MAT E Quiz Questions Test 2
True or false: Copper has a higher thermal conductivity than aluminum.
True
True or false: Ductile specimens are less affected by poor quality surface finish, since the propagation of microscopic flaws as cracks is generally less likely compared to plastic deformation.
True
True or false: Even though metal parts are often intended to endure only elastic (reversible) strain, they should generally offer at least some ductility to account for local stresses in a specimen that may exceed the metal's yield stress.
True
True or false: Gray iron is a microstructure that tends to result when a cast iron of appropriate composition is cooled fairly quickly.
True
True or false: High-strength aluminum alloys that leverage secondary phase hardening are generally more susceptible to corrosion compared to pure aluminum.
True
True or false: In general, Ni exhibits properties that are similar to Fe.
True
True or false: Nickel is susceptible to corrosion when it contains chromium impurities or is exposed to environments with sulfur.
True
True or false: Nucleation and growth transformations are commonly referred to as diffusion-controlled transformations.
True
True or false: Pure aluminum is generally much more ductile than aluminum alloys.
True
True or false: The Na-K alloy system features a eutectic point, and this composition is useful as a low-melting point liquid coolant with high thermal conductivity, for applications whose ambient is relatively inert.
True
True or false: 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
A metal that forms a very hard ceramic carbide for cutting tools and wear resistant coatings. Most of the annual extraction of this metal from the earth is utilized to form its carbide.
Tungsten (W)
The highest melting point pure metal.
Tungsten (W)
True or false: The extremely high bond strengths of the PGMs result in very low thermal expansion coefficients and extremely high elastic moduli.
true
What processes will tend to strengthen a typical pure metal?
-Cold-working the pure metal -Adding solute to form a solid solution -Precipitation a secondary phase -Melting then casting the pure metal -Increasing the dislocation density (dislocations count per unit volume)
Which is a commonly observed property/behavior for crystalline ceramic materials (compared to other classes of materials such as the general behavior of metals) ?
-High elastic modulus -High hardness -Low thermal conductivity
What are possibilities related to annealing and cooling a polycrystalline material ?
-Recrystallization of grains (small grains "merging" over time, producing a larger average grain size) -Dislocation annihilation -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) -Diffusion of atmosphere components into the specimen (or diffusion of a host component out of the specimen and into the ambient atmosphere)
What factors 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.
What is definitely true (without more information) if a crystalline compound AB12 is the stable state for a single specific overall composition over a variety of temperatures at 1 atmosphere ?
-The system is below its melting or solidus temperature -The compound under these conditions has a lower Gibbs free energy compared to other phases or phase combinations -Since just the compound itself is said to be stable, the system would be single-phase in equilibrium
The exact temperature at which a transformation proceeds (for isothermal transformations), or the exact rate at which a specimen's temperature is changed (for cooling rate transformation) can influence what aspects of a phase transformation ?
-the identity of the phase(s) that form -the rate of transformation -the amount of time required for the transformation to actually commence -the elapsed time of the transformation itself (measured from commencement to termination) -the microstructure(s) that form(s) -the properties of the material after transformation
What is the carbon content of a 1020 steel, in wt% C ?
0.2
Rank the microstructures of steel in terms of their relative hardness, assuming they each feature the same overall composition and, as applicable, the same fractions of the phases present. (1 = most hard, 6 = least hard) spheroidite, fine pearlite, coarse pearlite, tempered martensite, bainite, and matensite
1. martensite 2. tempered martensite 3. bainite 4. fine pearlite 5. coarse pearlite 6. spheroidite
Rank the microstructures of steel in terms of their relative ductility, assuming they each feature the same overall composition and, as applicable, the same fractions of the phases present. (1= most ductile, 6 =least ductile) spheroidite, fine pearlite, coarse pearlite, tempered martensite, bainite, and matensite
1. spheroidite 2. coarse pearlite 3. fine pearlite 4. bainite 5. tempered martensite 6. martensite
What is a reasonable value for the elastic modulus of a typical structural metal?
300 GPa
What is a reasonable value for the yield stress (yield point) of a typical structural metal?
4 GPa
What is the expected slip system for the simple cubic crystal structure ?
<100>{100}
What is Poisson's ratio?
A material property that allows one to convert between perpendicular and oppositely-signed elastic strains.
What is elasticity?
A measure of a material's ability to absorb mechanical energy in the form of stretched bonds.
What is ductility?
A measure of a material's ability to deform plastically prior to failure.
What is hardness?
A measure of a material's ability to withstand local deformation or wear. This value is correlated with the yield point.
What is elastic modulus?
A quantity that is correlated with the bond strength of a material.
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
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
This is the lowest-melting alkali metal, and therefore the most susceptible to creep deformation at room temperature. (Ignore the extremely rare metal francium, which has never been produced in bulk metallic form).
Cesium (Cs)
A metal added to steels to drastically improve their corrosion resistance.
Chromium (Cr)
A shiny metal that is completely brittle below 300 degrees C
Chromium (Cr)
What is engineering stress?
Engineering stress is defined as the instantaneous force applied to a material, divided by the original cross sectional area over which the stress acts. Engineering strain is defined as the instantaneous dimension change a material exhibits along an axis of interest, divided by the original dimension of the material along that axis.
The crystal structure of an iron-carbon solid solution at 1000oC is __________.
FCC
True or false: A 10XX series steel is generally referred to as a stainless steel.
False
True or false: Small and sharp features on a metal specimen generally experience stress levels that are much lower than the nominal / macroscopic stress that is applied to the bulk specimen.
False
True or false: To be "truly ductile", according to most design engineers, a metal must offer at least 5% or greater tensile plastic elongation.
False, should be 15%
True or false: A specimen containing iron and 4.12 wt% carbon is considered a steel.
False: steels are between 0.022 and 2.14 wt% carbon. Before are irons and after is cast iron
_______ is a material property that pertains to local resistance to plastic deformation, such as scratching or denting. It is often measured by poking a material with a very hard tip (like diamond) and measuring the size and depth of the resulting crater that forms.
Hardness
An alkali metal whose +1 ion is very small, making this ion useful for battery applications where the diffusion of positive charge through an electrolyte needs to be fast.
Lithium (Li)
A metal that is quite similar to aluminum, but is less ductile and highly susceptible to corrosion.
Magnesium (Mg)
An alkali metal whose +1 ion is relatively big compared to typical components of modern silicate glasses. Addition of this metal's +1 ion to such glasses tends to introduce compression on the covalent glass network.
Potassium (K)
A metal added to nickel-based superalloys to stabilize the precipitation of the secondary phase (gamma-prime) that strengthens such alloys.
Rhenium (Re)
The pure metal with second-highest melting point.
Rhenium (Re)
Crack propagation in ductile materials is termed _________ (stable or unstable) crack growth, since additional stress is required for the crack to propagate further.
Stable
What is ultimate tensile strength?
The maximum stress that a material can withstand before it breaks
What is yield point?
The stress at which dislocation motion and/or twinning is assumed to become the dominant response upon loading a material.
A metal whose oxide is more commonly produced (approximately 60x more by weight). The identity of this oxide mineral is rutile.
Titanium (Ti)
A relatively low-density but high-strength metal that has excellent corrosion resistance as a cool solid, but not as a very hot solid or liquid. The thermal conductivity of this metal is very low, making it difficult to machine since it doesn't effectively dissipate the heat produced at the cutting tool location.
Titanium (Ti)
True or false: A significant fraction of magnesium that is produced ends up acting as an alloying element in aluminum.
True
True or false: Aluminum alloys are generally superior to pure aluminum, in terms of yield strength, because their microstructures often contain precipitate phases that strain the lattice, thereby hardening the alloy relative to pure aluminum.
True
True or false: Aluminum is relatively abundant in the earth's crust.
True
True or false: As an alloying element, Nickel tends to increase the composition and temperature ranges over which FCC iron is stable (nickel acts as an austenite stabilizer)
True
A ____________ (fine/coarse) pearlite structure is produced when austenite is allowed to transform into pearlite at a temperature that is relatively close to the eutectoid temperature, and such a structure will be relatively soft and ductile when compared to other a fully pearlitic structural possibilities.
coarse
The formation of pearlite, spheroidite, and bainite are examples of _____________ (diffusion-controlled/diffusionless) transformation, whereas the formation of martensite is referred to as a ___________ (diffusion-controlled/diffusionless) transformation.
diffusion-controlled, diffusionless
Completely brittle failure occurs while the loading is
elastic
True or false: All other factors the same, it is generally more difficult to form a fully martensitic microstructure for a hypoeutectoid steel compared to a hypereutectoid steel.
false
True or false: All phase transformations proceed via a nucleation & growth mechanism.
false
True or false: Aluminum alloys are generally not viable as lightweight structural materials in humid environments because they are highly susceptible to corrosion by water vapor.
false
True or false: Aluminum and its alloys are difficult to liquify in air, so they are not desirable metals for casting purposes.
false
True or false: Aluminum is not very workable at high temperatures in air, in terms of extrusion and rolling, because a non-protective oxide grows and consumes the metal, converting it to a hard and brittle ceramic.
false
True or false: Because PGMs tend to donate so many electrons to the bulk metal when forming metallic bonds (up to 8 donated electrons), these metals feature a high concentration of "free" electrons that result in extremely high electrical conductivities compared to metals that feature a more typical valence state (1-2 donated electrons).
false
True or false: Beryllium has a lower melting point than aluminum.
false
True or false: Bronze alloys with more than 20 wt% tin are quite ductile and easily cold-worked compared to alloys with 5 wt% tin or less, because large additions of the soft metal tin enhance the ductility of copper.
false
True or false: Coarsening refers to the scenario where, upon heating and/or annealing for sufficient time, the scale of a microstructure tends to reduce (e.g. grains become smaller, secondary phase particles separate into smaller particles and become more finely dispersed, often reverting to high aspect ratio or high surface-area-to-volume ratio configurations.
false
True or false: Compared to most other metals, like steel, pure aluminum is very resistant to creep deformation.
false
True or false: Copper does not work-harden at an appreciable rate, so it can be bent/deformed repeatedly in a location without significant loss of ductility.
false
True or false: Copper is a minor component (by weight) of most brass alloys.
false
True or false: Copper is much more abundant in the earth's crust compared to iron or aluminum.
false
True or false: Even highly polished aluminum is a poor reflector of optical and infrared radiation.
false
True or false: Fast cooling rates tends to promote transformations that result in relatively course structures (e.g. for a reaction resulting in multiple product phases, the secondary phase particles are (i) fewer in count (ii) larger in size and (iii) relatively spherical).
false
True or false: For a system below its melting point, a glass (or non-crystalline / amorphous) configuration is the most energetically stable configuration that is possible (offers the lowest Gibbs free energy).
false
True or false: For a transformation that involves nucleation and growth of the product phase(s), the nucleation of all evolving phase particles must occur before they are allowed to grow to consume the remaining volume of the system.
false
True or false: Francium is the most abundant of all metals and is therefore the least expensive metal per kilogram.
false
True or false: Gold is the most ductile metal because it has a very low density (less mass to deform per unit volume).
false
True or false: Liquid silver has extremely low solubility of oxygen.
false
True or false: Magnesium is highly resistant to corrosion, even when placed in contact with other metals.
false
True or false: NaCl is commonly found as a modifying compound in modern silicate based glasses, such as soda-lime glass and borosilicate glass.
false
True or false: Nickel is inherently susceptible to the formation of nitrides if exposed to room temperature air.
false
True or false: Nickel-based superalloys feature remarkable strength and corrosion resistance up to 2100oC.
false
True or false: Nucleation and growth transformations are an exclusive transformation that is unique to metals.
false
True or false: Platinum group metals that were exposed to air are extremely corrosion resistant and unreactive because of the very strong and coherent oxide layer that forms on their surfaces.
false
True or false: Pure aluminum has an exceptionally high ductile-to-brittle transition temperature, so it cannot be plastically deformed below about -20oC.
false
True or false: Radium is useful for x-ray applications, such as an x-ray transparent window, because radium itself is radioactive.
false
True or false: Sodium metal is the most expensive metal per kilogram (comparing approximate bulk prices).
false
True or false: The density of copper is closer to that of aluminum than it is to iron.
false
True or false: The formation of a glass from a liquid typically requires extremely slow cooling rates, thereby taking on the order of years or even centuries to produce.
false
True or false: The melting point and elastic modulus of beryllium are remarkably low, compared to its neighbors on the periodic table.
false
True or false: The primary reason that alkali metals are submerged in mineral oil for storage is that the mineral oil changes color when these metals undergo radioactive decay, thereby acting as a color indicator for radiation release.
false
True or false: The transformation of austenite to martensite only proceeds when austenite is held at temperature for a long time at temperatures below about 225oC.
false
True or false: When measured experimentally, most materials tend to exhibit the same exact temperature value for both melting and freezing (crystallization).
false
True or false: Nickel is extremely abundant in the earth's crust.
false, it is abundant in the Earth's core
Martensite is formed whenever austenite (all or just a part of a specimen's microstructure) is cooled extremely _________(slow/fast) .
fast
The fracture surface of a brittle material is often___________ and ____________.
flat, smooth
A high value of elastic modulus implies a __________ (high or low) magnitude of slope on the force-separation curve ( bonding curve, F versus r ) at the equilibrium bond distance (ro) for the material of interest.
high
Hooke's Law applies in the __________ regime of the stress-strain curve for materials that exhibit a linear elastic response.
initial
The ____________ (kinetics/thermodynamics) 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
Without any other information to consider, it is reasonable to assume that a material with a low elastic modulus will have a _____ melting point.
low
Metals with HCP packing (like magnesium) are often less ductile than metals with FCC packing (like aluminum), because the HCP structure has:
lower number of slip systems than FCC.
Martensite is a/n _______________ (equilibrium non-equilibrium) phase of steels, so it does not appear on the Fe-Fe3C phase diagram.
non-equilibrium
The Fe-Fe3C system features how many eutectic and eutectoid points?
one and one
For most materials, a tensile stress results in a ___________ strain, whereas a compressive stress results in a __________ strain.
positive, negative
Macroscopic stress applied to a real specimen is magnified at __________ features, especially at microscopic internal voids, as well as surface scratches.
sharp
At best, the __________ (kinetics/thermodynamics) 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
True or false: Aluminum has a higher density than magnesium.
true
True or false: Beryllium and Magnesium are the only alkaline metals that have use as structural materials, since Ca, Sr, Ba, and Ra are susceptible to corrosion in air.
true
True or false: Beryllium metal is toxic.
true
True or false: Copper and its alloys form a green tarnish over time, consisting of sulfides and carbonates.
true
True or false: Copper is one of just a few metals that can be found in metallic form in nature (found in the ground as native copper).
true
True or false: Copper is one of the best conductors of heat (features a high thermal conductivity).
true
True or false: Copper is relatively resistant to corrosion by neutral and even mildly basic water.
true
True or false: Liquid gold can be purified by bubbling oxygen gas through the molten metal, thereby reacting with other metal impurities to form oxides which are easily removed. This is fairly effective for extracting impurities other than silver and platinum, which are also fairly non-reactive with oxygen.
true
True or false: Lithium is the smallest metal atom within the alkali group.
true
True or false: Of all elements found in Earth's crust, only eight have a weight percentage above 1%, and four of these eight are either alkali or alkaline metals.
true
True or false: PGM's are extremely rare in the earth's crust, resulting in extremely high prices and limited-quantity use for specialty applications.
true
True or false: Silver is a better conductor of electricity compared to gold.
true
True or false: Silver is a better conductor of heat compared to copper.
true
True or false: The electrical conductivity of somewhat impure copper alloys can actually be increased by introducing a small amount of oxygen into the copper, provided the oxygen reacts with impurities and coalesces them into larger oxide particles.
true
True or false: The lower members of the platinum group metals, especially, are extremely dense because their crystal structures are close-packed and these atoms tend to offer numerous d electrons in a metallic bond, resulting in highly efficient packing of relatively heavy metal ions in the bulk metal.
true
True or false: The outer s1 electrons of alkali metal atoms are very loosely bound to their positive nuclei, rendering these metals fairly reactive, chemically, when compared to other metals.
true
True or false: Unlike other alkali metal atoms, the sole valence electron of a Li atom is not shielded from the nucleus by a filled p shell. Therefore, Li tends to be the least reactive when compared to other alkali metals.
true
