1.6 Eutectic composite materials

Eutectic point is the point of intersection of the two drop-down liquidyou. The composition of the eutectic point of the CoE is determined by the inverse lever rule. If the composition of the eutectic is on the ordinate is almost a pure component, such eutectic is called degenerate.

State diagrams allow us not only to determine the sequence of phase transitions when changing the system parameters, but also to make quantitative calculations of the content of phases in multicomponent systems. The basis for these calculations is the so-called lever rule, which in General form is formulated as follows: "If one phase when you change the parameters of the system decomposes into two other phases, the quantitative ratio of the formed phases will be inversely proportional to the lengths of the lever rule segments from the point of the initial phase to the points of the compositions of the resulting phases".

1.6.1 Application of the rules of linkage in two-component systems

For two-component systems, the lever rule is reduced to consideration of the relevant conned, the ends of which show the points of compositions of phases in equilibrium, and the vertical Kannada original composition is divided into two sections, the length of which (in inverse proportion) characterize the equilibrium number of phases. Suppose the initial melt composition M/ (figure 12) cooled to temperature t.

Figure 12 – application of the rules of the lever in the two-component phase diagrams

At this temperature in equilibrium are the liquid phase, the composition of which is expressed by the point n, and the solid phase (crystals of the compound AB), whose composition is expressed by a point k lying on the vertical part of the connection of AV. The original composition can be expressed by the point M, which lies at the intersection of Kennedy nk with the vertical of the initial composition of M t (compositions M and M are the same). According to the lever rule the contents at temperature t the liquid phase (point p) and the crystalline phase of AB (point k) will be determined from the expression:

the content of the liquid phase: (1)

the content of crystals (2)

1.6.2 Application of the regulation lever in ternary systems

In ternary diagrams of the three types of problems using the rule of lever.

1.6.2.1 Determination of quantitative content of phases formed during the crystallization if the system is liquid and one solid phase

This takes place when the point of liquid phase composition located in the primary field of crystallization of any compound. Let the melt composition M chilled to a temperature of t2 (figure 13).

Figure 13 – application of the regulation lever in ternary phase diagrams

At this temperature the equilibrium will be the liquid phase composition of t and crystals as released in the process of cooling the original melt. In accordance with the lever rule, the content of these phases for the entire path of crystallization (from temperature t1 to t2) will be determined from the expressions:

the content of the liquid phase: (3)

the content of crystals (4)

1.6.2.2 Determination of quantitative content of phases formed during the crystallization in the presence of liquid and two solid phases

This corresponds to the case when the point of liquid phase composition located on the boundary curve. Let the crystallization of the same melt composition M was continued to a temperature t3. At this temperature in equilibrium there are three phases: liquid composition of a point p lying on the boundary curve, and two solid — crystals and AC. The problem of determining their content for the entire path of crystallization from the temperature t1 to t3 into two pieces. First, determine the content of the liquid and all solid phases (the total content of crystals+as), and then the content of crystals In and AC separately in the total mass of the solid phase (then you can calculate the percentage of each phase separately in relation to the total mass of all substances).

To solve these problems, we combine the direct point of the composition of liquid phase p with a point source of the melt M and continue this line to the intersection with connection line as V, the corresponding edge curve Е1Е2, which is in equilibrium with the liquid phase are crystals In and AC. The intersection point k lying on the line connecting al—In, will characterize the total composition of the solid phase (In + AU) and will share this connecting line by two lines (AC—k and k—In), the length of which will determine the content in the solid phase, respectively, of the crystals and the AU (inverse proportionality). Thus, the content of phases is determined from the following expressions:

the content of the liquid phase: (5)

the total content of tvrdos phase: (6)

the content of AU in the solid phase (7)

the contents In the solid phase (8)

1.6.2.3 Determination of quantitative proportions of solid phases produced from the melt at the moment of crystallization

The quantitative ratio of the two solid phases forming from the melt upon cooling is congruent along the boundary curve in the General case is not constant but is changed (constant, this ratio will be only in the case when an edge line is a straight line). To determine this ratio in every moment of crystallization, i.e. at a given temperature and melt composition, it is necessary to the boundary curve at the point corresponding to this temperature, draw a tangent and extend it until intersection with the curve corresponding to this connecting line. The point of intersection divide a connecting line segments, the length of which (in inverse proportion) will characterize the relationship between the two evolved during the crystallization of solid phases. For example to determine the proportion of crystals as In, released when the temperature t3 of the hot melt composition of the point p lying on the boundary curve congruent Е1Е2. hold at the point p the tangent to this curve and continue to the intersection of this curve with the corresponding line connector AC—In (point k). The quantitative ratio of eye-catching solid phases determined from the expression:

(9)

Properties EKM depend on:

1) properties of matrix and inclusion;

2) crystallization rate (of non-equilibrium in the resulting eutectic solid);

3) type and concentration specially introduced impurities, or the third component.

Advantages of EKM. The structure of eutectic composites is created naturally, not by artificial introduction of reinforcing phase in the matrix and has:

1) high strength;

2) thermal stability up to temperatures close to the melting point of the eutectic;

3) lacks many of the shortcomings associated with chemical compatibility between the matrix and the inclusion of artificial KM;

4) the alloys can be Ме1-ME2, metal-semiconductor = IU-PP, PP1-PP2, IU Sol (oxide), organic-organic, etc.;

5) product and material KM can be obtained in one operation, eliminating labor-intensive processes of manufacturing reinforcing fibers, the introduction and the orientation of their in the matrix.

Disadvantages EKM:

1) increased requirements to the purity of the initial components;

2) the dependence of the properties of EKM from crystallization rate;

3) limited ability to change the volume content of inclusions. This is determined by the 2 and 3rd phase diagrams.

The use of EKM:

1) all multi-phase alloys;

2) magnetoresistor (change the resistivity in a magnetic field);

3) refractory polarizers of infrared radiation;

4) superhard alloy;

5) "metallic glass";

6) alloys with derivative properties, etc.