EFFECT OF SINTERING TEMPERATURE ON MECHANICAL PROPERTIES AND
MICROSTRUCTURE OF POWDER METALLURGY AL-NITI-SIC SMART
COMPOSITES
PURUSOTHAMAN M1, RAJESH S2, MAYANDI K3 & RAJINI N4
1Research Scholar, Department of Mechanical Engineering, Kalasalingam Academy of Research and Education (KARE),
Krishnankoil, Tamilnadu, India
2,3,4Department of Mechanical Engineering, Kalasalingam Academy of Research and Education (KARE), Krishnankoil,
Tamilnadu, India
ABSTRACT
Smart materials are its composites are new kind of materials and mostly used in biomedical applications. The aim of present work is to study the effect of sintering temperature on mechanical properties and its microstructures. In this work, aluminium & NiTi, SiC is used as matrix and reinforcement materials. The fabricated composites are subjected to sintering process, the sintering temperature are maintained as 500oC, 550oC and 600oC for 60 minutes of time. The mechanical properties of the sintered smart composites are measured and reported. The density, porosity and Compression strength of the smart composites is measured as per the ASTM standard and it is found that addition of reinforcements increases the compression strength and same trend is observed while increasing the sintering temperature. KEYWORDS: NiTi, SiC, Aluminum, Density, Porosity, Compression Strength
Received: Jun 10, 2020; Accepted: Jun 30, 2020; Published: Aug 29, 2020; Paper Id.: IJMPERDJUN2020953
INTRODUCTION
Aluminium MMC plays a major role in industries sector for their better mechanical properties especially in the field of aerospace, automotive and other appliances. By powder metallurgy techniques, the fabrication of Al based reinforcements attain a near net shape and would increase the mechanical properties such as ultimate tensile strength, compressive strength, hardness, wear rate[1] Among the various Al based reinforcements, NiTi(Shape Memory Alloy) composites shows an improved results in mechanical properties of the materials. NiTi is a material which has sublime characteristics that is to recover its original shape after it gets deformed [2]. G.A. Porter et al [3] experimentally proved that the alteration of particle sizes in NiTi powders has been made through mechanical milling and shape memory effect has also been successfully retained. K.Sadrnezhaad et al. [4] found the effects of mechanical alloying and sintering on NiTi. It is noted that by rising the milling time, porosity percentage and quantity of intermetallic compounds gets reduced. Young Chul Park et al [5] worked out to fabricate Al/NiTi to synthesize microstructure and mechanical properties of the composites. It was marked that the yield stress of the composite materials increased with increasing the volume fraction of NiTi and by the sintering of the composites. By scanning with the electron microscope and Energy Dispersive Spectroscopy, the composites display a good interface bonding between them. Dixit et al. [6] experimentally found, by accession of NiTi in the Al matrix shows an improved mechanical property in the prepared material. San Martina et al. [7] produced NiTip/AA2124 metal matrix composites and investigated the properties of this composite material. It is found that the composite material showed the improvements in compressive and ultimate tensile strength by the accession of NiTi particulates than
heating temperature. In this present work, Al/NiTi composites is fabricated using PM process. With the help of steel ball mill the mixture of compositions such as Aluminium, 5% of Ni,Ti composites were fabricated using direct compaction of powders & by frequent sintering in argon atmosphere. The compression strength, hardness of the composites was obtained by measuring with Universal testing machine, Vickers hardness, The determination of microstructure and chemical composition of the samples are calculated with the help of SEM and Energy dispersive spectroscopy.
MATERIALS AND METHODS
Fabrication of the composites and test specimens are completely created by PM techniques using Al, Ni,Ti, SiC powders which are commercially available in the markets as per applicant convenient. The composite powders purity, particle size, purchase orders are as listed in Table 1.The prerequisite elemental powders of aluminium(Al) as matrix and Nickel(Ni),Titanium(Ti) and Silicon Carbide(SiC) as reinforcements were weighed by electronic balancing machine and it was blended by using planetary ball mill of about 10 mm diameter stainless steel ball for milling purpose. The mixture ratio was maintained as three compositions are as listed in Table 2 and milled at a speed of 200 rpm with hold of duration 2hr in argon atmosphere. The mixed powders were then compressed in a cylindrical die applying load varying from 200 KN to 300 KN in universal testing machine to make an interfacial bond between matrix and reinforcements. The samples
when compacted are to be sinter in a furnace with argon atmosphere at a varying temperature of 500oC, 550oC, 650oC for
one hour thenceforth the sample is to be cooled and it is removed when it comes down around 50oC. With the help of water
& sandpaper, polishing is done by step by step process in which the samples are rubbed against different grades of sandpapers from rough to smooth evenly. The grades of sandpapers are increased from 400 grit sizes to 2000 grit size. At last the sample is rubbed against diamond cloth by applying diamond paste to get a polished surface. Furthermore, the chemical composition of samples was also observed with the aid of EDAX. With the help of Vickers hardness machine, the samples were examined for hardness under a load of 100g and repeated measurements have made to see the effects of the composites for a dwell period of about 10s. The compression strength was also measured by using tensile testing machine according to ASTM standard B783 (diameter 9.53 mm and length 25.53 mm). An average of three times of compression strength was taken experimentally for every sample.
Experimental Process
a) Collected Aluminium for Matrix b) Collected Nickel (Ni) for
Primary Reinforcement
d) Collected Silicon Carbide (SiC) for Secondary Reinforcement
e) Used Crucible for Mixing
Powders f) Components of Die
g) Assembled Die for fabrication h) Compaction Done in Universal
Testing machine (UTM) i) Fabricated Samples
j) Sintering Done for fabricated Composites
k) During Sintering of Fabricated Composites
l) Used Sandpaper for Polishing the
Composites
m) Microstructure Analysis through SEM
n) Compression Strength Measurements of a Composites
o) Vickers Hardness Measurements of a Composites
p) Surface Roughness Measurements
Table 1: Purity and Particle Size of used Metallic Powders
S. No Metal (Powder) Purity (wt%) Purchased Order Particle Size(µm)
1 Al 99.7 United Scientific 41µm
2 Ni 99.5 Iobalchemit >44µm
3 Ti 98 Oxford Laboratory >45µm
4 SiC 99 Metal Industries 45 to 65 nm
Table 2: Composition of Samples Metals Composition
Al + NiTi 95:5
Al + NiTi 90:10
Al + NiTi 85:15
RESULTS & DISCUSSIONS
Microstructural Examination
Figure 2: (a-d) Microstructure of Matrix and Reinforcement Particles. Microstructure of Powder Particles
Microstructure of Fabricated Composites
Figure 3: (a, c) Effects of Microstructure of the Composites During Sintering.
The microstructure of Sintered samples i.e.) 5000C, 5500C, 6000C shows a homogenous distribution of grains in
the composites. At the magnification factor of 100x from three different varying composites, it is shown that matrix, primary and secondary reinforcement where it is known that by the duration of sintering temperature, the distribution of particles and strength of the composites will be differs. Figure 3. (a, c) shows the microstructure of fabricated composites by scanning electron microscope with magnification of 100x, 500x & 1000x. Once the sintering temperature of the composites increased the grain size of the samples will also shows the increment. The extension of heating process results in growth of grain size and decline of porous is predicted using scanning electron microscope. The above figure declares that the sample’s fine structure sintered at lower and higher temperature becomes heterogeneous and homogeneous respectively. In Figure 3 (a, c) it is noted that small pores are identified on the fabricated composites at sintering of 500oC
but latter its reduced and this might happen due to reinforcement particles grain growth. With the amount of increasing sintering temperature, it was found that the strong bonding interface has been done between matrix and reinforcement. From this composite, it is observed that grain size depends on the variation of sintering temperature. The size of grains in the sample was small and large at reduced and increased temperature of sintering respectively. During sintering temperature changes the grain size has been improved and the addition of SiC particles the microstructure shows a homogenous composite.
Hardness Measurement
the addition of SiC particles results in increase in hardness of AMC. The Vickers hardness value of Al (Un reinforced) shows increment in its value by increasing the SiC content and the maximum hardness value is received with the accession of weight 20% SiC (reinforced matrix composites) (23). Aluminium matrix with addition of Ni50Ti50 particles was observed and shows an increment in composite sample with the accession of reinforcements (Ni & Ti). The particles of nickel & titanium will enhance the hardness of the aluminium matrix composites (24). The compositions (Al+Ni) seem to be increasing gradually with the temperature of 500oC to 550oC and it is decreased when the temperature rises to 600oC.
Obviously with the additional SiC particles the composites seem to be increased by comparing with unreinforced SiC particles.
Figure 4: Hardness Measurement with Variable Temperature.
MECHANICAL PROPERTIES EVALUATION
Compression Strength
It is to be note there are so many tests available for characterizing the fabricated composite samples. Among these, compression test is the one to get a clear clarification about the property (or) nature of the fabricated composite samples. Here, compression test is experimented on the UTM by making one head in stable and another it as movable. A load gauge is also be fitted for recording the loads applied and samples were tested for various load with their corresponding intervals. The solidity of Al-Ni50Ti50 compound is greater than that of the pure Al-Ni50Ti50 particle can improve the mechanical strength of Al matrix. The composite which yields strength about 134 ± 9 MPa is Al-20 wt% Ni50Ti50 (24).In this composites it was observed that the Compression strength of sintered composite shows a gradual increase at 550oC but
later it was maintained the same after further sintering. At 600oC Sintered temperature shows the increment in compression
strength with the accession of SiC particles as shown in table 3.
Figure 5: Compression Strength with Variable Temperature.
SURFACE ROUGHNESS MEASUREMENT
Roughness plays a major factor for representing the surface of the sample. The roughness tester precisely measures the roughness of the samples and evaluates the surface texture of the sample. The surface roughness of the sample was measured by Surface Roughness Tester SJ-310 MITUTOYO and measurements have been taken at three various locations on the sintered composite materials in which average values are reported in the machine. The speed and measuring range of 0.5 mm/s and 12.5 mm were maintained and stylus probe of twice measurements have been made for different places on the surfaces. It is found that samples which are sintered at higher temperature have decreased surface roughness; surface roughness is decreased with increase in compression load of the samples.
Figure 6: Surface Roughness Tester SJ-310 MITUTOYO.
CONCLUSIONS
The output describes the mechanical properties of the samples which is purely based upon the quantity of SiC Particulates. Uniform distribution of particles was observed at sintered temperature of about 5500C with 1000x magnification factor.
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