Thermal cycling damage accumulation processes in an advanced metal matrix composite.

摘要

The dissertation research investigates the response to thermal cycling of a set of W-1%ThO{dollar}sb2{dollar} reinforced Fe-25CR-8Al-.50Y superalloy matrix composites. During this research, unique composite materials were produced by powder metallurgical processing. These materials were three aligned composites of differing reinforcement aspect ratio, and a hierarchic composite which included fine diameter Al{dollar}sb2{dollar}O{dollar}sb3{dollar} fibers. After HIP processing, specimen blanks were cut from the HIP billets by abrasive water-jet after which specimens were turned using a conventional engine lathe. The specimens were then thermal sprayed with an oxidation resistant FeCrAlY coating identical to the matrix material. The specimens were then thermal cycled between 1100 C and 352 C and between 1100 C and 534 C for 100, 500, or 750 cycles on a specially built thermal cycling machine. The dimensional change of each specimen was measured. It was found that the initial longitudinal growth per thermal cycle was small. After many thermal cycles however the longitudinal growth per thermal cycle became much larger.; A severe growth of fiber-matrix interfacial damage was documented with Scanning Electron Microscopy. The growth of two interfacial reaction phases was determined with a KEVEX dispersive x-ray analysis. The mechanical properties of the interfacial material were investigated with a Vickers microhardness test. Finally, the basic mechanical response of the material was investigated with room temperature tensile testing.; The experimental results were analyzed using a new micro-mechanics model. It was found that the predictions of the model agreed with experimental data from the W-FeCrAlY, the W-Cu, and the SiC-Al composite systems. The model was then able to qualitatively explain the measured increase in longitudinal strain per thermal cycle with increasing interfacial damage. Finally, based on model and experimental results, a multi-scale hybrid metal matrix composite configuration which is not expected to develop a large longitudinal growth per thermal cycle is recommended.