ALBERT

Notes: Conclusions The sintering of mixtures of titanium and iron powders at temperatures above the eutectic point is accompanied by a strong reaction between the metals in contact, which manifests itself in a stepwise change in the dimensions of the compact being sintered. The rate of the growth in specimen volume due to the formation of an intermetallic compound during sintering at temperatures above the eutectic point increases with increasing fineness of the powders used and with rising sintering temperature.

Notes: Conclusions The results of simultaneous differential thermographic and dilatometric analyses have shown that the diffusional reaction accompanying the sintering of an equiatomic mixture of titanium and nickel powders takes place in several distinct stages: solid-phase reactive diffusion; diffusion in the presence of a liquid phase forming as a result of contact melting; and solid-phase reaction. Data yielded by dilatometric and differential thermographic analyses match. The following phenomena are observed: shrinkage in the range of the ascending branch of the first heat evolution peak; shrinkage or growth, depending on the porosity in the range of the descending branch; stepwise growth in the range of the second peak; and shrinkage in the third stage. Growth is apparently due to the difference in the partial diffusion coefficients of ß titanium and nickel. The phase composition of the sintering products depends on the specimen porosity. With increasing porosity the material becomes more homogeneous, which is apparently due to a rise in the true temperature attained in the specimen during sintering as a result of a change in the relative rates of heat evolution and removal.

Notes: Conclusions During the sintering of compacts from titanium + iron and titanium + iron + nickel powder mixtures exothermic effects are observed indicating the crystallization of new phases. The initial temperatures of the exothermic effects depend on the particle sizes of the powders used and heating rates. The Ti-Fe and Ti-Fe-Ni systems exhibit no ΔT effect.

Notes: Abstract The process of contact melting in iron-carbon systems was investigated using a dilatometric method. Specimens of iron, and diamond or graphite of various structures were studied at different temperatures and pressures. The thickness of the layer of eutectic melt formed and removed from the interface of contact was measured. The experimental data were analyzed and the process mechanism discussed.

Notes: Conclusions In a general case the solid-phase reaction of aluminum with titanium leading to the formation of TiAl3 is controlled by dual kinetics. In the initial period the rate of the TiAl3 is controlled by dual kinetics. In the initial period the rate of the TiAl3 formation process at the interface between titanium and aluminum is constant with time. The temperature dependence of the formation rate constant under kinetic conditions obeys Arrhenius' equation. The energies of activation of TiAl3 formation in the linear stage, Es = 170 ± 30 in the solid-phase reaction and e1 = 127 ± 30 kJ/mole in the reaction of titanium with liquid aluminum, match, allowing for errors in the determination of Es and e1, the standard heat of formation of TiAl3, ΔH298 = 142 ± 4 kJ/mole [11]. It is therefore reasonable to conclude that the mechanism of contact reaction in the linear stage of layer growth is the same in both cases and is determined not by diffusional transport but by chemical kinetics. Differences between values of rate constants of the reactions of titanium with solid and liquid aluminum are apparently mainly due to the method employed in processing experimental data. The true area of the reaction surface between titanium and liquid aluminum is considerably larger than the surface area of the starting titanium specimen. Consequently, calculation in this case yields larger values of reaction rate constants. During the reaction of titanium with solid aluminum the growing thickness of the TiAl3 phase layer increasingly hinders the supply of aluminum to the reaction front, and this then becomes the limiting stage of the process. As a result, the conditions of layer growth change from kinetic to diffusional. When titanium reacts with liquid aluminum, the thickness of the thin layer of columnar TiAl3 crystals adjacent to titanium and the number of capillaries crossing this layer do not vary as functions of reaction time (up to 5.5 h at 850°C). The rate of growth of this layer is therefore equal to the rate of its disintegration on the outer boundary. In this case, since the length of the capillaries does not vary owing to constancy of the layer thickness, the flow of aluminum to the titanium surface remains unchanged. Thus, during the reaction of titanium with liquid aluminum the intermetallic compound layer grows according to a law which is always linear, never changing to parabolic.

Notes: Conclusions Replacing 1 or 3% Ni with Fe in the sintering of an equiatomic titanium-nickel mixture has an inhibit. effect on the reactive diffusion process. Thermograms recorded during the sintering of 50% Ti-49% Ni-1% Fe and 50% Ti-47% Ni-3% Fe mixtures exhibit three clearly defined heat evolution peaks. The first peak is linked with a solid-phase reaction, and the second with reactive diffusion in the presence of a liquid phase forming as a result of contact melting. Data yielded by differential dilatometric analysis accord well with thermograms. Specimens from the three-component mixture, unlike those from the two-component mixture, experience elongation only after the attainment of contact melting temperatures.

Notes: Conclusions The capillary force between two spherical particles due to entrapped liquid has been studied theoretically and experimentally. A simple procedure and an equipment for measuring the capillary forces have been worked out. A formula has been derived for determining the capillary force between spherical particles as a function of the amount of liquid, the contact angle, and other characteristics of the system. It is proved that the adhesive force drops with the amount of liquid. The agreement between the theoretical and the experimental values of the capillary force is satisfactory; hence, formula (3) may be used in practical calculations on capillary systems.