Powder Metallurgy Lecture Notes Flashcards

Flashcards for reviewing Powder Metallurgy lecture notes.

What is Powder Metallurgy?

A branch of metallurgy dealing with the production of metal and nonmetal powders and subsequent manufacture of components using these powders.

What are the steps involved in Powder Metallurgy component production?

Powder production, Blending or mixing, Compacting, Sintering, Sizing or impregnation, Testing and inspection.

What are the methods used for Powder Production?

Machining, Crushing, Milling, Shotting, Graining, Automization, Condensation

What does the Mechanical process of Machining produce?

Filings, turnings, chips, irregular shape

What is used to crush solid materials in the Crushing process?

Hammers, jaw crushers, gyratory crushers

What shapes are the powder particles in the Crushing process?

Angular for brittle, flaky for ductile

What equipment is used for Milling?

Ball mills, rod mills, eddy mills

What happens in the Shotting method?

Molten metal is poured on a vibrating screen and liquid droplets are solidified

What is the main difference between Shotting and Graining?

Molten metal droplet solidification is done in water

What is involved in Automization?

Injecting molten metal through a small orifice, broken by jets of inert gas, air, or water

What does the size of the particle formed in Automization depend on?

Temperature of the metal, Metal flowrate, Pressure of jet, Nozzle size and jet characteristics

What happens in the Condensation process?

Metal vapors are condensed to obtain metal powders

What kind of metals are large quantities produced from the Condensation process?

Zn, Mg, Cd

What are the Characteristics of Metal Powder?

Chemical composition, Particle shape, size and its distribution, Particle porosity, Specific surface, Compacting properties, Sintering properties

What is powder conditioning?

Mechanical, chemical, or thermal treatments or alloying

What are the benefits of Annealing?

Eliminates work hardening effect, reduces the oxide content and impurity level, alters the apparent density

When Annealing, in what conditions is it usually done?

Reducing atmosphere or vacuums

Why is Mixing or Blending done?

To obtain desired properties during compaction, sintering and in the final sintered component.

What does Mixing or Blending give during compaction?

Uniform distribution of particles

What is usually added to the powder during Mixing or Blending?

Lauryl alcohol or camphor

What are the roles certain materials like graphite, stearic acid, and stearates play during mixing?

Acts as a lubricant, creates porosity during sintering, acts as a binder

What happens during Compacting?

Powder mix is fed in to the die cavity through a hopper and feed shoe

What are the most important effects of Compacting?

Reduces voids, produces adhesion and cold welding, plastically deforms the powder

What is Sintering?

Heating the compact to some temperature under controlled conditions with or without pressure

What processes is Sintering concerned with?

Diffusion, densification

How hot are Parts headed during Sintering?

Heating compacts to approximately 80% of the metal's melting temperature.

Why do you carry out Sintering?

To increase strength and hardness

What are the classifications of Sintering based on temperature?

Solid phase sintering and liquid phase sintering

What is Sizing?

Placing the component in a master die and applying pressure

What are the various test that are conducted for Testing and Inspection?

Compressive strength, tensile strength, porosity, density, hardness, composition, microstructure, etc.

What can P/M parts possibly be done to?

P/M parts may be welded, brazed, machined, heat treated, plated or impregnated

What are some Advantages of powder metallurgy?

Controlled porosity can be obtained, components with properties similar to the parent metals can be produced, cemented carbide cutting tools.

What are some limitations of powder metallurgy?

High initial investment, limitation in size with presses available, complex shaped parts are not easy

What metals are fine powders of some of the metals likely to explode?

Mg, Al, Zr, Ti

What is the con of having P/M part porous?

Poor corrosion resistance

What is Specific surface?

The total surface area of a powder per unit weight

What is apparent density?

Mass per unit volume of loose or unpacked powder

What is Tap density?

Density of the powder after it has been mechanically shaked or tapped

What is Flow rate?

The rate at which a metal powder will flow under gravity from container through orifice

What is compressibility?

Powder's ability to undergo deformation under applied pressure

What is compactibility?

Minimum pressure required to produce a compact of given green strength

What is Green density?

Density of a cold compact

What is Green strength?

Mechanical strength of green compact

What design considerations should be kept in mind?

Shape of the compact needs to be simple, avoid variations in thickness, avoid high length-to-diameter ratios.

What should be provided to avoid damage to the edges during ejection?

Chamfers

What kind of dimensional tolerances should PM parts be made with?

PM parts should be made with the widest acceptable dimensional tolerances

Part walls should generally not be less than ____ thick.

1.5 mm

In what direction should letters be pressed?

Should be perpendicular to the direction of pressing

What should be incorporated into a long flange?

Draft around the flange, a radius at the bottom edge, and a radius at the juncture

What is preferred for pressing in design considerations?

Chamfers or flats