Kwangseon Shin

Effect of cathodic hydrogen charging on mechanical properties of Al 8090

It has been well established that precipitation hardened, high-strength Al alloys are often susceptible to external hydrogen embrittlement. Al 8090 has been developed to reduce the mechanical anisotropy and improve the toughness by introducing S{prime} (Al{sub 2}CuMg) precipitates. Recently, Chen et al. studied the effects of cathodic hydrogen charging on tensile properties of Al 8090 sheet, and observed that hydrogen embrittlement affects the tensile properties of Al 8090 significantly, suggesting that hydrogen embrittlement may play an important role in SCC of Al 8090. It has often been demonstrated that the presence of notch greatly alters the hydrogen-assisted mechanical behavior of metals. Therefore, the main objective of the present study was to examine the effects of cathodic hydrogen charging on tensile and fracture behaviors of Al 8090.

Decomposition of NO on the surface of Al-Cu-Fe quasicrystal at high temperature

Since quasicrystals, the well-ordered but aperiodic structures with classically forbidden rotational symmetries, were discovered by Shechtman et al. [1] in 1984, research has been focused mostly on understanding the atomic structure [2] and the phase equilibria [3, 4]. Up until now over 100 binary to quaternary metallic alloy systems that contain quasicrystalline phases have been found [5]. In recent years, the increasing interest in quasicrystals has shifted from basic structural studies to the development of engineering applications. Due to the unique properties of quasicrystals, applications in surface coatings, wear resistance, corrosion protection, thermal insulation, and optical or electronic response have been explored [6]. Some quasicrystals were found to be useful as new hydrogen-storage materials [7–9]. More recently, Thiel et al. [10–12] carried out an extensive study of the surface oxidation of icosahedral quasicrystalline Al-Cu-Fe (i-Al-Cu-Fe) and Al-Pd-Mn alloys using O2 as an oxidant at room temperature. In the present work, the reaction between i-Al-Cu-Fe alloy powder and nitrogen oxide (NO) at high temperature is investigated. Two quasicrystal powder samples (S1 and S2, average prticle size 28 μm) with a nominal composition of Al63Cu25Fe12 were prepared using the gas-atomization method described by Sordelet et al. [13]. The as-atomized sample S2 was further annealed under vacuum at 750 ◦C for 14 h to obtain the sample S3 [13]. X-ray powder diffraction (XRD) patterns were obtained using a Rigaku D/Max-3c diffractometer using Cu Kα radiation. The selected area diffraction (SAD) patterns were obtained using a Philips CM-20 (200 KV) transmission electron microscope. From XRD patterns of samples (Fig. 1a), one can clearly observe that the as-atomized samples (S1 and S2) contained a two-phase mixture of the quasicrystalline (ψ) and cubic (β) phases [13]. After vacuum annealing, the β phase in the sample S3 was almost disappeared and thus a nearly single-phase ψ structure was obtained. Table I lists the ψ phase weight percent of each sample determined by the method proposed by Sordelet et al. [13] The sample S3 was also hotisostatically pressed into a dense monolith [10] to prepare a sample for the electron diffraction investigation.