G.A. Gogotsi/ Ceramics International 29(2003)777-784 length and radius were measured with optical(Olimpus For the recording of the load-deflection curves, a hi BX5IM)and scanning electron microscopes (x500 or sensitivity LVDT-based deflectometer was suspended better) on a specimen(Fig. 2)and was in no way connected to the testing arrangement [13]. The LVDT was located 23. Procedures outside the heating chamber in case of high-temperature The specimens were tested in three-point (16 mm span In all the experiments, the speed of the testing between the bearing rollers) or four-point flexure(20-40 machine crosshead was constant and equal to 0.5 mm, machine and fitted with a hard load cell, a system for Fracture toughness, Kle values were calculated in precision displacement of a loading rod, and loading accordance with ASTM standard [14](three-point flex- supports. The latter are equipped with an attachment ure tests) and Din one [15](four-point flexure tests) for the rotation of the bearing rollers during specimen Additional procedures for evaluating Klc and other loading. Three-point flexure required the precise align- mechanical characteristics are described elsewhere [16] ment of a specimen on the bearing rollers, with the axis a micro-Raman imaging m of the central bearing roller and the radius of the v- JSA)with a 514.5 nm excitation line of an argon laser notch root being in the same plane as the applied load .(100 objective and a- l-um diameter spot) was used In high-temperature tests, we used a loading block to examine the surfaces of fractured Y-PSZ specimens which is similar to that used in room temperature tests. by a procedure described in Ref [171 3. Results and discussion The results of comparative three-and four-point flex ure tests of monolithic ceramics and particular ceramic composites are summarized in Table 3, where the data obtained within the RRFT97 program are also cited The variation of Ki values as a function of notch root Fig. 2. Loading scheme for three-point flexure(a) and deflectometer radius was studied for silicon nitride and zirconia( Fig 3) Ispended on a specimen 3x4x45 mm'(b) Load-deflection diagrams for V-notched specimens are Table 2 Characteristics of some material Material Density (g/cm Strength at 20C(MPa) Hardness(GPa) Method of manufacture 14.1 GPSS 224 Y-PSZ 05 425 IP sintered Material of RRTF97 Comparative fracture toughness tests(MPa m/2) Three-point flexure(a/wa point flexure(a/Wa0. 2...0.3 Our results RRFT97 results 5.5±0.07(5 5.35±0.16(5) GPSS 5.3±0.04(5) 5.2±0.18(5) 5.36±0.34(129) Si3 N4+30%SiC+ 3% Mgo 27±0.14(4) 240±0.16(5) SSiC 266±0.20(4) 2.61±0.18(56) SiC+ 50%oRb,+10% BC 3.59±0.12(3) 3.51±0.15(3) A2O3998 3.5±0.05(5) 3.6±0.06(5) 3.57±0.22(135) 5.7±0.17(5) 59±0.19(5) ± Standard deviation. The number of specimen tested (in parentheses)length and radius were measured with optical (Olimpus BX51M) and scanning electron microscopes (500 or better). 2.3. Procedures The specimens were tested in three-point (16 mm span between the bearing rollers) or four-point flexure (20–40 mm spans between the bearing rollers) on a home-made Ceramtest block, mounted on a universal testing machine and fitted with a hard load cell, a system for precision displacement of a loading rod, and loading supports. The latter are equipped with an attachment for the rotation of the bearing rollers during specimen loading. Three-point flexure required the precise align￾ment of a specimen on the bearing rollers, with the axis of the central bearing roller and the radius of the V￾notch root being in the same plane as the applied load. In high-temperature tests, we used a loading block which is similar to that used in room temperature tests. For the recording of the load–deflection curves, a high￾sensitivity LVDT-based deflectometer was suspended on a specimen (Fig. 2) and was in no way connected to the testing arrangement [13]. The LVDT was located outside the heating chamber in case of high-temperature tests. In all the experiments, the speed of the testing machine crosshead was constant and equal to 0.5 mm/ min. Load cell and deflectometer readings were recorded with a coordinate potentiometer. Fracture toughness, KIc values were calculated in accordance with ASTM standard [14] (three-point flex￾ure tests) and DIN one [15] (four-point flexure tests). Additional procedures for evaluating KIc and other mechanical characteristics are described elsewhere [16]. A micro-Raman imaging microscope (Renishaw, USA) with a 514.5 nm excitation line of an argon laser (100 objective and a1-mm diameter spot) was used to examine the surfaces of fractured Y-PSZ specimens by a procedure described in Ref. [17]. 3. Results and discussion The results of comparative three- and four-point flex￾ure tests of monolithic ceramics and particular ceramic composites are summarized in Table 3, where the data obtained within the RRFT’97 program are also cited. The variation of KIc values as a function of notch root radius was studied for silicon nitride and zirconia (Fig. 3). Load–deflection diagrams for V-notched specimens are Fig. 2. Loading scheme for three-point flexure (a) and deflectometer suspended on a specimen 3445 mm3 (b). Table 3 Comparative fracture toughness tests (MPa m1/2) Test method Three-point flexure (a/W0.5) Four-point flexure (a/W0.2...0.3) Our results RRFT’97 results Si3N4 5.50.07 (5)a 5.350.16 (5) – GPSSN 5.30.04 (5) 5.20.18 (5) 5.360.34 (129) Si3N4+30%SiC+3% MgO 2.270.14 (4) 2.400.16 (5) – SSiC 2.45 (1) 2.660.20 (4) 2.610.18 (56) SiC+50%ZrB2+10% B4C 3.590.12 (3) 3.510.15 (3) – Al2O3-998 3.50.05 (5) 3.60.06 (5) 3.570.22 (135) Y-PSZ 5.70.17 (5) 5.90.19 (5) –  Standard deviation. a The number of specimen tested (in parentheses). Table 2 Characteristics of some materials Material Density (g/cm3 ) Strength at 20
C (MPa) Hardness (GPa) Method of manufacture Si3N4 3.14 700 14.1 HIP GPSSN 3.23 >920 13.5 Gas-pressure sintereda SSiC 3.15 – 22.4 Sintereda Al2O3-998 3.86 350 19.3 Sintereda Y-PSZ 6.05 425 12.1 IP + sintered a Material of RRTF’97. G.A. Gogotsi / Ceramics International 29 (2003) 777–784 779