EXPERIMENTAL INVESTIGATION OF CREEP … · Zirconium-di-oxide with LM25 by creep testing machine....

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International Journal of Mechanical Engineering and Technology (IJMET) Volume 6, Issue 8, Aug 2015, pp. 126-138, Article ID: IJMET_06_08_012 Available online at http://www.iaeme.com/IJMET/issues.asp?JTypeIJMET&VType=6&IType=8 ISSN Print: 0976-6340 and ISSN Online: 0976-6359 © IAEME Publication

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EXPERIMENTAL INVESTIGATION OF

CREEP BEHAVIOUR OF ALUMINIUM ALLOY (LM25) AND ZIRCONIUM DI-

OXIDE (ZRO2) PARTICULATE MMC

A. R. Sivaram

Assistant Professor, Department of Mechanical Engineering,

AMET University, Chennai, India.

K. Krishnakumar

Assistant Professor, EGS Pillay Engineering college,

Nagapattinam, India.

Dr. R. Rajavel

Professor and HOD, Department of Mechanical Engineering,

AMET University, Chennai, India.

R. Sabarish

Assistant Professor, Dept. of Mechanical Engineering, Bharath University, Chennai, India.

ABSTRACT

Aluminium metal matrix composites are one of the new materials used for various applications due to their less cost and light weight. Creep is the

tendency of solid material to slowly move or deform permanently under the influence of stresses when subjected to high temperatures for long duration of time. So creep is one of the major considerations while analyzing the

materials which are used for high temperature for long durations. Creep analysis of composite material has a wide scope of research. In this paper, an

Aluminum composite material is produced by mixing high strength low weight material with zirconium di-oxide for different proportions (0%, 3%, 6%, and 9%) by using stir casting technique. In this paper experimental tests were

carried out to determine the creep strength for different proportions (0%, 3%, 6%,9%) of Zirconium-di-oxide with LM25 by creep testing machine. SEM and

microstructure analysis was also done to see the distribution and presence of ZrO2 particles in aluminium alloy.

Experimental Investigation of Creep Behaviour of Aluminium Alloy (LM25) and Zirconium Di-Oxide (ZrO2) Particulate MMC


Key words: Composite material, Aluminium alloy composite, SEM, Elapsed strain.

Cite this Article: Sivaram, A. R., Krishnakumar, K., Dr. Rajavel, R. and Sabarish, R. Experimental Investigation of Creep Behaviour of Aluminium

Alloy (LM25) and Zirconium Di-Oxide (ZrO2) Particulate MMC. International Journal of Mechanical Engineering and Technology, 6(8), 2015, pp. 126-138.

http://www.iaeme.com/IJMET/issues.asp?JTypeIJMET&VType=6&IType=8

1. INTRODUCTION:

Composite material is a material composed of two or more distinct phases (matrix phase and reinforcing phase) and has bulk properties significantly different from those

of any of the constituents. Many of common materials (metals, alloys, doped ceramics and polymers mixed with additives) also have a small amount of dispersed phase s in

their structures, however they are not considered as composite materials since their properties are similar to those of their base constituents (physical property of steel are similar to those of pure iron) . Favorable properties of composites materia ls are high

stiffness and high strength, low density, high temperature stability, high electrical and thermal conductivity, adjustable coefficient of thermal expansion, corrosion

resistance, improved wear resistance etc. Metal Matrix Composites are composed of a metallic matrix (Al, Mg, Fe, Cu etc) and a dispersed ceramic (oxide, carbides) or metallic phase( Pb, Mo, W etc). Ceramic reinforcement may be silicon carbide, boron,

alumina, silicon nitride, boron carbide, boron nitride etc. whereas Metallic Reinforcement may be tungsten, beryllium etc . MMCs are used for Space Shuttle,

commercial airliners, electronic substrates, bicycles, automobiles, golf clubs and a variety of other applications. From a material point of view, when compared to polymer matrix composites, the advantages of MMCs lie in their retention of strength

and stiffness at elevated temperature, good abrasion and creep resistance properties. Most MMCs are still in the development stage or the early stages of production and

are not so widely established as polymer matrix composites. The biggest disadvantages of MMCs are their high costs of fabrication, which has placed limitations on their actual applications. There are also advantages in some of the

physical attributes of MMCs such as no significant moisture absorption properties, non- inflammability, low electrical and thermal conductivities and resistance to most

radiations. Li Xu-Dong et al [1] have carried out a experimental investigation to estimate the reliable effect of prior corrosion state on fatigue micro-crack initiation and early stage propagation behaviour of aluminum alloy based on scanning electron

microscopy (SEM) in situ observation. Results indicated that multi-cracks initiation occurred almost at the corrosion pits and the early stage of fatigue micro crack

propagation behaviour can be described by KI/KII-mixed mode. Ashley D. Spear et al [2] have carried out a experimental investigation to study the effect of alkaline chemical milling used for dimensionally reducing aluminum-alloy structures in terms

of total fatigue life and crack- initiation mechanisms. Chemically milled Al–Mg–Si specimens exhibited a 50% reduction in average fatigue lives compared to

electropolished Al–Mg–Si specimens at comparable peak-applied loads above macroscopic yield. D. Q. Peng et al [3] have studied the effect of aluminum ion implantation on the aqueous corrosion behavior of zirconium, specimens were

implanted with aluminum ions with fluence ranging from 1×1016 to 1×1017 ions/cm2, using a metal vapor vacuum arc source (MEVVA) at an extraction voltage of 40 kV.

A. R. Sivaram, K. Krishnakumar, Dr. R. Rajavel and R. Sabarish


The valence states and depth distributions of elements in the surface layer of the samples were analyzed by X-ray photoelectron spectroscopy (XPS) and auger

electron spectroscopy (AES), respectively. LUO Yun-rong et al [4] have studied the Effects of Strain Rate on Low Cycle Fatigue Behaviors of High-Strength Structural

Steel. S. Huang et al [5] have carried out a experimental study to investigate Effects of laser energy on fatigue crack growth (FCG) properties of 6061-T6 aluminum alloy subjected to multiple laser peening (LP) were investigated. LP experiments and

typical FCG experiments were performed on the compact tension (CT) samples. The results showed that compressive RS induced by LP can effectively decrease FCG rate

and increase FCG lives of CT samples. The fatigue behavior of aluminium alloy was investigated under different conditions [6–9]. K. Mori et al [10] have studied the static and fatigue strengths of mechanically clinched and self-pierce riveted joints in

aluminium alloy Sheets and compared with those of a resistance spot welded joint. D. Khireddine et al [11] have carried experimental tests to investigate the Low cycle

fatigue behaviour of an aluminium alloy with small shearable precipitates. V. Balasubramanian et al [12] have studied Influences of pulsed current welding and post weld aging treatment on fatigue crack growth behaviour of AA7075 aluminium alloy

joints. The role of microstructural variability on the fatigue behavior aluminum metal matrix composites were studied by using different techniques [13–17]. In this paper,

an Aluminum composite material is produced by mixing high strength low weight material with zirconium di-oxide for different proportions (0%, 3%, 6%, and 9%) by using stir casting technique. In this paper experimental tests were carried out to

determine the creep strength for different proportions (0%, 3%, 6%, and 9%) of Zirconium-di-oxide with LM25 by creep testing machine. SEM and microstructure

analysis was also done to see the distribution and presence of ZrO2 particles in aluminium alloy.

2. EXPERIMENTAL WORK

2.1. Stir casting process

Three steps are involved in this casting process are,

1. Heating metal till it becomes molten

2. Pouring the molten metal into a mould

3. Allowing the metal to cool and solidify in the shape of the mould.

Stir Casting is a liquid state method of composite materials fabrication, in which a dispersed phase (ceramic particles, short fibers) is mixed with a molten matrix metal

by means of mechanical stirring. Stir Casting is the simplest and the most cost effective method of liquid state fabrication. Liquid state fabrication of Metal Matrix Composites involves incorporation of dispersed phase into a molten matrix metal,

followed by its Solidification. In order to provide high level of mechanical properties of the composite, good interfacial bonding (wetting) between the dispersed phase and

the liquid matrix should be obtained. Wetting improvement may be achieved by coating the dispersed phase particles (fibers). Proper coating not only reduces interfacial energy, but also prevents chemical interaction between the dispersed phase

and the matrix. The aluminium alloy is casted in a stir casting machine as shown in Figure 2.1. When setting up the stir caster before an experiment the rotor was first

lowered into the crucible, its height was accurately adjusted to form a partial seal at the exit such that it was held concentrically during stirring. Only a partial sealing of the outlet was allowed to ensure that torque pick-up from the rotor-crucible was



negligible. An external plug attached to the batch casting trolley provided a full seal at the exit. After the caster set-up, metal melted in an induction furnace was transferred

to a resistance holding furnace where it was stabilized at a temperature 20 °C above the liquidus temperature. The melt was then poured into the stir caster furnace which

had been preheated to 570 °C for A356 and to 595 °C for Al–4% Si. Once the temperature of the semi-solid melt (Tss) was stabilized, giving the desired fs, via the element controllers, rotation of the stirrer was started. After shearing the alloy at the

specified shear rate and for the specified length of time, the rotor was raised, the plug on the batch casting trolley. Stir casting setup consists of digital control muffle

furnace and a stirrer made of graphite as shown in Figures 2.2 and 2.3 which is connected to electric motor with speed range of 22–840 rpm. SiC particles were artificially oxidized in air at 1000 °C for 150 min to form a layer of SiO2 on them and

improve their wet ability with molten aluminium. This treatment helps the incorporation of the particles while reducing undesired interfacial reactions. Batches

of the matrix alloy were melted in a clay-bonded graphite crucible of 1.5 kg capacity using a small muffle furnace. The temperature of the alloy was first raised to about 800 °C and then stirred at 540 rpm using an impeller fabricated from graphite and

driven by a variable ac motor.

2.1.1. Synthesis of composite

The synthesis of composite is done by stir casting route. The parameters which are important in this work are stirrer design, preheating temperature for particulate and stirring speed. These parameters are discussed below.

2.1.2. Stirrer design

It is essentially requires for vortex formation for the uniform dispersion of particles.

There is a no uniform dispersion of particles in case of no vortex formation.

2.1.3. Particle preheating temperature

Preheating of particulate is necessary to avoid moisture from the particulate otherwise

there is chance of agglomeration of particulate due moisture and gases. Along this SiC particles are heated at 1000 °C to form a oxide layer on the SiC particles which make

it chemically more stable and by the oxide layer formation wet ability will increase so particles will get effectively embedded in aluminium matrix and there will be only less number of porosities in casting. After oxide layer formation preheating of

particulate is done on temperature of 400° C.

2.1.4. Stirring speed

In this process, stirring speed was 240 rpm which was effectively producing vortex without any spattering. Stirring speed is decided by fluidity of metal speed, dispersion of particulates are not proper because of ineffective vortex.



Figure 2.1 Aluminium Stir casting Machine

Figure 2.2 Muffle furnace

Figure 2.3 Graphite stirrer

2.2. Materials

The Percentage of composition on each phase and the number of specimens required are listed below. The specimens are as shown in Figure 2.4. The specimens are,

a) 0.97 weight fraction of LM25 and 0.03 Weight fraction of ZrO2,



b) 0.94 weight fraction of LM25 and 0.06 Weight fraction of ZrO2,

c) 0.91 weight fraction of LM25 and 0.09 Weight fraction of ZrO2,

d) 100% weight fraction of LM25.

The heat-treated alloy has fairly good machining properties, but tools should

preferably be of high speed steel and must be kept sharp. A moderately high rate of tool wear may be expected. Liberal cutting lubricant should be employed. As with LM6, resistance to corrosive attack by sea water and marine atmospheres is high

with this alloy. A protective anodic film can be obtained by either the sulphuric or chromic acid process, but the grey opaque character of coatings of normal thickness

precludes their colouring in light shades for decorative purposes. There are three common heat treated conditions for LM25: TE (precipitation treated), TB7 (solution treated and stabilized, and TF (fully heat treated).

Figure 2.4 LM25 + 0% ZrO2, LM25 + 3% ZrO2, LM25 + 6% ZrO2, LM25 + 9% ZrO2

2.3. Microstructure analysis

The well-polished samples as shown in Figure 2.5 were then observed under an optical microscope. Micrographs were taken with the help of CCD camera attached to the optical microscope which is shown in Figure 2.6 and are further viewed on

computer with optical image analyzer software at magnification of 200X.

Figure 2.5 Al +3%ZrO2, Al +6%ZrO2, Al +9%ZrO2

http://www.mrt-castings.co.uk/aluminium-diecasting-lm6.html



Figure 2.6 Optical Microscope

2.4. Creep Test

Creep occurs as the result of long term exposures to levels of stress that are below the yield strength of material. Creep always increases with temperature. The rate of this

deformation is a function of material properties, exposure time, exposure temperature, and the structural applied load. The creep testing machine and the testing of the specimen in the creep testing machine is shown in Figure 2.7.

Figure 2.7 Creep Testing Machine



3. RESULTS & DISCUSSIONS

3.1. Microstructure Analysis by Optical Microscope

The images of the micro structural characterization carried out by optical microscope

for the 3% , 6%, 9% weight fraction of the particle reinforced composite is shown in Figures 3.1, 3.2, 3.3.

Figure 3.1 Optical Image of LM25 & 3%ZrO2



The grain size estimation for LM25 & 3%, 6%, 9% weight fraction of the particle reinforced composite is shown in Table 3.1.



Table 3.1 Grain Size Estimation

Parameter LM25 & 3%

ZrO2 LM25 & 6%

ZrO2 LM25 & 9%

ZrO2

Field measured 2 1 1

Total area 0.88474 sqmm 0.44237 sqmm -

Standard ASTM E1382 ASTM E1382 ASTM E1382

ASTM GRAIN

SIZE# 1.5 0.6 3.3

INTERCEPTS 286 85 3

MEAN Int. LENGTH

190.2425 256.6118 13969.6

STANDARD DEVIATION

0.117 - 5018.157

95%CI 0.229 - 8042.722

RA% 120.248 - 57.573

3.1.1. MICROSTRUCTURE ANALYSIS BY SCANNING ELECTRON

MICROSCOPE

The micro structural characterization carried out by scanning electron microscope for

the 3%, 6%, 9% weight fraction of the particle reinforced composites are shown in Figures 3.4–3.10.

Figure 3.4 SEM Image of LM25 & 3%ZrO2 for 250 k

Figure 3.5 SEM Image of LM25 & 3%ZrO2 for 250 SE





From the micro structural analysis, it is found that the Zirconium di-oxide particles are of non-uniform size, irregularly shaped and randomly dispersed in the

alloy matrix. Agglomeration or clustering of the particles is also observed, resulting in particle-rich and particle depleted regions. This material in homogeneity is generally higher in these types of composites than the unreinforced matrix alloy. This was

probably formed during composite fabrication, by reaction between the Zirconium di-oxide particles and LM25 matrix aluminum alloy. Moreover the particle clusters are

found to be more when compared with others. These results, also often reported for particle reinforced composites, are generally related to the intrinsic micro structural in homogeneity of these materials, as regards to distribution.

3.2. Creep Test Analysis

Figure 3.11 Comparison on variation of displacement with respect to load for different proportions of particle reinforced composite.

160

165

170

175

180

185

190

195

200

0 2 4 6 8 10

Dis

pla

cem

ent(

mm

)

Load(kg)

Pure LM25

LM25 & 3% ZrO2



From the Figure 3.11, it can be observed that, the creep strength is low for LM25 & 3% of ZrO2. LM25 & 6% ZrO2 have same creep strength as that of pure LM25.

LM25 & 9% ZrO2 have the highest creep strength of all the samples. It is seen that with the increase in addition of ZrO2 with LM25 the creep strength of the composite

material increases. It is also seen that with the increase in load displacement increases.

4. CONCLUSION:

Based on the experimental investigations of the role of ZrO2 particulates with LM25

aluminum alloy metal matrix composites, the following conclusions can be made.

1. The Creep strength of the Aluminium alloy (LM25) reinforced with Zirconium di-oxide (ZrO2) particulate composites is generally higher than that of unreinforced Aluminium alloy and consistent with other studies on particle reinforced metal matrix composites.

2. The beneficial effect of particle addition on Creep strength is more evident at lower stress levels and there is no appreciable change in creep strength with increasing weight fraction of particulates at higher stress level.

3. The Creep strength of the Aluminium alloy (LM25) - Zirconium di-oxide (ZrO2) particulate composite, which may be attributed to its coarser grain size and in homogeneity of particle distribution and this also consistent with micrographs of the composites.

4. It is seen that with the increase in addition of ZrO2 with LM25 the creep strength of the composite material increases. It is also seen that with the increase in load displacement increases. Moreover, the weight fraction of above 3% particle reinforcement has no appreciable effect on creep properties.

In future, the results of this study can be compared with other combination of

matrix and reinforcement to develop cost effective material with respect to applications.

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EXPERIMENTAL INVESTIGATION OF CREEP … · Zirconium-di-oxide with LM25 by creep testing machine....

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