Metallography reveals the true internal structure of tungsten carbide beyond what bulk properties alone can show.
At Langsun Carbide, metallographic examination is used to assess WC grain size, binder distribution, porosity level and secondary phases. This microstructural insight ensures that each grade delivers the designed balance of hardness, toughness and wear resistance.
Metallographic Examination Procedure
1.Sample Preparation
Samples are cut from representative areas of the product, then mounted, ground, and polished. The entire process is tightly controlled to avoid introducing artifacts.
2.Chemical Etching
A selective etchant is applied to create contrast between tungsten carbide grains, the cobalt binder, and any secondary phases (such as η-phase or free carbon).
3.Microscopic Examination
Using an optical microscope or higher-resolution microscopy, we evaluate grain size, porosity, binder distribution, and phase composition.
4.Quantitative Evaluation
Observations are compared against reference microstructures and internal specification ranges for grain size and porosity grades.
Why Metallography Is Essential for Tungsten Carbide
Even when hardness and density appear to meet requirements, microstructural defects can severely reduce the reliability of cemented carbide:
● Excessive Porosity — Large pores or clustered porosity can become crack initiation sites under bending or impact loads.
● Abnormal Grain Growth — Grain coarsening reduces hardness and wear resistance.
● η-Phase — A hard, brittle phase caused by insufficient carbon that lowers toughness and makes the material more prone to cracking.
● Free Carbon — Carbon-rich regions caused by excess carbon can weaken the matrix and reduce wear performance.
● Poor Binder Distribution — Segregated cobalt pools or cobalt channels can lead to localized strength loss or uneven wear.
By observing and quantifying these features, we ensure each tungsten carbide grade maintains the intended microstructural balance between hardness, toughness, and wear resistance.
Langsun Carbide Metallographic Inspection Expertise
● Microstructure–Performance Correlation — Metallographic findings are interpreted together with hardness, density, coercivity, magnetic saturation, and mechanical property test results.
● Reference Microstructures — Each grade has reference images and acceptance criteria for grain size and porosity, ensuring long-term consistency.
● Process Development Support — During new grade development or process improvement, metallographic analysis is used to validate changes and prevent potential defects.
● Customer Support — Upon request, we can provide metallographic documentation for qualification programs or failure analysis.
Through systematic metallographic inspection, Langsun Carbide ensures its tungsten carbide products not only meet specifications, but also deliver structural reliability under demanding service conditions.
Phase Symbols and Definitions in GB/T 3488
|
Symbol |
Definition |
|
α |
Hard phase (tungsten carbide) |
|
β |
Carbides with a cubic lattice (e.g., TiC, TaC). These carbides can contain other carbides (e.g., WC) in the form of a solid solution. |
|
γ |
Binder phase (e.g., Co, Ni, etc.) |
|
η |
Decarburized phase: tungsten carbide–cobalt with a cubic lattice, typically an approximately equal mixture of Co and W |
|
C |
Uncombined carbon; macroscopic carbon (graphite) deposits |
Typical Microstructural Characteristics of Selected Grades
The table below summarises typical microstructural features for representative WC–Co grades. These are indicative and may be refined for specific grade families.
|
Grade |
wCo/% |
WC Grain Size (Qualitative) |
Porosity Level (Typical) |
Typical Applications |
|
WC-6Co |
6 |
Fine |
Low; isolated fine pores |
High-wear nozzles, wear plates, seal faces |
|
WC-11.5Co |
11.5 |
Fine to medium |
Low; controlled porosity |
General wear parts, bushings, sleeves |
|
WC-15Co |
15 |
Medium |
Low; optimised for toughness |
Impact-prone tools, heavy-duty inserts and wear parts |
Note: Microstructural descriptions are indicative.