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Fabrication and interaction mechanism of Ni-encapsulated ZrO2-toughened Al2O3 powders reinforced high manganese steel composites
Advanced Powder Technology 30 (2019) 2160–2168
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Advanced Powder Technology journal homepage: www.elsevier.com/locate/apt
Original Research Paper
Fabrication and interaction mechanism of Ni-encapsulated ZrO2toughened Al2O3 powders reinforced high manganese steel composites Juanjian Ru a,⇑, Han He b, Yehua Jiang b,⇑, Rong Zhou b, Yixin Hua a,c a
Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, China Faculty of Material Science and Engineering, Kunming University of Science and Technology, Kunming, Yunnan Province 650093, China c State Key Lab of Complex Nonferrous Metal Resources Clean Utilization, Kunming 650093, China b
a r t i c l e
i n f o
Article history: Received 29 November 2018 Received in revised form 9 May 2019 Accepted 27 June 2019 Available online 11 July 2019 Keywords: Interface layer Ni-encapsulated ZTA Electroless deposition Ionic liquid additive High manganese steel composites
a b s t r a c t In order to solve the cast-infiltration difficulty and low interface bonding strength of ZrO2-toughened Al2O3 (ZTA) powders reinforced high manganese steel (HMS) matrix composite, uniform and continuous Ni-encapsulated ZTA powders (ZTAp@Ni) as reinforced phase are fabricated by electroless deposition assisted with ionic liquid additive. The effects of Ethaline concentration, temperature, ZTA concentration and deposition times on the morphology of ZTAp@Ni have been investigated. Experimental results show that the thickness of Ni coating is about 7–10 lm, and there is no casting crack or shrink on the composite, so compact bonding between ceramic and matrix is obtained. In addition, the impact abrasive wear resistance testing demonstrates that the performance of ZTAp@Ni reinforced HMS composite is superior to that of matrix. On the basis of experimental analysis, a schematic illustration of the cast-infiltration process is put forward. It implies that Ni-encapsulated ZTA can be wetted with molten HMS matrix to form a ZTA/Al2NiO4-Al2MnO4/Fe interface layer through Ni diffusion and reactive wetting. The interdiffusion of Ni and other elements at ZTA interface layer can reinforce the interfacial bonding strength to form an interface layer between metal and hard phases. Ó 2019 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
1. Introduction Ceramic particles reinforced high manganese steel composites are widely applied in industrial and technological aspects such as cement production, mineral processing, and wear-resistant tools on account of their high hardness, good fatigue resistant performance and salient wear resistance [1,2]. With its low cost and enhanced fracture toughness, zirconia-toughened alumina (ZTA) is emerging as a promising reinforcement among numerous ceramic particles [3]. Zheng and Sui et al. [4,5] indicated that the existence of ZTA particles among iron-based composites could effectively improve their wear resistance properties. Unfortunately, the bottleneck encountered in fabrication process of abovementioned composites is the mutual exclusion between liquid metal and ceramic phase as a result of their poor wettability. Previous works explicitly indicate that the wettability of zirconia (ZrO2) and alumina (Al2O3) by liquid iron (Fe) are poor [6]. The contact angles of liquid Fe on ZrO2 and Al2O3 reach up to 116° and ⇑ Corresponding authors. E-mail addresses: [email protected] (J. Ru), [email protected] (Y. Jiang).
140°, respectively [7,8]. Undoubtedly, the interfacial bonding between reinforcement and matrix phase plays a key role in the performances of ceramic-reinforced metal matrix composites, including ductility, toughness, and fracture mode. From an interface point of view, the determinant for the wettability by liquid metal is the increase in overall surface energy of ZTA ceramic [9]. Thus, the surface modification of ZTA particles by metals is one of the best effective ways to enhance interfacial bonding strength. The surface modification of ceramic particles can be carried out ordinarily by electroless deposition, ball milling, sol-gel, precipitation deposition and so on [10–13]. Tang et al. [14] reported that active elements Ni and Ti were added to Al2O3/Fe interface and reacted with Al2O3 to obtain tightly bonded composite interface. Mousavian et al. [15] successfully prepared aluminum matrix-SiC composites by hot extrusion process and SiC particles were ball milled firstly with Cr, Cu, and Ti to improve SiC incorporation. Wang et al. [16] reported Ti-coated and Mo-coated SiC particles can be prepared by discharge treatment on a mixture of SiC and metal powders in SPS system. Metal deposition on ceramics has been recognized as an effective technique to form new interface on different materials along with wettability, spreading, diffusion, and adhesion. Electroless plating has been extensively applied in
https://doi.org/10.1016/j.apt.2019.06.031 0921-8831/Ó 2019 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
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surface metallization of conductive and nonconductive materials because of its advantages such as lower cost, uniform deposits, and independency on the electrical properties of materials [17,18]. But there are some inevitable phenomenon, for example large particle size and non-uniform distribution of the coating layer, resulting from the fast reaction rate and poor dispersion of ceramic particles. Therefore, an efficient additive, ionic liquid, has been introduced into the electroless plating process [19]. It has low vapor pressures and melting points, good conductivity, and non-flammability, and many researches have reported the applications of ionic liquid as additive [20]. Herein, Ni-encapsulated ZTA powders (ZTAp@Ni) as precursors to reinforce high manganese steel (HMS) matrix composites are fabricated by electroless deposition assisted with choline chloride-ethylene glycol (Ethaline) ionic liquid. The morphology, phase composition and element distribution of ZTAp@Ni reinforced HMS composite are analyzed. A schematic illustration of the castinfiltration process is proposed to elaborate the interaction mechanism of Ni-encapsulated ZTA and HMS matrix. Besides, the impact abrasive wear resistance of the composite is also compared with matrix material. 2. Experimental 2.1. Chemicals The raw chemicals used in present experiment were purchased with analytical grade (purity > 99.9%) from Aisinaladdin-e.com, China. As shown in Fig. 1, the particle size of ZTA powders was about 150–180 lm and the X-ray diffraction pattern indicated that these powders were composed of Al2O3 and ZrO2, without other forms basically. The specific surface area of ZTA powders was about 2.18 m2g1 tested by Brunauer-Emmett-Teller analysis (Micromeritics ASAP 2060 model). The metal matrix of the composite material in this work was HMS, and the composition and content have been listed in Table 1. 2.2. Fabrication of Ni-encapsulated ZTA powders 2.2.1. Pretreatment of ZTA powders The fabrication of ZTAp@Ni consisted of two steps: pretreatment and electroless deposition. Firstly, ZTA powders were pretreated by washing, coarsening and activation treatment to obtain coarse and catalytic surface, as shown in Table 2. ZTA powders were immersed in an acetone solution for 15 min to clean their surfaces. Then, the powders were coarsen in HNO3 solution. A special activation pretreatment of ZTA particles by Ni(Ac)2containing activator was performed to improve activation effi-
Table 1 The components of high manganese steel matrix. Component
C
Cr
Mn
Fe
wt.%
1.1
2.0
12.0–13.0
Bal.
Table 2 The composition and content of the chemicals used in the pretreatment process. Stage
Composition
Content
Pretreatment process
Washing Coarsening Activation
Acetone HNO3 (37 wt.%) Ni (Ac)2 + NaH2PO2 + C2H6O + H2O
– 40 vol.% 1:1:15:2 (vol. ratio)
15 min 30 min Ultrasonic vibration 10 min, 170 °C for 20 min
ciency and lower cost. After each step mentioned above, these powders were washed with distilled water until pH = 7 and dried in vacuum oven at 353 K for 3 h. 2.2.2. Ionic liquid assisted deposition of Ni coatings on ZTA powders The Ethaline ionic liquid assisted electroless plating of Ni on ZTA powders was carried out in a cylindrical electroless bath (13.0 cm in diameter and 15.0 cm in height). Homogeneous and colorless Ethaline additive was obtained by mixing choline chloride and ethylene glycol (molar ratio 1:2) at 80 °C, as described in previous report [21]. The composition of chemicals and operating parameters were presented in Table 3. The electroless plating was performed in a nickel bath containing nickel sulfate (NiSO46H2O) as main salt, sodium hypophosphite (NaH2PO2H2O) as reducing agent, acid boric (H3BO3) as buffer, tri-sodium citrate
Table 3 Chemical composition of the electroless nickel plating bath and operating parameters. Role in bath or operating parameters
Composition
Concentration or conditions
Main salt
Nickel sulfate (NiSO46H2O) Sodium hypophosphite (NaH2PO2H2O) Tri-sodium citrate (C6H5Na3O72H2O) Acid boric (H3BO3) Ionic liquid (Ethaline) Sodium hydroxide (NaOH) – – – –
40 g/L
Reducing agent Complexing agent Buffering agent Addictive pH adjuster ZTA powders Mechanical stirring Temperature pH
Fig. 1. (a, b) SEM micrograph and (c) X-ray diffraction pattern of ZTA powders.
24 g/L 28 g/L 18 g/L 0–60 g/L To adjust pH 60–180 g/L 500 rpm 60–80 °C 8–9
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(C6H5Na3O72H2O) as complexing agent and activated ZTA particles. The effects of Ethaline concentration, reaction temperature, ZTA concentration, and reaction times were discussed. All procedures were performed with a mechanical stirring speed of 500 rpm, and the Reynolds (Re) number was calculated about 1.07 104. In addition, the samples after electroless plating were washed with distilled water for several times to neutral, filtrated and dried in a vacuum oven at 353 K for 3 h. 2.3. Preparation of HMS matrix composites The ZTAp@Ni reinforced HMS matrix composites were prepared by cast-infiltration technology. The ZTAp@Ni were blended with a homemade binder to form a honeycombed preform, as previously reported [22]. There were many cylindrical vacancies throughout the ceramic bulk which benefits to the infiltration process of metal matrix. The pouring temperature of HMS melt was controlled at 1480–1550 °C. 2.4. Measurement and characterization The impact abrasive wear resistance properties of the HMS matrix and ZTAp@Ni reinforced composites were measured by dynamic load abrasion testing (MLD-10 model). The size of the abrasion specimen was 9 mm 9 mm 30 mm. The quartz sand (0.85–1.70 mm) was used as abrasive and the sand flow was 80 kgh1. The testing was run for 80 min and the quartz sand was replaced with a new sample after 20 min. The wear loses were determined by the volume loss technique. So, the specimen after every abrasion testing was washed with distilled water, dried and recorded the weight loss. The density of the composite qcom can be calculated by Eq. (1), where VZTA and qZTA were the volume fraction and density of the ZTA powders in 24.3% and 4.3 gcm3, respectively; Vmatrix and qmatrix were the volume fraction and density of the matrix in 75.7% and 7.9 gcm3, respectively.
qcom ¼ V ZTA qZTA þ V matrix qmatrixnn
ð1Þ
The morphology, cross section and elemental constituents of the samples were examined by SEM and EDS (TESCAN VEGA 3 and ZEISS model, HV 20 kV). The cross section of the sample was prepared by encasing the ZTAp@Ni in resin, followed by mechanical polishing. The composite specimen with dimensions of 10 mm 10 mm 30 mm was sectioned from the middle portion of the cast material and polished according to standard metallographic techniques. Then the specimen was etched with 4% FeCl3 solution and examined by Metallographic Microscope (Leica EZ4D model). The composite phases were analyzed by XRD (D/ Max-2200 model) with Cu Ka radiation at a scan rate of 10°min1 in the range of 2h = 10–90°. 3. Results and discussion 3.1. Fabrication of Ni-encapsulated ZTA powders 3.1.1. Effect of Ethaline concentration The effect of Ethaline additive on the morphology of ZTAp@Ni fabricated by electroless deposition are presented in Fig. 2. From Fig. 2a and a0 , small amount of Ni grains are deposited on ZTA surface without the addition of Ethaline. But lots of spherical Ni grains have been observed in the plating bath which can be attributed to the too fast reaction rate and there is no enough time for the nucleation and growth of Ni grains on ZTA powders. When the Ethaline concentration is 20 gL1, the Ni-encapsulation of ZTA powders is uncompleted and some ZTA surface are still exposed (Fig. 2b and b0 ). At 40 gL1, continuous and compact Ni coatings on ZTA surface
are obtained and almost no Ni grains fall off from the surface, as shown in Fig. 2c and c0 . When the Ethaline concentration is elevated to 60 gL1, Ni coatings are compact while the reaction time is very long due to the inhibition effect of Ethaline on reaction rate. Therefore, uniform ZTAp@Ni can be prepared by electroless deposition assisted with 40 gL1 Ethaline additive. 3.1.2. Effect of reaction temperature Fig. 3 is the morphologies of ZTAp@Ni fabricated by electroless deposition at different reaction temperatures. As clearly can be seen, the Ni coatings on ZTA surface are compact at 50–60 °C, and the particle size of Ni grains is about 200–400 nm (Fig. 3a– b0 ). But during the plating process, the incubation period is very long resulting from the lower reaction temperature. At 70 °C, the incubation period is significantly shorten and uniform ZTAp@Ni also can be obtained (Fig. 3cc0 and Fig. S1). When the temperature is elevated to 80 °C, the fast reaction rate leads to poor adhesion between the Ni grains and ZTA surface, as illustrated in Fig. 3d and d0 . Based on above analysis, compact ZTAp@Ni with short incubation period is obtained at 70 °C. 3.1.3. Effect of ZTA concentration The morphologies of ZTAp@Ni fabricated by electroless deposition with different ZTA loading capacities are shown in Fig. 4. From Fig. 4a–c0 , continuous and compact Ni coatings on ZTA surface are observed when the ZTA concentration is in the range of 60– 150 gL1. However, Ni coating is porous with poor adhesion and some Ni grains drop into the plating bath leading to the uncompleted encapsulation of ZTA powders (Fig. 4d and d0 ). The ratio of Ni concentration to surface area of ZTA was calculated, as shown in Table 4. When the ZTA concentration is increased, the ratio of Ni concentration to the surface area of ZTA is decreased at a constant Ni2+ ion concentration. The increased surface area of ZTA powders can effectively increase their nucleation sites, so that the particle size of Ni grains is finer as well as thin coating layer. Thus, the ZTA concentration of 150 gL1 is chosen as the optimum level to prepare ZTAp@Ni by electroless plating. 3.1.4. Effect of deposition times Fig. 5 is the morphologies of ZTAp@Ni fabricated by electroless deposition with different deposition times. From Fig. 5a–c0 , uniform and compact Ni coatings on ZTA surface are formed when the deposition times are increased from 1 times to 3 times. At 5 deposition times, the surface morphology of ZTAp@Ni is similar with that obtained after 4 times. The XRD results of the ZTAp@Ni are presented in Fig. 6. The main phases of the samples are Al2O3 (JCPDS card 46-1212), ZrO2 (JCPDS card 65-1022, 81-1544) and metallic Ni (JCPDS card 65-2865). By contrast, the peak intensity of metallic Ni is increased with the increase of deposition times (the red1 dashed box) which implies that the thickness of Ni coating layer is increased as deposition times. Fig. 7 is SEM and EDS micrographs of the cross section of ZTAp@Ni fabricated with 5 times deposition. It can be seen that Ni coating layer is 7–10 lm in thickness and the surface layer around the ZTA particle is metallic Ni. 3.2. Interaction mechanism of ZTAp@Ni reinforced HMS matrix composite The morphologies of ZTAp@Ni reinforced HMS matrix composite are shown in Fig. 8. Uniform distribution of ZTA powders into HMS matrix can be observed and there is no cracks, pores and shrinks (Fig. 8a and d). The as-cast microstructure of HMS includes
1 For interpretation of color in Fig. 6, the reader is referred to the web version of this article.
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Fig. 2. SEM micrographs of ZTAp@Ni fabricated by electroless deposition assisted with different Ethaline concentrations: (a, a0 ) 0 gL1, (b, b0 ) 20 gL1, (c, c0 ) 40 gL1, (d, d0 ) 60 gL1. T = 70 °C, CNiSO4 = 40 gL1, CZTA = 50 gL1.
Fig. 3. SEM micrographs of ZTAp@Ni fabricated by electroless deposition at different reaction temperatures: (a, a0 ) 50 °C, (b, b0 ) 60 °C, (c, c0 ) 70 °C, (d, d0 ) 80 °C. CNiSO4 = 40 gL1, CEthaline = 30 gL1, CZTA = 50 gL1.
austenite and net-like carbides precipitated along crystal boundary, mainly M3C. From the interface between HMS matrix and the compound region (Fig. 8b), it is found that austenite grain size of the composite is decreased significantly compared to that of HMS matrix. This can be explained by the large temperature difference between ZTA powders and molten iron. It leads to fast crystallization rate and refine austenite grains. Besides, the diffusion of Ni grains originated from Ni coatings on ZTA surface can also effectively enhance the nucleation rate of molten iron nearby ZTA powders. From Fig. 8c and e–g, obvious interface layer is formed in the
thickness of about 2.35 lm. The EDS analysis of ZTAp@Ni reinforced HMS matrix composite is illustrated in Fig. 9. By comparison, it can be observed that elements Ni, Mn and O are diffused with each other at the interface. The diffusion processes include: diffusion of element Ni from ZTA surface to HMS matrix, diffusion of element O from ZTA to HMS matrix, and diffusion of element Mn from HMS matrix to ZTA surface. According to Ref. [23], nickel aluminate spinel (Al2NiO4) can be formed at the interface of Al2O3 phase and Ni phase at high casting temperature, as presented in Eq. (2). For HMS matrix, molten iron
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Fig. 4. SEM micrographs of ZTAp@Ni fabricated by electroless deposition with different ZTA concentration: (a, a0 ) 60 gL1, (b, b0 ) 100 gL1, (c, c0 ) 150 gL1, (d, d0 ) 180 gL1. T = 70 °C, CNiSO4 = 40 gL1, CEthaline = 30 gL1.
Table 4 Ratio of the Ni concentration C2+ Ni to the surface area of ZTA SZTA. ZTA concentration/gL1 C2+ Ni :
SZTA/(gL
1
2
): (m g
1
)
60
100
150
180
63.49
38.10
25.40
21.16
matrix is easily infiltrated onto ZTA surface during the casting process due to the same crystal structure of Ni and austenitic highmanganese steel. Except for the generation of Al2NiO4, interdiffusion of element Ni and molten iron, element Mn diffuses from ZTA surface into HMS matrix, which can react with Al2O3 to form nickel manganese spinel (Al2MnO4), as shown in Eq. (3) [24]. However, the formation of large amount of interfacial products may result in volume expansion of composite which is not beneficial to the combination of ceramic phase and matrix phase. On the con-
trary, a slight interface reaction is useful in improving the wettability between ceramic and matrix [4,25]. In addition, the distribution of element Ni at the interface is totally different from the Ni coating layer on ZTA surface after electroless (Fig. 2). This can be explained by the diffusion of molten Ni grains into HMS matrix to bond with each other by diffuse interface when ZTAp@Ni is contacted with high-temperature molten iron.
Al2 O3 + Ni + O ! Al2 NiO4
ð2Þ
Al2 O3 + Mn + O ! Al2 MnO4
ð3Þ
Therefore, the schematic illustration of ZTA@Ni performs and molten HMS matrix during the cast-infiltration process is put forward in Fig. 10. At the initial stage, when Ni grains nearby ZTA surface are touched with molten HMS, they will become soft and
Fig. 5. SEM micrographs of ZTAp@Ni fabricated by electroless deposition with different deposition times: (a–a0 ) 1 times, (b–b0 ) 2 times, (c–c0 ) 3 times, (d–d0 ) 4 times, (e–e0 ) 5 times. T = 70 °C, CNiSO4 = 40 gL1, CEthaline = 30 gL1, CZTA = 50 gL1.
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small amount of Al2NiO4 and Al2MnO4 may be formed on ZTA/Fe interface, which can be wetted easily with molten HMS to achieve good wettability on the ZTA/Al2NiO4- Al2MnO4/Fe interface (Fig. 10c). Thus, the interface of ZTAp@Ni reinforced HMS matrix composite is constructed through mechanical bonding, interdiffusion of elements and small amount of reactive wetting.
3.3. Impact abrasive wear resistance
Fig. 6. XRD analysis of ZTAp@Ni fabricated by electroless deposition: (a) 1 times, (b) 3 times, (c) 5 times. T = 70 °C, CNiSO4 = 40 gL1, CEthaline = 30 gL1, CZTA = 50 gL1. Insert: the magnification of (a–c) and the peak intensity of metal Ni.
migrate into HMS matrix (Fig. 10a) and the empty surface of ZTA is occupied by fluent iron. Meanwhile, because metallic Ni has the same crystal structure as austenitic HMS, it is easy to form infinitude solid solution with Fe. This is in favor of the interdiffusion of Ni grains and alloying elements between ZTA surface and HMS matrix during the cast-infiltration process, so that the wettability of ceramic and matrix can be improved (Fig. 10b). In addition,
The volume loss of ZTAp@Ni reinforced HMS matrix composites and the matrix after impact abrasive wear is shown in Fig. 11. From Fig. 11a and b, both of the matrix and composite materials have large volume loss in every testing process, but the impact abrasive wear resistance performance of ZTAp@Ni reinforced composite is more excellent. Fig. 11c–f is the surface morphologies of the composites and matrix after impact abrasive wear. The traces and dropped layers formed by abrasive are found on wearing surface of the HMS matrix (Fig. 11c and d). Due to high hardness of quartz sands compared with that of HMS matrix, deep grooves and plastic deformation are generated. While, the ZTAp@Ni reinforced HMS matrix composites after impact abrasive wear is completely different (Fig. 11e and f). In such case, major loads are transferred from matrix to ZTA powders. The ZTA powders play an important role in protection of metal matrix from impact abrasive wear of quartz sands. There is no serious scratches, pit defects and embedding of abrasive powders at the composite region. After a long time of impact, although brittle fracture of some protrusive ZTA powders on matrix surface are observed, the remaining parts are still tightly bonded with the matrix. So, surrounding metal matrix effectively support ZTA powders, avoiding the totally debonding of them. As mentioned above, the interdiffusion of Ni and alloys elements at the interface layer can reinforce the interfacial bonding strength to form a diffuse interface layer between metal and hard phases.
Fig. 7. SEM and EDS micrographs of the cross section of the ZTAp@Ni fabricated by electroless deposition with 5 times deposition. T = 70 °C, CNiSO4 = 40 gL1, CEthaline = 30 gL1, CZTA = 50 gL1.
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Fig. 8. Morphologies of the ZTAp@Ni reinforced HMS matrix composite. (a–c) optical photographs, (d-g) SEM micrographs.
Fig. 9. EDS analysis of the ZTAp@Ni/HMS matrix composite.
Fig. 10. Schematic illustration of ZTAp@Ni performs and molten HMS during the cast-infiltration process.
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Fig. 11. (a) Volume loss of every testing process and (b) overall volume loss; SEM micrographs of (c and d) HMS matrix material, (e and f) ZTAp@Ni reinforced HMS matrix composites after impact abrasive wear.
4. Conclusions (1) ZTA powders are successfully encapsulated by Ni coatings through electroless plating assisted with Ethaline additive. Dense and uniform Ni coating with a thickness of 7–10 lm is obtained with 40 gL1 Ethaline additive and 150 gL1 ZTA concentration in the bath at 70 °C. (2) ZTAp@Ni reinforced HMS matrix composites with good interfacial bonding are prepared by nonpressure casting infiltration. Impact abrasive wear resistance testing shows that the abrasive wear resistance of the composite are greatly enhanced. (3) The interaction mechanism of Ni-encapsulated ZTA and HMS matrix is analyzed, and a schematic illustration of the castinfiltration process is put forward. It elaborates that a ZTA/ Al2NiO4-Al2MnO4/Fe interface layer is formed through Ni diffusion and reactive wetting, which can greatly reinforce the bonding strength of composites.
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Contents lists available at ScienceDirect
Advanced Powder Technology journal homepage: www.elsevier.com/locate/apt
Original Research Paper
Fabrication and interaction mechanism of Ni-encapsulated ZrO2toughened Al2O3 powders reinforced high manganese steel composites Juanjian Ru a,⇑, Han He b, Yehua Jiang b,⇑, Rong Zhou b, Yixin Hua a,c a
Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, China Faculty of Material Science and Engineering, Kunming University of Science and Technology, Kunming, Yunnan Province 650093, China c State Key Lab of Complex Nonferrous Metal Resources Clean Utilization, Kunming 650093, China b
a r t i c l e
i n f o
Article history: Received 29 November 2018 Received in revised form 9 May 2019 Accepted 27 June 2019 Available online 11 July 2019 Keywords: Interface layer Ni-encapsulated ZTA Electroless deposition Ionic liquid additive High manganese steel composites
a b s t r a c t In order to solve the cast-infiltration difficulty and low interface bonding strength of ZrO2-toughened Al2O3 (ZTA) powders reinforced high manganese steel (HMS) matrix composite, uniform and continuous Ni-encapsulated ZTA powders (ZTAp@Ni) as reinforced phase are fabricated by electroless deposition assisted with ionic liquid additive. The effects of Ethaline concentration, temperature, ZTA concentration and deposition times on the morphology of ZTAp@Ni have been investigated. Experimental results show that the thickness of Ni coating is about 7–10 lm, and there is no casting crack or shrink on the composite, so compact bonding between ceramic and matrix is obtained. In addition, the impact abrasive wear resistance testing demonstrates that the performance of ZTAp@Ni reinforced HMS composite is superior to that of matrix. On the basis of experimental analysis, a schematic illustration of the cast-infiltration process is put forward. It implies that Ni-encapsulated ZTA can be wetted with molten HMS matrix to form a ZTA/Al2NiO4-Al2MnO4/Fe interface layer through Ni diffusion and reactive wetting. The interdiffusion of Ni and other elements at ZTA interface layer can reinforce the interfacial bonding strength to form an interface layer between metal and hard phases. Ó 2019 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
1. Introduction Ceramic particles reinforced high manganese steel composites are widely applied in industrial and technological aspects such as cement production, mineral processing, and wear-resistant tools on account of their high hardness, good fatigue resistant performance and salient wear resistance [1,2]. With its low cost and enhanced fracture toughness, zirconia-toughened alumina (ZTA) is emerging as a promising reinforcement among numerous ceramic particles [3]. Zheng and Sui et al. [4,5] indicated that the existence of ZTA particles among iron-based composites could effectively improve their wear resistance properties. Unfortunately, the bottleneck encountered in fabrication process of abovementioned composites is the mutual exclusion between liquid metal and ceramic phase as a result of their poor wettability. Previous works explicitly indicate that the wettability of zirconia (ZrO2) and alumina (Al2O3) by liquid iron (Fe) are poor [6]. The contact angles of liquid Fe on ZrO2 and Al2O3 reach up to 116° and ⇑ Corresponding authors. E-mail addresses: [email protected] (J. Ru), [email protected] (Y. Jiang).
140°, respectively [7,8]. Undoubtedly, the interfacial bonding between reinforcement and matrix phase plays a key role in the performances of ceramic-reinforced metal matrix composites, including ductility, toughness, and fracture mode. From an interface point of view, the determinant for the wettability by liquid metal is the increase in overall surface energy of ZTA ceramic [9]. Thus, the surface modification of ZTA particles by metals is one of the best effective ways to enhance interfacial bonding strength. The surface modification of ceramic particles can be carried out ordinarily by electroless deposition, ball milling, sol-gel, precipitation deposition and so on [10–13]. Tang et al. [14] reported that active elements Ni and Ti were added to Al2O3/Fe interface and reacted with Al2O3 to obtain tightly bonded composite interface. Mousavian et al. [15] successfully prepared aluminum matrix-SiC composites by hot extrusion process and SiC particles were ball milled firstly with Cr, Cu, and Ti to improve SiC incorporation. Wang et al. [16] reported Ti-coated and Mo-coated SiC particles can be prepared by discharge treatment on a mixture of SiC and metal powders in SPS system. Metal deposition on ceramics has been recognized as an effective technique to form new interface on different materials along with wettability, spreading, diffusion, and adhesion. Electroless plating has been extensively applied in
https://doi.org/10.1016/j.apt.2019.06.031 0921-8831/Ó 2019 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
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surface metallization of conductive and nonconductive materials because of its advantages such as lower cost, uniform deposits, and independency on the electrical properties of materials [17,18]. But there are some inevitable phenomenon, for example large particle size and non-uniform distribution of the coating layer, resulting from the fast reaction rate and poor dispersion of ceramic particles. Therefore, an efficient additive, ionic liquid, has been introduced into the electroless plating process [19]. It has low vapor pressures and melting points, good conductivity, and non-flammability, and many researches have reported the applications of ionic liquid as additive [20]. Herein, Ni-encapsulated ZTA powders (ZTAp@Ni) as precursors to reinforce high manganese steel (HMS) matrix composites are fabricated by electroless deposition assisted with choline chloride-ethylene glycol (Ethaline) ionic liquid. The morphology, phase composition and element distribution of ZTAp@Ni reinforced HMS composite are analyzed. A schematic illustration of the castinfiltration process is proposed to elaborate the interaction mechanism of Ni-encapsulated ZTA and HMS matrix. Besides, the impact abrasive wear resistance of the composite is also compared with matrix material. 2. Experimental 2.1. Chemicals The raw chemicals used in present experiment were purchased with analytical grade (purity > 99.9%) from Aisinaladdin-e.com, China. As shown in Fig. 1, the particle size of ZTA powders was about 150–180 lm and the X-ray diffraction pattern indicated that these powders were composed of Al2O3 and ZrO2, without other forms basically. The specific surface area of ZTA powders was about 2.18 m2g1 tested by Brunauer-Emmett-Teller analysis (Micromeritics ASAP 2060 model). The metal matrix of the composite material in this work was HMS, and the composition and content have been listed in Table 1. 2.2. Fabrication of Ni-encapsulated ZTA powders 2.2.1. Pretreatment of ZTA powders The fabrication of ZTAp@Ni consisted of two steps: pretreatment and electroless deposition. Firstly, ZTA powders were pretreated by washing, coarsening and activation treatment to obtain coarse and catalytic surface, as shown in Table 2. ZTA powders were immersed in an acetone solution for 15 min to clean their surfaces. Then, the powders were coarsen in HNO3 solution. A special activation pretreatment of ZTA particles by Ni(Ac)2containing activator was performed to improve activation effi-
Table 1 The components of high manganese steel matrix. Component
C
Cr
Mn
Fe
wt.%
1.1
2.0
12.0–13.0
Bal.
Table 2 The composition and content of the chemicals used in the pretreatment process. Stage
Composition
Content
Pretreatment process
Washing Coarsening Activation
Acetone HNO3 (37 wt.%) Ni (Ac)2 + NaH2PO2 + C2H6O + H2O
– 40 vol.% 1:1:15:2 (vol. ratio)
15 min 30 min Ultrasonic vibration 10 min, 170 °C for 20 min
ciency and lower cost. After each step mentioned above, these powders were washed with distilled water until pH = 7 and dried in vacuum oven at 353 K for 3 h. 2.2.2. Ionic liquid assisted deposition of Ni coatings on ZTA powders The Ethaline ionic liquid assisted electroless plating of Ni on ZTA powders was carried out in a cylindrical electroless bath (13.0 cm in diameter and 15.0 cm in height). Homogeneous and colorless Ethaline additive was obtained by mixing choline chloride and ethylene glycol (molar ratio 1:2) at 80 °C, as described in previous report [21]. The composition of chemicals and operating parameters were presented in Table 3. The electroless plating was performed in a nickel bath containing nickel sulfate (NiSO46H2O) as main salt, sodium hypophosphite (NaH2PO2H2O) as reducing agent, acid boric (H3BO3) as buffer, tri-sodium citrate
Table 3 Chemical composition of the electroless nickel plating bath and operating parameters. Role in bath or operating parameters
Composition
Concentration or conditions
Main salt
Nickel sulfate (NiSO46H2O) Sodium hypophosphite (NaH2PO2H2O) Tri-sodium citrate (C6H5Na3O72H2O) Acid boric (H3BO3) Ionic liquid (Ethaline) Sodium hydroxide (NaOH) – – – –
40 g/L
Reducing agent Complexing agent Buffering agent Addictive pH adjuster ZTA powders Mechanical stirring Temperature pH
Fig. 1. (a, b) SEM micrograph and (c) X-ray diffraction pattern of ZTA powders.
24 g/L 28 g/L 18 g/L 0–60 g/L To adjust pH 60–180 g/L 500 rpm 60–80 °C 8–9
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(C6H5Na3O72H2O) as complexing agent and activated ZTA particles. The effects of Ethaline concentration, reaction temperature, ZTA concentration, and reaction times were discussed. All procedures were performed with a mechanical stirring speed of 500 rpm, and the Reynolds (Re) number was calculated about 1.07 104. In addition, the samples after electroless plating were washed with distilled water for several times to neutral, filtrated and dried in a vacuum oven at 353 K for 3 h. 2.3. Preparation of HMS matrix composites The ZTAp@Ni reinforced HMS matrix composites were prepared by cast-infiltration technology. The ZTAp@Ni were blended with a homemade binder to form a honeycombed preform, as previously reported [22]. There were many cylindrical vacancies throughout the ceramic bulk which benefits to the infiltration process of metal matrix. The pouring temperature of HMS melt was controlled at 1480–1550 °C. 2.4. Measurement and characterization The impact abrasive wear resistance properties of the HMS matrix and ZTAp@Ni reinforced composites were measured by dynamic load abrasion testing (MLD-10 model). The size of the abrasion specimen was 9 mm 9 mm 30 mm. The quartz sand (0.85–1.70 mm) was used as abrasive and the sand flow was 80 kgh1. The testing was run for 80 min and the quartz sand was replaced with a new sample after 20 min. The wear loses were determined by the volume loss technique. So, the specimen after every abrasion testing was washed with distilled water, dried and recorded the weight loss. The density of the composite qcom can be calculated by Eq. (1), where VZTA and qZTA were the volume fraction and density of the ZTA powders in 24.3% and 4.3 gcm3, respectively; Vmatrix and qmatrix were the volume fraction and density of the matrix in 75.7% and 7.9 gcm3, respectively.
qcom ¼ V ZTA qZTA þ V matrix qmatrixnn
ð1Þ
The morphology, cross section and elemental constituents of the samples were examined by SEM and EDS (TESCAN VEGA 3 and ZEISS model, HV 20 kV). The cross section of the sample was prepared by encasing the ZTAp@Ni in resin, followed by mechanical polishing. The composite specimen with dimensions of 10 mm 10 mm 30 mm was sectioned from the middle portion of the cast material and polished according to standard metallographic techniques. Then the specimen was etched with 4% FeCl3 solution and examined by Metallographic Microscope (Leica EZ4D model). The composite phases were analyzed by XRD (D/ Max-2200 model) with Cu Ka radiation at a scan rate of 10°min1 in the range of 2h = 10–90°. 3. Results and discussion 3.1. Fabrication of Ni-encapsulated ZTA powders 3.1.1. Effect of Ethaline concentration The effect of Ethaline additive on the morphology of ZTAp@Ni fabricated by electroless deposition are presented in Fig. 2. From Fig. 2a and a0 , small amount of Ni grains are deposited on ZTA surface without the addition of Ethaline. But lots of spherical Ni grains have been observed in the plating bath which can be attributed to the too fast reaction rate and there is no enough time for the nucleation and growth of Ni grains on ZTA powders. When the Ethaline concentration is 20 gL1, the Ni-encapsulation of ZTA powders is uncompleted and some ZTA surface are still exposed (Fig. 2b and b0 ). At 40 gL1, continuous and compact Ni coatings on ZTA surface
are obtained and almost no Ni grains fall off from the surface, as shown in Fig. 2c and c0 . When the Ethaline concentration is elevated to 60 gL1, Ni coatings are compact while the reaction time is very long due to the inhibition effect of Ethaline on reaction rate. Therefore, uniform ZTAp@Ni can be prepared by electroless deposition assisted with 40 gL1 Ethaline additive. 3.1.2. Effect of reaction temperature Fig. 3 is the morphologies of ZTAp@Ni fabricated by electroless deposition at different reaction temperatures. As clearly can be seen, the Ni coatings on ZTA surface are compact at 50–60 °C, and the particle size of Ni grains is about 200–400 nm (Fig. 3a– b0 ). But during the plating process, the incubation period is very long resulting from the lower reaction temperature. At 70 °C, the incubation period is significantly shorten and uniform ZTAp@Ni also can be obtained (Fig. 3cc0 and Fig. S1). When the temperature is elevated to 80 °C, the fast reaction rate leads to poor adhesion between the Ni grains and ZTA surface, as illustrated in Fig. 3d and d0 . Based on above analysis, compact ZTAp@Ni with short incubation period is obtained at 70 °C. 3.1.3. Effect of ZTA concentration The morphologies of ZTAp@Ni fabricated by electroless deposition with different ZTA loading capacities are shown in Fig. 4. From Fig. 4a–c0 , continuous and compact Ni coatings on ZTA surface are observed when the ZTA concentration is in the range of 60– 150 gL1. However, Ni coating is porous with poor adhesion and some Ni grains drop into the plating bath leading to the uncompleted encapsulation of ZTA powders (Fig. 4d and d0 ). The ratio of Ni concentration to surface area of ZTA was calculated, as shown in Table 4. When the ZTA concentration is increased, the ratio of Ni concentration to the surface area of ZTA is decreased at a constant Ni2+ ion concentration. The increased surface area of ZTA powders can effectively increase their nucleation sites, so that the particle size of Ni grains is finer as well as thin coating layer. Thus, the ZTA concentration of 150 gL1 is chosen as the optimum level to prepare ZTAp@Ni by electroless plating. 3.1.4. Effect of deposition times Fig. 5 is the morphologies of ZTAp@Ni fabricated by electroless deposition with different deposition times. From Fig. 5a–c0 , uniform and compact Ni coatings on ZTA surface are formed when the deposition times are increased from 1 times to 3 times. At 5 deposition times, the surface morphology of ZTAp@Ni is similar with that obtained after 4 times. The XRD results of the ZTAp@Ni are presented in Fig. 6. The main phases of the samples are Al2O3 (JCPDS card 46-1212), ZrO2 (JCPDS card 65-1022, 81-1544) and metallic Ni (JCPDS card 65-2865). By contrast, the peak intensity of metallic Ni is increased with the increase of deposition times (the red1 dashed box) which implies that the thickness of Ni coating layer is increased as deposition times. Fig. 7 is SEM and EDS micrographs of the cross section of ZTAp@Ni fabricated with 5 times deposition. It can be seen that Ni coating layer is 7–10 lm in thickness and the surface layer around the ZTA particle is metallic Ni. 3.2. Interaction mechanism of ZTAp@Ni reinforced HMS matrix composite The morphologies of ZTAp@Ni reinforced HMS matrix composite are shown in Fig. 8. Uniform distribution of ZTA powders into HMS matrix can be observed and there is no cracks, pores and shrinks (Fig. 8a and d). The as-cast microstructure of HMS includes
1 For interpretation of color in Fig. 6, the reader is referred to the web version of this article.
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Fig. 2. SEM micrographs of ZTAp@Ni fabricated by electroless deposition assisted with different Ethaline concentrations: (a, a0 ) 0 gL1, (b, b0 ) 20 gL1, (c, c0 ) 40 gL1, (d, d0 ) 60 gL1. T = 70 °C, CNiSO4 = 40 gL1, CZTA = 50 gL1.
Fig. 3. SEM micrographs of ZTAp@Ni fabricated by electroless deposition at different reaction temperatures: (a, a0 ) 50 °C, (b, b0 ) 60 °C, (c, c0 ) 70 °C, (d, d0 ) 80 °C. CNiSO4 = 40 gL1, CEthaline = 30 gL1, CZTA = 50 gL1.
austenite and net-like carbides precipitated along crystal boundary, mainly M3C. From the interface between HMS matrix and the compound region (Fig. 8b), it is found that austenite grain size of the composite is decreased significantly compared to that of HMS matrix. This can be explained by the large temperature difference between ZTA powders and molten iron. It leads to fast crystallization rate and refine austenite grains. Besides, the diffusion of Ni grains originated from Ni coatings on ZTA surface can also effectively enhance the nucleation rate of molten iron nearby ZTA powders. From Fig. 8c and e–g, obvious interface layer is formed in the
thickness of about 2.35 lm. The EDS analysis of ZTAp@Ni reinforced HMS matrix composite is illustrated in Fig. 9. By comparison, it can be observed that elements Ni, Mn and O are diffused with each other at the interface. The diffusion processes include: diffusion of element Ni from ZTA surface to HMS matrix, diffusion of element O from ZTA to HMS matrix, and diffusion of element Mn from HMS matrix to ZTA surface. According to Ref. [23], nickel aluminate spinel (Al2NiO4) can be formed at the interface of Al2O3 phase and Ni phase at high casting temperature, as presented in Eq. (2). For HMS matrix, molten iron
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Fig. 4. SEM micrographs of ZTAp@Ni fabricated by electroless deposition with different ZTA concentration: (a, a0 ) 60 gL1, (b, b0 ) 100 gL1, (c, c0 ) 150 gL1, (d, d0 ) 180 gL1. T = 70 °C, CNiSO4 = 40 gL1, CEthaline = 30 gL1.
Table 4 Ratio of the Ni concentration C2+ Ni to the surface area of ZTA SZTA. ZTA concentration/gL1 C2+ Ni :
SZTA/(gL
1
2
): (m g
1
)
60
100
150
180
63.49
38.10
25.40
21.16
matrix is easily infiltrated onto ZTA surface during the casting process due to the same crystal structure of Ni and austenitic highmanganese steel. Except for the generation of Al2NiO4, interdiffusion of element Ni and molten iron, element Mn diffuses from ZTA surface into HMS matrix, which can react with Al2O3 to form nickel manganese spinel (Al2MnO4), as shown in Eq. (3) [24]. However, the formation of large amount of interfacial products may result in volume expansion of composite which is not beneficial to the combination of ceramic phase and matrix phase. On the con-
trary, a slight interface reaction is useful in improving the wettability between ceramic and matrix [4,25]. In addition, the distribution of element Ni at the interface is totally different from the Ni coating layer on ZTA surface after electroless (Fig. 2). This can be explained by the diffusion of molten Ni grains into HMS matrix to bond with each other by diffuse interface when ZTAp@Ni is contacted with high-temperature molten iron.
Al2 O3 + Ni + O ! Al2 NiO4
ð2Þ
Al2 O3 + Mn + O ! Al2 MnO4
ð3Þ
Therefore, the schematic illustration of ZTA@Ni performs and molten HMS matrix during the cast-infiltration process is put forward in Fig. 10. At the initial stage, when Ni grains nearby ZTA surface are touched with molten HMS, they will become soft and
Fig. 5. SEM micrographs of ZTAp@Ni fabricated by electroless deposition with different deposition times: (a–a0 ) 1 times, (b–b0 ) 2 times, (c–c0 ) 3 times, (d–d0 ) 4 times, (e–e0 ) 5 times. T = 70 °C, CNiSO4 = 40 gL1, CEthaline = 30 gL1, CZTA = 50 gL1.
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small amount of Al2NiO4 and Al2MnO4 may be formed on ZTA/Fe interface, which can be wetted easily with molten HMS to achieve good wettability on the ZTA/Al2NiO4- Al2MnO4/Fe interface (Fig. 10c). Thus, the interface of ZTAp@Ni reinforced HMS matrix composite is constructed through mechanical bonding, interdiffusion of elements and small amount of reactive wetting.
3.3. Impact abrasive wear resistance
Fig. 6. XRD analysis of ZTAp@Ni fabricated by electroless deposition: (a) 1 times, (b) 3 times, (c) 5 times. T = 70 °C, CNiSO4 = 40 gL1, CEthaline = 30 gL1, CZTA = 50 gL1. Insert: the magnification of (a–c) and the peak intensity of metal Ni.
migrate into HMS matrix (Fig. 10a) and the empty surface of ZTA is occupied by fluent iron. Meanwhile, because metallic Ni has the same crystal structure as austenitic HMS, it is easy to form infinitude solid solution with Fe. This is in favor of the interdiffusion of Ni grains and alloying elements between ZTA surface and HMS matrix during the cast-infiltration process, so that the wettability of ceramic and matrix can be improved (Fig. 10b). In addition,
The volume loss of ZTAp@Ni reinforced HMS matrix composites and the matrix after impact abrasive wear is shown in Fig. 11. From Fig. 11a and b, both of the matrix and composite materials have large volume loss in every testing process, but the impact abrasive wear resistance performance of ZTAp@Ni reinforced composite is more excellent. Fig. 11c–f is the surface morphologies of the composites and matrix after impact abrasive wear. The traces and dropped layers formed by abrasive are found on wearing surface of the HMS matrix (Fig. 11c and d). Due to high hardness of quartz sands compared with that of HMS matrix, deep grooves and plastic deformation are generated. While, the ZTAp@Ni reinforced HMS matrix composites after impact abrasive wear is completely different (Fig. 11e and f). In such case, major loads are transferred from matrix to ZTA powders. The ZTA powders play an important role in protection of metal matrix from impact abrasive wear of quartz sands. There is no serious scratches, pit defects and embedding of abrasive powders at the composite region. After a long time of impact, although brittle fracture of some protrusive ZTA powders on matrix surface are observed, the remaining parts are still tightly bonded with the matrix. So, surrounding metal matrix effectively support ZTA powders, avoiding the totally debonding of them. As mentioned above, the interdiffusion of Ni and alloys elements at the interface layer can reinforce the interfacial bonding strength to form a diffuse interface layer between metal and hard phases.
Fig. 7. SEM and EDS micrographs of the cross section of the ZTAp@Ni fabricated by electroless deposition with 5 times deposition. T = 70 °C, CNiSO4 = 40 gL1, CEthaline = 30 gL1, CZTA = 50 gL1.
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Fig. 8. Morphologies of the ZTAp@Ni reinforced HMS matrix composite. (a–c) optical photographs, (d-g) SEM micrographs.
Fig. 9. EDS analysis of the ZTAp@Ni/HMS matrix composite.
Fig. 10. Schematic illustration of ZTAp@Ni performs and molten HMS during the cast-infiltration process.
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Fig. 11. (a) Volume loss of every testing process and (b) overall volume loss; SEM micrographs of (c and d) HMS matrix material, (e and f) ZTAp@Ni reinforced HMS matrix composites after impact abrasive wear.
4. Conclusions (1) ZTA powders are successfully encapsulated by Ni coatings through electroless plating assisted with Ethaline additive. Dense and uniform Ni coating with a thickness of 7–10 lm is obtained with 40 gL1 Ethaline additive and 150 gL1 ZTA concentration in the bath at 70 °C. (2) ZTAp@Ni reinforced HMS matrix composites with good interfacial bonding are prepared by nonpressure casting infiltration. Impact abrasive wear resistance testing shows that the abrasive wear resistance of the composite are greatly enhanced. (3) The interaction mechanism of Ni-encapsulated ZTA and HMS matrix is analyzed, and a schematic illustration of the castinfiltration process is put forward. It elaborates that a ZTA/ Al2NiO4-Al2MnO4/Fe interface layer is formed through Ni diffusion and reactive wetting, which can greatly reinforce the bonding strength of composites.
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