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MM1504: Powder Metallurgy and Ceramics

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MM1504: Powder Metallurgy and Ceramics MM1504: Powder Metallurgy and Ceramics Dr. Sanjay Kumar Vajpai [email protected] Assistant Professor, Department of Metallurgical and Materials Engineering, National Institute of Technology, Jamshedpur Syllabus and Lecture Schedule: MM1504: Powder Metallurgy and Ceramics (3-1-0) UNIT-I: (8 Lectures) Powder Production (Chemical Methods, Electrolytic Methods, Atomization, Mechanical Methods) UNIT-II: (5 Lectures) Powder Characterization (Chemical Composition and Structure, Particle Size and Surface Topography, Pyrophorocity and Toxicity) UNIT-III: (12 Lectures) Powder Compaction, Phenomenological Aspects of Sintering, Solid State Sintering, Analytical Approach to Sintering, Non Isothermal Sintering, Microstructural Evolution UNIT-IV: (12 Lectures) Liquid Phase Sintering, Stages of Liquid Phase Sintering, Super solidus Sintering, Activated Sintering, Pressure Assisted Sintering, Microwave Sintering, Select Case Studies. UNIT-V: (13 Lectures) General overview of Ceramics: Structure and properties of ceramics, Types according to various applications; Various consolidation methods, casting of ceramics, conventional and advanced sintering processes for ceramics References Books 1. Powder Metallugy Science, 2nd ed R.M. German. 2. Powder Metallurgy: Science, Technology and Materials by A. Upadhyaya, G.S. Upadhyaya, 3. ASM Handbook, Volume 7: Powder Metal Technologies & Applications (1998) 4. Introduction to Ceramics by Kingery W.D, Bowmen H. K., Uhlmann D.R Powder Metallurgy ➢ Raw Material: Powder form of Metals, Alloys, Ceramics Cost ➢ Extended ability to fabricate Complicated shapes Effectiveness ➢ Controlled Microstructure + ➢ Reduced Machining Cost: Near-Net-Shape Processing Uniqueness ➢ Easy to handle difficult-to-machine shapes ➢ Minimum wastage of material and Energy Savings ➢ Composites Conventional Powder Metallurgy Steps: Powder manufacture → Blending → Consolidation/Compaction → Sintering Additive Manufacturing: A Recent Development of Powder Metallurgy Processing PM Automotive Parts Courtesy: Western Sintering Camshaft Cap in Engine The Roller Finger Follower is used in the valve Courtesy: GKN train of passenger cars as part of a cam follower system that is capable of shutting off a cylinder while the engine is running. As a very complex shape design with several High strength and wear resistant materials integrated functions, the PM Metal Injection High dimensional accuracy Moulding (MIM) process technology is the Optimized for minimum friction and valve perfect choice clearance compensation • Systems that optimize camshaft or valve timing are of increasing importance for fuel consumption and CO emissions. • PM has proven to be an ideal solution for variable valve timing (VVT) components. • For VVT Stators the PM process can facilitate freedom of design and deliver highly precise, complex products. ADVANTAGES •Compact lightweight designs WT stator-sprocket •Reduced machining with multi part design •Low friction with custom surface geometry Products 1. Porous products such as bearings and filters. 2. Tungsten carbide, gauges, wire drawing dies, wire-guides, stamping and blanking tools, stones, hammers, rock drilling bits, etc. 3. Various machine parts are produced from tungsten powder. Highly heat and wear resistant cutting tools from tungsten carbide powders with titanium carbide, powders are used for and die manufacturing. 4. Refractory parts such as components made out of tungsten, tantalum and molybdenum are used in electric bulbs, radio valves, oscillator valves, X-ray tubes in the form of filament, cathode, anode, control grids, electric contact points etc. 5. Products of complex shapes that require considerable machining when made by other processes namely toothed components such as gears. 6. Components used in automotive part assembly such as electrical contacts, crankshaft drive or camshaft sprocket, piston rings and rocker shaft brackets, door, mechanisms, connecting rods and brake linings, clutch facings, welding rods, etc. 7. Products where the combined properties of two metals or metals and non-metals are desired such as non-porous bearings, electric motor brushes, etc. 8. Porous metal bearings made which are later impregnated with lubricants. Copper and graphite powders are used for manufacturing automobile parts and brushes. 9. The combinations of metals and ceramics, which are bonded by similar process as metal powders, are called cermets. They combine in them useful properties of high refractoriness of ceramics and toughness of metals. They are produced in two forms namely oxides based and carbide based. Powder Rolling General Flow diagram of the PM processing Powder Production Methods The methods for powder production affect the powder characteristics, hence, the method is selected wrt type of application and desired properties of the final product. 1.Chemical Methods: 1. For Metal Powders: Chemical Reduction and Chemical Decomposition of compounds (Oxides, Hydrides, halides, or any other salt) are the major techniques. Generally used for producing pure elemental powders. 2. Ceramic Powders: Carbonates, hydroxides, nitrates, sulphates, acetates, oxalates, alkoxides or any other metal salts are used as raw material. 2. Electrolytic Method: It involves primarily electrodeposition process, i.e. dissolution of the impure metal from anode and subsequent deposition on the cathode. Generally used for pure elemental powders. 3. Atomisation Method: Widely used commercial process. Used for producing a wide variety of elemental powders as well as alloys. 4. Mechanical Methods: It can be used for metals, alloys, and ceramics. It is not a primary method. Chemical Methods For Metal Powders 1. Solid State: Reduction of Iron or Tungsten Oxide (WO3) with a reducing gas. 2. Gaseous State: Reduction of Titanium Chloride (TiCl4) vapors with molten magnesium. 3. Aqueous Solution: Precipitation of cement Copper from Copper sulphate solution. 4. Direct Decomposition of Metal Hydrides: Ti, Zr, Hf V, Th, or U (MH) 5. Direct Decomposition of Metal Carbonyls (MCo5): e.g. Fe, Ni, etc. For Ceramics Powders There can be three methods, similar to metal powders, solid-state reactions, liquid solutions, and vapor phase reactions. Chemical Methods: Solid State Reduction The gas flow is required, and the gas/solid contact is achieved by mechanical stirring of the particulate bed by raking, by tumbling in the reactor -→ fluidized bed reactor • Reduction With CO 3 Fe2O3 (s) + CO → 2 Fe3O4+ CO2 (g) Fe3O4 (s) + CO(g) → 2 FeO(s)+ CO2 (g) FeO(s) + CO(g) → Fe(s)+ CO2 (g) C + O2 → CO2 CO2 + C → 2CO • Reduction of higher oxide to lower oxide. • For each oxide and reaction temperature, a critical Co/Co2 ratio in the gas mixture need to maintained. o • Fe2O3 (s) → Fe3O4 occurs between 200-500 C and a minimum -4 Co/CO2 ratio of approximately 10 . o • Fe3O4 (s) → FeO occurs between 500-900 C. • FeO (s) → Fe occurs between 900-1300 oC. • Fe2O3 → Fe3O4 → FeO → Fe • Hematite → Magnetite → Wustite → Iron Chemical Methods: Solid State Reduction • Reduction With H2 4WO (s) + H → W O + H O 3 Fe2O3 (s) + H2 → 2 Fe3O4+ H2O 3 2 4 11 2 W O (s) + H → WO (s)+ H O Fe3O4 (s) + H2 → 3 FeO(s)+ H2O 4 11 2 2 2 WO (s) + H → W(s)+ H O FeO(s) + H2 → Fe(s)+ H2O 2 2 2 Fe3O4 (s) + 4H2 → 3 Fe + 4H2O Fe2O3 (s) + 3H2 → 2 Fe + 3H2O • Hydrogen is the best reduction gas dealing with high temperatures. • Other metals such as Ni, Co, etc. can also be produced using hydrogen reduction process. • The metals which form hydrides are generally not preferred through this process, especially at low temperatures. • The reduction of halides by hydrogen can also be carried out, similar to oxides and sulphides, e.g., VCl3, ZrCl4, or TiCl4. • Hydrogen gas is costly, but it is preferred due to cleanliness of the process. • CO-H2 mixture can also be used for reduction in few cases. Chemical Methods: Solid State Reduction • Below Any Ellingham Line, the metal is stable relative to the Oxide. • If the element A can reduce the Oxide BxOy in the diagram, the Ellingham line for AxOy lies below that for BxOy. • Certain Metal oxides can also be reduced using relatively more stable metals. Chemical Methods: Hydro-metallurgical Reduction • Metals can directly be produced from aqueous solutions through, (i) Reduction with another metal (ii) Gaseous Reduction. ➢ 1. Reduction of metal ions from a solution of another metal is known as cementation process. for any reaction, Mn+ + ne → M, The reduction potential is given by E = Eo – (RT/nF) ln(aM/aM+) “The more negative the electrode potential, the more stable the ions are in the solution.” A comparison of the electrode potentials of different metals, the more stable metal ion can be determined. ➢ 2. In gaseous reduction, commercial gasses used are: H2S, SO2, Co, and H2. e.g. Reduction of metal species in solution by Hydrogen can only take place if the hydrogen is at a lower potential than the metal ions at the appropriate metal concentration. 2+ + Ni (aq) + H2 (g) = Ni(s) + 2H (aq) Chemical Methods: Direct Synthesis • This method is carried out at high temperature for pure compound ceramics and intermetallics. • Also known as self-propagating high-temperature synthesis. • Porous compact is heated at high temperatures. • Exothermic seif-sustaining reaction. Production of Carbonyl Iron, Copper, and Sponge Titanium Powder Powder Production Methods The methods for powder production affect the powder characteristics, hence, the method is selected wrt type of application and desired properties of the final product. 1.Chemical Methods: 1. For Metal Powders:
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