Single-Phase Alloys and Phase Diagrams Practice Flashcards

These practice flashcards cover the strengthening mechanisms of single-phase alloys, the interpretation of Pb-Sn and Fe-Fe3C phase diagrams, and the time-temperature-transformation (TTT) behaviors of steels including the formation of pearlite and martensite.

How does plastic deformation primarily occur in metal atoms?

It occurs by the motion of dislocations.

What are the three mechanisms used to modify the stress-strain curves of metals for strengthening?

Strain hardening, solid-solution strengthening, and grain-size reduction.

What are the five common methods used to shape metal parts?

Rolling, extrusion, drawing, forging, and deep drawing.

Which forming process is typically used to create aluminum rods?

Extrusion.

How is dislocation density defined in material science?

The total dislocation length per unit volume, typically measured in units like $\text{cm/cm}^3$.

What is the typical dislocation density of an as-received metal compared to a heavily deformed metal?

An as-received metal is approximately $1 \times 10^8\,\text{cm/cm}^3$, while a heavily deformed metal is approximately $1 \times 10^{13}\,\text{cm/cm}^3$.

How does increasing the amount of cold-working affect the yield strength, tensile strength, and ductility of a metal?

Yield strength and tensile strength increase, while ductility decreases.

In solid-solution hardening, how do impurity atoms strengthen the metal?

Impurity atoms distort the crystal lattice and generate lattice strains that act as barriers to dislocation motion.

What equation relates the yield-strength of a metal to its grain size?

The Hall-Petch equation.

According to the Hall-Petch equation, how is yield-strength related to grain size?

Yield-strength is inversely proportional to the square-root of the grain size ($\text{yield-strength} \propto d^{-1/2}$).

What are the three stages of the annealing process for cold-worked metals?

Recovery, recrystallization, and grain-growth.

What occurs during the recovery phase of annealing to reduce dislocation density?

Dislocations are reduced by the process of annihilation.

At what temperature range relative to the melting temperature is hot working performed?

At temperatures greater than half (0.5) the melting temperature ($T_m$).

What is the general temperature range for the recrystallization of a metal relative to its melting temperature?

Between $0.3$ and $0.6$ times the melting temperature.

In the Pb-Sn solder alloy system, what are the characteristics of the alpha ($\alpha$) and beta ($\beta$) phases?

The $\alpha$ phase is Pb-rich with an FCC crystal structure, and the $\beta$ phase is Sn-rich with a BCT (body-centered tetragonal) structure.

What are the common names for the $\alpha$-iron and $\gamma$-iron phases in the Fe-Fe3C phase diagram?

$\alpha$-iron is called ferrite, and $\gamma$-iron is called austenite.

What is the chemical name and physical characteristic of the compound $Fe_3C$?

Cementite; it is an iron carbide that is hard and brittle.

What is the eutectic composition and eutectic temperature for a Pb-Sn alloy?

The composition is approximately $62\,\%\,\text{Sn}$ and the temperature is approximately $183\,^\circ\text{C}$.

How is a hypoeutectic alloy defined in a binary phase diagram?

An alloy composition to the left of the eutectic composition, containing less of component B than the eutectic concentration.

What is the Carbon-Iron percentage range that classifies an alloy as a steel versus a cast iron?

Steels range from $0.008\,\text{wt}\%$ to $2.14\,\text{wt}\%$ Carbon; cast irons range from $2.14\,\text{wt}\%$ to $6.7\,\text{wt}\%$ Carbon.

What are the specific eutectic and eutectoid temperatures in the Fe-Fe3C phase diagram?

The eutectic temperature is $1147\,^\circ\text{C}$ and the eutectoid temperature is $727\,^\circ\text{C}$.

In the naming convention for steel, what do the first 2-3 digits and the last 2-3 digits represent separately?

The first digits represent the alloy type (e.g., 10xx for plain carbon), and the last digits represent the $\text{percentage carbon} \times 100$.

What microstructure results from the lamellar transformation of austenite under eutectoid conditions?

Pearlite, which consists of alternating layers (lamellae) of $\alpha\text{-ferrite}$ and $Fe_3C\text{-cementite}$.

What is the difference between coarse pearlite and fine pearlite regarding formation temperature and mechanical properties?

Coarse pearlite forms at higher temperatures (near $700\,^\circ\text{C}$) and is softer; fine pearlite forms at lower temperatures (near $580\,^\circ\text{C}$) and is harder.

What non-equilibrium phase is formed by the rapid quenching of austenite, and what is its crystal structure?

Martensite; it has a BCT (body-centered tetragonal) crystal structure.

Why is the transformation of austenite to martensite considered diffusionless?

The quenching is so rapid there is no time for carbon to diffuse, causing carbon to get stuck and distort the lattice.

How does the Carbon content of a steel affect the properties of formed martensite?

Increasing the $\text{wt}\%$ carbon increases both the hardness and the tensile strength of martensite.

At what approximate transformation temperature is the rate of austenite-to-pearlite transformation the fastest (the nose of the C-curve)?

Approximately $550\,^\circ\text{C}$.