《复合材料 Composites》课程教学资源（学习资料）第五章 陶瓷基复合材料_brittleness14

JOURNAL OF RARE EAR vol. 25, Suppl., Jun. 2007 Thermal Shock Resistance of Al2 O3/ZrO2(Y203)Composites Ma weimin(马伟民), Wen lei(闻雷), Sun Xudong(孙旭东}, Cui Tong(崔桐), Qiu guanming(邱关明) (I. Department of Materials Science and Engineering, Shenyang Institute of Chemical Technology, Shenyang 110142 China; 2. Shenyang National Laboratory for Materials Science, Institute of Metal Research, The Chinese Academy of Sciences, Shenyang 110016, China; 3. Institute of Materials and Metallurgy, Northeastern University Shenyang 110044, China; 4. Changchun University of Science and Technology, Changchun 130022, China) Abstract: ZrO2 containing 2 %(mol fraction) Y203 and 3%(mol fraction)Y203 were added into A12O3 matrix, composit ing composites with 15% volume fraction of addictives mentioned above. The testing of property and analysis of SEM pre sented that, after vacuum sintering at 1550C, thermal shock resistance of two composites was superior to Al2O3 ceramic The experiment showed that the properties of Al2O3 composites was higher than Al2O3 ceramic, and Al2O3/ZO2(3Y)was higher than Al203/ZH02(2Y)in thermal shock resistance. Improvement of thermal shock resistance of composites was at tributed to many toughness machanisms of ZrO2(Y203). By calculation, the fracture energy of A1203, Al203/ZrO2(2Y) d Al203/ZrO2(3Y)was 38100. 8 and 126.2 Jm-2, respectively. Cracks initiation resistance(R,)of A1203/ZH02(3Y) and Al203/Z 02(2Y)was higher than Al2O3 ceramic by 1. 57 and 1. 41 time, respectively, and cracks propagation resis- tance(r")was higher than Al2O3 ceramic by 1. 46 and 1.38 time, respectively, which was corresponding to the results Key words: fracture energy; transformation toughness; Al203/Zr02(Y203)composites; thermal shock resistance; inor- ganic non-metallic material rare earths CLC number: TG174453; TG 113. 25 Document code: A Article ID: 1002-0721(2007)-0053-05 ing ceramic material because of its beneficial proper- strength of thermal shock experimen ng to residual Alumina is one of the most widely used engineer- stability. The results are corresponding to residual ties, such as high wear resistance, chemical stability high temperature strength and creep resistance. But 1 Experimenta ceramic materials have high brittleness, high Youngs modulus, negligible plastic yields and poor thermal 1.I Preparation procedure conductivity. They are so sensitive to thermal transient The starting materials were AL,O3 (99.99%)pow and thermal fatigue that the strength of materials can der of 0.2 um, Zr0, (2Y)(99.9%)powder of 0.02 be weakened and this situation may lead to catastrophe ic failure. Therefore, as a structural material of high um and ZrO2(3Y)powder of 0.02 um.A120,/15% temperature usage, its thermal shock resistance or ZrO2(2Y)and Al2,/15% ZrO2(3Y powders were fabricated by milling composite powders of Al2O the service life of such material. Obviously, there are ZO2(2Y)and Z102(3Y )for 48 h, respectively.The two methods to improve the thermal shock resistance of mixed powders were dried, loaded with two-face model ceramic materials: to decrease power-damage and to and then isostatically pressed at 200 MPa. The spec enhance thermal shockresistance, which are effective mens were preheated at 600 C in a box-furnace for thermal shock resistance of vacuum-sintered Al2O 2 h and then sintered at 1550℃for2hinaⅤ SF vac 15%Zr02(2Y)and Al203/15%Z102(3Y)composites, uum sintering furnace with the vacuum degree lov a calculation of cracks initiation resistance and cracks than 1 x 10-3Pa. The dimension of specimens reached propagation resistance and an analysis of heat-shock mm x5 mm x 5mm Received date: 2006-09-26: revised date: 2007-03-13 Foundation item: Project supported by the Natural Science Foundation of Liaoning Province( 20032002)and the Key Program of Science and Biography: Ma Weimin(1956-), Male, Doctor, Professor wCorrespondingauthor(e-maii:maweimin56@163.com

JOURNAL OF RARE EARTHS Vol.25, Suppl., Jun. 2007, p.53 Thermal Shock Resistance of A12 03/Zr02 ( Y2 O3 ) Composites Ma Weimin (4#58)’* , Wen Lei (PTJ (1, Department .f Materials Science and Engineering, Shnyang Institute of Chemical Technology , Shenyang 110142, China ; 2. Shenyang National Laboratory for Materials Science , Institute of Metal Research , The Chinese Academy of Sciences , Shenyang I1 001 6, China ; 3. Institute of Materials and Metallurgy , Northeastern University , Shenyang 110044, China ; 4. Changchun University of Science and Technology, Changchun 130022, China) %)’, Sun Xudong Cui Tong (B k)3, Qiu Guanming (sF%tVJ)4 Abstract: ZrO2 containing 2% (mol fraction) Y203 and 3% (mol fraction) Y203 were added into A1203 matrix, composit￾ing composites with 15 % volume fraction of addictives mentioned above. The testing of property and analysis of SEM pre￾sented that, after vacuum sintering at 1550 “c , thermal shock resistance of two composites was superior to AI2O3 ceramic. The experiment showed that the properties of A1203 composites was higher than A1203 ceramic, and A1203/Zr02(3Y) was higher than A1203/ZrO2(2Y) in thermal shock resistance. Improvement of thermal shock resistance of composites was at￾tributed to many toughness machanisms of ZrO2(Y203) . By calculation, the fracture energy of A1203, A1203/Zr02 (2Y) and A1203/Zr02(3Y) was 38100.8 and 126.2 J~rn-~, respectively. Cracks initiation resistance (R’) of A1203/2&(3Y) and A1203/ZrO2(2Y) was higher than A1203 ceramic by 1.57 and 1.41 time, respectively, and cracks propagation resis￾tance ( Rrr”) was higher than A1203 ceramic by 1.46 and 1 .38 time, respectively, which was corresponding to the results of residual strength. Key words : fracture energy ; transformation toughness ; A1203/Zr02 ( Y203 ) composites ; thermal shock resistance ; inor￾CLC number: TG174.453; TG113.25 ganic non-metallic material ; rare earths Document code: A Article ID: 1002-0721(2007) -0053-05 Alumina is one of the most widely used engineer￾ing ceramic material because of its beneficial proper￾ties, such as high wear resistance, chemical stability, high temperature strength and creep resistance. But ceramic materials have high brittleness, high Young’s modulus, negligible plastic yields and poor thermal conductivity. They are so sensitive to thermal transient and thermal fatigue that the strength of materials can be weakened and this situation may lead to catastroph￾ic failure. Therefore, as a structural material of high temperature usage, its thermal shock resistance or thermal fatigue is one of the key factors determining the service life of such material. Obviously, there are two methods to improve the thermal shock resistance of ceramic materials : to decrease power-damage and to enhance thermal shockresistance, which are effective ways for ceramics. This paper shows a research on thermal shock resistance of vacuum-sintered A1203/ 15%zr02(2Y) and A1203/15%Zr02(3Y) composites, a calculation of cracks initiation resistance and cracks propagation resistance and an analysis of heat-shock Received date : 2006 - 09 - 26 ; revised date : 2007 - 03 - 13 stability. The results are corresponding to residual strength of thermal shock experiments. 1 Experimental 1.1 Preparation procedure The starting materials were A1203 (99.99% ) pow￾der of 0.2 pm, Zr02(2Y) (99.9%) powder of 0.02 pm and ZrOz ( 3Y) powder of 0.02 pm . Al2O3/15% Zr02 (2Y) and A1203/15% Zr02 ( 3Y ) powders were fabricated by milling composite powders of A1203, ZrOz( 2Y) and ZrOz (3Y) for 48 h , respectively. The mixed powders were dried, loaded with two-face model and then isostatically pressed at 200 MPa. The speci￾mens were preheated at 600 “c in a box-furnace for 2 h and then sintered at 1550 “c for 2 h in a VSF vac￾uum sintering furnace with the vacuum degree lower than 1 x Pa. The dimension of specimens reached 30mm~5mm~5mm. Foundation item: Project supported by the Natural Science Foundation of Liaoning Province (20032002) and the Key Program of Science and Technologies of Shenyang (1053090-2-05) Biography: Ma Weimin ( 1956 - 1, Male, Doctor, Professor * Corresponding author (E-mail : rnaweimin56 @ 163. corn )

JOURNAL OF RARE EARTHS, VoL 25, Suppl., Jun, 2007 MPa'm"2)is higher than that of Al2O, ceramic(3. 2 Characterization MPa.m The fracture toughness was examined by SENB The resistance of thermal shock of AlO3/ZrO2 technique and can be calculated according to the fol- composites is improved greatly compared with that of lowing equation AL2O3 ceramic. The strength of Al2O3 decreases quick 3PLa (1) ly according to Fig. 1. The loss of strength is 30%at 300 C, after that it changes slowly. The loss of where Y is a geometrical constant, P is the fracture strength is 85.2% at 900 C. In the same condition load(kW),b and W are related to the width and the strength of A120,/15%ZrO2(3Y)composite de thickness, respectively, and a is the depth of speci- creases slowly after one time quenching from 300 mens center crack. The SENb technique was used to 900 C. However, strength of the composite decreases induce controlled cracks( depth of specimen center is smoothly below 700 C and decreases significantly 0.025 mm) on face of polished specimens. Thermal above 700C after five quenching cycle times. The shock properties were measured by quenching method loss of strength after one cycle and after five cycles ob- Then specimens were annealed for I h in air at 1300 viously increases about 25% and 37.3% at 1100C C to maximize the amount of tetragonal ZrO2 and to respectively. The strength of A1,03/15% ZrO2( 2Y relieve surface compression stress by particle-induced composite shows decrease slower than that of A120, transformation. The specimens were heated at 300 5%Z02(3Y)at the temperature below 900C, but 500, 700,900 and 1100C, respectively. Holding it rapidly decreases above 900 C, which is 29% and 20 min at each temperature then put into boiling water 37. 6%, respectively. Therefore, because of the Zro, rapidly. All specimens were cyclically quenched (Y203)transformation toughness mechanism, the ther 1 time and 5 times. Instron 4206 machine with load- mal shock resistance of composites is higher than that eed 0.05 mm min"was used to measure specimens of Al2O3 ceramic. The difference between Al203/15% bending strength, fracture toughness and residual bending resistance of quenched specimens. Elastic ZrO2 (3Y)composite and AL O3/15% ZrO2 (2Y )com modulus, Poissons ratio, thermal expansion coef posite is the major effect of transformation toughness cient and heat conductivity of specimens were mea mechanism, expansion coefficient and heat conductivi- sured according to literature 7). The fracture surface of ty. These differ rence shows that composites have the specimens before and after thermal shock fracture were character of thermal shock crack propagation of static observed with a scanning electron Microscope( Model state expansion, which is corresponding to the bal EPM-810Q ance of the elastic strain energy and the absorption of fresh fracture surface energy. Fig. I illustrates that the 2 Results and Discussion posites after five cycles decreas 2.1 Thermal shock resistance ites after one cycle time The physical and mechanical properties of Al2O3 ceramic and the composites are shown in Table 1. The hermal shock properties of Al2O, ceramic and the shown in Fig. 1 15%Z:02(2Y )and A1,0,/15% ZrO2(3Y )composites is 361, 637 and 779 MPa, respectively. After intro- ducing SENB method, the corresponding strengths is 189,474 and 641 MPa, respectively. The strength of three materials decreases about 50%, 35. 8% and 27.5%, respectively. It was known that, owning to the fracture toughening effects, sensitivity to cracki Fig. I Residual strength of Al,O, ceramic and Al,O,3/rO2 of A1203/15% Zr02(3Y)and A1203/15%Zr02 (2Y) composites after quenching at various temperature dif- lower than that of Al20, ceramic. It matches with the Al203/ZrO(3Y ) Single quench; A A1,0, /Z102(3Y)Five Its that the fracture toughness of Al2 03/15% ZrO quenches;* Al 0, /Z0,(2Y)Single quench:+ A120a/Zro2 )(7. 8 MPa.")and A120 /15% Zr02(2Y)(6.7 (2Y)Five quenches; A120, Single quench

54 JOURNAL OF RARE EARTHS, Vol. 25, Suppl. , Jun . 2007 1.2 Characterization The fracture toughness was examined by SENB technique and can be calculated according to the fol￾lowing equation”’ : 3PL 2bW2 KIc = Y ---A where Y is a geometrical constant, P is the fracture load (kW), b and W are related to the width and thickness, respectively, and a is the depth of speci￾mens center crack. The SENB technique was used to induce controlled cracks (depth of specimen center is 0.025 mm) on face of polished specimens. Thermal shock properties were measured by quenching method. Then specimens were annealed for 1 h in air at 1300 “c to maximize the amount of tetragonal ZrOz and to relieve surface compression stress by particle-induced transformation. The specimens were heated at 300, 500, 700, 900 and 1100 “c , respectively. Holding 20 min at each temperature then put into boiling water rapidly. All specimens were cyclically quenched 1 time and 5 times. Instron 4206 machine with load￾speed 0.05 mm * min- ’ was used to measure specimens bending strength, fracture toughness and residual bending resistance of quenched specimens . Elastic modulus, Poisson’ s ratio, thermal expansion coeffi￾cient and heat conductivity of specimens were mea￾sured according to 1iteratu1-e‘~’. The fracture surface of specimens before and after thermal shock fracture were observed with a scanning electron Microscope ( Model EPM-810Q). 2 Results and Discussion 2.1 Thermal shock resistance The physical and mechanical properties of A1203 ceramic and the composites are shown in Table 1. The thermal shock properties of A1203 ceramic and the composites are shown in Fig. 1. As shown in Fig. 1, the bending strengths of single phase Alz03, A12O3/ 15%ZrOz( 2Y) and Al20,/15% Zr02 (3Y) composites is 361, 637 and 779 MPa, respectively. After intro￾ducing SENB method, the corresponding strengths is 189, 474 and 641 MPa, respectively. The strength of three materials decreases about 50%, 35. 8% and 27.5 % , respectively. It was known that, owning to the fracture toughening effects, sensitivity to cracking of A1203/15%Zr02(3Y) and Al2O3/l5%ZrO2(2Y) is lower than that of A1203 ceramic. It matches with the results that the fracture toughness of A1203/15% ZrOz (3Y) (7.8 MPa milz ) and A1203/15% ZrOz (2Y) (6.7 MPa*m’/’) is higher than that of Alz03 ceramic (3. 1 MPa*rn’”). The resistance of thermal shock of A1203/Zr02 composites is improved greatly compared with that of A1203 ceramic. The strength of A1203 decreases quick￾ly according to Fig. 1. The loss of strength is 30% at 300 “c, after that it changes slowly. The loss of strength is 85.2% at 900 “c . In the same condition, the strength of Al2O3/15% ZrOz ( 3Y ) composite de￾creases slowly after one time quenching from 300 to 900 “c . However, strength of the composite decreases smoothly below 700 “c and decreases significantly above 700 “c after five quenching cycle times. The loss of strength after one cycle and after five cycles ob￾viously increases about 25 % and 37.3 % at 1100 “c , respectively. The strength of Al2O3/15% ZrO2 ( 2Y ) composite shows decrease slower than that of A1203/ 15%zr02(3Y) at the temperature below 900 T, but it rapidly decreases above 900 “c , which is 29% and 37.6% , respectively. Therefore, because of the ZrOz ( Y203) transformation toughness mechanism, the ther￾mal shock resistance of composites is higher than that of A1203 ceramic. The difference between A1203/15% zrO~(3Y) composite and Al2o3/15% ZrOz(2Y) com￾posite is the major effect of transformation toughness mechanism , expansion coefficient and heat conductivi￾ty. These differences shows that composites have the character of thermal shock crack propagation of static state e~pansion‘~], which is corresponding to the bal￾ance of the elastic strain energy and the absorption of fresh fracture surface energy. Fig. 1 illustrates that the loss of strength of composites after five cycles decreas￾es significantly compares with the strength of compos￾ites after one cycle time. 7001 I 0 200 400 600 800 1000 1200 Temperature difference/‘(: Fig. 1 Residual strength of A1203 ceramic and A1203/Zr02 composites after quenching at various temperature dif￾ference 0 A1203/ZrO~ (3Y) Single q;ench; A A1203/Zr02 ( 3Y) Five quenches; * A1203/Zr02 (2Y Single quench; + A1203/Zr02 (2Y) Five quenches; A1203 Single quench

Ma W M et al. Thermal Shock Resistance of A1,0,/zro2 (Y203) mal shock resistances of A1203 /15% ZrO2(3Y )and A1203/15%Zr02(2Y )composites is lent than that of Al,O. ceramic. Moreover, thermal shock resistance of Al203/15% ZrO2(3Y )composite is more excellent than that of A1,0,/15% ZrO2(2Y) composite 2.2 Microstructure factures of fracture surface 0-20040060080010001200 Scanning electron macrographs(SEM)of fracture surface of A120, ceramic are shown in Figs. 3(a)and b). Fracture surface is smooth before quenching and Fig 2 Strength loss factor of Al20, ceramic and Al0,/Z 0, t is an obvious phenomenon of single crack. Fracture differences surface is rough after quenching from 1100 C. More o A1,0,/1O2(3Y)Single quench; A A1, 0, /ZH02 (3Y)Five cracks appear and macro-cracks are observed. Frac quenches:* Al,0, /ZrO2(2Y)Single quench;. A1 0, /Z102 ture surface is broken up a few parts during bending ches: Al,O, Single quench Fig 2 shows that the loss factor of strength is re The fracture surfaces of Al,0, /15% ZNO2(3Y) lated to different thermal shock temperatures, the loss and Al203/15% ZrO2( 2Y )composites are show factor increases with increasing temperature differ Figs 4 and 5. Fr racture ence. The strength loss factors of Al2O3, Al203/15% ZrO2(3Y)and A12O3/15%Zr02(2Y ) is about 85.2% distinct. Under high thermal shock temperature, spee 18 and 12. 4%, respectively at 900C. After five imens do not break up into few parts. Because of sev cycles, the strength loss factor of these composites eral times of rupture difficult to observe 7. 3 and 37. 6%0, respectively. It shows that the thermal-shock resistance of composites is excellent Fig 3 SEM of fracture surfaces of AL2O, ceramic before(a)and after(b) quenching from 1100C 4μm 4 u m Fig 4 SEM of fracture surfaces of Al203/15% ZrO2(3Y)composites before(a)and after(b)quenching from 1100 C

Ma W M et a1 . Thermal Shock Resistance of A1203/Zr02 ( Y2O3 ) 55 / / Temperature difference/”(: Strength loss factor of A1203 ceramic and A1203/Zr02 composites after quenching with various temperature differences 0 A1203/Zr0, (3Y ) Single quench ; A A1203/Zr02 ( 3Y ) Five quenches; * A1203/Zr02 ( 2Y ) Single quench ; + A120JZr02 (2Y) Five quenches ; Alz03 Single quench Fig.2 shows that the loss factor of strength is re￾lated to different thermal shock temperatures, the loss factor increases with increasing temperature differ￾ence. The strength loss factors of A1203, Al&/15% ZrOz(3Y) and Al2O3/15%Zr0,(2Y) is about 85.2%, 18% and 12.4%, respectively at 900 “c. After five cycles, the strength loss factor of these composites is 37.3% and 37.6% , respectively. It shows that ther￾mal shock resistances of Al2O3/15% ZrO, (3Y) and Al2O3/15 %ZrO2( 2Y) composites is much more excel￾lent than that of A1203 ceramic. Moreover, thermal shock resistance of Al2O3/15% Zr02( 3Y) composite is more excellent than that of A1,O3/15% ZrO, (2Y) composite. 2. 2 Microstructure factures of fracture surface Scanning electron macrographs (SEM) of fracture surface of A1203 ceramic are shown in Figs. 3 (a) and (b) . Fracture surface is smooth before quenching and it is an obvious phenomenon of single crack. Fracture surface is rough after quenching from 1100 “c . More cracks appear and macro-cracks are observed. Frac￾ture surface is broken up a few parts during bending test. The fracture surfaces of A1203/15% ZrO, (3Y ) and &o3/15% ZrOz ( 2Y ) composites are shown in Figs. 4 and 5. Fracture surface is smooth with small particles before quenching. The toughening phase is distinct. Under high thermal shock temperature, spec￾imens do not break up into few parts. Because of sev￾eral times of rupture, it is difficult to observe macro￾cracks. Therefore, these photographs present that thermal - shock resistance of composites is excellent to Fig.4 SEM of fracture surfaces of A1203/15% ZrOz(3Y) composites before (a) and after (b) quenching from 1100 T

JOURNAL OF RARE EARTHS, Vol 25, Suppl., Jun. 2007 (a) 德说漫 Fig 5 SEM of fracture surfaces of Al,0, /15% ZrO2 (2Y)composites before (a) and after(b)quenching frpm 1100C Al, O, ceramics. The surfaces of A1,, /15%Z02(3Y) coefficient of thermal expansion, W is the work of and Al203/15%Z 02(2Y composites without appear- fracture, 2yr is the fresh fracture surface energy ing cracks after quenching at 300 C compares with Therefore, for most materials, it is hard to enhance that of Al2O3 ceramic with appearing cracks. At 1100 rupture thermal shock parameter Rand breakage pa C, surface of composites can be shown cracks which rameter R"at the same time. If the work of rupture is are difficult to observe, the thermal cracks on AL,, enhanced, rupture parameter R'and breakage param ceramic surfaces begin to increase and propagate with eter R" should be enhanced simultaneously increasing of thermal shock temperature difference Thermal shock parameter Rand breakage pa These results illustrate that the micro-cra om rameter R"can be calculated according to Egs.(2) transformation toughness can absorb stress-strain and(4). Heat conduction ratio A and Poissons ration energy equations: 2.3 Calculation of thermal shock parameter ER=E2(1-g1)+E1 There are two theories on thermal shock resis- A=2(1-1)+A1P1 tance. Firstly, the point of view is based on elastic y=v2(1-g1)+y1g1 machanics. Secondly, on the view of fracture mechan cs, The physical meaning of thermal shock parameter R and breakage parameter R"is crack-initiation re- Q-a k2(1-91+a ka, e pansion a is given by and the coefficient of thermal ex sistance and crack-spread resistance, respectively K2(1-g1)+K1g1 Therefore, the thermal shock parameter Rand break- where suffix 1 and 2 represent toughness-increase age parameter R"are given by the volume λ(1-y)a ea (2) ratio of toughness-increase phase, K is the volume shrinkage factor EW, 2EY (3) where K2=3(1-22) because of K=√2EY (10) s0R=a(1- (4) The physical constants and mechanical properties of where or is the rupture stress, v is the Poisson's Al,O, ceramic, A120, /15%ZrO2(2Y)and Al203/15% tion, E is the modulus of elasticity, a is the linear ZrO2(3Y)composites are listed in Table 1 Table 1 Physical and mechanical properties of AlO, ceramic and composites E/GPa MPa KC/(MPa.m"2 ZrO(3Y) 217.0 3.300 9.900 ZrO2(2Y) Al2O3/ZrO2(3Y)355.6 25.145 8,412 A2Oy/ZO2(2Y)345.2 0.183

56 JOURNAL OF RARE EARTHS, Vol. 25, Suppl. , Jun . 2007 Fig. 5 SEM of fracture surfaces of Ai2O3/15 % ZrOz( 2Y) composites before (a) and after (b) quenching frpm 1100 T A1203 ceramics. The surfaces of A1203/15%Zr02(3Y) and Al2O3/15 % Zr02 (2Y) composites without appear￾ing cracks after quenching at 300 "c compares with that of A1203 ceramic with appearing cracks. At 1100 "c , surface of composites can be shown cracks which are difficult to observe, the thermal cracks on A1203 ceramic surfaces begin to increase and propagate with increasing of thermal shock temperature difference . These results illustrate that the micro-cracks from transformation toughness can absorb stress-strain energy[*' . 2.3 Calculation of thermal shock parameter There are tn, theories on thermal shock resis￾tance. Firstly, the point of view is based on elastic machanics . Secondly, on the view of fracture mechan￾ics. The physical meaning of thermal shock parameter R ' and breakage parameter R" is crack-initiation re￾sistance and crack-spread resistance, respectively. Therefore, the thermal shock parameter R ' and break￾age parameter R" are given by: R" = EWf - 2EYf 0x1 - Y) - &1- u) because of Klc = KIcZ a;( 1 - Y) So R"= (4) where of is the rupture stress, Y is the Poisson's ra￾tion, E is the modulus of elasticity, a is the linear coefficient of thermal expansion. Vf is the work of fracture, 2yf is the fresh fracture surface energy. Therefore, for most materials, it is hard to enhance rupture thermal shock parameter R ' and breakage pa￾rameter R" at the same time. If the work of rupture is enhanced, rupture parameter R' and breakage param￾eter R" should be enhanced simultaneously. Thermal shock parameter R' and breakage pa￾rameter R" can be calculated according to Eqs. (2) and (4) . Heat conduction ratio A and Poisson's ration u can be calculated according to the following equations : E,= 91) + El91 (5) (6) Y = Y2(1- 91) + Vl9, (7) A = Az(1- 91) + A191 and the coefficient of thermal expansion a is given by: where suffix 1 and 2 represent toughness-increase phase and matrix phase, respectively, 9 is the volume ratio of toughness-increase phase, K is the volume shrinkage factor. E2 3( 1 - 2~2) where K2 = EI 3( 1 - 2~1) K1 = The physical constants and mechanical properties of A1203 ceramic, A1203/15 %ZxQ (2Y) and Al2O3/15 % Zr02 ( 3Y) composites are listed in Table 1 . Table 1 Physical and mechanical properties of A1203 ceramic and composites Composites EIGPa A/(J.~-*-~-'.K-~) d10-~ v of* /MPa Kc "/(MPa*m"2) A1203 380.0 29. OM) 8.237 0.260 361 3.1 Zdz ( 3y 217 .O 3.300 9.900 0.250 - - zroz (2Y) 148.0 2.100 10.100 0.250 - - AIz03/Zr02(3Y) 355.6 25.145 8.412 0.183 779 7.8 A1zO3/ZrOz(2Y 1 345.2 24.965 8.371 0.183 637 6.7 * Experimental date

Ma w M er al. Thermal Shock Resistance of Al20,/ZrO2(Y2 0, Table 2 Thermal shock resistance intensity factor of materials of Al2O3 ceramic by 2.16 and 1.82 times and their crack-spread resistances(R" )was higher than R'/(Jm-2·s-1) that of Al2O3 ceramic by 1. 23 and 1. 37 times, respec- A2O3/15%ZrO2(3Y) 122.7 A12O3/15%ZrO2(2Y) 135,9 2. Toughness- increase phase transformation of The calculated values of R' and R" are shown in Al203 matrix. Both composites improved thermal shock Table 2. Crack initiation resistance and crack propaga fracture resistance and thermal shock damage tion resistance of A1, 0, /15% Zr02(3Y)and Al,0/ tance. Fracture energy of Al203, Al203/15% 15% ZNO2 (2Y)are both higher than that of ALO, ce-(3Y)and Al203/15% Zr02(2Y)was 24, 162 and ramic according to Table 2, respectively. Crack initia- J-m, respectively. The resistance to thermal shock tion resistances R' of A1,0,/15%z0,(3Y )and of Al 203/15% ZrO2(3Y)was superior to that of Al203 A1,0,/15% Z102 (2Y)composites is higher than that of ceramic and AL203/15% ZrO2(2Y)composite Al2O3 ceramic by 2. 16 and 1. 82 times, respectively 3. The stress induction transformation tough Crack propagation resistances R"of two composites mechanism and micro-crack toughing mechanism took higher than that of Al2O, ceramic by 1.23 and 1.37 an important role in improving material's thermal shock times, respectively. Obviously, thermal shock resis tances of composites are excellent to Al2O, ceramics, It References matches with the result of experiment. At the same [1] Zhang Qingchun, Yu Xi time, the result of calculation illustrates that enhance- nermal shock resistance behavior and ment of crack-spread resistance improves the thermal on for Al-Y-TZP ceramics [J]. Journal of shock resistance of Al203/15% ZrO2(3Y )and A12O3/ Materials,1991,6(2):177 [2 Becher P F. Transient thermal stress behavior in ZHo 15% ZrO2(2Y)composites toughened Al2O,[J].J.Am.Ceram.Soc.,1981,64 Generally, it is (1):37 strength and toughness could simultaneously increase [3] Biswas N C. Effect of thermal-shock and autoclave treat and R". But it is possible to and r"si- Ceramics International, 1997, 23 69 lultaneously if rupture work of materials increases; [4] Ma Weimin, Xiu Zhimeng, Wen Lei, Sun Xudong.Ef- A1203 /15% ZrO2(3Y)and A120, /15% ZNO2 (2Y)com- ct of PSz (3Y )content on the mechanical properties of posites are examples. Rupture work of material is re- ALO, ceramic [J]. Acta Metallurgica Sinica,2003,39 place strain state AGu,&y of crack propagation on placed with released ener [5] Green DJ. An Introduction to the Mechanical Properties of Cermics [M]. U.s.A. Originnal language published △G= KC(1-y2) by the Press of the University of Cambridge, 2001 [6] Wu Hongbiao. Inorganic Nonmetallic Materials where Kic is the fracture toughness, ER is modulus of ment [M]. Beijing China: Chemistry Industry 2002.6 elastivity and v is Poissons ratio. Fracture work of [7] Zhou Yu, Lei Tingquan. Ceramic Materials [M].Har- Al2O3 ceramic, A1, 03/15% ZNO, (3Y) and Al, 03/15% bin China: Harbin Institute of Technology Press, 1995 ZrO2(2Y )composites are 24, 162 and 1126 J-m 263 [8] Lange FF. Sine effects associated with the respectively. The increase of thermal shock capability armIes of constrained transformations [J].J e thermody of materials can be realized by means of increasing rup- Sci.,1982,(17):225. ture work of materials. Therefore, thermal shock resis- [9] Chen Huahui, Deng Haijin, Li Ming It is beneficial to the improvement of te Materials [M]. Beijing China: Substance crease 998.78 [10] Zhang Fang. Processing and properties of a-AL2O, ultra- 3 Conclusions fine powder and Al20, /Ni composites [D].Northeastern university, China, 2001 1. Both mechanical properties and thermal shock [11] Swain M V, et al. Guo Jingkun translation. Structure resistance of Al,03/15% ZNO2(3Y )and A1203/15 Beijing, China: Science Z:O2(2Y )composites were higher than that of single [12] FF. Effect of temperat hase l,O, ceramic. The calculations showed th ess[].J. Mater.Sci.,1982,(17):255 crack initiation resistances(R,) of Al203/15% ZO, [13] Liox. xui x m Ceramics Engineering [M]. Beijing, China: Chi (3Y )and Al203/15% Z:O2 (2Y)was higher than that Architecture Press, 1992. 8

Ma W M et a1 . Thermal Shock Resistance of A1203/Zr02 ( Y203 ) 57 The calculated values of R' and R" are shown in Table 2. Crack initiation resistance and crack propaga￾tion resistance of Al2O3/15% ZrOz ( 3Y) and AlZO3/ 15% ZrOz(2Y) are both higher than that of Alz03 ce￾ramic according to Table 2, respectively. Crack initia￾tion resistances R' of A12O3/15% ZrOz ( 3Y ) and A12O3/15% ZrOZ(2Y) composites is higher than that of Alz03 ceramic by 2. 16 and 1 .82 times, respectively. Crack propagation resistances R" of two composites is higher than that of A1203 ceramic by 1.23 and 1.37 times, respectively. Obviously, thermal shock resis￾tances of composites are excellent to ceramics. It matches with the result of experiment. At the same time, the result of calculation illustrates that enhance￾ment of crack-spread resistance improves the thermal shock resistance of A1203/15 % ZrOz ( 3Y ) and A1203/ 15 % ZrO2 ( 2Y ) composites . Generally, it is impractical that the change of strength and toughness could simultaneously increase R ' and R" . But it is possible to increase R ' and R" si￾multaneously if rupture work of materials increases ; AlZo3/15% zrOz(3Y) and Al2O3/15% ZrOz(2Y) com￾posites are examples. Rupture work of material is re￾placed with released energy of crack propagation on place strain state A G[I3' : where Klc is the fracture toughness, ER is modulus of elastivity and v is Poisson's ratio. Fracture work of Alz03 ceramic, Al2O3/15% Zr02( 3Y) and AlZo3/15% ZrOz(2Y) composites are 24, 162 and 1126 Jam-', respectively. The increase of thermal shock capability of materials can be realized by means of increasing rup￾ture work of materials. Therefore, thermal shock resis￾tances increased. It is beneficial to the improvement of thermal. 3 Conclusions 1. Both mechanical properties and thermal shock resistance of Al2O3/15% ZrOz (3Y) and Al2O3/15% ZrO2( 2Y) composites were higher than that of single phase A1203 ceramic. The calculations showed that crack initiation resistances ( R') of A12O3/15% ZrOz (3Y) and AlZo3/15 % Zr02 (2Y) was higher than that of A1203 ceramic by 2.16 and 1.82 times, respectively, and their crack-spread resistances (R") was higher than that of A1203 ceramic by 1.23 and 1.37 times, respec￾tively. 2. Toughness-increase phase transformation of ZrOz( 3Y) and ZrOz (2Y) changed the properties of A1203 matrix. Both composites improved thermal shock fracture resistance and thermal shock damage resis￾tance. Fracture energy of AlZ03, A1203/15% ZrO2 (3Y) and AlZo3/15% Zr02(2Y) was 24, 162 and 126 J * m-2, respectively. The resistance to thermal shock of A1203/15% Zroz(3Y) was superior to that of A1203 ceramic and A120J 15 % ZrO2 ( 2Y ) composite . 3, The stress induction transformation toughing mechanism and micro-crack toughing mechanism took an important role in improving material's thermal shock resistance. References : Zhang Qingchun, Yu Xiangdong . Relation between thermal shock resistance behavior and phase transforma￾tion for AI-Y-TZP ceramics [J]. Journal .f Inorganic Materials, 1991, 6(2) : 177. Becher P F. Transient thermal stress behavior in ZrOz￾toughened A1203[J]. J. Am. Cerurn. SOC., 1981, 64 Biswas N C . Effect of thermal-shock and autoclave treat￾ment on the microstructure of A1203-Zr02 composite [ J] . Ceramics International, 1997, 23: 69. Ma Weimin , Xiu Zhimeng , Wen Lei, Sun Xudong . Ef￾fect of PSZ (3Y) content on the mechanical properties of AI2O3 ceramic [ J ] . Actu Metullurgicu Sinicu , 2003, 39 Green D J . An Introduction to the Mechanical Properties of Cermics [ M ] . U . S . A. Originnal language published by the Press of the University of Cambridge. 2001. Wu Hongbiao . Inorganic Nonmetallic Materials Experi￾ment [ M ] . Beijing China: Chemistry Industry Press, 2002. 6. Zhou Yu , Lei Tingquan. Ceramic Materials [ M 1. Har￾bin China: Harbin Institute of Technology Press, 1995. 263. Lange F F. Sine effects associated with the thermody￾namics of constrained transformations [ J ] . J . Muter . Sci . , 1982, (17) : 225. Chen Huahui , Deng Haijin , Li Ming . Modem Compos￾ite Materials [ M ] . Beijing China : Chinese Substance Press, 1998. 78. Zhang Fang. Processing and properties of a-AlzO3 ultra￾fine powder and A1203/Ni composites [ D ] . Northeastern university, China, 2001. 1. Swain M V, et al. Guo Jingkun translation. Structure and Properties of Ceramics [MI. Beijing, China: Science Press, 1998. 90. Lange F F. Effect of temperature and alloy on fracture toughness [J]. J. Muter. Sci., 1982, (17): 255. Dai W, Li Q X, Xui Xiufang, Xian Wen translating. Modem Ceramics Engineering [MI. Beijing, China: Chi￾na Architecture Press, 1992. 8. (1): 37. (9): 999