P.Y. Lee

High temperature corrosion behavior of iron aluminides containing ternary additions in H2/H2S/H2O mixed gases

Abstract The high-temperature corrosion behavior of four iron aluminides containing Fe–18Al (in at.%) and three Fe–18Al–5M alloys (where M was Cr, Mn, or Mo) was studied over the temperature range of 700–900°C in a H 2 /H 2 S/H 2 O atmosphere. The corrosion kinetics followed the parabolic rate law in all cases, regardless of temperature and alloy composition. The parabolic rate constants decreased with decreasing temperature, and the addition of ternary elements resulted in various decreases in the corrosion rate compared with Fe–18Al. It was found that Mo was effective to improve the corrosion resistance at T ≤800°C while Cr had a better improvement at 900°C. The scales formed on all iron aluminides were strongly dependent on temperature and ternary addition.

Amorphization of transition metal-Si alloy powders by mechanical alloying

Amorphization of TM‐Si (TM: trasition metal) alloy powders by mechanical alloying has been systematically investigated. Pure element powder mixtures were mechanically alloyed for ten hours with a high energy ball mill. The results show that amorphous metallic silicide powders were successfully synthesized in Ti‐Si, Zr‐Si, Nb‐Si, and Ta‐Si systems. Prediction of the amorphization range of mechanically alloyed TM‐Si powders by the Miedema model is inappropriate. The possible criteria for the amorphization of TM3Si powders after mechanical alloying 10 h in a shaker ball mill are (a) the free energy of amorphous state of TM3Si powders is less than −31.95 kJ/mole, and (b) the silicon to trasition metal atomic radius ratio is less than 0.985.

Investigations of mechanically alloyed Ni-Zr-Ti-Si amorphous alloys with significant supercooled regions

Abstract This study examined the amorphization behavior of Ni 57 Zr 20 Ti 23− x Si x ( x =0, 1, 3) alloy powders synthesized by mechanical alloying technique. According to the results, after 5 h of milling, the mechanically alloyed powders were amorphous at compositions of Ni 57 Zr 20 Ti 23− x Si x ( x =0, 1, 3). The amorphization behavior of Ni 57 Zr 20 Ti 20 Si 3 was examined in details. The conventional X-ray diffraction and synchrotron EXAFS results confirm that the fully amorphous powders formed after 5 h of milling. The thermal stability of the Ni 57 Zr 20 Ti 23− x Si x amorphous powders was investigated by differential scanning calorimeter (DSC). As the results demonstrated, the amorphous powders were found to exhibit a large supercooled liquid region before crystallization. The supercooled liquid regions, defined by the difference between T g and T x , (i.e. Δ T = T g − T x ), are 95 K, 66 K, and 88 K, for Ni 57 Zr 20 Ti 23 , Ni 57 Zr 20 Ti 22 Si 1 , and Ni 57 Zr 20 Ti 20 Si 3 , respectively.