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Flashcards in Powder Metallurgy Review Questions Deck (15)
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1

importance of PM

  • Mass produced to create net-shape and near net-shape
  • Very little waste of materials
  • PM parts have a specific level of porosity
  • Can made shapes that are difficult for other methods
  • certain metal alloy combos and cermets can be formed
  • Tolerances around +/- 0.13mm
  • PM production methpods can be automated for economical production

2

disadvantage of PM

  • tooling and equipment cost are high
  • metallic powders expensive
  • difficulties in storing and handling powders
  • limitations in part geometries. powders dont flow laterally
  • variations in metal density throughout part may be a problem

3

What are principle methods used to produce PM powders

atomization

 

electrolytic

 

chemical

4

what are three basic steps used to produce PM

  1. blending and mixing of powders
  2. compaction
  3. sintering

5

what is technical difference between blending and mixing in PM

blending - when powders of same chemical composition but different particle sizes are intermingled

 

mixing - when powders of different chemistries are combined

6

what are some ingredients usually added to metallic powders during blending and/or mixing

  1. lubricants
  2. binders
  3. delocculants

7

what is meant by green compact

Pressed but not yet sintered

8

describe what happens to individual particles during compaction

Particles are repacked into a more efficient arrangement; followed by deformation of particles as pressure increases

9

what are 3 steps in sintering cycle of PM

  1. preheat - lubricants/binders burned off
  2. sintering
  3. cool down

10

What are some reasons why a controlled atmosphere furnace is desirable in sintering

  1. protect against oxidation
  2. provide reducing atmosphere to remove existing oxides
  3. provide carburizing atmosphere
  4. remove lubricants and binders from pressing

11

What is the difference between impregnation and infiltratrion in PM

impregnation - oil or other fluid is permeated into pores of sintered PM part

 

infiltration - molten metal is permeated through pore of sintered part

12

How is isostatic pressing distinguished from conventional pressing and sintering in PM

isostatic pressing - hydrostatic pressure applied to all sides of the mold

 

conventional pressing - uniaxial pressure

13

describe liquid phase sintering

two powders are mixed together and heated at a temp higher than the lowest melt temp of the two powders but not the melt temp of the other. melted metal wets the solid particles, creating a dense structure with bonding between the metals upon solidification

14

what are 2 basic classes of metal powders as far as chemistry is concerned

Elemental - pure metal and used when high purity is needed

 

Pre-Alloyed - each particle is an alloy composed of desired chemical compositions

15

why is PM Technology so well suited to production of gears and bearings

  • tolerances
  • near net shape
  • mass production
  • little to no waste material

 

(1) geometries lend themselves to PM Pressing

(2) porosity allows impregnation