XRD (Panalytical) with CuKa radiation, SEM Vega 5135 (Tescan) with EDS PGT Prism 200 Avalon (Princeton Gamma-Tech), AFM Q-Scope 250 (Quesant), and TEM CM 20 Super Twin (Philips). For the AFM and SEM observations, all the bulk samples were grinded up to 1000 grit, polished in the [Al.sub.2][O.sub.3] suspension, and etched in an [H.sub.2]S[O.sub.4] +HN[O.sub.3] + HF mixture to reveal the grain morphology. More details regarding the above equipment used by the authors have been provided in [23].

The mechanical properties were measured using a Picodentor HM500 (Fischer) nanoindentation tester. The following parameters were measured: HV, Vickers hardness; Err, indentation modulus; CIT1, indentation creep; Wt, total mechanical work of indentation; and Npiast, plastic deformation portion. The indentation force load was 300 mN for 20 s. The load-displacement curves were recorded. For the measurement of the mechanical properties, the authors used unetched samples to avoid incorrect measurement results.

3. Results

The tantalum metal of a cubic structure (Figures 1(a), 2(a), and 3(a)) was mixed and milled with ceramic [Y.sub.2][O.sub.3] (cubic), Zr[O.sub.2](monoclinic), and TaC(cubic) powders (Figures 1(b), 2(b), and 3(b), resp.) of different crystallographic parameters. During the intense milling, the ceramic phase is homogenously distributed in the mixture of powders. For the Ta composites of low ceramic content (Figures 1(c), 2 (c), and 3(c)), the MA process results mainly in the formation of a solid solution or a highly dispersed ceramic phase in the tantalum matrix. No visible peaks of the oxide ceramic phase are present (Figures 1(c) and 2(c)); however, carbides are visible (Figure 3(c)). An increase in the content of the ceramic phase leads to a typical composite structure, showing peaks (tantalum and the ceramic phase) (Figures 1 (d), 2(d), and 3(d)). The consolidation process conducted at an elevated temperature in a graphite die can lead to additional carburization and formation of additional tantalum carbides (Figures 1(e) and 1(f)). High temperature can lead to diffusion of oxygen from the oxides and formation of (Y, Ta) O at a higher ceramic phase content (Figure 1(f)). The made materials are classified as composites, in which the metallic phase coexists with the ceramic phase.

During the milling process, the ceramic phase affects the crystallographic parameters of the tantalum (Figure 4(a)) and vice versa--the tantalum affects the crystallographic parameters of the ceramic phase (Figure 4(b)). The ceramic phase has significantly different lattice parameters compared to tantalum. All the used materials have a cubic-type structure, but the lattice constant for the Ta, [Y.sub.2][O.sub.3], Zr[O.sub.2], and TaC is 3.306, 10.604, 5,065, and 4.456 [Angstrom], respectively. The volume of the unit cell for these materials is 35.127, 1192.365, 129.939, and 88.478 [[Angstrom].sup.3], respectively. Only [Y.sub.2][O.sub.3] of the highest lattice constant leads to an increase in the lattice and volume of the unit cell of the tantalum matrix, whereas Zr[O.sub.2] and TaC participate in a slight reduction of these parameters for tantalum (Figure 4(a)). Alternatively, the tantalum can affect the lattice constant of the ceramic phase (Figure 4(b)) leading to a decrease in the lattice constant and volume of the unit cell, especially for a high [Y.sub.2][O.sub.3] content.

The example TEM images of Ta and Ta-[Y.sub.2][O.sub.3] have been shown in Figure 5. The results confirm the two-phase nanostructure of the composite powders. Ta and the presented Ta-[Y.sub.2][O.sub.3] have a grain size of approximately 40-100 nm. The dark spots, clearly visible in Figures 5(b)-5(d), belong to the [Y.sub.2][O.sub.3] grains that are uniformly distributed in the Ta matrix. Generally, an increase in the [Y.sub.2][O.sub.3] content leads to a tantalum matrix grain size reduction.

The grain size reduction with the increased [Y.sub.2][O.sub.3] content was confirmed in the AFM measurements (Figure 6). The grains of nanocrystalline Ta (170 nm) were estimated earlier [24]. The introduction of nanocrystalline [Y.sub.2][O.sub.3] significantly shifts the grain size towards lower values. For 5% [Y.sub.2][O.sub.3], the average grain size was estimated at 76 nm, whereas for 10, 20, and 40 wt.% of [Y.sub.2][O.sub.3] it changed to 55, 70, and 42 nm, respectively. The increases in the [Y.sub.2][O.sub.3] concentration lead to a narrower grain size distribution as well as a smaller size of the largest grains.

The comparison of the Ta-based composite microstructure with different ceramic phases (all 40 wt.% for [Y.sub.2][O.sub.3], Zr[O.sub.2], and TaC) has been shown in Figure 7. The smallest grains have their composites reinforced with nanocrystalline [Y.sub.2][O.sub.3] (a, b), whereas the largest grains have the composites reinforced with TaC (e, f), but are the most homogenous. As for the tantalum-based composites reinforced with Zr[O.sub.2], they are inhomogeneous and concentrated Zr[O.sub.2] precipitations are present (c).

The average grain size (estimated using AFM) of all the investigated bulk composites has been shown in Figure 8. In all the composites, the grains are smaller in comparison to pure nanocrystalline tantalum. The smallest grains have the composites reinforced with [Y.sub.2][O.sub.3] and Zr[O.sub.2]. Generally, the majority of the composites have the grain size significantly below 100 nm.

The ceramic phase grains are well visible on the TEM images of the powders (Figure 5) and are well identified by AFM in the bulk samples (Figure 9). The example

Composite composition

microstructure of the Ta-20Zr[O.sub.2] bulk nanocomposite shows two-phase morphology (Figure 9(a)), with slightly larger Ta grains (Figure 9(b)) compared to the Zr[O.sub.2] grains (Figure 9(c)). The corresponding EDS spectra show the grain composition of both the metallic and the ceramic phases. On the lower magnified image (Figure 9(a)), the ceramic phase grains are well visible, because after chemical etching, they are flatter compared to the Ta grains (the samples for the microscopic observations were grinded, polished, and chemically etched to reveal the grains, hence, the etched craters among the sintered agglomerate particles).

The mechanical properties (Figure 10, Table 1) show that the nanocrystalline materials have high strength. The hardness of pure microcrystalline Ta (447 HV) is lower compared to pure nanocrystalline Ta (584 HV). An introduction of the reinforced ceramic phase results in an increase in the hardness up to 1398 HV for Ta-10TaC. Up to the 20 wt.% content of the ceramic phase, the hardness remains very high for all the investigated materials: the highest for the Ta-TaC and the lowest for the Ta-Zr[O.sub.2] composites. As for the composites of the 40 wt.% content of the ceramic phase, their content is too high to achieve full material integration at the sintering temperature of 1300[degrees]C (this needs further investigation at a higher consolidation temperature); therefore, the hardness is significantly lower compared to other composites. Young's modulus increases from 164 GPa for nanocrystalline Ta to the highest value of 346 GPa for Ta-40TaC nanocomposites. The other parameters for composites ([W.sub.t], total mechanical work of indentation; [N.sub.plast], plastic deformation portion; and [C.sub.IT], indentation creep) are the highest for the 40 wt.% content of the ceramic phase, pointing to the too low sintering temperature (or time) to achieve full integrity of the samples (especially in the case of oxide-reinforced composites). The load-displacement curves (5 indents made on each sample at different spots) in most cases overlap one another indicating very good homogeneity of the microstructure and uniform material deformation during force loading-unloading. Consequently, the mechanical properties have a low value of standard deviation. At the highest oxide ceramic phase content, the curves have a relatively broad spectrum, which is reflected in the low mechanical properties of these composites.

4. Discussion

The mechanical alloying applied to the tantalum and the ceramic phase particles leads to the formation of nanocrystalline mixture of both tantalum and ceramic grains. The grains have the size of several nanometers. The hot pressing in the PPS mode (performed at an elevated but relatively low temperature) leads to diffusion processes, which is necessary for strong particle bonding. The elevated temperature, however, is also the driving force for the grain growth. The relatively fast heating rate, short sintering time, and low sintering temperature result in a limited grain growth. The large volume of the grain boundaries of the nanocrystalline material should improve the densification process through the sliding mechanism. The agglomerates (formed in the mechanical alloying), which have significant voids between them work against high densification [25]. The pressure acting on the powders when the temperature increases (to the constant sintering temperature) improves the densification and reduces the voids between the consolidated powders. In general, for the densification of the nanocrystalline material, the consolidation temperature can be significantly lower compared to the microcrystalline material [13, 25]. The ceramic phase in the tantalum-based composites can suppress grain growth during consolidation. Hence, all the nanocomposites have a significantly lower grain size compared to pure nanocrystalline tantalum. The higher content (40 wt.%) of the oxide phase acts as a diffusion barrier; thus, in the Ta-40Zr[O.sub.2] and Ta-40[Y.sub.2][O.sub.3] composites, full microstructure integration during hot pressing at given conditions was not obtained. This is reflected in the mechanical properties, which are the worst for the Ta-40Zr[O.sub.2] and Ta-40[Y.sub.2][O.sub.3] composites. The high affinity of tantalum to oxygen leads to the formation of grain boundary oxides that cause embrittlement and grain size growth and the high temperature intensifies this effect [26]. In the case of the Ta-40TaC composite, the aforementioned process is limited. The high-temperature contact of the Ta-based powders with the graphite die and the punches leads to the diffusion of carbon and the formation of tantalum carbides, which was also observed by other authors [27].

The nanocomposites (composed of refractory tantalum as the metal matrix with the embedded refractory ceramic phase such as [Y.sub.2][O.sub.3], Zr[O.sub.2], and TaC) have very high mechanical properties, particularly the nanocrystalline Ta-TaC materials, which are promising in terms of heavy load conditions.

5. Conclusions

In this work, nanocomposites based on the Ta matrix reinforced by the ceramic phase of the [Y.sub.2][O.sub.3], Zr[O.sub.2], and TaC particles were developed. The mechanical alloying followed by hot pressing working in the pulse plasma sintering mode was applied for the bulk nanocomposite formation. We made Ta composites with addition of up to 40% of the ceramic phase. The nanocomposite materials have the average grain size of approximately 40-100 nm, significantly lower than nanocrystalline Ta (170 nm). The lowest grain size has the composites reinforced by oxides. Both reinforced factors, the fine-grained nanostructure and the ceramic phase, lead to significant increase in the hardness as well as Young's modulus. For Ta-10TaC, the hardness and the Young's modulus reach 1398 HV and 336 GPa, respectively. For comparison, pure nanocrystalline Ta has the value of 584 HV and 164 GPa, respectively, whereas microcrystalline Ta has the value of447 HV and 211 GPa, respectively. The combination of the MA and PPS processes has a potential in developing nanocomposites of high mechanical properties.

https://doi.org/10.1155/2018/2085368

Data Availability

The original data files are the property of the Poznan University of Technology and are located in its repository.

Access will be considered by the corresponding author upon request.

Conflicts of Interest

The authors declare that there are no conflicts of interest regarding the publication of this paper.

Acknowledgments

The work has been financed by the National Science Centre, Poland, under project identification DEC-2015/19/B/ST5/02595.

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J. Jakubowicz [ID], (1) M. Sopata, (1) G. Adamek, (1) P. Siwak, (2) and T. Kachlicki (1)

(1) Institute of Materials Science and Engineering, Poznan University of Technology, Jana Pawla II 24, 61-138 Poznan, Poland

(2) Institute of Mechanical Technology, Poznan University of Technology, Piotrowo 3, 60-965 Poznan, Poland

Correspondence should be addressed to J. Jakubowicz; jaroslaw.jakubowicz@put.poznan.pl

Received 19 February 2018; Accepted 9 May 2018; Published 3 June 2018

Academic Editor: Akihiko Kimura

Caption: Figure 1: XRD of the pure Ta (a) and [Y.sub.2][O.sub.3] (b) powders; Ta-5[Y.sub.2][O.sub.3] (c) and Ta-40[Y.sub.2][O.sub.3] (d) nanocomposites' powder mixture after mechanical alloying; and Ta-5[Y.sub.2][O.sub.3] (e) and Ta-40[Y.sub.2][O.sub.3] (f) bulk nanocomposites after consolidation.

Caption: Figure 2: XRD of the pure Ta (a) and Zr[O.sub.2] (b) powders; Ta-5Zr[O.sub.2] (c) and Ta-40Zr[O.sub.2] (d) nanocomposites' powder mixture after mechanical alloying; and Ta-5Zr[O.sub.2] (e) and Ta-40Zr[O.sub.2] (f) bulk nanocomposites after consolidation.

Caption: Figure 3: XRD of the pure Ta (a) and TaC (b) powders; Ta-5TaC (c) and Ta-40TaC (d) nanocomposites' powder mixture after mechanical alloying; and Ta-5TaC (e) and Ta-40TaC (f) bulk nanocomposites after consolidation.

Caption: Figure 4: The effect of the [Y.sub.2][O.sub.3], Zr[O.sub.2], and TaC content in the Ta-x[Y.sub.2][O.sub.3], Ta-xZr[O.sub.2], and Ta-xTaC composites on the Ta lattice constant and the Ta volume of the unit cell (after MA process) (a) and the effect of the Ta content in the Ta-x[Y.sub.2][O.sub.3], Ta-xZr[O.sub.2], and Ta-xTaC composites on the [Y.sub.2][O.sub.3], Zr[O.sub.2], and TaC lattice constant and the volume of the unit cell (b); x = 0, 5, 10, 20, and 40 wt.%.

Caption: Figure 5: TEM images of the mechanically milled nanocrystalline Ta (a) and mechanically alloyed Ta- 5[Y.sub.2][O.sub.3] (b), Ta-10[Y.sub.2][O.sub.3] (c), Ta-20[Y.sub.2][O.sub.3] (d), and Ta-40[Y.sub.2][O.sub.3] (e) nanocomposite powders; the smaller and darker particles correspond to ceramic phase, whereas bigger and lighter to tantalum matrix; the example grains are marked.

Caption: Figure 6: AFM pictures (a, c, e, g) and grain size distribution (b, d, f, h) of the mechanically alloyed and consolidated bulk nanocomposites: Ta-5[Y.sub.2][O.sub.3] (a, b), Ta-10[Y.sub.2][O.sub.3] (c, d), Ta-20[Y.sub.2][O.sub.3] (e, f), and Ta- 40[Y.sub.2][O.sub.3] (g, h).

Caption: Figure 7: Example of SEM (a, c, e) and AFM (b, d, f) images of the consolidated bulk Ta-40[Y.sub.2][O.sub.3] (a, b), Ta-40Zr[O.sub.2] (c, d), and Ta-40TaC (e, f) nanocomposites.

Caption: Figure 8: Average grain size for the Ta-x[Y.sub.2][O.sub.3], Ta-xZr[O.sub.2], and Ta-xTaC bulk nanocomposites (x = 0, 5, 10, 20, and 40 wt.%); data measured using AFM (not all AFM images and grain size distributions have been shown in this paper).

Caption: Figure 10: Load-displacement curves for consolidated bulk nanocrystalline composites: Ta-5[Y.sub.2][O.sub.3] (a), Ta-10[Y.sub.2][O.sub.3] (b), Ta-20[Y.sub.2][O.sub.3] (c), Ta40[Y.sub.2][O.sub.3] (d), Ta-5Zr[O.sub.2] (e), Ta-10Zr[O.sub.2] (f), Ta-20Zr[O.sub.2] (g), Ta-40Zr[O.sub.2] (h), Ta-5TaC (i), Ta-10TaC (j), Ta-20TaC (k), and Ta-40TaC (l); for comparison bulk consolidated nanocrystalline Ta (m) and microcrystalline Ta (n).
Table 1: Mechanical properties of the investigated hot-pressed Ta-
ceramic nanocomposites (data for micro-and nanocrystalline Ta for
comparison).

                                     Mechanical properties

                                    HV              [E.sub.IT] (GPa)

Ta micro                      447 [+ or -] 17         211 [+ or -] 5
Ta nano                       584 [+ or -] 19         164 [+ or -] 8
Ta nanocomposites:
Ta-5[Y.sub.2][O.sub.3]       1055 [+ or -] 23         248 [+ or -] 2
Ta-10[Y.sub.2][O.sub.3]       835 [+ or -] 23         234 [+ or -] 2
Ta-20[Y.sub.2][O.sub.3]      1165 [+ or -] 8          242 [+ or -] 1
Ta-40[Y.sub.2][O.sub.3]       436 [+ or -] 52         114 [+ or -] 10
Ta-5Zr[O.sub.2]               821 [+ or -] 24         231 [+ or -] 4
Ta-10Zr[O.sub.2]              920 [+ or -] 24         240 [+ or -] 8
Ta-20Zr[O.sub.2]             1003 [+ or -] 3          246 [+ or -] 1
Ta-40Zr[O.sub.2]              366 [+ or -] 44         115 [+ or -] 3
Ta-5TaC                       984 [+ or -] 21         273 [+ or -] 3
Ta-10TaC                     1398 [+ or -] 46         336 [+ or -] 5
Ta-20TaC                     1252 [+ or -] 69         303 [+ or -] 11
Ta-40TaC                      994 [+ or -] 48         346 [+ or -] 12

                                     Mechanical properties

                           [W.sub.t] ([micro]J)    [N.sub.plast] (%)

Ta micro                    0.17 [+ or -] 0.01     81.6 [+ or -] 0.5
Ta nano                     0.16 [+ or -] 0.01     71.1 [+ or -] 2.5
Ta nanocomposites:
Ta-5[Y.sub.2][O.sub.3]      0.12 [+ or -] 0.01     63.6 [+ or -] 0.7
Ta-10[Y.sub.2][O.sub.3]     0.14 [+ or -] 0.01     68.7 [+ or -] 0.5
Ta-20[Y.sub.2][O.sub.3]     0.12 [+ or -] 0.01     60.0 [+ or -] 0.2
Ta-40[Y.sub.2][O.sub.3]     0.20 [+ or -] 0.04     70.3 [+ or -] 3.5
Ta-5Zr[O.sub.2]             0.14 [+ or -] 0.01     69.6 [+ or -] 1.0
Ta-10Zr[O.sub.2]            0.13 [+ or -] 0.01     67.3 [+ or -] 0.5
Ta-20Zr[O.sub.2]            0.13 [+ or -] 0.01     64.7 [+ or -] 0.1
Ta-40Zr[O.sub.2]            0.21 [+ or -] 0.02     75.5 [+ or -] 2.6
Ta-5TaC                     0.13 [+ or -] 0.01     67.8 [+ or -] 0.4
Ta-10TaC                    0.11 [+ or -] 0.01     61.6 [+ or -] 0.9
Ta-20TaC                    0.12 [+ or -] 0.01     63.5 [+ or -] 1.2
Ta-40TaC                    0.12 [+ or -] 0.01     70.1 [+ or -] 1.6

                           Mechanical properties

                              [C.sub.IT] (%)

Ta micro                    1.92 [+ or -] 0.08
Ta nano                     1.54 [+ or -] 0.19
Ta nanocomposites:
Ta-5[Y.sub.2][O.sub.3]      1.14 [+ or -] 0.08
Ta-10[Y.sub.2][O.sub.3]     1.56 [+ or -] 0.07
Ta-20[Y.sub.2][O.sub.3]     1.26 [+ or -] 0.03
Ta-40[Y.sub.2][O.sub.3]     1.70 [+ or -] 0.48
Ta-5Zr[O.sub.2]             1.66 [+ or -] 0.08
Ta-10Zr[O.sub.2]            1.72 [+ or -] 0.09
Ta-20Zr[O.sub.2]            1.30 [+ or -] 0.03
Ta-40Zr[O.sub.2]            2.15 [+ or -] 0.17
Ta-5TaC                     1.29 [+ or -] 0.05
Ta-10TaC                    1.01 [+ or -] 0.05
Ta-20TaC                    1.17 [+ or -] 0.07
Ta-40TaC                    2.17 [+ or -] 0.69

HV, Vickers hardness; EIT, indentation modulus; Wt, total mechanical
work of indentation; Nplast, plastic deformation portion; CIT,
indentation creep.

Figure 9: Example AFM images and EDS analysis showing the phase
distribution in the consolidated bulk Ta-20Zr[O.sub.2]
nanocomposite: larger area view (a), magnified area of the Ta
grains (b), and Zr[O.sub.2] grains (c) with the corresponding EDS
analysis.

(kev)

Element    Line     Wt.%      At.%

Ta         LA1       98.61     93.59
Zr         LA1        0.00      0.00
Y          LA1        0.22      0.42
O          KA1        0.00      0.00
Fe         KA1        0.44      1.35
Al         KA1        0.73      4.64
Total               100.00    100.00

(kev)

Element    Line     Wt.%      At.%

Ta         LA1       60.56     36.62
Zr         LA1       33.79     40.54
Y          LA1        0.85      1.05
O          KA1        2.35     16.08
Fe         KA1        2.00      3.92
Al         KA1        0.44      1.79
Total               100.00    100.00
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Title Annotation:Research Article
Author:Jakubowicz, J.; Sopata, M.; Adamek, G.; Siwak, P.; Kachlicki, T.
Publication:Advances in Materials Science and Engineering
Date:Jan 1, 2018
Words:5356
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