Mechanical Properties Evaluation of Generation-I SX-SiC

Abstract

Mechanical properties of a developmental high strength and high toughness SiC, Generation I SX, have been evaluated under a Department of Energy (DOE)/Oak Ridge National Laboratory (ORNL) subcontract. The mechanical properties determined included flexural strength, tensile strength, and fracture toughness at room and elevated temperatures. Stress rupture, dynamic fatigue and creep at elevated temperatures also have been evaluated. The strength limiting factors have been identified at room and elevated temperatures. The strength controlling mechanisms are discussed. The microstructure-mechanical property relationship has been established.

Process Optimization of Hexoloy SX-SiC Towards Improved Mechanical Properties

“…Moreover no slow crack growth was evidenced at 1232°C since no strength drop at lower stress rates was observed. This observation is consistent with the earlier published results for the same material [2]. Hence the room temperature flexural strength (MOR) was considered to be the primary response for different densification conditions.…”

“…It is interesting to note that higher strength was observed with lower sintering temperatures and also corresponded to fewer volume flaws or "pools". The "pool" of second phase clusters appeared to form due to the reaction of SiC with yttrium aluminate as suggested by Omori [5] and from the Scanning Auger Electron Microscopic studies on the same material reported previously [2]. It is believed that at lower processing temperatures, the reaction is not severe enough to form many, large "pools".…”

“…In almost all cases, the strength limiting defects were identified to be "pools" of second phase clusters. The origination of such "pools' was related to reaction of SiC with the second phase and was reported in detail in an earlier publication [2]. A typical strength limiting "pool" is shown in Figure 3 corresponding to a sample made from powder "A".…”

“…Slow crack growth accompanied by glass phase formation has been determined to be the failure mechanism at 1370°C for samples fabricated from each of the powder sources. The slow crack growth mechanism has been explained in an earlier publication [2]. Though the slow crack growth parameter appears to be high for powders B and F, the strength levels are low.…”

“…The mechanical properties determined and published earlier [2] included flexural strength, tensile strength, and fracture toughness at room and elevated temperatures. Stress rupture, dynamic fatigue and creep at elevated temperatures were also reported.…”