MEEN 360 Final

How can Aluminum Alloys be strengthened with Titanium and Boron?

Ti and B will create nucleation sites and smaller grain sizes will provide boundaries that block dislocation motion

What are some non-ferrous alloys that can be used in space?

Ti, Mg, Al, Be for high specific strength Ti, Ni, for high temperature resistence Cu, Ag, Au, for conductivity/mobility

T/F? At the eutectic composition, an alloy can solidify at a constant temperature.

True

T/F? Austenitic stainless steels are non-magnetic.

True

T/F? Beach marks and striations on a fracture surface are associated with fatigue failures

True

T/F? Both BCC metals and polymers experience ductile-to-brittle transition with change of temperature.

True

T/F? Ceramics are primarily held by ionic and covalent bonds.

True

T/F? Ceramics have large compressive strengths but low tensile strengths.

True

T/F? Ceramics may be crystalline, partially crystalline, or amorphous.

True

T/F? Certain materials can age harden at room temperature.

True

T/F? Faster solidification results in smaller interlamellar spacing

True

T/F? Heterogeneous nucleation needs to overcome less energy barrier than homogeneous nucleation

True

T/F? Heterogeneous nucleation requires less free energy for nucleation than homogeneous nucleation

True

T/F? Higher Degree of Polymerization increases the mechanical properties such as strength and toughness

True

T/F? Higher Degree of Polymerization increases the mechanical properties such as strength and toughness.

True

T/F? Highly cross-linked polymers are difficult to recycle

True

T/F? Homogeneous nucleation requires more undercooling than heterogeneous nucleation

True

T/F? Hot rolling produces poor surface finish and poor dimensional accuracy.

True

T/F? In the AISI system for designating steels, the first two numbers refer to the major alloying elements of the steel.

True

T/F? Intermetallic compounds are usually hard and brittle.

True

T/F? Nickel and cobalt are corrosion resistant.

True

T/F? Over-aging can occur when the aging temperature is large enough such that incoherent precipitates form.

True

T/F? Planar growth is promoted when the temperature of the liquid just ahead of a solid/liquid interface is larger than the melting temperature

True

T/F? Polymers with higher crystallinity have higher melting temperature.

True

T/F? Quenching hardens most steels while tempering increases the toughness.

True

T/F? TTT Diagrams assume isothermal Transformations

True

T/F? Tempering of martensitic steel increases its ductility

True

T/F? The fracture toughness of ceramics can be determined by indentation

True

T/F? The higher the percent crystallinity in a semi-crystalline polymer, the higher its density.

True

T/F? Ti alloys are highly resistant to fatigue damage.

True

Explain why cracking may occur when martensite is formed in a steel component.

When steels are quenched, the surface of the quenched steel cools rapidly and transforms to martensite. When the austenite in the center later transforms, the hard surface is placed in tension, while the center is compressed. If the residual stresses exceed the yield strength, quench cracks form at the surface.

Precious Metals

rare metals, which are usually natural substances, that have known value around the world. Au, Ag, Pt, Pd, Rh

Spheroidizing

A thermal process used for steel, heat-treating below the eutectoid temperature to produce spheroidite in order to improve machinability.

Process Annealing

Annealing of previously cold-worked products (commonly steel alloys in sheet or wire form) below the lower critical (eutectoid) temperature. This reduces and eliminates residual stress.

Modulus of resilience is defined as a.Ability of a material to be permanently deformed without fracture. b.Ability of a material to absorb elastic energy. c.Ability of a material to absorb energy at low temperatures. d.Energy absorbed by the material prior to fracture in a tensile test.

B

We distinguish steels and cast irons based on... (a) Eutectoid point (b) 2.11%C (c) Eutectic point (d) 6.67%C (e) Cr content of 17%

B

Which of the following materials should NOT be used in human body (i.e., which is NOT bio-compatible)? (a) Austenitic stainless steels (b) Be (c) Co-Cr (d) Ti (e) All of the above can be used

B

Which statement in not true about increasing degree of polymerization? a.Increases creep and wear resistance b.Decreases cross-linked density c.Increases impact toughness d.Increases tensile strength

B

Why are BCC Metals not used at low temperatures?

BCC metals have a DBTT

The 304 stainless steel is often used in medical applications due to its ductility and non-magnetic. Based on these characteristics, what type of stainless steel (SS) does it belong to? (a) Ferritic SS (b) Martensitic SS (c) Austenitic SS (d) Precipitation hardened SS

C

Which of the following cannot be described by an equation with the form of 𝑅=𝛾exp⁡(−𝐸𝑎𝑅𝑇)? a.Diffusion b.Creep c.Fatigue d.Nucleation

C

Which of the following statements is not true about casehardening: (a) Can be accomplished by inducing the formation martensite on the surface of a steel. (b)The surface must first reach temperatures required to form austenite at the surface. (c) Requires slow cooling rates after heating. (d) Surface heating techniques include induction heating

C

Which of the following statements is not true for age hardening? a. Requires a decreasing solid solubility with decreasing temperature in the phase diagram. b. Requires formation of coherent precipitates. c. It does not require quenching. d. Titanium alloys can be age hardened.

C

Which of the following statements is not true for an alloy system to have unlimited solid solubility? a.The difference in diameter of solute and solvent atoms must be < 15%. b.The crystal structure of solute and solvent atoms must be the same. c.The valence of solute and solvent atoms must be different d.The electronegativity of solute and solvent atoms must be approximately the same.

C

Why is creep accelerated by heat?

Creep is time dependent deformation under high stress/load at high temperatures. Diffusion of atoms in a grain is faster at high temperature which is why creep happens at high temperatures.

A hypereutectoid steel often presents hard and brittle cementite along the grain boundaries of pearlite. Which of the following heat treatments can alleviate this problem by changing the micro-structure? (a) Annealing (b) Normalizing (c) Austenizing (d) Spheroidizing (e) Process-annealing

D

Refractory metals are used with coatings to avoid oxidation at high temperatures. The coatings must (a) have a high melting temperature (b) provide a diffusion barrier to oxygen (c) have a coefficient of thermal expansion similar to that of the refractory metal (d) all of the above

D

What of the following temperature is a fixed value? a.Glass transition temperature and melting temperature of LDPE b.Melting temperature of HDPE. c.Recrystallization temperature of cold worked copper. d.Melting temperature of pure crystalline aluminum.

D

Which of the following doesn't prevent dislocation movement? a.More grain boundaries b.Larger dislocation density c.More foreign atoms. d.More vacancies.

D

Which of the following nonferrous alloys has the highest specific strength? (a) Al (b) Ni (c) Cu (d) Ti (e) Mg

D

What is a dendrite? Why do they form during solidification?

Dendrites are branched protuberances that form along the surface of a solid into a poorly inoculated solution in a n undercooled environment.

FACT: heavily cross-linked PVC will undoubtedly have a higher tensile modulus, and, also a higher strength, and will most likely fail in a brittle manner

FACT: The branched PVC will probably display the stress-strain behavior of a plastic

FCC Metals are used at low temperatures, why?

FCC Metals display no transition temperature, instead the impact energies decrease with temperature.

T/F? All aluminum alloys are age-hardenable

False

T/F? Atactic polypropylene has higher crystallinity than isotactic polypropylene.

False

T/F? Brittle fracture is associated with extensive plastic deformation.

False

T/F? Cast irons containing graphite are formed under a metastable eutectic reaction

False

T/F? Dispersed needle-like particles are better than round particles for dispersed strengthening

False

T/F? Fatigue failure can happen at any applied stress range.

False

T/F? For effective dispersion strengthening, the dispersed phase should be continuous

False

T/F? For effective dispersion strengthening, the dispersed phase should be needle-like, as opposed to round

False

T/F? Hardenability refers to the ease with which a steel can be quenched to form pearlite.

False

T/F? Heterogeneous nucleation commonly occurs on the surfaces of casts

False

T/F? Heterogeneous nucleation usually occurs in a well-inoculated solution

False

T/F? High carbon steels are easily welded.

False

T/F? Higher Crystallinity decreases the polymer density.

False

T/F? In ceramics, a large porosity results in large strength

False

T/F? Increasing grain boundaries improves creep resistance.

False

T/F? Inorganic glasses do not have a glass transition temperature.

False

T/F? Martensitic transformations only occur in the Fe-C system

False

T/F? Metallic glasses have higher elasticity because they are strain hardened.

False

T/F? Mg alloys are highly ductile

False

T/F? Microscopic dimples are associated with brittle fractures surfaces in metals

False

T/F? Pure metals can be age hardened.

False

T/F? Recovery reduces the strength of a cold worked metal significantly

False

T/F? Stoichiometric intermetallic compounds exist over a range of compositions.

False

T/F? Tempered glass is heat treated to generate tensile residual stresses on the surface.

False

T/F? Tensile test can be easily performed on ceramics.

False

T/F? Thermoset Plastics are generally more ductile than thermoplastics

False

T/F? Thermoset plastics are easily recycled

False

T/F? Thermoset plastics are easily recycled.

False

T/F? Weibull modulus indicates the strength of the tested specimen.

False

T/F? The glass transition temperature refers to when a polymer melts

False, it is the temperature below which polymers behave like glass

Normalizing

For ferrous alloys, austenitizing above the upper critical temperature, then cooling in air to produce fine pearlite. The objective of this heat treatment is to enhance toughness by refining the grain size.

Tempering

Heat a steel to below the eutectoid temperature, to transform the martensite to the thermodynamically stable 𝛼 and Fe3C phases precipitate in order to improve ductility and toughness.

Austenizing

Heating a metal to produce homogeneous Austenite. The purpose is to to transform them into the required shape and to provide strength and resistance to the material.

Annealing

Heating a steel above a certain temperature and slowly cooling it in a furnace to produce coarse pearlite. The main purpose of annealing heat treatment is to soften the steel, regenerate overheated steel structures or just remove internal tensions. It also reverses the affects of cold working

What does Hume-Rothery Rule determine?

If a metal or compound has unlimited solubility

Refractory metals

Metals that can be used in excess of temperatures of 1650 degrees C. Often used in Space. Nb, W, Mo, Ta

What are the Hume-Rothery Conditions?

<15% radial difference Same crystal structure, Valency, Electronegativity

Engine blocks made of cast iron need to perform good strength, thermal conductivity, damping capability, and wear resistance. Which of the following irons is commonly used? (a) Gray iron (b) White iron (c) Malleable iron (d) Nodular Iron (e) Pure Iron

A

If you wish to buy a low carbon steel on McMaster Carr, which of the following AISI steel should you pick? (a) 1010 (b) 1080 (c) 4340 (d) 52100 (e) 8610

A

Which of the following has the same unit of fracture toughness? a.Stress intensity factor b.Tensile Toughness c.Stress concentration factor d.Impact toughness

A

Which of the following is not casted ingot structure? a. Elongated grains b. Chill grains. c. Columnar grains d. Equiaxed grains.

A

What is a Ceramic?

A nonmetallic, inorganic solid

What are coherent and incoherent precipitates? Which produces higher strength alloys?

Coherent precipitates have an atomic arrangement that matches (has a continuous relationship) its surrounding matrix. This arrangement displaces atoms in the matrix, producing strain fields in the matrix. Incoherent precipitates have an atomic arrangement that does not match (has no relationship to) its surrounding matrix. These precipitates do not disrupt the matrix. Coherent precipitates are stronger due to their disrupting the matrix

Quenching

Dunking hot metal in cool water or oil to avoid atomic diffusion and to create non-equilibrium super-saturated solid solution

Crystalline ceramics are typically brittle and hard because (a) they typically have small dislocation densities (b) their free electrons are mobile (c) they typically have large dislocation densities (d) their bonds are typically weak (e) their atomic structures result in a large resistance to dislocation motion

E

Which of followings is NOT the main purpose of adding alloy elements to the steels? (a) Solid solution strengthening (b) Precipitation strengthening (c) Improved corrosion resistance (d) Improved hardenability (e) Improved thermal conductivity

E

Which of the following are considered ceramics? (a) Diamond (b) Silica (c) Alumina (d) Ice (e) All of the above

E