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ScienceDirect Materials Today: Proceedings 4 (2017) 2975–2980
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5th International Conference of Materials Processing and Characterization (ICMPC 2016)
Development of Ni-WC composite clad using microwave energy Lohit R Ba, Prabakhar M Bhovib * a b
Department of Mechanical Engineering, BVBCET, Hubli-580031, India Department of Mechanical Engineering, BVBCET, Hubli-580031, India
Abstract
Cladding of suitably designed materials on functional surface which are subjected to sever tribological loading can lead to increase in components life. Development of clad includes several techniques such as thermal spraying, High velocity oxy fuel and laser cladding. However cladding done through the above listed process pertain certain defects like cracks, distortion, poor adhesion strength etc.In the present work a new process method has been developed to clad Ni (matrix)-80 wt.%WC (reinforcement)-20 wt.% powder on poor wear resisting material through microwave irradiation of frequency 2.45GHz. The characterization of developed clad is done using X-ray diffraction (XRD), Field emission electron microscope (FE-SEM), Back scattered electron image and Vickers micro hardness. XRD pattern of developed composite clad showed presence of compounds like NiSi, NiW, and W2C phase. The wear resistant complex carbide phase have been seen in the structure of the clad transverse section showed good metallurgical bonding between the substrate and the developed clad. ©2017 Published by Elsevier Ltd. Selection and peer-review under responsibility of Conference Committee Members of 5th International Conference of Materials Processing and Characterization (ICMPC 2016). Keywords: Microwave radiations; Cladding; XRD; FE-SEM; Ni-WC Clad; Metallurgical bonding.
1. Introduction: Wear is a phenomenon of degradation of functional surface of certain material as a result of mechanical interaction between surfaces in contact. Wear is related to interactions between surfaces and more specifically the removal of material on opposite surface. Wear is an intrinsic material characteristic of the engineering system which depends on load, speed, temperature, hardness, presence of foreign material and the environmental condition [1]. The primary reason for failure of engineering components is wear and corrosion in aggressive interacting environments. The life of such components can be increased in two ways, first designing a bulk material with high Corresponding author. Tel.: +91 08362378103; fax: +08362374985. E-mail address:
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2214-7853©2017 Published by Elsevier Ltd. Selection and peer-review under responsibility of Conference Committee Members of 5th International Conference of Materials Processing and Characterization (ICMPC 2016).
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wear and corrosion resistance and second functional surfaces are modified so as to satisfactorily perform in aggressive working environments. Austenitic stainless steel have great utility as engineering materials in various applications across the industries, as they exhibit excellent corrosion resistance by virtue of its properties however they exhibit poor friction and wear characteristics surface modification of stainless steel can enhance its functional properties which can be done through different techniques like carburizing, cyaniding, nitriding and coating/cladding etc.[2]. The most economical solution for the improvement in wear resistance of the functional surface would be coating/cladding with suitable overlaying material, which can be done through various methods like thermal spraying, plasma spraying, physical vapour deposition, laser cladding etc. laser cladding has been one of the most popular surface techniques among the widely practiced anti-wear industrial solutions. However this process has some limitations like high distortion, development of porosity and interface cracking apart from high setup and running cost. Recently application of microwave energy for developing wear resistance cladding has been explored successfully [3]. The novel process possess high potential to emerge as one of the practical surfacing solutions owing to its higher speeds of processing, higher degree of processing uniformity. Clads produced through microwave heating exhibit significantly lesser thermal distortion and nearly are free from solidification cracks and pores because of volumetric nature of heating associated with microwave processing. Many researches in the area of microwave processing has been done in the domain of sintering and joining of ceramic and composites. The properties of functional surface enhanced by application by microwave processing is reported to be superior to that obtained by conventional thermal processing [4-10].application of microwave energy in processing metallic material is, on the other hand, quite challenging owing to the fact that microwave absorption co efficient for metals at 2.45 GHz radiation (common allowable frequency for industrial use) is significantly less at room temperature [11]. Joining of bulk metallic materials using microwave irradiations on development of wear resistant cladding on bulk metallic substrates have been hardy reported [12]. In present work, cladding of Ni based –WC powder on austenitic stainless steel (SS-316L) substrate through microwave hybrid heating (MHH) technique has been carried out using a multimode domestic microwave oven at 2.45 GHz frequency and power 900 W, and the obtained composite clads were characterized through x-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), back scattered electron image (BSE), energy dispersive x-ray spectroscopy (EDS) and Vickers micro hardness. 2. Experimental procedure and Materials: Composite claddings are always developed with a certain focused objective. The quality of cladding is influenced by a number of factors. In the present work, wear resistant cladding is developed on a metallic substrate using microwave irradiation as the heating source. Processing bulk metallic materials with microwave heating is unusual. However the partial dilution of the bulk metallic substrate is achieved in this work. The following sections briefly describe the development and characterization of the cladding. Tungsten carbide has good hardness and wear resistance, but poor toughness. To improve the toughness, Ni-based powder has been used as matrix in the composite clad. Tungsten carbide provides better wear resistance while bonded dispersed in a tough phase. Thus, 20% WС added as reinforced particle in to the Ni based matrix could be one of the best systems for a combination of high hardness and toughness. In order to develop cladding on austenitic stainless steel, Ni based-WC powder was used. Austenitic steel (SS-316L) plates machined to dimensions 30mm x12mm x6mm were used as substrate material. Chemical composition of SS-316L used as substrate as shown in Таble1. Table 1. Elemental weight composition of the substrate material (SS-316L) SS-316L C Si Mn Ni Cr Wt%
0.08
0.75
2
14
17
Mo
Fe
P,S, Cu, Zn
2
Bal.
1
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2.1 Development of Cladding In the present work the functional surface is cladded with a composite containing (Ni (80wt%)-WC (20wt %)). Substrates were cleaned with alcohol in an ultrasonic bath prior to deposition of powder. Developed clad consisting of tungsten carbide (WC) based reinforcement particles in Ni- matrix were intermixed properly and preheated at 100°C for 24 hour in a conventional muffle furnace. Thus removing all the possible moisture in the powder. The powder was preplaced manually on SS-316L substrate maintaining an approximate uniform thickness of 2 mm. The absorption of microwave energy depends on powder particle size. The properly mixed powder cannot interact with the microwave radiations to produce heat, instead it reflects the microwaves. In order to overcome the problem of microwave being reflected by Ni-based WC powder (80%wt and 20%wt) cladding were developed by microwave hybrid heating (MHH) using a suitable susceptor. The susceptor material absorbs the microwave energy and transfers it to the powder particles of the substrate. To avoid the possible contamination of cladding by the susceptor used in MHH. A 99% pure graphite was used as a separator between the susceptor and the powder as shown inFigure 2.1. The figure shows a schematic representation of MHH arrangement.Optimized microwave processing parameters for composite clad development are shown in table 2.
Fig. 2.1(a) Microwave oven
(b) Schematic representation of processing Ni-WC clad
Table 2. Optimized microwave processing parameters for composite clad development Parameters Applicator Frequency Exposure time Exposure power
Description Multimode(Make:LG,Model: Solar DOM) 2.45GHz 360sec 900W
3. Results and discussion: Results along with the discussion are presented in this section for the experiments. The results presented accordingly in line to the objectives mentioned. In the present work, microwave cladding of Ni based alloy as matrix, WC reinforcement particle powder has been successfully carried out on austenitic stainless steel (SS-316L) substrate using a multimode domestic microwave oven, operated at 900W and 2.45GHz. 3.1 Metallurgical Characterization The metallurgical characterization like XRD, Microstructure through FE-SEM and elemental analysis of clad samples were discussed as follows:
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3.1.1 XRD Analysis of Composite Clad The XRD patterns were obtained at room temperature in a Bruker AXS diffractometer with Cu -Kα X-ray. The scan rate used was 1° min-1 and the scan range was from 20° to 80°. The analysis of microstructures and chemical composition of the clads were carried out with the help of a field emission scanning electron microscope at an acceleration voltage of 20kV equipped with energy dispersive x-ray detector (Model: Quanta 200 FEG).Hardness of mating surfaces plays an important role in the process of material loss from the interacting surfaces. A typical XRD spectrum of the composite clad developed through microwave hybrid heating is presented in Fig. 3.l.The XRD pattern of Ni-WC reveals the detected phases in the composite clad contains metallic carbides of chromium, W, and Ni. The presence of complex phases like NiSi, NiW in microwave clad confirms the metallurgical bonding to the substrate. The XRD patterns confirms the presence of free tungsten.
Fig.3.1: A typical XRD spectrum of the Ni based-WC composite cladding (radiation: Cu-Kα).
3.1.2 Microstructure of the composite clad The microstructure of the composite clad Ni- WC is studies through FE-SEM. The back scattered electron image of transverse section of microwave composite clad is as shown in fig 3.2 It shows uniform distribution of reinforcement particles in the tough, ductile Ni based matrix. The cladding with an average thickness of 500µm shows good metallurgical bonding with substrate through partial diffusion of element like iron, silicon from the substrate to clad. The developed clad is free from interfacial cracks and has significantly less porosity which indicates uniform heating has taken place during the MHH.
Fig. 3.2: BSE image of transverse Ni-WC clad
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3.1.3 Elemental Analysis of Composite clad
Fig. 3.3BSE image of Ni-WC clad with XRD
Energy dispersive x-ray spectroscopy involves analysis of the intensity of emitted x-ray as a function of their energy. The characteristic elemental x-ray energies are plotted as peaks in a spectrum. The intensity of the peaks can be correlated with the concentration of each element using mathematical models. Analysis can also be done at specific points as shown in Fig.3.3 3.2 Micro Hardness Study Hardness of a material is one of the most important factors, which influence wear performance of the material. Generally, increasing the hardness of components can enhance the wear resistance ability although the effect of hardness is not straight forward. The microhardness of composite clad Ni WC discussed briefly as follows.
Fig 3.4. Vicker’s micro hardness distribution through a typical section of Ni-WC composite clad.
The Vicker's microhardness of clad layer over the cross-section has been evaluated. The distribution of microhardness is shown in Fig.3.4. Microhardness of the transverse section of the claddings and substrate were evaluated using Vicker's microhardness tester (Mini load, Leitz, Germany) at the load of 100g applied for 30s. The indentations for Vicker's hardness measurements were made at the interval of 75µm starting from the top of the clad surface to the substrate material. The average microhardness of the clad section is 477.5Нv.The distribution of microhardness in the clad section is not observed to be uniform and significant standard deviation were present in microhardness observations. The high standard deviation can be attributed to the indentations being carried out at the harder carbide phase as well as at the tougher matrix phase.
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4. Conclusions · · · · ·
The clad developed by using microwave radiation with frequency 2.45GHz and power of 900W for a period of 360 s was found to be having a thickness of 500µm. The clad has metallurgical bonding with the substrate due to partial diffusion of elements. The WC particles are reinforced in nickel matrix which is tougher and ductile matrix. The average microhardness at center of the clad was found to be 477.5Hv. The developed clad can be effectively used in wear resistance application.
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