The effect of alloying additions on secondary hardening behavior in Fe-Mo-C steels has been investigated by means of the successive alloying additions of Cr, Co, and Ni. The Cr additions promote M 3 C cementite formation. The Ni additions destabilize the cementite formation, while the Co additions retard dislocation recovery and present the necessary sites for M 2 C formation which provides the secondary hardening.

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Diffusion barrier characteristics and electrical properties of self-aligned MgO layers obtained from a Cu(Mg) alloy film have been investigated. Self-aligned surface and interfacial MgO layers were formed upon annealing a Cu(Mg) film in an oxygen ambient and prevented interdiffusion of Cu in SiO2 up to 700 °C. The thermal stability of a pure Cu/TiN/Si multilayer system has been significantly enhanced up to 800 °C by the MgO layers by forming a MgO/Cu/MgO/TiN/Si multilayer system. A combined structure of Si3N4(500 Å)/MgO(100 Å) increased the breakdown voltage up to 20 V from 15 V and reduced the leakage current density down to 3×10−9 A/cm2 from 1×10−8 A/cm2 compared to a pure copper system. Consequently, the deposition of Cu(Mg) alloy followed by annealing in an oxygen ambient gives rise to the formation of a self-aligned MgO layer with excellent diffusion barrier and electrical characteristics and the film can be applied as a gate electrode in thin-film transistor/liquid-crystal displays, resulting in a reduction of process steps.

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14Co-10Ni-2Cr-1Mo-0.16C) [1] and Aermet100 (13.4Co-11.1Ni-3.1Cr-1.2Mo-0.23C), [2] possess superior toughness even at ultrahigh strength levels. These steels are based on the design of HY180 (8Co-10Ni-2Cr-1Mo-0.1C). [3,4] The precipitates providing the secondary hardening are fine M 2 C-type carbides that are formed by the dissolution of M 3 C-type cementite during aging at temperatures near 500 ЊC for the high-Co-Ni secondary hardening alloy steels. The alloying elements Mo and W form the carbides of M 2 C type. In contrast, because Cr alone does not form M 2 C carbides but M 7 C 3 or M 23 C 6 carbides, hardening with precipitates of the latter carbides could only occur by Cr additions greater than about 9 wt pct. [5,6] However, even the lower Cr contents combined with Mo and/or W additions can contribute to the formation of M 2 C carbides in which Cr is also dissolved.Recently, the effect of alloying additions on the secondary hardening behavior has been systematically analyzed for alloy systems from the basic system of the Fe-C-Mo ternary alloy, which has a strong M 2 C carbide former Mo, to the multicomponent high Co-Ni alloy system by means of the stepwise alloying additions of Cr, Co, and Ni. [7] However, another M 2 C carbide former W has been neglected because W has a weak effect on secondary hardening. Because the 14Co-10Ni addition to the 2Mo-3Cr steel, which exhibited little hardening, results in a strong secondary hardening by the fine dispersion of M 2 C carbides, there may be a similar effect in W-containing steels. Although the secondary hardening behavior in some Wcontaining steels, such as 6W, [8,9] 6W-3Ni, [10,11] 6W-6Ni, [11,12] and 3W-3Cr, [13] was studied in our laboratory, no systematic approach to the high Co-Ni steels containing W has been conducted.In contrast, many studies on the fracture behavior and toughness of commercial high Co-Ni systems containing Mo have been made by Garrison and co-workers. [14,15,16] Kwon and co-workers reported the fracture behavior of both the basic secondary hardening steels containing the M 2 C carbide forming elements 17] and the MoCr, MoCrCo, and MoCrCoNi steels. [18]