Journal of Advanced Materials in Engineering (Esteghlal)

Precipitation has always been one of the important methods in the preparation of ceramic nanopowders. In this study, the most important parameters, ageing time and concentration parameters, have been studied. Yttrium oxide (Yttria) nanopowder was synthesized by precipitation method. Yttria micropowder and ammonium hydrogen carbonate were used as precursor materials. The study involved aging time and concentration in four and three levels, repectively (3, 6, 12 and 24h for ageing time and 0.25, 0.5 and 0.75 mol/L for concentration). Synthesized phases, thermal behavior and particle size were studied by X-ray diffraction pattern (XRD), thermogravimetry (TG), differential thermal analysis (DTA) and field emission scanning electron microscopy (FE-SEM). Fourier transform infrared spectroscopy analysis (FTIR) was used for studying bonding before and after the heat treatment at 900, 1000 and 1100 ^°C.

This study aims at investigation of the hydrogen damage after dissolution annealing and two-stage aging in aluminum 7075 alloy. Dissolution annealing was performed at 500 to 575 ^°C for duration of 1 to 20 hours. The first stage of two-stage aging was performed at 180, 200 and 220 ^°C for 30 minutes. The second stage was carried out at 120 and 150 ^°C for 10, 15 and 20 hours. Structural characteristics and chemical composition of precipitates was investigated using SEM and EDS methods, respectively. Reduction of the tensile strength in T6 process after hydrogenation reached to 150 MPa, although it decreased only, about 50 MPa in the two-stage process. Overall, tensile strength after hydrogen charging was significantly increased in the two-stage aging compared to the T6 process.