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وبسایت تخصصی متالورژی - متالورژی پودر
یکشنبه 9 اسفند 1388  01:24 ق.ظ

تاریخچه:

 

متالورژی پودر از قدیمی ترین و در عین حال مدرنترین فرایندهای تولید فلزات است.

·        3000 B.C. Egyptians made tools with powder metallurgy

·        1900’s tungsten filament for light bulb

·        1930’s carbide tool materials

·        1960’s automobile parts

·        1980’s aircraft engine turbine parts

·        Currently, North American P/M sales are over $5billion annually

·        Industry spreads many applications as well as many countries.

 

 

مزیت ها:

     Ability to create complex shapes

           در ادامه مطلب ..........

متالورژی پودر

 

تاریخچه:

 

متالورژی پودر از قدیمی ترین و در عین حال مدرنترین فرایندهای تولید فلزات است.

·        3000 B.C. Egyptians made tools with powder metallurgy

·        1900’s tungsten filament for light bulb

·        1930’s carbide tool materials

·        1960’s automobile parts

·        1980’s aircraft engine turbine parts

·        Currently, North American P/M sales are over $5billion annually

·        Industry spreads many applications as well as many countries.

 

 

مزیت ها:

·        Ability to create complex shapes

·        High strength properties

·        Good microstructure control

·        Uses more than 97% of the starting raw material in the finished part

·        Eliminates or minimizes machining

·        Maintains close dimensional tolerances

·        Wide variety of alloys

·        Mass production

·        Cost and energy efficient

 

معایب:

·        Creation of residual pores

·        High tooling costs

·        Strength and stiffness may be inferior to wrought alloys of similar composition.

·        Porosity and low ductility may impair durability.

·        Fracture Toughness may be low.

·        Potential workforce health problems due to atmospheric contamination

 

 

مراحل اصلی در فرایند متالورژی پودر:

·        Powder Productionتولید پودر

·        Blending or Mixingخرد کردن یا مخلوط کردن

·        Powder Consolidationشکل دادن پودر

·        Sinteringتفجوشی کردن

·        Finishingعملیات نهایی (تکمیلی)

 

1. Powder Production

·        Many methods: extraction from compounds, deposition, atomization, fiber production, mechanical powder production, etc.

·        Atomization is the dominant process

 

2. Blending or Mixing

 

·        Blending a coarser fraction with a finer fraction ensures that the interstices between large particles will be filled out.

·              Powders of different metals and other materials may be mixed in order to impart special physical and mechanical properties through metallic alloying.

·        Lubricants may be mixed to improve the powders’ flow characteristics.

·        Binders such as wax or thermoplastic polymers are added to improve green strength.

·        Sintering aids are added to accelerate densification on heating.

 

3. Powder Consolidation

 

·                    Cold compaction with 100 – 900 MPa to produce a “Green body”.

  Die pressing

  Cold isostatic pressing

  Rolling

  Gravity

·        Injection Molding small, complex parts.

 

Friction problem in cold compaction

 

·        The effectiveness of pressing with a single-acting punch is limited. Wall friction opposes compaction.

·        The pressure tapers off rapidly and density diminishes away from the punch.

·        Floating container and two counteracting punches help alleviate the problem.

 

4. Sintering

·        Parts are heated to 0.7~0.9 Tm.

·        Transforms compacted mechanical bonds to much stronger metallic bonds.

Shrinkage always occurs:

 

5. Finishing

 

·        The porosity of a fully sintered part is still significant (4-15%).

·        Density is often kept intentionally low to preserve interconnected porosity for bearings, filters, acoustic barriers, and battery electrodes.

·        However, to improve properties, finishing processes are needed:

  Cold restriking, resintering, and heat treatment.

  Impregnation of heated oil.

  Infiltration with metal (e.g., Cu for ferrous parts).

  Machining to tighter tolerance.

 

فلزات متداول در صنایع متالورژی پودر:

·        ابتدا متالورژی پودر بر روی فلزاتی مانند آهن و مس انجام می شد، ولی پس از مدتی به فلزات دیرگداز دیگر مانند W، Mo ، Zr ، Ti و Rh و آلیاژهای آنها نیز سرایت کرد.

·        این تکنیک همچنین در مورد سرامیک های مورد استفاده در هسته های الکتریکی و مغناطیسی نیز استفاده گردید ( مانند فریت های نرم و سخت)

·        از مثال های دیگر می توان به Ni-base super alloys و نیز oxide dispersion strengthened alloys اشاره نمود

 

 


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