Crystallographic features of second phases and the effect of nitrogen addition on the microstructural evolution in superaustenitic Fe-22Cr-21Ni-6Mo-(N) (all in wt pct) stainless steels during isothermal aging at 900 ЊC were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Both alloys with and without nitrogen contained sigma phase and M 23 C 6 carbides in the solution treated condition. While four phases (sigma, M 23 C 6 , M 6 C, and chi) of intermetallics and carbides appeared sequentially as a function of aging time in the nitrogen-free alloy, two nitrides (Cr 2 N and AlN) were additionally observed after long time aging of the nitrogen-containing alloy. The addition of nitrogen into Fe-22Cr-21Ni-6Mo steel promoted a finer and more uniform distribution of precipitates during isothermal aging. The exact identification and crystallography of various second phases were confirmed from the analyses of selected area diffraction patterns from various orientations, stereographic projection, and energy dispersive spectroscopy. The orientation relationships between the precipitates and austenite matrix can be summarized as follows: (1) two carbides (M 23 C 6 and M 6 C): cube-on-cube orientation relationship; (2) chi phase: Kurdjumov-Sachs (K-S) orientation relationship; (3) two nitrides (Cr 2 N and AlN): (1120) nitrides //(211) ␥ and [0001] nitrides //[111] ␥ ; and (4) sigma phase: (1) (111) ␥ //(001) and [110] ␥ //[110] or (2) (110) ␥ //(110) and [112] ␥ //[113]. For the sigma phase, the former orientation relationship was predominant throughout aging, and the latter orientation relationship was occasionally observed under limited aging conditions.

The effect of thickness on the mechanical properties of Al 6K21-T4 sheet specimens under uniaxial tension was investigated. In order to reduce the thickness of the specimens without changing the microstructure and grain size, chemical etching was carried out, resulting in Al sheets ranging from 0.40 mm to 1.58 mm in thickness. Additionally, the effect of surface roughness was determined by finite element (FE) calculations performed using FE code MARC 2007. Tensile specimens of varying surface roughness were modeled and simulated. An analysis of the combined effects of the thickness and surface roughness revealed that the yield and tensile strengths decreased when the number of grains over the thickness was decreased. The ductility also decreased when reducing the thickness. An FE simulation showed that both the surface roughness and thickness affected the flow-curve shape. Moreover, the effect of the surface roughness tended to increase when decreasing the sheet thickness of specimens having the same roughness.

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