Powder Metallurgy Overview

A set of flashcards covering key concepts, methods, and processes related to Powder Metallurgy.

Powder Metallurgy

A manufacturing process used to create metal parts from powdered materials.

Fabrication methods

Techniques used to convert raw materials into usable parts or products, specifically in metalworking.

Mechanical comminution

A method of reducing bulk material into powder form using mechanical means, such as machining or milling.

Inexpensive method of turning scrap or junk into powder.

Pros of machining

Contamination and coarse material that necessitates additional milling, introducing dirt into the process.

Cons of machining

Milling

A process in which metal is placed in a jar with hard balls to break it down into a fine powder.

Mechanical alloying

A technique allowing the mixing of metals that cannot be melted together, using extreme attrition.

Electrolytic Deposition

A process using electric current and electrolysis laws to deposit metal particles on electrodes.

Spongey vs. Dense

Two types of materials produced through electrolytic deposition, varying in density and structure.

Oxide reduction

A chemical reaction (under the solid phase section) that converts metal oxides into pure metal through heating in a reducing atmosphere.

creates very pure metal

Oxide reduction Pro

has a very dangerous step and u need to be careful 

Oxide reduction Con

Carbonyl process

A method involving the reaction of solid metals with carbon monoxide to produce metal vapors that condense into a liquid form. (under chemical reaction solid phase reduction)

very very pure metal

Carbonyl process Pro

poisonous

Carbonyl process Con

Thermal decomposition

A process that induces chemical changes in a material solely through the application of heat.

Liquid Metal Automization

A technique that transforms molten metal into powder by breaking it down into droplets. types include liquid, gas, and centrifugal

Gas automization

A type of liquid metal automization where gas is used to blow powder into shape.

Centrifugal automization

A process that pours molten metal onto a spinning disc to create powder through centrifugal force.

conventional uniaxial die pressing

pressing blended metal powders into dies to consolidate them into a desired shape. This process is performed by having an upper punch descend into the die, forcing the powder to achieve particle-to-particle contact and create a part strong enough for further processing. The resulting piece is called a green compact because of its low strength.

density gradients

inevitable variation throughout a compacted powder part, it occurs because of friction between the metal particles themselves and between the particles and the punch and die walls during compaction, to combat use multiple punches

isosstatic pressing

compacted part is subjected to hydrostatic pressure from all directions to achieve more uniform compaction and density

Wet bag isostatic pressing

metal powder is placed inside a flexible rubber mold (bag), and the assembly is submerged in a liquid (usually water) inside a high-pressure chamber.

uniform density and pressed strength is higher

Wet bag isostatic pressing Pros

labor intensive, can’t control pressure

Wet bag isostatic pressing Cons

dry bag isostatic pressing

rubber mold is reusable and remains inside the high-pressure chamber. The metal powder is placed inside the mold, and the pressure is applied using water or a rubber diaphragm, used to form parts like PM cylinder

process time as short as 10s, good for small parts,

dry bag isostatic pressing pros

hot isostatic pressing

produce almost 100% dense compacts by subjecting the material to high pressure (up to 100 MPa) and high temperature (up to 1200∘C) using an inert gas or vitreous fluid. It is often used to close internal porosity in superalloy and titanium castings

powder/metal injection molding

fine metal powders are blended with a polymer or wax-based binder, mixture injected into a mold at a high temp, molded part is debound (the plastic is burned off) and then sintered. It can produce complex shapes with good dimensional tolerances and is economical for small investment-cast and machined parts

hot uniaxial die pressing

consolidation process where pressure is applied along a single axis to a powdered material while simultaneously applying heat, heat and pressure reduces porosity, resulting in a part that is denser and stronger,, used for material with high melting points

mixing

combining 2 different metals for the purpose of creating alloys or improving properties.

blending

combing two different sized particles but they are the same metal

bonding during sintering: solid state transport

atoms move closer to contact point and build a weld b/n them,atoms overalp and become 1

bonding during sintering: vapor phase transport

atoms go into vapor that asurrounds them, net grows and grows until weld together

bonding during sintering: liquid phase

when 1 metal (tungsten) has realy high melting pt. you add another metal that has relatively low melting point (cobalt), the sintering temp is high enough to melt the lower metal but not the higher one, so you have metal one joined together by metal 2

Toughening glass: Thermal Tempering

surface of hot glass is cooled rapidly by a blast of air. rapid cooling causes the surface layers to shrink and develop permanent compressive residual stresses, and interior develops tensile stresses. These compressive stresses improve the strength of the glass

Toughening glass: Chemical Tempering

glass is heated in a molten salt bath, such as KNO3, ion exchange occurs when larger atoms replace smaller atoms on the surface of the glass, this process induces compressive residual stresses on the surface, which strengthens the glass. (requires longer treatment times than thermal tempering)

Toughening glass: laminated glass and bulletproof glass

two pieces of flat glass are joined with a thin, tough sheet of plastic placed in between. If glass cracks, plastic holds the pieces together, preventing them from scattering. Other method uses thick laminate of glass and polymer (usually polycarbonate) to resist ballistic impact

wire netting

Flat glass for glazing can be strengthened by embedding wire netting (such as chicken wire) into the glass during production, If shatters, the embedded wire holds the pieces together due to its strength and ductility

Slip casting steps

prepare powder, slip preparation, and mold preparation

Slip casting: powder preparation steps

size control, particles need to be around 45 microns, we use screening method whcih involves passing the metal powder through sieves (screens) of various mesh sizes

Slip casting: slip preparation steps

mix all additives(wetting agents, defloculants, sintering aids, water), pour into bowl and mix, de-air, screening to remove any agglomeration

Slip casting mold prep: case mold

permanent mold made from rubber, has particualr shape of working mold, used to create working molds, durable long term master molds

Slip casting mold prep: working mold

made of posous plaster of paris, pour slurry into here, once used they are broken

plaster of paris

is a quick-setting material made from gypsum, commonly used for creating molds and casts, requires a significant amount of water to achieve the desired consistency for mold-making. excess water particles will sit b/n gypsum particles, once dried water goes away and creates holes

Slip casting

most common casting for ceramics, liquid suspension of ceramic particles in water, called the slip, is poured into a mold, plaster mold absorbs the water from the slip's outer layers. The remaining liquid slip is then poured out by inverting the mold, leaving a thin, solidified layer of ceramic ("green part") coating the walls, Typically results in a hollow object

sillicate tetrahedron

building block for sillicate structures, has 4 valence electrons, one silicon, and 4 oxygen