Mat E exam

Imagine rapidly (instantaneously) cooling austenite to 575oC and holding it at this temperature. How long does it take, approximately, before the decomposition of austenite begins to occur?

1.00 Sec

Imagine rapidly (instantaneously) cooling austenite to 500oC and holding it at this temperature. How long does it take, approximately, before the decomposition of austenite is complete (no austenite remains)?

10.0

Which material cold-works "the fastest" (the most rapidly with strain) upon initial plastic deformation?

1040 Steel

What is the maximum elastic service temperature that a tungsten rod may experience if it supports a fixed tensile stress of 10 MPa?

1500 c

What is the expected slip system for the simple cubic crystal structure ?

<100>{100}

The crystal structure of an iron-carbon solid solution at 1500oC is

BCC

The crystal structure of an iron-carbon solid solution at 600oC is

BCC

What is the expected microstructure if austenite is preserved to 500oC, held there for 100 seconds, and then quenched to room temperature? Choose the option that best describes the expected microstructure upon cooling.

Bainite

Recalling that most brass for structural use is a single-phase alloy of Cu and Zn, what is the primary reason why brass is stronger than copper when comparing any two pieces of these materials that feature the same level of prior cold-working (and presumably the same grain size)?

Brass leverages solution hardening

For the flawed and brittle specimen depicted below, which flaw is the least likely to propagate under the indicated tensile loading scenario?

C

A [Select] pearlite structure is produced when austenite is allowed to transform into pearlite at a temperature that is relatively [Select] the eutectoid temperature, and such a structure will be relatively soft and ductile when compared to other a fully pearlitic structural possibilities.

Coarse Close to

An aluminum metal rod is heated to 300oC and, upon equilibration at this temperature, it features a diameter of 25 mm. If a tensile force of 1 kN is applied axially to this heated rod, what is the expected mechanical response? Note: Aluminum melts at 660oC

Creep

A measure of a material's ability to deform plastically prior to failure.

Ductility

A tungsten metal rod is heated to 2000oC and, upon equilibration at this temperature, it features a diameter of 50 mm. If a tensile force of 0.20 kN is applied axially to this heated rod, what is the expected mechanical response?

Elastic

A quantity that is correlated with the bond strength of a material.

Elastic Modulus

A measure of a material's ability to absorb mechanical energy in the form of stretched bonds.

Elasticity

The crystal structure of an iron-carbon solid solution at 1000oC is

FCC

(b) Silica-based glass that has a green appearance / tint (especially along its edges) is guaranteed to have been thermally tempered during its production.

False

(c) Tempered glass is unique from ordinary (annealed) glass because it can be "cut" to shape rather simply ... often by producing a score with a diamond tip tool and then snapping along the score line.

False

(e) Tempered glass is usually weaker than ordinary (annealed) glass, since it tends to grow numerous cracks rapidly with even the slightest of applied stress. Ordinary glass typically survives to much higher stress levels than tempered glass.

False

A specimen containing iron and 4.12 wt% carbon is considered a steel.

False

At such temperatures, the bond strength of atoms across grain boundaries is significantly weaker compared to the bond strength of atoms within the bulk of the grain.

False

It is relatively easy for dislocations to move across grain boundaries.

False

Parts 3 and 7 exhibited similar lifetimes (cycles to failure) even though Part 7 endured a higher mean stress.

False

Parts 7, 8, and 9 experienced the largest mean stress (of all parts) during stress cycling.

False

The Schmid factor is, by definition, the same for each grain in a polycrystalline metal under load.

False

The fracture surface of a brittle material is often: Completely brittle failure occurs while the loading is:

Flat and Smooth Elastic

A measure of a material's ability to withstand local deformation or wear. This value is correlated with the yield point.

Hardness

In response to local shear stress, dislocations prefer to glide along [Select] density planes and in [Select] density directions.

High High

The [ Select ] of a system dictates the rate(s) and mechanism(s) of phase transformations, thereby dictating the microstructure(s) that a system adopts for a given transformation path (transformation temperature, heating / cooling rate, complex transformation pathway, etc.). Furthermore, this also dictates the time over which these microstructure(s) tend to exist.

Kinetics

What is the expected microstructure if austenite is preserved to 300oC, held there for 10 seconds, and then quenched to room temperature? Choose the option that best describes the expected microstructure upon cooling.

Martensite

Martensite is a/n [Select] phase of steels, so it [Select] appear on the Fe-Fe3C phase diagram. Martensite is formed whenever austenite (all or just a part of a specimen's microstructure) is cooled extremely [Select] .

Non-equilibrium Does not Fast

The Fe-Fe3C system features [Select] eutectic point(s) and [Select] eutectoid point(s).

One One

What is the expected microstructure if austenite is preserved to 600oC, held there for 1000 seconds, and then quenched to room temperature? Choose the option that best describes the expected microstructure upon cooling.

Pearlite

Macroscopic stress applied to a real specimen is magnified at [select] features, especially at microscopic internal voids and surface defects, such as scratches, chips, notches, etc.

Sharp

Crack propagation in ductile materials is termed [select] crack growth, since [Select] stress is required for the crack to propagate further.

Stable Additional

Which of the following materials offers a yield point of around 200 MPa ?

Structural Steel (Mild Steel)

Which of the following is the least likely to be manufactured out of thermally tempered glass?

The front windshield of a modern civilian car

At best, the [ Select ] of a system tell us the phase(s) that are stable as well as their composition(s) & fraction(s), for a given set of state variables such as temperature, pressure, and overall composition.

Thermodynamics

Based on crystal structure only, which of the following metals is expected to be the least ductile under standard thermodynamic conditions (0oC and 1 atm)?

Titanium, Ti

(a) Both photographs below feature broken pieces of - what was likely - thermally tempered glass .

True

(d) Tempered glass often has a very patterned (almost "checkerboard") appearance when viewed with polarized light at the proper angle. These "dots" are a remnant of the cooling method used to produce tempered glass.

True

(f) Tempered glass tends to fracture into numerous small granular pieces, rather than large sharp shards.

True

Ductile specimens are less affected by poor quality surface finish, since the propagation of cracks near stress concentrators is usually preceded by significant plastic deformation.

True

For a given mean stress, higher stress amplitudes result in reduced part lifetimes (cycles to failure).

True

If Parts 4, 5, and 6 had been cooled to a much lower temperature during their stress cycling, they would have likely exhibited lifetimes similar to parts 1, 2, and 3, respectively (opposed to lifetimes similar to Parts 7, 8, and 9, respectively).

True

Parts 3, 6, and 9 experienced the same approximate stress amplitude during their respective stress cyclings.

True

The presence of varying grain orientations in a polycrystalline metal limits the ability of the grains to deform via slip until essentially all of the grains experience a stress equal to at least the critical resolved shear stress.

True

The shape, position, and identities of "microstructure fields" on the IT curves for a steel depends on the overall composition of the steel. In other words, the austenite decomposition kinetics and as-cooled microstructure possibilities for a steel depend on the overall composition of the steel.

True

Select the two fundamental mechanisms that allow ductile metals to deform plastically at low temperatures (e.g. near room temperature) before they fail.

Twinning Dislocation Motion

The stress at which dislocation motion and/or twinning is assumed to become the dominant response upon loading a material.

Yield Point

Metals with HCP packing (like magnesium) are often less ductile than metals with FCC packing (like aluminum), because the HCP structure has:

a lower number of slip systems than FCC.

Which of the following steel microstructures seems to be fully pearlitic (no proeutectoid phase) ?

b

The formation of pearlite, spheroidite, and bainite are examples of [Select] transformation, whereas the formation of martensite is referred to as a [Select] transformation.

diffusion-controlled diffusionless

If a BCC single crystal is loaded along the [001] axis, which of the following candidate slip systems is the least likely to experience slip?

(110) [1 1 1]

For the factors / conditions listed, select those that tend to alleviate creep deformation for a metal sample with a random polycrystalline microstructure.

*Substitute the metal for one with a higher melting point. *Decrease the applied stress on the metal part. *Apply an insulative (non-structural) ceramic coating to the part. *Switch to a single crystal or textured polycrystalline microstructure.

Which of the following is not a commonly observed property/behavior for crystalline ceramic materials (compared to other classes of materials such as the general behavior of metals) ?

*high strength under tensile loads *low melting temperature *high toughness

Which of the following are possibilities related to annealing and subsequent cooling of a polycrystalline material?

*recrystallization of grains during annealing (small grains "merging" over time, producing a larger average grain size) *dislocation annihilation during annealing *overall microstructure change during an annealing process (perhaps during the heating stage to the annealing temperature, or even while the material is held at temperature) *crystal structure change(s) during an annealing process (perhaps during the heating stage to the annealing temperature, or even while the material is held at temperature) *crystal structure change(s) during the cooling stage after an annealing process *overall microstructure change(s) during the cooling stage after an annealing process *chemical reaction with the annealing atmosphere components (e.g. oxidation) during annealing and/or cooling *diffusion of atmosphere components into the specimen (or diffusion of a host component out of the specimen and into the ambient atmosphere) during annealing and/or cooling