Detailed Introduction to Powder Metallurgy

I. Basic Concepts

II. Core Process Steps

1. Powder Preparation
   • Methods: Mechanical crushing (e.g., ball milling, jaw crushing), physical vapor deposition (PVD), chemical reduction (e.g., hydrogen reduction for iron powder), atomization (water/air atomization for alloy powders).
   • Key Parameters: Powder particle size (micron-level, affecting forming density), purity, and morphology (spherical/irregular, influencing flowability).
     [Image: Powder atomization equipment producing spherical alloy powders]
2. Mixing and Modification
   • Blend metal powders with non-metallic additives (e.g., carbon, copper for hardness) and lubricants (e.g., zinc stearate for moldability).
3. Forming
   • Compression Molding: High pressure (50–300 MPa) in molds to form "green compacts," suitable for simple symmetrical shapes.
   • Metal Injection Molding (MIM): Powder-binder mixture is injected into molds, debound, and sintered for complex precision parts (e.g., watch gears, medical devices).
   • Isostatic Pressing: Uniform pressure via liquid (cold/hot isostatic pressing) for high-density materials (e.g., aerospace superalloy components).
     [Image: Schematic of cold isostatic pressing equipment]
4. Sintering
   • Heating in a protective atmosphere (argon, hydrogen) or vacuum to 60–80% of the metal’s melting point, bonding particles via atomic diffusion to improve density and strength.
   • Critical Parameters: Temperature, holding time, and atmosphere control.
5. Post-Processing
   • Densification: Repressing/re-sintering; hot forging for mechanical properties.
   • Surface Treatment: Electroplating, painting, carburizing.
   • Machining: Minor cutting (drilling, grinding) for high precision.

III. Technical Features

1. Advantages
   • High Material Efficiency: Near-net shaping reduces waste (<5%), lowering costs.
   • Complex Structure Fabrication: Directly forms parts with microholes, multi-material composites, or gradient properties (e.g., oil-impregnated bearings, gearboxes).
   • High-Performance Materials:
     • Refractory metals (tungsten, molybdenum) and composites (metal-matrix ceramic reinforcements).
     • Porous materials (filters, heat sinks) and antifriction materials (self-lubricating bearings).
   • Energy-Efficient: Lower energy use than casting/forging, ideal for mass production.
2. Limitations
   • Porosity Impact: Sintered materials retain 5–20% porosity, requiring post-processing for density.
   • Mold Dependence: High-precision molds are costly and complex, suitable for medium-large scale production.
   • Size Constraints: Traditional molding limits part size (tens of cm); large components need isostatic pressing or 3D printing.

IV. Major Materials and Applications

1. Common Materials
   • Iron/Copper-Based: 70%+ of applications, used for gears, bearings, and structural parts (e.g., automotive engine components).
   • Refractory Metals: Tungsten, molybdenum alloys for aerospace high-temperature parts (rocket nozzles, satellite heat sinks).
   • Special Alloys: Titanium alloys, superalloys (Inconel) for aircraft engine blades and medical implants (titanium bone screws).
   • Composites: Metal-ceramic (diamond saw blades), porous metals (energy absorption, catalyst supports).
2. Typical Applications
   • Automotive: Engine valve seats, transmission gears (30% weight reduction), turbocharger components.
   • Electronics: MIM-based smartphone camera brackets, 5G heat sinks (high thermal conductivity copper), magnetic powders (inductors).
   • Aerospace: Hot isostatic pressed superalloy turbine disks, titanium structural parts (weight reduction).
   • Medical: Porous titanium implants (bone cell integration), MIM dental frameworks.
   • New Energy: Lithium battery electrode powders (NCM), fuel cell bipolar plates (stainless steel).
     [Image: Powder metallurgy components in an electric vehicle motor]

V. Cutting-Edge Technologies and Trends (2025 Outlook)

1. Integration with Additive Manufacturing
   • Metal 3D Printing (SLM/LMD): Directly prints complex parts (e.g., aerospace impellers) from powders, overcoming traditional molding limits.
   • Binder Jetting 3D Printing: Cost-effective for mass-producing small parts, cheaper than conventional MIM.
     [Image: 3D-printed titanium aerospace component via SLM]
2. Nanopowders and High Performance
   • Nanocrystalline Powders (e.g., nano-copper, nano-titanium) boost strength by 50%+ for high-end tools and armor.
   • Gradient Materials: Layered powder forming for parts with surface wear resistance and internal toughness.
3. Green Manufacturing