1. Materials Science Overview

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Questions and Answers

What is the primary characteristic of Macor that makes it suitable for certain applications?

High hardness and wear resistance

Excellent electrical and thermal insulation (correct)

Low dielectric constant

High thermal shock resistance

Which of the following is NOT a characteristic of ceramics?

Corrosion resistant

Insulating

Brittle

Highly ductile (correct)

What is the recommended chip load for milling Macor?

0.2 mm per tooth

0.1 mm per tooth

0.01 mm per tooth

0.05 mm per tooth (correct)

Which material has high fracture toughness and is used in applications requiring toughness?

Zirconia Signup and view all the answers

What is the suggested cutting speed range for milling Macor?

23 to 35 sfpm Signup and view all the answers

What is the main purpose of tempering in the hardening process?

To relieve internal stresses and enhance toughness Signup and view all the answers

Which of the following alloys is known for its extreme corrosion resistance and is used in marine fittings?

Silicon bronze Signup and view all the answers

Which non-ferrous alloy is typically mixed with zinc to create brass?

Copper Signup and view all the answers

What is the primary characteristic of aluminum alloys when mixed with magnesium?

Higher strength Signup and view all the answers

What material is involved in the production of galvanized steel?

Zinc Signup and view all the answers

What is a characteristic of naval brass?

Commonly used for ships' fittings Signup and view all the answers

What occurs to the surface of dead mild steel during case hardening?

It absorbs carbon from charcoal Signup and view all the answers

Which characteristic is associated with Gun-metal as an alloy?

88% Copper, 10% Zinc, and 2% Tin Signup and view all the answers

What is a disadvantage of adding too much tin to tin bronze?

Increases brittleness Signup and view all the answers

Which of the following is a property of cupro-nickels?

Exhibits extreme corrosion resistance Signup and view all the answers

Which type of wood is ideal for laser cutting that is thicker than 3 mm?

Hardwood Signup and view all the answers

Which property of thermosetting polymers is true?

They undergo a chemical reaction during curing. Signup and view all the answers

What is true about mild steel concerning its carbon content?

It has a carbon content between 0.15% and 0.3%. Signup and view all the answers

What happens during the annealing process?

Internal stresses are relieved by slow cooling. Signup and view all the answers

What is the primary characteristic of high carbon steel?

It has a carbon content between 0.7% and 1.3%. Signup and view all the answers

Which material is classified as a thermoplastic polymer?

Polycarbonate Signup and view all the answers

What type of steel is used for applications requiring high corrosion resistance?

Austenitic stainless steel Signup and view all the answers

What distinguishes thermoplastic from thermosetting polymers?

Thermoplastics can be remelted and reshaped. Signup and view all the answers

What is one characteristic of carbon reinforced composites?

Low thermal conductivity and localized heat distribution. Signup and view all the answers

Which type of steel is known for its ability to withstand high temperatures while maintaining hardness?

High Speed Steel (HSS) Signup and view all the answers

What is an important factor in the heat treatment of carbon steels?

Cooling rate is the most critical factor. Signup and view all the answers

What type of cast iron has a carbon content greater than 1.7%?

Cast iron Signup and view all the answers

What does the term 'normalizing' refer to in the context of steel treatment?

Heating and cooling in still air for a quicker cooling process. Signup and view all the answers

What is a primary use of elastomeric polymers?

High stretchability applications. Signup and view all the answers

Study Notes

Wood

Hardwood: Oak, Maple, Walnut, Mahogany, Ash, Hickory, Birch, Teak
- Easy to cut in a lathe.
- Thick pieces: CNC cut (greater than 3mm)
- Thin pieces: Laser cut (less than 3mm)
- MDF with resin burns in laser cut
- Good surface properties
- Engravement possible
Softwood: Pine, Spruce, Cedar, Cypress, Redwood
- Better to laser cut
- Upcut and downcut choice for surface finish

Plastics

Thermosetting polymers: Resin and curing agents react chemically
- Curing process hardens material
- Process is irreversible
- Not recyclable
- Examples: Epoxy, Vinyl ester, Polyester
Thermoplastic polymers: Amorphous or semi-crystalline
- Can be remelted and reformed
- Recycling changes material properties
- Examples: Polyamides, Polyethylene, PLA, ABS, PC
Elastomeric polymers: High stretchability
- Examples: TPU, Vulcanized Rubber

Ferrous Alloys: Iron (Fe) + Carbon (C) = Steel

Cementite (Fe3C): Hard and brittle inter-metallic compound
Carbon Content and Classification
- Low Carbon Steel (C < 0.15%):
 - Good weldability and ductility
 - Drawn tubes, thin sheets, wire rods
 - Surface hardening possible for wear resistance
- Mild Steel (C: 0.15-0.3%):
 - Structural work
 - Weldability up to 0.25% C
 - Forgings, stampings, sheets, plates, bars, rods, tubes
- Medium Carbon Steel (C: 0.3-0.7%):
 - Stronger and better wearing properties
 - Railway axles, rotors and discs, wire ropes, marine shafts, agricultural tools
- High Carbon Steel (C: 0.7-1.3%):
 - Harder when quenched
 - Used in cold conditions (less than 150°C)
- Cast Iron (C > 1.7% up to 4%):
 - Lower melting temperature, easy to cast
 - Cooling rate dictates type: Gray, White, Malleable, Ductile cast iron
Above 2% carbon, it is considered cast iron. Cooling rate and other alloying elements are important

Steel Alloys

Less than 2% carbon and other alloying elements
- Ferritic Stainless Steel (0.15% C, 6-12% Cr, 0.5% Ni):
  - Magnetic, cannot be hardened
  - Food processing plants, dairy equipment
  - Low price
- Martensitic Stainless Steel (0.15-1.25% C, 12-18% Cr):
  - Hardening possible, but reduces corrosion resistance
  - Surgical knives, bolts, nuts, screws, blades
- Austenitic Stainless Steel (0.08-0.2% C, higher nickel content):
  - 18/8 Steel: 18% Cr, 8% Ni, 1.25% Mn, 0.75% Si
  - High corrosion resistance
  - Chemical plants, household utensils
  - High price
- Tool steels (cut steel at high speeds):
  - Retain hardness at elevated temperatures (600°C): Red Hardness
  - High-Speed Steel (HSS): 18% Tungsten (expensive, T-series)
  - HSS: 6% Tungsten, 6% Molybdenum (M-series)
  - Super HSS: 10% Cobalt, 20% Tungsten
- Special Steel Alloys
  - Manganese Steels:
    - Wear resistant
    - Used in railway points and crossings
  - Nickel Steels:
    - Corrosion resistance
    - Non-magnetic, low thermal expansion coefficient
    - Used in turbine blades, internal combustion engine valves
    - With chromium, increased UTS and IZOD strength
  - Silicon Steels:
    - Around 3% Silicon decreases magnetic hysteresis
    - Used in transformers, electric machines
    - Silico-manganese steels for springs

Heat Treatment of Carbon Steels

Improve mechanical properties:
- Heat up to a homogeneous temperature
- Controlled cooling rate is critical
Types of Heat Treatment:
- Annealing:
  - Heating rate is not decisive
  - Around 3 minutes per millimeter thickness for even temperature distribution
  - Softening material through slow cooling
  - Relieves internal stresses
  - Increases ductility (grain growth)
- Normalizing:
  - Same heating as annealing, but cooling in still air (faster)
  - No softening, but internal stresses relieved ("normalized" to zero)
- Hardening:
  - Rapid cooling (quenching) in water/oil mixture
  - Requires high carbon content (greater than 0.25%)
  - Creates hard, but brittle material
- Tempering:
  - Heated to 150-600°C and cooled slowly
  - Reduces brittleness of hardened material
- Case Hardening:
  - Used for dead mild steel (low carbon)
  - Heat in charcoal for several hours to introduce carbon to the surface
  - Creates a hard surface (1-2mm) with a soft, tough interior

Non-Ferrous Alloys

Copper:
- Corrosion resistance, best conductor
- Wire drawn, sheet beaten
- Alloyed with: Zinc (brass), Tin (bronze), Nickel (cupro-nickels)
Aluminum:
- Corrosion resistance, good conductor
- Ductile and malleable (thin sheets, cables)
- Alloyed with Magnesium for improved properties
Tin:
- Resistant to acidic conditions
- Low melting point, used in solders
Zinc:
- High corrosion resistance
- Coating for steel (galvanized steel)

Non-Ferrous Alloys (Continued)

Brass:
- Cartridge Brass (70% Cu, 30% Zn): Deep drawing cartridges
- Admirability Brass (70% Cu, 29% Zn, 1% Sn): Ship fittings
- Muntz’s Metal (Cu, 40-45% Zn): Condenser tube, heat exchanger, preheater
- Naval Brass (60% Cu, 39% Zn, 1% Sn): Ship fittings
Tin Bronze (up to 10% tin):
- Increases strength and hardness
- Too much tin creates brittle intermetallic compound Cu3Sn
- Phosphor Bronze (0.5% phosphorous): Better fluidity for fine casting
- Leaded Bronze (less than 2% Lead): Better machinability, self-lubricating
- Gun-metal (88% Cu, 10% Sn, 2% Zn): Bearing bushes, glands, pumps
- Bell-metal (20-25% tin): Cymbals
Other
- Silicon Bronze (1-4% Si to copper): Extreme corrosion resistance (boilers, marine fittings)
- Manganese Bronze (55-60% Cu, 40% Zn, 3-5% Mn): Ship propellers
Special Alloys
- Cupro-nickels (copper and nickel): Extreme corrosion resistance (thermocouples, resistors)
- Aluminum Alloys (L-M series, mixed with Magnesium for strength): Extrusions in profiles
- Duraluminum (Al, 4% Cu, 0.5% Mg, 0.5% Mn):
- Nickel Alloys:
  - German Silver (60% Cu, 30% Ni, 10% Zn): Household Devices
  - Inconel (Nickel-chromium-based superalloy): High temperature, corrosive applications (gas turbine blades, Formula 1 exhaust systems)
    - Alloy 625: Inconel 625, Chronin 625, Altemp 625, Haynes 625, Nickelvac 625 Nicrofer 6020 and UNS designation N06625
    - Alloy 600: NA14, BS3076, 2.4816, NiCr15Fe (FR), NiCr15Fe (EU), NiCr15Fe8 (DE) and UNS designation N06600.
    - Alloy 718: Nicrofer 5219, Superimphy 718, Haynes 718, Pyromet 718, Supermet 718, Udimet 718 and UNS designation N07718

Ceramics

Hard, brittle, corrosion resistant, sometimes insulating material
Machinable Ceramics: (Soft)
- Macor: Excellent electrical and thermal insulator, machinable with carbide tools
- Shapal: High thermal conductivity and mechanical strength
- Boron-Nitride: High heat capacity, thermal conductivity, low dielectric constant
Hard Ceramics (Tough, difficult to cut)
- Zirconia: High hardness, wear resistance, high fracture toughness
- Silicon Carbide: Extremely hard, exceptional thermal shock and impact resistance.

Macor, Characteristics and Milling

Macor:
- Excellent electrical and thermal insulator
- Machinable with carbide tools
Milling Macor:
- Typical head speeds: 1000-1500 RPM
- Chip load: 0.05mm per tooth
- Depth of cut similar to turning
- Climb milling prevents material pull-off from the edge
- Recommended milling tool: Carbide or equivalent, two or four flute, helical cutters
- Avoid using rouging or chipbreaker mills
Milling Macor Speeds and Feeds:
- Cutting speed: 23-35 SFPM (1-1.4 meters per minute)
- Feed rate: .002" per tooth (.05mm per tooth)
- Depth of cut: .15-.2" (4-5mm)

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Description

Explore the key concepts of materials science, focusing on the properties of wood, plastics, and ferrous alloys. This quiz covers hardwood and softwood characteristics, thermosetting and thermoplastic polymers, and the fundamentals of steel production. Assess your understanding and application of these material types.