S.P. Lee

Effect of aging treatment on irradiation-induced segregation of high Mn-Cr steel

Abstract To investigate the effect of aging treatment on irradiation-induced segregation of high Mn-Cr steel, specimens for electron-beam irradiation were prepared from the high Mn-Cr austenitic steel which was solution treated at 1 373 K for 1 h and aging treated at 573 K for 1 000 h, respectively. The electron-beam irradiation was performed at 573 K up to doses of 5.4 dpa in a 1 250 kV HVEM and irradiation-induced segregation analyses were carried out by an EDX in a 200 kV FE-TEM. The results show that void formation is not observed in both solution treated and aging treated ones. The amount of Cr segregation at the grain boundary decreases in the aged one; however, that of Mn is not changed in solution treated one.

Microstructure and Mechanical Property of SiCf/SiC and Cf/SiC Composites

The mechanical properties of SiC based composites reinforced with different types of fabrics have been investigated, in conjunction with the detailed analyses of their microstructures. The thermal shock properties of SiCf/SiC composites were also examined. All composites showed a dense morphology in the matrix region. Carbon coated PW-SiCf/SiC composites had a good fracture energy, even if their strength was lower than that of PW-Cf/SiC composites. SiCf/SiC composites represented a great reduction of flexural strength at the thermal shock temperature difference of 300 °C.

Evaluation of fracture toughness of ceramic matrix composites using small specimens

Abstract Ceramic matrix composites (CMC) are being developed for high temperature utilization in aerospace and other industrial application. They offer several attractive features including high strength and modulus, improved fracture toughness, light weight, low thermal expansion coefficient and high thermal conductivity which contribute to good thermal shock resistance and high temperature stability in chemical and oxidative environments. Though the enhancement of fracture toughness is one of key issues for the development of these materials, the standardized evaluation method for the characterization of fracture toughness has not been established yet. Miniaturization of the test specimen for these tests has been also considered to be one of the most necessary issues because of the high cost of materials and the restriction of experimental environments. In this study, the influences of specimen size on the fracture resistance properties of plain-woven (P/W) Carbon/Carbon and Tyranno-LoxM/SiC composite were investigated. The fracture toughness tests with the unloading–reloading sequences were conducted with the compact tension specimens of different thicknesses and widths. The initiation fracture toughness JQ of both materials increased with increasing of specimen thickness. It seems that interlayer frictional sliding between layered fabrics is one of energy dissipating mechanism in these materials. The initiation fracture toughness, JQ, of both materials also increased with increasing of specimen width. The specimen width and the fabric condition affect the size of fracture process zone in 2D woven CMC.