Examen Final Flashcards
Thermoset polymers result from a “phase transformation” reaction which generates only a low degree of spatial crosslinking.
FALSE
Undercooling is defined as the difference of Treal minus Tequilbrium
FALSE
Bainite is a coarser microstructure than pearlite, and thus harder and tougher.
FALSE
Malleable cast iron is the result of heat-treating a white cast iron which typically has a carbon equivalent of 3 to 3.4%
TRUE
The Avrami equation (K-J-M-A) is a mathematical model of the effect of time on a phase transformation process at a given temperature.
TRUE
When adding lateral groups to a polymer, as the case of PVC instead simple polyethylene, the transition temperature increases and as well as its ability to crystallize.
TRUE
The Weibull distribution is a statistical function that is used, amongst many other applications, to predict the hardness of ceramic of Volumen V0 whose material has a characteristic stress S0 and a sensitivity exponent m.
FALSE
For recrystallization to occur on annealing of a metallic alloy, a minimum amount of temperature is required, otherwise grain growth will set in.
FALSE
In XYZZ designation of steels (AISI-SAE) X is the type of the steel, Y the modification and ZZ the carbon content in hundredths of a per-cent
TRUE
In a two-phase material consisting of a matrix and secondary particles that exist in thermodynamic equilibrium the larger particles tend to integrate smaller once (large particles
“eat” little once). Why is this tendency?
R=Because the surface energy increases with D 2 and internal energy decreases with D 3
The dihedral angle between two phases is what controls the rate of transformation of
the new phase.
FALSE
The speed at which the martensitic transformation occurs is controlled by diffusion in the solid alloy.
FALSE
Sinterization is a solid state process which densifies a particulate material. The processis self-diffusion driven, diffusion which arises because of a:
R= surface energy reduction.
Atactic polymers tend to be less crystalline than the isotactic or syndotactic once.
TRUE
Titanium has a higher specific stiffness than steels.
FALSE
Copper alloys can be strengthened by deformation, solid solution, grain size reduction,
and / or precipitation of secondary phase particles.
TRUE
Homogenization is a product of the redistribution of solute in the solid material as it is
cooled during certain periods of time.
FALSE
The PVC and polystyrene are more resistant than polyethylene because links within their chains are stronger.
FALSE
The dihedral angle formed between two adjacent phases is a function of their melting
temperatures.
FALSE
A simple, binary, eutectic phase diagram presents only one solid phase.
FALSE
Get high hardness and
toughness simultaneously in martensite.
TEMPERING
Reach maximum hardness in steels.
QUENCHING
Soften metals which produce precipitates on slow cooling.
HOMOGENIZIRING
Relieve residual stresses.
PRONCESS ANNEALING
Hardening solid solutions by precipitation.
AGEING
Improve machinability of steels with medium and high carbon.
SPHEROIDIZING.
Recrystallize cold worked
microstructures.
ANNEALING
Refine grain size.
NORMALIZING
Maximize strength and
toughness in medium carbon steels.
AUSTEMPERING
Harden only the surface of a low carbon steel.
CARBURIZING AND QUENCHING
Keeping in mind the state of strain and stress, and the cost of the component; what kind of composite material would you use to manufacture a control surface (aileron) for airplanes?
Long unidirectional fiber
laminates stacked in
different orientations.
the firewall of a motorcar
(wall separating the enginecompartment from thepassengers compartment)?
Short random
orientation fiber.
a horizontal panel for a home cabinet or wardrobe close
Honeycomb sandwich.
0a storage tank for high
pressure air?
Long wound fiber
filament winding
A simply supported beam
under flexion?
Long unidirectional fiber.
the engine hood of a tractor trailer?
Short random orientation fiber.
the washing sink in a hairdressers shop?
Short random orientation fiber.
the lid of a domestic water
tank?
Short random orientation fiber.
front fender (panel that extend from the front bumper to the car's doors) a compact car?
Short random orientation fiber.
a suspension arm for an
off-road vehicle?
Long unidirectional fiber.
The elastomers typically acquire mechanical properties by crosslinking through sulfur atoms.
TRUE
The more severe the quench media, the larger the critical diameter of a given steel.
TRUE
The critical diameter of a steel is the one that produces 50% ferrite at the center of a properly quenched cylindrical rod.
FALSE
The Arrhenius equation relates the fraction transformed with time and temperature at which this transformation occurs.
TRUE
The density of Ti-based superalloys is greter than that of low alloy steels.
FALSE
The amount of- and rate of nucleation of a new phase within an existing phase is function of the undercooling present.
TRUE
During solidification, the position of the liquidus line will be depressed with increasing undercooling, and this is because the diffusion in the liquid is slower that in the solid.
FALSE
Crystallization of plastic is easier if the degree of polymerization is high
TRUE
A copolymer is an alloy of two or more types of polymers.
FALSE
Ceramic glasses can suffer dynamic as well as static fatigue.
TRUE
Crystallization of plastic is easier if the degree of polymerization is high.
TRUE
Thermodynamics tells us what phases are to be formed and kinetics provides information on the morphology of the new phases.
FALSE
Obtuse precipitates are better reinforcers than acute ones.
TRUE
Thermal shock resistance is measured as the maximum temperature a material can resist without cracking.
FALSE
Hardenability of steels can be measured with a Vickers quench test.
FALSE
Solid solution strengthening is because the deformations of the lattice introduced by the
foreign atom reduce the mobility of vacancies.
FALSE
In low alloy steels, the modulus of elasticity is a function of carbon content.
FALSE
The eutectoid pearlite structure is formed faster than the eutectic ledeburite structures.
FALSE
For an alloy to be adequately strengthened by precipitation of a secondary phase, it
must have an appreciable maximum solubility of the solute at high temperature and much lower maximum solubility at room temperature.
TRUE
The phase rule of Gibbs states: C=F + P + 2
FALSE
F=C-P+2
How much eutectic is present in a A-30% B alloy which solidified in equilibrium and is
held at 180⁰C?
R = 1/4 ó 25%
The thermoset polymers exhibit a steeper softening behavior than thermoplastic polymers.
FALSE
The apparent porosity of ceramic material is usually smaller than the true porosity.
TRUE
Copolymers are “alloys” of momomers which generally have better mechanical properties than their individual components.
TRUE
Nickel base super-alloys have a similar specific strength than low alloy steels.
TRUE
The toughness of polymers is the same as that of metals.
FALSE
Martensite of steels is a metastable solid solution with a body-centered cubic structure.
FALSE
A phase is material which has a specific structure and atomic arrangement, is
homogeneous in composition and properties, and exhibits a defined interfaces with other phases.
TRUE
The M s and M f temperatures of carbon steels depend on the C content, and tend to
increase with increasing C content.
FALSE
The peritectic reaction involves a liquid that becomes a new liquid plus a new solid.
TRUE
Ceramic materials have difficulty to deform elastically because their Burgers Vector is
usually large.
FALSE
Of the 4 Hume-Rothery rules for infinite solubility the most important factor is the valence rule.
FALSE
The electrical conductivity of polymers is similar to that of metals.
FALSE
- Ceramic powder mining or
synthesis - Grinding to a specific
granulometry - Mixing with plasticizer and
additives - Forming of the product
- Binder removal
- Densification by sintering
- Post-processing
ORDEN 1 A 7
