| 1. Raw Material Selection | Tungsten powder is blended with a ductile binder system, commonly nickel–iron or nickel–copper. The selected composition depends on the required density, strength, machinability, and magnetic properties. | Verify powder identity, chemical composition, particle-size distribution, moisture level, and contamination control. Tungsten content in heavy alloys is commonly within the 90–97 wt% range, depending on the grade. | Supplier certificate of analysis; chemical analysis by XRF, ICP-OES, or equivalent validated laboratory method. |
| 2. Powder Blending | Tungsten and binder powders are mixed uniformly, often with a controlled lubricant or process additive to improve powder flow and compaction behavior. | Check batch identification, blend uniformity, powder flow, apparent density, and the absence of foreign particles. Mixing parameters should be recorded for traceability. | Documented internal work instructions; powder-flow and apparent-density procedures may be based on recognized powder-metallurgy laboratory methods. |
| 3. Compaction or Forming | The blended powder is compacted in a die or formed using a suitable powder-processing method. Complex parts may require tooling designed to compensate for sintering shrinkage. | Inspect green-part mass, dimensions, density uniformity, surface condition, cracks, edge damage, and correct orientation. Dimensional allowances must reflect the selected alloy and sintering cycle. | Drawing requirements, approved process-control plans, calibrated dimensional gauges, and documented sampling procedures. |
| 4. Debinding and Pre-Sintering | Organic additives are removed under a controlled atmosphere before liquid-phase sintering. Heating rates and atmosphere control are important for preventing distortion, oxidation, and internal defects. | Monitor furnace temperature, atmosphere, pressure or gas flow, heating profile, and batch loading. Parts should be checked for cracking, warpage, discoloration, and residual binder-related defects. | Validated furnace recipes, calibrated thermocouples, atmosphere monitoring, and batch records. |
| 5. Liquid-Phase Sintering | Tungsten heavy alloys are commonly densified by liquid-phase sintering. Industrial sintering temperatures are typically around 1,400–1,500 °C, but the exact cycle depends on composition, geometry, and furnace design. | Control peak temperature, soak time, vacuum or protective atmosphere, heating and cooling rates, and furnace uniformity. The objective is high density with controlled grain growth and minimal dimensional distortion. | Validated sintering cycle; furnace uniformity surveys; metallographic examination; density measurement by Archimedes method. |
| 6. Density Verification | Density is evaluated after sintering because it strongly influences radiation shielding, inertia, balance, and dimensional performance. | Typical sintered tungsten heavy-alloy density is approximately 17.0–18.6 g/cm³, depending on tungsten content and binder chemistry. The contractual requirement should be defined by alloy grade and product specification. | Archimedes density measurement; ASTM B311 or an equivalent validated density procedure may be specified for sintered metal materials. |
| 7. Heat Treatment | Heat treatment may be applied when required to adjust strength, ductility, residual stress, or dimensional stability. The treatment must be compatible with the binder system and final application. | Record furnace temperature, holding time, atmosphere, cooling method, and part orientation. Verify hardness, tensile properties, dimensional stability, and surface condition after treatment. | Customer-approved heat-treatment procedure; ASTM E18 for Rockwell hardness or ASTM E384 for microhardness where applicable. |
| 8. Machining and Surface Finishing | Sintered tungsten alloys may be machined by carbide tooling, grinding, electrical-discharge machining, or other suitable methods. The process is selected according to geometry, tolerance, and surface-finish requirements. | Inspect dimensional tolerances, flatness, concentricity, perpendicularity, burrs, edge condition, surface roughness, and machining-induced cracks. Final values must follow the approved engineering drawing. | Calibrated CMM, micrometers, gauges, profilometers, and visual or magnified inspection according to the drawing and inspection plan. |
| 9. Chemical Composition Control | Finished or representative samples are tested to confirm tungsten, nickel, iron, copper, and other specified alloying-element levels. | Composition must remain within the agreed material specification. Particular attention should be given to unintended elements that may affect sintering, corrosion behavior, ductility, or magnetic response. | ASTM E1476, XRF, ICP-OES, combustion analysis, or another validated chemical-analysis method selected for the material. |
| 10. Mechanical Testing | Representative specimens may be tested for tensile strength, elongation, hardness, impact resistance, or other properties required by the application. | Results should be reported with specimen orientation, test temperature, heat-treatment condition, batch number, and test direction where relevant. Mechanical requirements vary significantly with tungsten percentage and binder system. | ASTM E8/E8M for tensile testing; ASTM E18 for Rockwell hardness; ASTM E23 for Charpy impact testing when specified. |
| 11. Metallographic Examination | A polished and etched cross-section is examined to evaluate the tungsten grain structure, binder distribution, porosity, inclusions, cracks, and abnormal grain growth. | The microstructure should be continuous and uniform for the specified grade, with no unacceptable cracks, connected porosity, severe segregation, or processing-related inclusions. | ASTM E3 for metallographic specimen preparation and ASTM E407 for microetching practices, where applicable. |
| 12. Non-Destructive Inspection | Depending on size and geometry, parts may be inspected using penetrant testing, ultrasonic testing, radiography, or visual and dimensional examination. | Inspection should identify surface-breaking cracks, internal discontinuities, shrinkage-related defects, or machining damage. Acceptance limits must be defined in the purchase specification or drawing. | ASTM E1417/E1417M for liquid penetrant testing; ASTM E2375 for radiographic examination of metal castings or equivalent customer-approved procedures. |
| 13. Documentation and Traceability | Each production lot should be linked to raw-material batches, forming records, furnace cycles, inspection results, nonconformance records, and final release documentation. | A complete quality package commonly includes a certificate of conformity, material composition, density, dimensional inspection, test results, heat-treatment records, and nonconformance disposition when applicable. | ISO 9001 quality-management principles; customer-specific inspection and documentation requirements. |
