STUDY OF WEAR BEHAVIOUR OF ALUMINIUM BASED MICRO AND NANO COMPOSITES FABRICATED BY STIR CASTING TECHNIQUE
Paramvir Singh Bhagrana
Dept. Mechanical Engineering
BabaBandaSinghBahadurEngineeringCollege
Fatehgarh Sahib, Punjab, India
Dr. Niraj Bala a*
Prof. Avtar Singh a*
a* Assistant Professor
Dept. Mechanical Engineering
BabaBandaSinghBahadurEngineeringCollege
Fatehgarh Sahib, Punjab, India
ABSTRACT
In this present work, aluminum based metal matrix composites have been fabricated by using Silicon carbide(SiC) as reinforcement material by stir casting technique. Percentage of silicon carbide has been taken as 10% to the weight of matrix material aluminium. The commercial available micro size silicon carbide powder was converted to nano size using planetaryball milling machine. Characterization of the cast aluminium composite specimens was done by using Scanning Electron Microscopy (SEM) whichshowed uniform distribution of reinforcing particles in the aluminium matrix. Hardness and wear tests were also performed on the specimens to know the variations among pure Al,Al+SiC (micro), Al+SiC (nano). The fabricatedComposites also showed improvement in hardness and wear resistance over the pure aluminum metal. Considering all the factors, it can be concluded that aluminium based composite with 10% by weight SiC (nano) reinforcement possess better wear resistance properties as compared to pure Al and Al+SiC(micro).
Keywords: Aluminium matrix Composite, SiC particles, Stir casting, Wear, SEM.
I. INTRODUCTION
Aluminium is the most abundant metal in the Earth's crust, and the third most abundant element, after oxygen and silicon. It makes up about 8% by weight of the Earth's solid surface. Composite materials are the materials in which the desirable properties of different materials are
combined to form a single material system. Composite material is a combination or mixture of two or more materials. The composite material is usually better than its individual elements or components as regards their properties or characteristics such as stiffness and strength etc.[1]. When the matrix is a metal, the composite is termed as a metal matrix composite(MMC). In MMC’s the reinforcement usually takes the form of particles, whiskers, short fibers, or continuous fibers. Among different composites, metal matrix composite are promising new materials for recent engineering application having high specific strength, stiffness and their high temperature stability and widely used in aerospace and automotive industries[2].
A metal matrix composite (MMC) is composite material with at least two constituent parts, one being a metal necessarily, the other material may be a different metal or another material, such as a ceramic or organic compound. Aluminium matrix composites (AMC’s) refer to the class of light weight high performance aluminium centric material systems. The reinforcement in AMC’s could be in the form of continuous/discontinuous fibers, whisker or particulates, in volume fractions ranging from a few percent to 70%. Properties of AMC’s can be tailored to the demands of different industrial applications by suitable combinations of matrix, reinforcement and processing route. Presently several grades of AMC’s are manufactured by different routes. Three decades of intensive research have provided a wealth of new scientific knowledge on the intrinsic and extrinsic effects of ceramic reinforcement vis-a-vis physical, mechanical, thermo-mechanical and tribological properties of AMC’s [3]. In the last few years, AMC’s have been utilized in high-tech structural and functional applications including aerospace, defense, automotive, and thermal management, as well as in sports and recreation.
Aluminum is the most popular matrix for the metal matrix composites (MMC’s). The aluminium alloys are quite attractive due to their low density, low cost, its capability to strengthen by precipitation, good corrosion resistance, high electrical and thermal conductivity and improved tribological properties[4]. SiC is composed of tetrahedral of carbon and silicon atoms with strong bonds in the crystal lattice. This produces a very hard and strong material. SiC is not attacked by any acids or alkalis or molten salts up to 800°C. In air, SiC forms a protective silicon oxide coating at 1200°C and is able to be used up to 1600°C[5].
II. EXPERIMENTATION
In this research work aluminium was selected as a matrix because of its enormous advantages and applications. After the selection of matrix material, SiC was selected as the reinforcement material.The high thermal conductivity coupled with low thermal expansion and high strength gives this material exceptional thermal shock resistant qualities. Stir casting is a process in which base material is melted in a furnace and the reinforcement is poured into the crucible containing molten base material and a stirrer is used to stir the mixture and continuously disperse the reinforcement into the base material. After mixing the base material and reinforcement, mixture is poured into the mould or dies and is allowed to cool or solidify. After solidification, specimen is taken out of the die and can be used for further testing. The variable parameters are to be considered, while preparing the MMC’s by using stir casting that are stirring speed, stirring temperature, pouring temperature and mould temperature. Now, after the finalization of matrix and reinforcement material the following components were used to fabricate the composites by using stir casting technique.
Firstly, Furnace used was having a heating range of 0°-1200°C which was electrically operated. The door of the furnace was on the upper side. It is rectangular in shape with dimensions 2.5x2.5x2.5 feet.Secondly,to melt the material in a furnace it has to be placed in Crucible. The crucible which was used to melt the aluminium was made up of graphitewhich is mostly used for this purpose in industries also. The size of crucible is basically pre-fixed and these are available in the market having size numbers i.e. 1,2,3,4...etc. The size number 5 crucible of graphite was used because it could carry up to 2Kg of aluminium.
Thirdly, Purpose of stirrer is to mix the reinforcing materials properly and disperse them in the base material thoroughly. The stirrer is of great importance because if the design of stirrer is not proper then it will not provide whirling properly and the mixing will not take place accordingly. Finally,Mould is the component used in casting in which the molten material is poured and allowed to solidify. The mould used for casting composites was made up of mild steel. The mould was made by two 1 inch thick plates of dimensions 25 cm x 17 cm.It consisted of 6 cylindrical grooves of 2 cm diameter each with a depth of 8 cm. These grooves were joined at the bottom with a groove of 2 cm diameter and a gap of 1 cm was provided between each vertical groove.
III. RESULTS AND DISCUSSION
After the preparation of specimens, numbers of tests were done to analyze their properties. These tests include hardness, wear testing, and SEM analysis.
- Hardness Measurement
The hardness measurement was done by using Rockwell hardness testing method and 3samples were taken and for each sample 4 readings were taken so as to reduce the chances of error. Below graph shows the comparison of hardness at 60Kgf loadbetween pure Al, Al+SiC (micro)and Al+SiC(nano) after taking the mean values of all these specimens. The graph shows that hardness of Al+SiC(nano) is more as compare to Al+SiC (micro) this is due to small size and uniform distribution of nano particles.
Fig.1. Hardness of Pure Al, Al+SiC(micro) and Al+SiC(nano)
B. Wear Testing
The pure Al, Al+SiC(micro), Al+SiC(nano), composite specimens were subjected to standard sliding wear testing on a pin-on disk apparatus (ASTM standard G99-03) as per the procedure. The digital weighing scale used to take readings after every 3 minutes. The wear tests were done for load of 2Kg at constant speed 760 RPM and the disk diameter were taken 100mm for all the specimens.The below graph shows that wear resistance of Al+SiC(micro/nano) composites is more than the pure aluminium this is because of their greater hardness.
Fig. 2. Comparision of wear of Pure Al, Al+SiC(micro), Al+SiC(nano)
C. SEM analysis of the worn surface of the Specimen
In these section SEM of Pure Al, Al+SiC (micro), Al+SiC (nano), was taken after the wear testing of all the specimens. SEM of specimens has taken at one magnification range that isX100.It is evident from that all specimens have suffered significant damage of its surface in the form of craters, grooves, debris.Most of the grooves are parallel to thesliding direction; it isevident from the worn pins. Such features are characteristics of abrasion, in which hard asperities of the steel counter face, or hard reinforced particles in between the contacting surfaces, plough or cut into the pin, causing wear by the removal of small fragments of material.
(A) (B)
(C)
Fig. 3. SEM of (A), Al+SiC(nano), (B) Al+SiC(micro), (C) Pure Al.
Fig. 3 (A) shows the micrograph for Al+SiC(nano) in which craters formed can clearly be seen along with the grooves. Most of the grooves are parallel to the sliding direction; it isevident from the worn pins. Fig. 3 (B) shows the SEM microscopy of Al+SiC(micro) in which debris and grooves are clearly seen. Similarly Fig. 3 (C) shows the SEM microscopy of pure Al in which debris and cavities are clearly seen but the grooves are not visible properly.
IV. CONCLUSIONS
According to the results of the research work, the followings can be concluded:
1.There is a significant increase in the values of hardness of aluminium with the addition of the reinforcement.The trend shown by the specimens in case of hardness is: Al+SiC (nano) > Al+SiC (micro) > Pure Al. The maximum hardness was shown by Al+SiC(nano).So, it can be concluded that nano composite have more hardness as compare to the micro composite this is because of uniform distribution, small in size and low porosity of nano composite.
2.The wear resistance was found to increase significantly with the addition of reinforcements in aluminium. Wear resistance of Al+SiC (Nano) was found to be highest, while pure Al showed lowest wear resistance. The rate of wear is extremely higher in case of pure aluminium than the composites. The wear resistances of the Pure Al, Al+SiC (micro), Al+SiC (nano), composites at normal load of 2 Kg and 760 RPM followedthe trend given below: Al+SiC (nano) > Al+SiC (micro) > Pure Al..
3. SEM micrographs of the worn surfaces of the specimens have revealed the formation of craters along with the presence of grooves parallel to the sliding direction which is the result of abrasion by hard asperities of the steel counter face, or hard reinforced particles in between the contacting surfaces cutting into the pin.
5. From the current investigation it may be recommended that the Al+SiC (nano) composite is the best option considering all the parameters like wear resistance, hardness etc. among the investigated cases.
REFERENCES
1. G.R. Nagpal, khanna book publication co.Ltd. “Material science”, ISBN-81-87522 55-0.
2. C.R Dandekar, Shin ye. “Effect of porosity on the interface behaviour of an Al2O3 aluminum composite a molecular dynamics study”, vol. 71, pp. 350-6, 2011.
3. Sadhana, “Aluminium Matrix Composites: Challenges and Opportunities”, vol. 28, pp. 319-334,2003.
4. V. Rajput, R.K. Gautam, R. tyagi, “Tribological Behaviour of Al Based Self-Lubricating Composites”,pp. 108-110, 2015.
5. A. Alavudeen, N. Venkateshwaran, J.T. Winowlin Jappes, “A Textbook of Engineering Materials and Metallurgy”, 2006.