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Lecture 12

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chichi's version from 2018-04-30 17:21

Section 1

Question Answer
Attributes of mechanical alloying #1production of fine dispersion of second phase (usually oxide) particles
Attributes of mechanical alloying #2extension of solid solubility limits
Attributes of mechanical alloying #3refinement of grain sizes down to nanometer range
Attributes of mechanical alloying #4synthesis of novel crystalline and quasicrystalline phases
Attributes of mechanical alloying #5Development of amorphous (glassy) phases
Attributes of mechanical alloying #6disordering of ordered intermetallics
Attributes of mechanical alloying #7possibility of alloying of difficult to alloy elements
Attributes of mechanical alloying #8inducement of chemical (displacement) reactions at low temperatures
Attributes of mechanical alloying #9scalable process
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Section 2

Question Answer
Ball millingpowders with typical particle diameter on the order of 50-100 um are placed in a sealed container together with hardened steel or tungsten carbide (WC)--coated balls.
Types of mills:tumbler mills, shaker mills, vibratory mills,...
The method can be used to:Produce phase mixtures of systems that cannot be synthesized by conventional methods. Induce solid state alloying beyond equilibrium solubility limits. Form amorphous and nanostructured materials for a broad range of alloys, intermetallic, ceramics, and composites
Particles can be refined down to ______ (variable) depending on the milling conditions and milling time2-20 nm
Some of the important parameters that have an effect on the final constitution of the powder are:type of mill; milling container; milling speed; milling time; type, size, and size distribution of the grinding medium; ball-to-powder weight ratio; extent of milling the vial; milling atmosphere; process control agent; temperature of milling
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Section 3

Question Answer
What can lead to the formation of ultra-fine scale phase mixtures?Mechanical attrition of powder mixtures of powders
Mechanochemistry:chemical reactions induced by high-energy ball milling at room temperature
CNT produced by mechano-thermal process step 1:Ball milling of graphite powders in steel mill for 100-150 hours in Ar gas
CNT produced by mechano-thermal process step 2:Annealing of the milled sample at 1400C for several hours in Ar gas
Novel nanotube synthesis method step 1:High-energy ball milling-----> nucleation structure
Novel nanotube synthesis method step 2:Controlled thermal annealing----->growth
Top DownMechanical milling
Bottom UpThermal annealing
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Section 4

Question Answer
Friction stir processing utilizes a rotating tool with pin and shoulder, inserted in the material to be joined or processed, and traversed along the line of interest
A processed zone is producedby movement of materials from the front of the pin to the back of the pin
Significant grain refinementoccurs as a result of severe plastic deformation and material mixing
This method is usedto weld and process dissimilar materials, resulting in nano composite structure in the process zone
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