The effects of silicon additions up to 3.5wt% on the mechanical properties and microstructure of high speed steels 6W3Mo2Cr4v. W3Mo2Cr4V and W9Mo3Cr4V and W9Mo3Cr4V have been investigatied. In order to understand these effiects further, a Fe-16Mo-0.9C alloy is also used. The results show that silicon additions can increase the temper hardness of steels Fe-16Mo-0.9C, 6W3Mo2Cr4V and W3Mo2Cr4V, but yield an opposite influence on the temper hardness in W9Mo3Cr4V steel. A critical tempering temperature aeistsfor the bending strength of high speed steels containing silicon. If tempering is carried out at temperatureslower than the critical temperature, the bending strength of the high speed steels can be improved by the addition of silicon, otherwise their bending strength is decrcased. Transmission electron microscopyreveals that silicon addition can obviously refine secondary hardening carbides and inhibit the formationof M3C cementite at peak temperature. However, they are also found to accelerate both the depletion of martensite and the formation of coarse M6C precipites during temping. The mechanism wherebysilicon additions affect the secondary hardness of high speed steels is discussed in detail, and the types of high speed steel in which silicon additions can be used are suggested.

Two types of electric heating actuators used of SiCcvD fiber reinforced aluminum composite were successfully developed, which could be used at elevated temperature. The experimental results reveal that the temperature of the actuators increases with the increase of the given electric power. The maximum temperature was found to be higher the 150 and 200 C for 1-side electric heating actuator and 2-side electric heating actuator, respectively, when the electric power of about 10 W were given. It is found that the electric resistance of the actuators decreases obviously with the increase of temperature. A critical temperature was found to exist for the change of the displacement and curvature. The displacement and curvature almost remained unchanged when the temperature of the actuators was lower than the critical temperature. After that, the displacement and curvature increase with the rise of the actuator temperature, Because the 1-side and 2-side actuators have different response characteristics of the displacement and generated force, it is expected that the two types of actuators may be used in different areas.

The effects of silicon additions up to 3.5 wt% on the as-cast carbides, as-quenched carbides and as-tempered carbides of high-speed steels W3Mo2Cr4V, W6Mo5Cr4V2 and W9Mo3Cr4V have been investigated. In order to further understand these effects, a Fe-16Mo-0.9C alloy was also studied. The results show that a critical content of silicon exists for the effects of silicon on the types and amount of eutectic carbides in the high-speed steels, which is about 3wt%, 2wt% and 1wt% for W3Mo2Cr4V, W6Mo5Cr4V2 and W9Mo3Cr4V, respectively. When the silicon content exceeds the critical value, the M2C eutectie carbide almost disappears in the tested high-speed steels. Silicon additions were fotmd to raise the precipitate temperature of primary MC carbide in the melt of high-speed steels that contained δ-ferrite, and hence increased the size of primary MC carbide. The precipitate temperature of primary MC carbide in the high-speed steels without δ-ferrite, bowever, was almost not affected by the addition of silicon. It is found that silicon additions increase the amount of undissolved M6C carbide very obviously. The higher the tungsten content in the high speed steels, the more apparent is the effect of silicon additions on the undissolved M6C carbides. The amount of MC and M2C temper precipitates is decreased in the W6Mo5Cr4V and WgMo3Cr4V steels by the addition of silicon, but in the W3Mo2Cr4V steel it rises up to about 2.3wt%.

Effects of alloying elements* Si, Nb, Ti, W, Mo, V, AI and rare earth metals on the microstructure and properties of high speed steels (HSSs) have been reviewed. More attention is paid to effects of Si on the secondary hardening and V on the morphology of eutectic carbides in HSSs. A lot of work has been carried out on the hehavior of alloying elements in HSSs in the past decade, and some new types of HSSs containing silicon, aluminum or rare earth metals have been successfully developed in the world.

A simple model to estimate the work of adhesion in reactive metal/ceramic systems was developed based on the basic physicochemical principle. The work of adhesion in this model is composed of two terms. One is the Gibbs free energy change per unit area released by the reaction between the surface phases of the metal and the substrate ceramic. The other is the contribution of the work of adhesion for the metal on The initial substrate or on the reaction product formed during reaction. The present model is generally valid for not only The systems with a new phase formed at the interface, but also the ones with localized chemical bonds at the interface, and can unravel some confusion in the literature.