G.A. Gogotsi/ Ceramics international 29(2003)777-784 tested by the SEVNB method. The phz s a specimens residual stresses, phase transformations or other effects state on the fracture surfaces of zircon state was which often accompany the formation of stress analyzed by micro-Raman spectroscopy(Fig. 6), which concentrators by other procedures demonstrates. in contrast to fracture or saw notch sur- faces(Fig. 6a) or the edge of indentation(Fig. 6b),a polished V-notch surface does not contain the mono- Acknowledgements clinic phase(there is no effect inducing the phase trans- formation). This is an important advantage of the Thanks are expressed to Mr. V. Galenko and Mr. B SEVNB method in comparison with other fracture Ozersky (IPs, Ukraine)for their assistance in perform- toughness test methods for zirconia and similar ceramics. ing experiments. The investigation partially financed by The comparison of high-temperature Klc evaluations INCO-Copernicus Grants (contracts 15 CT 9607 for Si3N4 ceramics, presented both in Table 7 and in and 1CA2-CT-2000-10020) Ref [18], reveals their similarity. However, in our case, in contrast to [18, fracture of the V-notch surface did References not occur and we did not observe active oxidation in the icinity of the notch. It is noteworthy that in SEPB tests [1] G.A. Gogotsi, Fracture toughness studies on ceramics and cera- of similar ceramics [18], oxidation induced the blunting particulate composites at different temperatures, in: (healing) of the initial sharp crack and, as J.A. Salem, G D. Quinn, M.G. Jenkins(Eds ) Fracture Resis- consequence, the fracture toughness results varied tance Testing of Monolithic and Composite Brittle Materials It is necessary to emphasize the increase in the fracture (ASTM STP 1409), American Society for Testing and Material West Conshohocken, PA, 2002, pp. 199-2 toughness of ceramic particula [2J. KObler, Fracture toughness amics using the SevnB temperatures (Table 7). The o value varies moderately with ethod: preliminary results, in: J.P. Singh(Ed ) Ceramic Engi- this increase(0.81 for Si3 N4 30%SiC 3% MgO and neering& Science Proceedings, American Ceramic Society, Vol 0.71 for SiC 50% ZrB2+ 10% B,C). The changes in 3 G.A. Gogotsi, V.I. Galenko, Comparative analysis of fracture the load-deflection diagrams of these ceramics with test toughness tests methods for ceramics and crystals at room an temperatures are not so pronounced (Fig 4)and are con- lower temperatures, Strength of Materials 29(1997)287-297 nected with a certain increase in their inelastic deforma 4 Le Bac, Verfahren zum Feinkerben von Keramischen KOrpern tion. It should be noted that the load-deflection diagrams Patentschrift 146416, Deutsche Demokratische Republik- Amt for Si N4+30%SiC 3% MgO unnotched specimens (5).J. Dameny A Danzer, Method for fracture toughness testing and specimens with wide notches were linear. The oxida- n layers on fractured specimens are not strong and Riosand, K.J. Miller(Eds ) Fracture from Defects, Emas Pub. cannot affect the fracture toughness of the ceramics stud lishing,1998.pp.491-496 ied in high-temperature SEVNB tests And, probably, the 6J. Kubler, Fracture Toughness of Ceramics Using the SEVNB blunting of a stress concentrator does not occur as in [ 18], lethod: Round Robin, VAMAS Report No37/ESIS Document D2-99, EMPA, Swiss Federal Laboratories for Materials Testing where in SEPB tests crack healing and a considerable and Research. Bubendorf. switzerland increase in Kle values, even at 1200oC, were observed 7 G.A. Gogotsi, Fracture toughness matrix composites(SEVNB Method Ceramics-12(1998)7-13 4. Conclusions [8 G.A. Gogotsi, Fracture toughness tests of V-notched specimens Strength of Materials 32(2000)170-177 9 G.A. Gogotsi, V.I. Galenko, B.I. Ozerskiy, AD The test data confirm that the sevnb method can be v.I. Korban, Fracture resistance, strength, and other ch easier applied in practice and can be used for the tics of Y-TZP, Refractory and Industrial Ceramics 8 majority of advanced ceramics and ceramic particulate composites at different temperatures and in the oxida [0 G.A. Gogotsi, M I. Lugovy, V.N. Slyunyayev, N.A. Orlovskaya, Development of multilayered Si3 Na-based ceramics composite tion environment. The sevnb data for ceramics and ving an ability to arrest cracks, Proc. of Int. Conf. Science for ceramic particulate composites are independent of the laterals 2002, IPMS, Kiev, 2002, pp 247-248. flexure type and exhibit small scatter. For laminated [I G.A. Gogotsi, Several Experimental Results of High Perfor- ceramic composites them are also independent of width ance Ceramics Used in Heat Engine Components, IPS AN of the stress concentrator Therefore it commands the [12] G.A. Gogotsi, Private communication. attention of engineers involved in both certification [13] G.A. Gogotsi, V P Zavada, V 1. Nerodenko, USSR Patent No I testing and materials science research. It was found that 224551,15 December I984. the ratio between SEVNB and senb data equaled [14 ASTM C1421-99, Standard Test Method for the Determination bout 0.6 for elastic ceramics and ceramics particulate composites and over 0.9 for inelastic ones. The polish- [15] Draft Standard DIN 51 109, Testing of Advanced Technical ing-out of a V-notch root does not damage the surface Ceramics: Determination of Fracture Toughness KIc, DIN NMP layer formed on a zirconia; therefore, there are nostate on the fracture surfaces of zirconia specimens tested by the SEVNB method. The phase state was analyzed by micro-Raman spectroscopy (Fig. 6), which demonstrates, in contrast to fracture or saw notch sur￾faces (Fig. 6a) or the edge of indentation (Fig. 6b), a polished V-notch surface does not contain the mono￾clinic phase (there is no effect inducing the phase trans￾formation). This is an important advantage of the SEVNB method in comparison with other fracture toughness test methods for zirconia and similar ceramics. The comparison of high-temperature KIc evaluations for Si3N4 ceramics, presented both in Table 7 and in Ref. [18], reveals their similarity. However, in our case, in contrast to [18], fracture of the V-notch surface did not occur and we did not observe active oxidation in the vicinity of the notch. It is noteworthy that in SEPB tests of similar ceramics [18], oxidation induced the blunting (healing) of the initial sharp crack and, as a consequence, the fracture toughness results varied. It is necessary to emphasize the increase in the fracture toughness of ceramic particulate composites with test temperatures (Table 7). The ’ value varies moderately with this increase (0.81for Si3N4 + 30% SiC + 3% MgO and 0.71for SiC + 50% ZrB2 + 1 0% B4C). The changes in the load-deflection diagrams of these ceramics with test temperatures are not so pronounced (Fig. 4) and are con￾nected with a certain increase in their inelastic deforma￾tion. It should be noted that the load–deflection diagrams for Si3N4 + 30%SiC + 3% MgO unnotched specimens and specimens with wide notches were linear. The oxida￾tion layers on fractured specimens are not strong and cannot affect the fracture toughness of the ceramics stud￾ied in high-temperature SEVNB tests. And, probably, the blunting of a stress concentrator does not occur as in [18], where in SEPB tests crack healing and a considerable increase in KIc values, even at 1200
C, were observed. 4. Conclusions The test data confirm that the SEVNB method can be easier applied in practice and can be used for the majority of advanced ceramics and ceramic particulate composites at different temperatures and in the oxida￾tion environment. The SEVNB data for ceramics and ceramic particulate composites are independent of the flexure type and exhibit small scatter. For laminated ceramic composites them are also independent of width of the stress concentrator. Therefore it commands the attention of engineers involved in both certification testing and materials science research. It was found that the ratio between SEVNB and SENB data equaled about 0.6 for elastic ceramics and ceramics particulate composites and over 0.9 for inelastic ones. The polish￾ing-out of a V-notch root does not damage the surface layer formed on a zirconia; therefore, there are no residual stresses, phase transformations or other effects, which often accompany the formation of stress concentrators by other procedures. Acknowledgements Thanks are expressed to Mr. V. Galenko and Mr. B. Ozersky (IPS, Ukraine) for their assistance in perform￾ing experiments. The investigation partially financed by INCO-Copernicus Grants (contracts 15 CT 96 07 29 and 1CA2-CT-2000-10020). References [1] G.A. Gogotsi, Fracture toughness studies on ceramics and cera￾mic particulate composites at different temperatures, in: J.A. Salem, G.D. Quinn, M.G. Jenkins (Eds.), Fracture Resis￾tance Testing of Monolithic and Composite Brittle Materials (ASTM STP 1409), American Society for Testing and Materials, West Conshohocken, PA, 2002, pp. 199–212. [2] J. Ku¨bler, Fracture toughness of ceramics using the SEVNB method: preliminary results, in: J.P. Singh (Ed.), Ceramic Engi￾neering & Science Proceedings, American Ceramic Society, Vol. 18, Issue 4, 1997, pp. 155–162. [3] G.A. Gogotsi, V.I. Galenko, Comparative analysis of fracture toughness tests methods for ceramics and crystals at room and lower temperatures, Strength of Materials 29 (1997) 287–297. [4] Le Bac, Verfahren zum Feinkerben von Keramischen Ko¨rpern, Patentschrift 146416, Deutsche Demokratische Republik- Amt fu¨r Efindungs- und Patentwesen, 1979–1981. [5] D.J. Dameny, A. Danzer, Method for fracture toughness testing of ceramics—ready for standardisation, in: M.W. Brawn, E.R. Riosand, K.J. Miller (Eds.), Fracture from Defects, Emas Pub￾lishing, 1998, pp. 491–496. [6] J. Ku¨bler, Fracture Toughness of Ceramics Using the SEVNB Method: Round Robin, VAMAS Report No.37/ESIS Document D2-99, EMPA, Swiss Federal Laboratories for Materials Testing and Research, Dubendorf, Switzerland, 1999. [7] G.A. Gogotsi, Fracture toughness of ceramics and ceramic matrix composites (SEVNB Method), Refractory and Technical Ceramics 11–12 (1998) 7–13. [8] G.A. Gogotsi, Fracture toughness tests of V-notched specimens, Strength of Materials 32 (2000) 170–177. [9] G.A. Gogotsi, V.I. Galenko, B.I. Ozerskiy, A.D. Vasiliev, V.I. Korban, Fracture resistance, strength, and other character￾istics of Y-TZP, Refractory and Industrial Ceramics 8 (2000) 7– 13 (in Russian). [10] G.A. Gogotsi, M.I. Lugovy, V.N. Slyunyayev, N.A. Orlovskaya, Development of multilayered Si3N4-based ceramics composite having an ability to arrest cracks, Proc. of Int. Conf. Science for Materials 2002, IPMS, Kiev, 2002, pp. 247–248. [11] G.A. Gogotsi, Several Experimental Results of High Perfor￾mance Ceramics Used in Heat Engine Components, IPS AN USSR, Kiev, 1983 (in Russian). [12] G.A. Gogotsi, Private communication. [13] G.A. Gogotsi, V.P. Zavada, V.I. Nerodenko, USSR Patent No. 1 224 551, 15 December 1984. [14] ASTM C1421-99, Standard Test Method for the Determination of Fracture Toughness of Advanced Ceramics at Ambient Tem￾perature. [15] Draft Standard DIN 51 109, Testing of Advanced Technical Ceramics; Determination of Fracture Toughness KIc, DIN NMP 291, September 1991. G.A. Gogotsi / Ceramics International 29 (2003) 777–784 783