Sub‐Critical Crack Growth Behavior of a Low‐Temperature Co‐Fired Ceramic

Abstract

The strength of sintered low‐temperature co‐fired ceramic (LTCC) disks was measured under dry (<2% relative humidity [RH]) and wet (98% RH) conditions, using ring‐on‐ring, biaxial‐flexure testing in the stressing rate range of 0.002–2 MPa/s. The empirical sub‐critical crack growth parameters, n and A, were calculated. The values of the parameters in the wet environment were higher than in the dry environment. It is argued that the high RH n value is more representative of material behavior. Results of fractographic examination are reported and expected lifetime and safe design stresses for LTCC are calculated.

Microstructure and mechanical properties of an alumina–glass low temperature co-fired ceramic

“…Therefore, the co-existence of particle phase and matrix phase after the sintering engenders the "salami" structure. This type of microstructure was also observed by other authors 11,18 . The micrograph taken on the lateral fracture surface under low magnification in Fig.…”

“…(1) is appropriately used to calculate the fracture toughness. 18 The crack length along four angles may be different due to the difference in local microstructures and residual stress of the surface layer. It is found from the micrograph in Fig.…”

Influence of temperature and humidity on the strength of low temperature co-fired ceramics

“…Stress [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] It is interesting that for lower stress rates (i.e. 0.7 MPa/s) a reduction of strength is observed in samples tested both at RT and at 125 • C (see Table 2).…”

“…Such a phenomenon has been also reported in LTCC or in SOFC materials loaded under mechanical stress, especially in humid environments. [11][12][13][14][15] Among the different models proposed to describe the crack growth in these materials, a direct chemical attack of the environment on the crack tip seems to have the strongest experimental support. 7,9 Depending on the crack growth rate and environment, different mechanisms of SCCG exist, which can be recognised by different slopes in a double logarithmic plot of the v-K I curve, 6 where v represents the crack growth rate and K I the applied stress intensity factor at the crack tip.…”

“…The SCCG exponent was n = 35 ± 3, which is in agreement with other similar LTCC materials reported in literature. 11,12 In this work, the combined effect of humidity and temperature on the strength of the same LTCC material was evaluated at different temperatures (25 • C, 75 • C and 125 • C) and different atmospheres using an adapted ball-on-three-balls (B3B) testing jig. Samples were tested in ambient air at room temperature (RT) and different relative humidity (RH) to quantify the effect of humidity on the strength.…”