Effects of combustion and salt-fog exposure on fatigue behavior of two ceramic matrix composites and a superalloy

Abstract

Tension-tension fatigue behavior of two ceramic matrix composites (CMCs), SiC/SiC (Nicalon TM / SiC) & oxide/oxide (Nextel TM 720/AS), and a superalloy (René 41) was characterized under combustion environment as well as under alternate salt-fog exposure for 4 h and combustion fatigue for 6 h. The run-out limit was 25 h (90,000 cycles) of fatigue. Test temperatures were 900, 1050, and 1050°C for René 41, SiC/SiC, and oxide/oxide CMCs, respectively, and the applied maximum fatigue stress was 62 MPa. All three materials survived up to 25 h under combustion fatigue without any exposure to salt. René 41 and Nicalon TM /SiC survived up to 25 h (90,000 cycles) under the alternate exposure of salt-fog and combustion fatigue. However, exposure to salt-fog exposure (5 wt%) had very detrimental effect on the combustion fatigue resistance of Nextel TM 720/AS. The reduction in salt concentration to 0.5 wt% had less detrimental effect. These tests were supplemented with more tests, where applied stress level, test temperature, and salt concentration were changed. Out of these three gas turbine engine materials, Nicalon TM /SiC exhibited better fatigue performance in terms of applied temperature and stress level under combustion condition as well as when exposed to alternate salt-fog and combustion.

Fatigue damage modeling of ceramic‐matrix composites: A short review

“…(a) The service environment will be critical in determining the lifetime of any component. In the case of a CMCs in combustion, the desired service environment could be described as being very harsh . As the service environment of CMCs being very harsh as the components will be operating at temperatures in excess of 1000°C with varying loads as well as varying water vapor and impurities corrosion.…”

Tensile and fatigue behavior of oxide/oxide ceramic matrix composite with simulated foreign object damage in combustion environment

“…One major drawback in the previous FOD studies was the lack of an environmental chamber that more closely simulated the gas turbine engine combustion environment. This has been a challenge traditionally and has led to the development of a unique test facility where mechanical testing of CMC test coupons can be performed simultaneously in a combustion environment that closely simulates an aircraft gas turbine . This unique test facility uses a High‐Velocity Oxygen Fuel (HVOF) combustion gun that continually heats one side of the test coupons to the desired temperature while mechanical loads are applied simultaneously using a servohydraulic mechanical testing system .…”

“…In addition, it also has the capability to adjust and control the program for thermal and mechanical loading conditions, which enables testing a wide spectrum of thermal loading scenarios of the candidate materials including severe temperature excursions experienced and anticipated during the operation of an advanced aircraft engine. A number of tests have been successfully performed in this test facility on both oxide/oxide and carbide/carbide CMC systems under monotonic, cyclic, and sustained loads …”

“…This has been a challenge traditionally and has led to the development of a unique test facility where mechanical testing of CMC test coupons can be performed simultaneously in a combustion environment that closely simulates an aircraft gas turbine. [16][17][18][19][20][21][22] This unique test facility uses a High-Velocity Oxygen Fuel (HVOF) combustion gun that continually heats one side of the test coupons to the desired temperature while mechanical loads are applied simultaneously using a servohydraulic mechanical testing system. [16][17][18][19][20][21][22] The combustion system is capable of producing high speed flames with temperatures up to 2500°C.…”

“…[16][17][18][19][20][21][22] This unique test facility uses a High-Velocity Oxygen Fuel (HVOF) combustion gun that continually heats one side of the test coupons to the desired temperature while mechanical loads are applied simultaneously using a servohydraulic mechanical testing system. [16][17][18][19][20][21][22] The combustion system is capable of producing high speed flames with temperatures up to 2500°C. In addition, it also has the capability to adjust and control the program for thermal and mechanical loading conditions, which enables testing a wide spectrum of thermal loading scenarios of the candidate materials including severe temperature excursions experienced and anticipated during the operation of an advanced aircraft engine.…”