Mechanical Properties Of Zirconia Toughness Alumina Composite Using Cold Isostatic Pressing And Uniaxial Pressing Mohd Mustafa Al Bakri Abdullah
Ahmad Fauzi Mohd. Noor
School of Material Engineering, Kolej Universiti Kejuruteraan Utara Malaysia, P.O Box 77, d/a Pejabat Pos Besar, 01000 Kangar Perlis. Tel: 04 – 9852233
School of Material and Mineral Resources Engineering, Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal, Pulau Pinang, Malaysia
[email protected] du.my
[email protected]
[email protected]
Norazian Mohamed Noor
Che Mohd Ruzaidi Ghazali
Nur Khairiatun Nisa Mokhtar
School of Environmental Engineering, Kolej Universiti Kejuruteraan Utara Malaysia, P.O Box 77, d/a Pejabat Pos Besar, 01000 Kangar Perlis. Tel: 04 – 9798835
[email protected]
School of Material Engineering, Kolej Universiti Kejuruteraan Utara Malaysia, P.O Box 77, d/a Pejabat Pos Besar, 01000 Kangar Perlis. Tel: 04 – 9798192
Kamarudin Hussin School of Material School of Material Engineering, Kolej Universiti Kejuruteraan Utara Malaysia, P.O Box 77, d/a Pejabat Pos Besar, 01000 Kangar Perlis. Tel: 04 – 9798000
School of Material Engineering, Kolej Universiti Kejuruteraan Utara Malaysia, P.O Box 77, d/a Pejabat Pos Besar, 01000 Kangar Perlis.
[email protected] .
ABSTRACT Alumina-zirconia composite is an engineering material with a great potential to be developed for application as high temperature resistance structural material. In this research, zirconia toughness alumina (ZTA) was produced by physical reaction between Al2O3 powder and Y2O3-ZrO2 powder. Two composition of powder with different alumina:zirconia ratio was used, 70:30 and 80:20 by weight. Two different compaction methods, i.e. uniaxial pressing and cold isostatic pressing (CIP) with a maximum load of 150 MPa were used in this research to investigate the differences in properties of composites. Sintering process was done at four different temperatures with different heating rate 5ºC/ min with a soaking time of five hours. Mechanical testing, i.e. compressive strength and hardness was performed to all samples. The microstructure analysis using a Scanning Electron Microscope (SEM) was also studied. From the result, the composite with the ratio of 70:30 produced by CIP compaction method showed better mechanical properties as compared to 80:20 composite or by uniaxial pressing methods. Addition of zirconia in the composite gave an increased in toughness due to transformation toughening mechanism of tetragonal to monoclinic phase. As a conclusion the composites produced high compaction green density will improved the sintering process, resulting in improve mechanical properties.
Keywords Uniaxial Pressing; Cold Isostatic Pressing; ZirconiaAlumina Composite
1. INTRODUCTION Composite is the multiphase material which shows combination properties from its elements [1]. The earliest human made composite material was introduced in early 1960 [2]. Starting from that year, more than 80% of researches and development are based on composite. This percentage continue to increase proportional to the request of application using strong, stiff, light and high temperature resistance materials. Thus, composite can fulfill this request. Nowadays, ceramic matrix composite (CMC) is one of the advanced material which is developing in engineering field [3]. Researches have been done to develop engineering material and can be use as alternative material to the conventional metal which has lack of properties. One of an example of CMC is zirconia toughness alumina (ZTA). ZTA composite consist of alumina matrix which embedded inside of it zirconia particles whether zirconia half-stable or stable [4]. Earlier research also found that the fracture toughness of ZTA increased due to the increased of the contain of zirconia.
2. EXPERIMENTAL PROGRAMME This research is to learn the processing method of CMC; zirconia toughness alumina (ZTA) using cold isostatic pressing (CIP) and uniaxial pressing. The target of this experiment is to produce ZTA through physical reaction between Al2O3 powder and Y2O3-ZrO2 powder.
Alumina powder
This research also investigates connection between processing method and final properties. The microstructure analysis using SEM machine also presented and discussed. We will determine the strength and hardness. On the other hand, this study will observed the difference properties and microstructure produced by percentage composition of reinforcement to the different matrix. The overall process showed below in figure 1.
Zirconia powder
PEG, PVA Dispex N40
Mixing 1 hour in Zirconia Ball
Drying Temperature at 5560oC
Crushing and Sieving
Granulation 8-10% Water Uniaxial Pressing Method (Pre-compaction) 70 MPa
Sample Forming
Uniaxial Pressing 150 MPa
Cold Isostatic Pressing Method 150 MPa
Sintering Soaking Time 5 hour
Sintering Soaking Time 5 hour
Composite Characterization
Mechanical SEM Strength Hardness
Composite Characterization
Figure 1: Experimental process
3. RAW MATERIALS 3.1 Alumina Powder High purity of -alumina powder is used in this experiment. It is used to act as a matrix composite to give shape and to get the desire composite properties such as strength, stiffness and density.
3.2 Zirconia Powder Zirconia or Zirconium Oxide (ZrO2) is a unique ceramic material compared to the other ceramic engineering materials. Change of internal structure through the toughness mechanism will produced material more likely to ZrO2. This is the main advantage since other ceramic materials are brittle. In this research, Y2O3-ZrO2 used as reinforce with stabilizer 5.4% Yttria.
3.3 Distilled Water The usage of distilled water in the mixing process of raw materials is to catalyst the material to reach the high homogenous stage easily. On the other hand, distilled water can separate the sediments and give mixed with good flowing movement. The advantages of using distilled water are nontoxic, environmental friendly and easy to eliminate through drying. In this study, between 8-10% of water contain used to increase the glutinous force and to get the right shape with simple geometry.
3.4 Fastener PEG and PVA
Figure 2 (a): Diffraction pattern for powder alumina.
Polyvinyl Chloride (PVA) is a fastener that acts as a particles fastener during forming in order to get the suitable green body. PVA with molecular weight 22000 (fluca type) is used. While the PEG with molecular weight 900 (fluca type) was added to obtain the green body deformation properties. In this research, only 2% PEG and 1% PVA were used. This is based on research by former researcher [5].
3.5 Disconglomerate Disconglomerate agent used in this experiment is Dispex N40 in condensed liquid form. To obtain the good homogenous mixing, 4-5 drops Dispex N40 were dropped while the mixing process was done.
Figure 2 (b): Diffraction pattern for zirconia powder.
4.2 Fracture Strength Analysis 4. RESULTS AND DISCUSSION 4.1 Raw Materials Characterization From the research, it was found that particle size of alumina used is 2.16 m while the particle size of zirconia is between 0.1 m to 2.0 m. XRD analysis is done to determine the mineralogy phase of the raw materials used in this experiment. Phase determination is done by matching the diffraction pattern of XRD for alumina in the raw material with the database from International Center For Diffraction Data (ICDD). The match diffraction pattern of raw material of alumina with the data base in ICDD for Al2O3 (10-0173) shows that raw material of powder alumina is corundum. While, the match diffraction pattern of zirconia for ZrO2 (17-0923) and Yttria-Y2O3 (41-1105) show that zirconia are tetragonal and monoclinic phase. From the result, obviously, Y2O3 help in formation of halfstable zirconia and this is important to increase fracture strength through toughness transformation mechanism. Diffraction pattern for both powder show in figure 2(a) and 2(b)
Figure 3(a) show that almost all the sample produced, have optimum fracture strength value at temperature 1600oC for uniaxial pressing. Most of the sample have low fracture strength value at 1550oC and increased with the increased in every 5oC temperature. The increasing heat over 1600oC will decrease the fracture strength value. This is because of the forming of closed pore. The increased of pore caused the decreased of fracture strength value or the percentage of pore is proportional to the fracture strength value of composite. Beside that, high density by effective sintering reaction (related with body compaction before sinter) also affect the mechanical properties. Figure 3(a) show that composite produced by composition 70:30 have fracture strength higher than composite with 80:20. The addition of different reinforce zirconia phase give the considerable fracture value to the composite which produced by toughness transformation mechanism. It is related to the compaction body, ratio of 70:30 is more compact in the green body. In high density condition, the sintering process is higher. Result of the fracture strength test and Young’s Modulus through CIP method is shown in figure 3(b). The result obtained show that the composition produced have optimum strength at temperature 1550o C for both composition. The result also shows that composition of 70:30 give high fracture strength values; 330 MPa compared to the composition 80:20; 268 MPa. The high value in composition 70:30 occurs because of the present of high ZrO2. Zirconia is known to have high strength and stiffness
than alumina. The present of high ZrO2, will cause the function of toughness transformation mechanism increased, so that the stiffness fracture also increased and affecting the fracture strength to increase. This is based on the eq. below [6]:KIC a
f
where, - fracture strength - stiffness strength - defect size
f
KIC a
composite hardness value produced in this experiment is a bit lower than expected value that is 15002000HV. This is due to hardness that is related to the composite density occurrence of either open-pore or closed pore in the composite. Both kinds of pores affect the composite hardness. The present of pores make the distance of particles increased and affected the composite hardness. When the density of sintered composite is high, the hardness value will increase, due to the pore between particles Al2O3 and ZrO2. Hence, the pores properties and density as well as fracture toughness affect the composite hardness.
Graf Strength with Temperatures
Graf Kekuatan Melawan Suhu Yang Berlainan 350.00
300.00
70:30
Kekuatan (MPa)
250.00
, 200.00 MPa
80:20
150.00
100.00
50.00
0.00 1550
1600
1650
Suhu (o C)
Temperature, oC Kompos isi 70:30
Komposisi 80:20
Figure 3 (a): Fracture strength with different sinter temperature using uniaxial pressing method
Figure 4(b) shows the result of Vickers hardness test through CIP method. The hardness value reach 1552HV for composition 70:30 and 1446HV for composition 80:20. This value reached the reported range which is 1500-2000HV. Composition produced by CIP method reach the optimum hardness at sinter temperature that is 1550oC for both composite. After sintering temperature increased higher than 1550oC, the hardness experience linear decrease and reach the minimum value 1250 HV for composition 80:20 and 1380HV for composition 70:30. Hardness is related to the fracture strength as well as physical body properties. For an example, the present of pore either open-pore or closed-pore affects the hardness properties. Graph Hardness with Different Temperatures Graf Kekerasan Melawan Suhu Yang Berbeza
Graf Strength with Different Temperatures
1480.00
Graf Kekuatan Melawan Suhu Berbeza
1470.00
350.00 1460.00
300.00
1450.00 Kekerasan (HV)
, MPa
250.00
, MPa
200.00
80:20
1440.00 1430.00
70:30
1420.00
80:20 1410.00
150.00
1400.00
100.00 1390.00
50.00
1380.00 1550
1600
1650
o
Suhu ( C)
Temperature, oC
0.00 1500
1550
1600
Komposisi 70:30
1650
Komposisi 80:20
o
Suhu ( C) o Temperature, C Komposisi 70:30
Komposisi 80:20
Figure 4 (a): Hardness value with different sinter temperature using uniaxial pressing method
Figure 3 (b): Fracture strength with different sinter temperature using CIP method
Graph Hardness with Different Temperatures Graf Kekerasan Melawan Suhu Yang Berbeza 1800.00
4.3 Vickers Hardness Analysis
1600.00
Figure 4(a) shows the optimum value of hardness is at 1600oC for both composition through uniaxial pressing method but the composition of 70:30 have higher hardness value 1470 HV compared to the composition 80:20; 1440 HV. The hardness value increased due to the increased of ZrO2 in the composition. Generally, half-stable zirconia such as (Y2O3-ZrO2) that is used in this experiment is high in toughness strength due to toughness transformation mechanism. Small particles of zirconia will increase the compaction as well as the efficiency of sintering process. Vickers test is done at the range of producing composite that are 1410 – 1470 HV. From the test, the
1400.00
70:30 1200.00 Kekerasan (HV)
Kekuatan (MPa)
70:30
80:20
, MPa 1000.00 800.00
600.00
400.00
200.00
0.00 1500
1550
1600
1650
o
o Suhu ( C) Temperature, C
Komposisi 70:30
Komposisi 80:20
Figure 4 (b): Hardness value with different sinter temperature using CIP method
4.4 SEM Microstructure Analyses Figure 5 (a) and (b) show the microstructures composition of (70:30) using the same sintering temperature (1600oC). It was observed that the composite pore using CIP method is less compared to the composite produced using uniaxial pressing method. This is because at temperature 1600oC, the composite produced using CIP method contain closed pore cost by glassy phase due to over sintered. Glassy liquid entered the open pores and become closed-pore.
cause localized grain growth because of less resistance. Reversely, using CIP method, higher compaction will not cause localized grain growth. It is shown by the present of more uniform grain size of alumina and zirconia. Obviously, uniform microstructure CIP affect physical and mechanical properties of the produced sintered body as discuss in the previous result. Magnification scale 2000x
Magnification scale1000x
a) Composition 70:30 (Al2O3-ZrO2) using uniaxial pressing method.
a) Composition 70:30 (Al2O3-ZrO2) using uniaxial pressing method.
b) Composition 70:30 (Al2O3-ZrO2) using CIP method. b) Composition 70:30 (Al2O3-ZrO2) using CIP method. Figure 5: SEM micrograph using secondary backscattered electron to differentiate microstructure with same composition produced in this experiment with sintered temperature 1600o C using 1000x. a) Composition 70:30 (Al2O3-ZrO2) using uniaxial pressing method b) Composition 70:30 (Al2O3-ZrO2) using CIP method Figure 6 (a) and (b) shows the distribution of reinforce particles of ZrO2 in the matrix of ununiform Al2O3 due to inhomogeneous mixing. It can also be seen that, CIP method produced more uniform distribution of alumina grain than uniaxial pressing method. It is mentioned before that uniaxial pressing method will produced lower compaction and not rigidly fixed together. By using sintering process, those condition
Rajah 6: SEM micrograph using Back Scattered Electron to differentiate sample microstructure with same composition that produced in this experiment with sintered temperature 1600oC with magnification 1000x. a) Composition 70:30 (Al2O3ZrO2) using uniaxial pressing method b) Composition 70:30 (Al2O3-ZrO2) using CIP method
5. CONCLUSION This research is to determine the effect of different pressing method that are cold isostatic pressing and uniaxial pressing method to the composition alumina:zirconia by ratio based on different weight (70:30 dan 80:20) and sintered at various temperature between 1500oC to 1650oC.
From the result obtained, the composite with ratio 70:30 show better mechanical compared to the composite with ratio 80:20. Different pressing method also affect the properties of composite produced. Final result shown, that the mechanical properties using CIP method is better than uniaxial pressing method. Composite compacted by CIP method show better properties at lower sintered temperature compared to the uniaxial pressing method. The result show that by using CIP method the composite produced has good properties at sintered temperature of 1550oC while composite compacted using uniaxial pressing method reach optimum properties at temperature 50oC higher (1600oC). This is due to the green body compaction, where as by using CIP method will produced the green body with higher compaction and will increased the sintering rate.
6. ACKNOWLEDGEMENT School of Material and Mineral Resources Engineering, Universiti Sains Malaysia, Kampus Kejuruteraan, 14300 Nibong Tebal, Seberang Perai Selatan, Penang.
7. REFERENCES [1] Mustaffa, A. (1991). Sains Bahan. Jilid Satu. Kuala Lumpur: Dewan Bahasa dan Pustaka. P. 362-368 [2] Chawla, K. K. (1993). Ceramic Matrix Composites. London: Chapman & Hall [3] Strong, A. B. (1989). Fundamentals of Composites Manufacturing, Materials, Methods and Applications. Michigan: Society of Manufacturing Engineers. P. 39 [4] Casellas, D., Rafols, I., Llanes, L., Anglada, M. (1998). Fracture Toughness of Zirconia-Alumina Composites. International Journal of Refractory Metals & Hard Materials. 17:11-20 [5] Ahmad Fauzi, M. N (1995). Reformulation of Vitrified Quartz-containing Whitewares. Ph.D Thesis. University of Sheffield [6] Hull, D. and Clyne, T. W. (1996). An Introduction to Composite Materials. 2nd Ed. Cambridge: Cambridge University Press. P. 21
