Effect of Nano SiC Particles on Properties

ICAMMAS – 2017

Effect of nano SiC particles on properties and characterization of Magnesium matrix nano composites

S. Vijayabhaskar^a, T. Rajmohan^b, T.K. Vignesh^c and H. Venkatakrishnan^d

^{a ,b,c,d} Sri Chandrashekarendra Saraswathi Vishwa Mahavidyalaya University, Kanchipuram-631561, India

Abstract

The increasing demand and diverse design requirements with significant weight savings as well as high strength-to-weight ratio as compared to conventional materials have all raised a growing interest towards the field of composites. Ceramic silicon carbide has received wide attention because of its excellent oxidation resistance, corrosion resistance and low density and even at high temperatures. In recent years, Magnesium (Mg) matrix composites have been used in the automotive industry owing to their lightweight property. Mg matrix composites compromise a very high specific strength, excellent castability, good damping capacity and greater machinability. Nanoparticle reinforcements can considerably improve the mechanical properties of the matrix by more successfully stimulating the particle hardening mechanisms than micron-sized particles. The present paper deals with the fabrication and characterization of magnesium matrix reinforced with different wt % (0,0.5 and 1) of nano SiC particles prepared by solidification combined with ultrasonic cavitation process. Mechanical properties such as micro hardness and density and microstructure of the composites were observed. Microstructure of nano SiC composites were investigated by scanning electron microscope (SEM), X-ray diffraction (XRD) and Energy Dispersive X-ray (EDX). The results showed that the increase in weight % of nano SiC improve the mechanical properties.

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Selection and/or Peer-review under responsibility of International Conference on Materials Manufacturing and Modelling (ICMMM – 2017).

Keywords: Mg matrix Composites; Nano SiC particles; Ultra sonication; Scanning Electron Microscopy; Mechanical properties

1. Introduction

Magnesium is considered to be one of the lightest metallic structural materials and is a yet to be untapped for the industrial applications. The main application of magnesium is in automotive and aerospace industries where the major requirement is low fuel consumptions and lower pollution levels. The use of magnesium is limited mainly because of its low mechanical and wear properties [1, 2]. Particle reinforced magnesium matrix composites possess high specific tensile strength and modulus, as well as high wear resistance [3]. The addition of low volume fractions of nano ceramic reinforcements to Mg alloys results in enhanced mechanical properties like higher compressive yield strength. The wear resistance and strength of Mg and its alloys can be improved by reinforcing ceramic materials [4]. It is highly impossible for the conventional mechanical stirring method to disperse and distribute nano-scale particles uniformly in metal melts due to their low wettability and large surface-to0-volume ratio which easily induce clustering and agglomeration. Solidification processes combined with ultrasonic cavitation-based dispersion of nanoparticles in metal melts can be used in order to achieve a uniform dispersion and distribution of nanoparticles in magnesium matrix nanocomposites. In addition, ultrasonic treatment can efficiently degas Mg melt [5-7].

In the present investigation, mechanical properties such as density and micro hardness of the composites were observed. The microstructures of prepared composites were investigated by scanning electron microscope (SEM), X-ray diffraction (XRD) and Energy Dispersive X-ray (EDAX) [8-11]. X-Ray Diffraction (XRD) is used for the angular deflection of the material with which the 2θ values can be compared with standard files conforming the presence of Mg and nano SiC in the composite [12,13].

2. Materials and Methods

The initial materials used for synthesis were Mg billet procured from Micro Fine chemicals, India. and nano SiC particles from US Research Nanomaterials Inc, USA. Mg is used as the matrix material. Its chemical composition is shown in table 1.

Table. 1. Chemical composition of Mg Billet

Mg	Al	Fe	Si	Mn	Zn	Ni	Cu
99.92 %	0.0486%	0.021%	0.0070%	0.0014%	0.0013%	0.0004%	0.0003%

The Mg matrix was reinforced with 0-1 wt% of SiC nanoparticles with the particle size varying from 40 to 80nm. Ultrasonic cavitation method used to fabricate the Magnesium matrix nano composite (MMNC)

The ultrasonic cavitation setup shown in Fig. 1 is used for the fabrication. Mg billets were loaded in the furnace and heated to about 610°C.Nano SiC particles were added to the melt after preheating to 800°C for 1 h in the preheat chamber. The ultrasonic probe is dipped into the melt to carryout sonication process. The whole melt environment is protected by argon gas. Four specimen with varying nano SiC % were fabricated. The composition of the composites prepared along with corresponding densities and hardness were presented in the table 2.

Table 2. MMNC composition and Mechanical properties

S. No	Specimen	Composition	Density (g/cm3)	Hardness (HV)
1	Sample1	100 % Mg + 0% Nano SiC	1.720	174.00
2	Sample2	99.5 % Mg + 0.5% Nano SiC	1.783	192.66
3	Sample3	99 % Mg + 1% Nano SiC	1.820	210.45
4	Sample4	98.5 % Mg + 1.5% Nano SiC	1.900	212.33

2.1. Sample Preparation

Microstructure characterization of Vacuum Stir Casted Magnesium metal matrix reinforced with Nano SiC composite included metallographic examinations with SEM, EDX, and XRD analysis. The sample preparation for micro structural study was done first by polishing the sliced samples with emery paper up to 1200 grit size, followed by polishing with Al2O3suspension on a grinding machine using velvet cloth. Finally, the samples were polished with 0.5 µm diamond paste. Metallographic specimens of composites were prepared for micro structural observation by grinding up to 600 grits with SiC abrasive paper followed by consecutively polishing with diamond pastes of various sizes. The polished surface was etched with 10 % NaOH solution and examined using SEM. The sample after fabrication was cut (10X10X2 mm) to the required size which is used for the analysis mentioned below (SEM with EDX and XRD).

3. Results and discussion

3.1. SEM analysis with EDX

The micro structural and surface morphology of Mg metal matrix and SiC particles reinforced in magnesium matrix composites were done using scanning electron microscope with EDX. EDX was used to evaluate the dispersion of SiC in magnesium matrix composites.

Fig.2 Sample1: SEM with EDX-100% Magnesium + 0% Nano SiC

Fig.2. Sample1 shows the SEM micrograph of Pure Mg with 99% purity. The composite shows a crack free and well-polished surface. This crack free surface may be attributed to the proper distribution of pressure during compaction and proper polishing of sample. The micrograph also shows uniform distribution.

Fig.3 Sample 2: SEM with EDX-Mg + 0.5% SiC

Fig.3. Sample 2shows the SEM micrograph of Mg metal matrix reinforced with 0.5% SiC and bonding of silicon carbide particles can be found over the surface of Mg.

Fig.4. Sample 3: SEM with EDX-Mg + 1% SiC

Fig.5. Sample4: SEM with EDX-Mg + 1.5% SiC

In Fig.4. Sample 3 and in Fig.5. Sample 4, in order to confirm the presence of SiC particle, EDX analysis was done over a particular region. EDX analysis of the 1%, 1.5% SiC reinforced Mg matrix composite is shown. It is clear that the peaks for magnesium, oxygen, silicon and carbon were obtained. The oxygen peak is due to the presence of magnesium oxide that may be formed during the solidification process. The dispersion of SiC in Mg matrix is examined by SEM with EDX. The SEM of SiC Reinforced Mg matrix nano composite is presented. The micrograph shows the dispersion of SiC was regular and agglomeration was found. This can be attributed to the proper ultrasonic cavitation of SiC powder. EDX analysis of the Mg metal and 0.5, 1, 1.5% SiC reinforced Mg matrix composite is presented and it is clear that the peaks for magnesium, oxygen, silicon and Carbon are obtained. The EDX analysis confirms that Magnesium and SiC particles are present within the composites. Therefore, these SEM and EDX analysis are evidence of successful incorporation SiC particles in Mg matrix composites.

3.2. XRD Analysis

Diffraction pattern was collected using BRUKER D8 FOCUS (9 kW) at approximately 2 min intervals and all XRD analysis were matched with the JCPDS database available in the operating software to determine all phases present. The XRD pattern of the Mg metal matrix composites and SiC particles reinforced in Mg matrix composites are shown in Fig.6 As shown in Fig.1 the diffraction peaks at 2θ = 59°, 72°, 79° can be attributed to the reflection of SiC (JCPDS file), 2θ = 65°, 69°, 71° correspond to those of magnesium (JCPDS file).

Fig.6. Sample 1: XRD-Pure Magnesium

Fig.7. Sample 2: XRD-Mg + 0.5% SiC

The XRD pattern of the Mg metal matrix composites and SiC particles reinforced in Mg matrix composites are shown in Fig.7 As Shown in fig, the diffraction peaks at 2θ = 33°,38°,49°,70° can be attributed to the reflection of SiC (JCPDS file), 2θ = 35°,64°,70° correspond to those of magnesium (JCPDS file).

The XRD pattern of the Mg metal matrix composites and SiC particles reinforced in Mg matrix composites are shown in Fig.8 As shown in Fig.3, the diffraction peaks at 2θ = 33°, 38°, 59° can be attributed to the reflection of SiC (JCPDS file), 2θ = 35°, 49°, 64° correspond to those of magnesium (JCPDS file).

Fig.8. Sample 3: XRD-Mg + 1% SiC

Fig.9. Sample 4: XRD-Mg + 1.5% SiC

The XRD pattern of the Mg metal matrix composites and SiC particles reinforced in Mg matrix composites are shown in Fig.4.2.4 As shown in Fig.9, the diffraction peaks at 2θ = 59°,79°,74° can be attributed to the reflection of SiC (JCPDS file), 2θ = 65°,71°,73° correspond to those of magnesium (JCPDS file).

Conclusion

The following conclusions are made based on the work as follows:

• The synthesis of magnesium metal matrix composite reinforced with nano SiC was carried out successfully using ultrasonic cavitation based solidification process.
• The microstructural analysis of the MMNC revealed the agglomeration of SiC particles on the intergranular regions of the magnesium metal matrix composite which are evenly distributed over the composite
• The reinforcement of SiC nanoparticles in the Magnesium metal matrix composites enhance the microstructural properties and mechanical properties
• The presence of SiC particle were verified with XRD test by the correspondence of standard two theta values referring to JCPDS Values.

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