What is a feature of many metallic and ceramic systems?

Is solid solubility extended or limited?

What is called «liquidus» and «solidus»?

What does the Lever Rule state?

What does the solvus show?

How is it quickly possible to derive mass ratios and fractions?

8. Read text B and choose the best title for it:

Exothermic and endothermic reactions.

Criteria for equilibrium.

3. The concept of free energy.

Make sure that you know the following words and word combinations:

Enthalpy - энтальпия (термодинамическое свойство вещества)

Entropy – энтропия (функция состояния термодинамической системы)

Text B

Every material in a given state has a characteristic heat content or enthalpy, H, and the rate of change of heat content with temperature is equal to the specific heat of the material measured at constant pressure. A knowledge of the quantity H is clearly important to understand reactions but it does not provide a criterion for equilibrium, nor does it determine when a phase change occurs, as shown by the occurrence of both exothermic and endothermic reactions. To provide this criterion it is necessary to consider a second important property of state known as the entropy, S. In statistical terms S may be regarded as a measure of the state of disorder of the structure, but from classical thermodynamics it may be shown that for any material passing through a complete cycle of events = 0, where dQ is the heat exchanged between the system and its surroundings during each infinitesimal step and T is the temperature at which the transfer takes place.

 

Part III

 

1. Learn the words:

coring	отбор керна, взятие керновой пробы
composition	состав
to maintain	поддерживать
to adjust	регулировать
rapid	быстрый
grain	зерно
core	ядро
unduly	чрезмерно
outer regions	внешние области
etch	гравировать; травить (на металле, стекле)
polished specimen	полированный образец
dendritic segregation	дендритная сегрегация
chill-cast ingots	литейные слитки
extensive	экстенсивный, обширный
to impair	ухудшать
properties	свойства
annealing	отжиг
localized fusion	Локализованное слияние
practicable	реальный
advantage	преимущество
to intermingle	смешиваться
to reduce	уменьшaть
to accelerate	ускорять
to promote	содействовать
subsequent	последующий
equiaxed	равноосный

 

2. Guess the meaning of the following words and word combinations:

Microsegregation; freezing process; atomic migration; diffusion; composition gradients; non-uniform solid solution; cored grain; to cold-work; to be broken up by deformation; recrystallization; hot-working.

3. Identify the part of speech and translate the words:

To refer, reference, referred; to progress, progressive, progressively; consequent, consequently, consequences; to continue, continuous, continuously; to adjust, adjustment, adjustable; relative, relatively; rapid, rapidly, rapidity; to allow, allowance; extensive, extensively; to produce, producer, produced; to impair, impaired, impairment; to homogenize, homogenizer, homogenized; to select, selective, selection; advantage, advantageous; to promote, promoter, promoted; subsequent, subsequently; to eliminate, elimination, eliminated.

4. Match the words with their definitions:

liquid phase	температура плавления
industrial conditions	физическая и химическая гетерогенность
the cooling rate of the solid phase	выбранный с осторожностью
complete elimination of differences in composition	богатый металлом с низкой температурой плавления
physical and chemical hetereogeneity	полное устранение различий в составе
melting point	неравновесные скорости охлаждения
non-equilibrium cooling rates	скорость охлаждения твердой фазы
selected with care	промышленные условия
rich in low melting point metal	жидкая фаза

 

Text A

Coring

It is now possible to consider microsegregation in more detail. Referring again to the freezing process for a Ni–Cu alloy, it is clear that the composition of the α-phase becomes progressively richer in copper and, consequently, if equilibrium is to be maintained in the alloy, the two phases must continuously adjust their compositions by atomic migration. In the liquid phase such diffusion is relatively rapid. Under industrial conditions, the cooling rate of the solid phase is often too rapid to allow complete elimination of differences in composition by diffusion. Each grain of the α-phase will thus contain composition gradients between the core, which will be unduly rich in the metal of higher melting point, and the outer regions, which will be unduly rich in the metal of lower melting point. Such a non-uniform solid solution is said to be cored: etching of a polished specimen can reveal a pattern of dendritic segregation within each cored grain.

The faster the rate of cooling, the more pronounced will be the degree of coring. Coring in chill-cast ingots is, therefore, quite extensive. The physical and chemical hetereogeneity produced by non-equilibrium cooling rates impairs properties.

Cored structures can be homogenized by annealing. For instance, an ingot may be heated to a temperature just below the solidus temperature where diffusion is rapid. The temperature must be selected with care because some regions might be rich enough in low melting point metal to cause localized fusion. However, when practicable, it is more effective to cold-work a cored structure before annealing.

This treatment has three advantages. First, dendritic structures are broken up by deformation so that regions of different composition are intermingled, reducing the distances over which diffusion must take place. Second, defects introduced by deformation accelerate rates of diffusion during the subsequent anneal. Third, deformation promotes recrystallization during subsequent annealing, making it more likely that the cast structure will be completely replaced by a generation of new equiaxed grains. Hot-working is also capable of eliminating coring.

 

5. Translate the sentences, pay attention to the modal verbs: