Effect of temperature on the pre-creep mechanical properties of silicon nitride

Contact-mechanical properties at intermediate temperatures of ZrB2 ultra-high-temperature ceramics pressureless sintered with Mo, Ta, or Zr disilicides

“…Specifically, E exhibits a first linear fall that is in accordance with the theoretical expectation [47][48][49], and then a second accelerated fall between 400 and 600 • C that is attributable to the activation of reversible grain boundary sliding [47,48]. This two-stage decline in E is the usual trend observed in polycrystalline ceramics [36,[41][42][43][44][45][46]49]. It can also be seen that ZrB 2 + 20 vol%MoSi 2 is stiffer than ZrB 2 + 20 vol%ZrSi 2 and ZrB 2 + 20 vol%TaSi 2 , this last being the most compliant of the three UHTCs fabricated here.…”

“…It can be seen in Fig. 3 that the Hertzian curves have the typical shape reported for other polycrystalline ceramics [36,[41][42][43][44][45][46], with a first linear stretch attributable to the elastic deformation regime and a second nonlinear stretch associated with the quasiplastic deformation regime. The particular details of the curves depend however on the test temperature and on the metal disilicide used as sintering additive.…”

Effect of microstructure on the mechanical properties of liquid-phase-sintered silicon carbide at pre-creep temperatures

“…A slow linear decrease of the elastic modulus with increasing temperature is initially observed for all materials, but a sharper decay is observed above 800 • C. This modulus degradation above a certain temperature threshold is attributable to the activation of reversible grain boundary sliding and has been observed in other materials. [24][25][26] Also clear in Fig. 4 is the fact that the fSiC-5-2 h material exhibits an elastic modulus significantly greater (by 25%)-at room temperature its value is close to that of pure SiC (∼440 GPa 12 )-than the LPS-SiCs with a greater intergranular phase content.…”

“…Especially worrisome has to be the reduction in the critical loads for radial crack initiation, since this damage mode seriously jeopardizes the mechanical integrity of the material. Moreover, the presence of the intergranular phase, even in small amounts, clearly reduces the material's creep resistance: all the LPS-SiCs studied showed evidence of creep under contact stresses at a relatively low temperature (compared to other ceramics [24][25][26] of 1000 • C, and a clear degradation of their elasto-plastic properties even at 900 • C. The only somewhat beneficial effect of the presence of this intergranular phase is to allow the development of elongated, heterogeneous microstructures that enhance the toughness of the material.…”

“…This technique, based on Hertzian indentation in combination with finite element modelling (FEM), has been successfully applied to study the effect of temperature on the mechanical properties-such as Young's modulus, quasi-plastic yield stress, strain-hardening parameter, critical load for contact damage initiation, etc.-of zirconia (Y-PSZ), 24 alumina, 25 silicon nitride, 26 and zirconium diboride. 27 Here, the HTHT technique was applied to study the evolution with temperature from 25 • C to 900 • C of the mechanical properties of 4 LPS-SiC materials with different microstructures.…”