Solid State Phenomena Vols. 124-126

Abstract: The microstructure of an 11% Cr martensitic steel was investigated in normalized-andtempered condition. It was found that the microstructure was tempered martensite consisting of prior γ grains and laths. M23C6 precipitates were mainly distributed along prior γ grain boundaries and lath boundaries and small amount of M3B2 particles were aligned almost as a line along rolling direction. MX nano-particles were distributed in the matrix. Complex inclusions containing titanium were also found in the microstructure. Tensile cracks were easily to nucleate at the interface between matrix and M3B2 particles or inclusions.

Abstract: In this study, the ARB process is used and the Al(1100)/Mg (AZ31) alloys which is chosen. Steps of 12 layers are created. The ARB process creates a multilayer compound between Al/Mg layers with excellent bonding characteristics and fine grained microstructure. The bonding condition became ascendant gradually with increased from 1 to 3 cycles. The grain sizes of Al and Mg alloys were reached to 875 nm and 656 nm after 3 cycles. The hardness of the Al and Mg alloys were raised to 42Hv and 90Hv after 3 cycles.

Abstract: The aim of this study is to clarify the metal-mold reaction for the economic net-shape forming of titanium and titanium alloys. The metal-mold reactions between pure titanium, TiAl alloys and Al2O3 mold were examined in a plasma arc melting furnace. The alpha-case generation between pure titanium and Al2O3 mold could not be explained by the conventional α-case formation mechanism, which is known to be formed by the interstitials, especially oxygen dissolved from mold materials. However, based on the interstitial and substitutional α-case formation mechanism, the α-case formation between pure titanium and Al2O3 mold, and α-case free casting of TiAl alloys against Al2O3 mold can be explained. On the basis of the interstitial and substitutional α-case formation mechanism, α-case controlled net-shape forming of titanium and TiAl alloys can be possible for the structural materials.

Abstract: Plasma radical nitriding was performed to harden the surface of SCM 440 steel for 1-10 hours at temperature range of 450-550°C. No compound layer was formed during this process except the experiment carried out at 500
for 10 hours. A diffusion depth increased with increasing treatment temperature and time ( up to about 250). The surface hardness of radical nitrided layer was two times higher than that of the untreated surface. The main phase produced in the diffusion zone was identified to be γ΄-Fe4(N,C). The residual stress of the diffusion layer also increased with increasing treatment temperature and time due to the increase of precipitates.

Abstract: Identification of precipitates appearing during DSC scan of Al-2.1Li-2.9Cu-0.12Zr(wt. pct) alloy has been conducted as a function of temperature by using a differential scanning calorimetry (DSC) and transmission electron microscopy(TEM). In the as-quenched specimen from 540°C, three couples of heat evolution and absorption peaks are observed during the heating period of DSC experiments. It is found from TEM works that these peaks are associated with the formation and dissolution of GP zone, δ‘, and T1(+θ') phases. The heat evolution peak appearing in the temperature range over 36~78°C is due to the formation of GP zone. Heat absorption peak appearing in 78~140°C is associated with the dissolution of GP zone. Heat evolution peaking at 166°C in the temperature range over 140~190°C and next heat absorption peak are attributed to the formation and dissolution of δ‘ phase. Heat evolution peaking at 288°C in the temperature range of 254~332°C and heat absorption at high temperature are attributed to the formation and dissolution of T1(+θ'). The hump in DSC curve at the temperature of 425°C is considered as the formation of hexagonal structure T2 phase.

Abstract: As an alternative to degassing pipe and rotor blade using in molten aluminum industry, we investigate the mechanical properties of silicon nitride ceramic components prepared by nitrided pressureless sintered (NPS) process, which process is the continuous process of nitridation reaction process combined with pressureless sintering. Mechanical properties of silicon nitride prepared by NPS process with sintering additives of 5wt% Y2O3, 5wt% Al2O3 and 20wt% Si show high strength, >500 MPa, high hardness, 12.6 GPa, and superior damage tolerances with high fracture toughness, 9.8 MPam1/2.

Abstract: The FeAlCr intermetallic compound has a high possibility to be used as the material of the aerospace industry, in the internal combustion engine, in the heat exchanger and as the material of next-generation heat resistant material due to the low density, the excellence in oxidation resistance and corrosion and the high melting point. The study fixed the Cr content of 6% in FeAl alloy to improve the Ductile in the room temperature and added MO and Hf to improve the Grain Refinement and the mechanical properties. This alloy was manufactured by Osprey Forming Process to improve the ductile and the workability in room temperature and to try to get the low production cost as well. The microstructure and the Fracture phenomenon of specimens after homogenizing(1,000 °C , 168hour) and phase stabilizing heat treatment(500°C, 120hour) was observed by SEM, EDS, XRD, Hardness and Compression. The microstructure of FeAlCr intermetallic compound was changed from the coarse equixed structure to the minute equixed one because of the addition of Mo and Hf. The rates of hardness and yield strength of FeAlCr intermetallic compound were increased after Mo and Hf had been added in it.

Abstract: Mg is one of the most promising structural materials for lightweight applications due to its low density, good castability and damping capacity. In this study, we investigated the effect of silver (Ag) addition on alloy ageing behavior and mechanical properties of Mg-Al-Si-Sn-Sr-Ag alloys with variation of Ag contents (0.1, 0.5, 1.0, 2.0wt%). The ageing kinetics of Ag added alloys was determined and affected by Ag addition. Although the precipitation of platelets of Mg17Al12 within α-Mg matrix was not significantly affected by the silver, mechanical properties such as hardness and tensile properties were improved with increasing Ag contents.

Abstract: Hydrogen redistribution caused by thermotransport in the Zr-1.0Nb-1.0Sn-0.1Fe alloy under the temperature gradient which is likely to be encountered between nuclear fuel cladding and primary cooling water (300-340
) was investigated. The heat of transport (Q*) of hydrogen was determined by using a steady state technique to evaluate the magnitude and direction of thermotransport of hydrogen in the alloy. The values of Q∗ were 23.1, 23.7 and 27.1 KJ/mol for the hydrogen concentration of 73.4, 75.8 and 94.3 ppm by weight respectively. In other words, hydrogen was transported from hot region to cold region and the value of Q∗ increased with increasing overall hydrogen concentration. The Zr-1.0Nb-1.0Sn-0.1Fe alloy had the smaller Q∗ value than that of Zircaloy-4 when compared with same overall hydrogen concentration. Thus, Zr-1.0Nb-1.0Sn-0.1Fe alloy has better resistance to the formation of hydride due to thermotransport than Zircaloy-4 does.