GB/T 3488.1-2014 / ISO 4499-1:2008 — Hardmetals Metallographic Determination of Microstructure Part 1: Photomicrographs and Description

Standard: GB/T 3488.1-2014 / ISO 4499-1:2008

Title: Hardmetals – Metallographic Determination of Microstructure – Part 1: Photomicrographs and Description

Published: 2014-12-05  |  Implemented: 2015-08-01

Replaces: GB/T 3488-1983

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1. Scope

This part specifies the metallographic determination method for the microstructure of hardmetals (cemented carbides).

2. Normative References

• ISO 3878:1983 — Hardmetals — Vickers hardness test
• ISO 4499-2 — Hardmetals — Metallographic determination of microstructure — Part 2: Measurement of WC grain size

3. Terms and Definitions

3.1 α-phase

Tungsten carbide (WC) grains.

3.2 β-phase

Binder phase (e.g., based on Co, Fe, Ni).

3.3 γ-phase

Carbides with cubic lattice (e.g., TiC, TaC), which may contain other carbides (e.g., WC) in solid solution.

4. Apparatus and Equipment

• 4.1 Metallographic microscope: magnification up to 1,500x
• 4.2 Scanning electron microscope (SEM): magnification exceeding 1,500x
• 4.3 Specimen preparation equipment

5. Specimen Preparation

The polished surface for metallographic examination shall be free of grinding marks and polishing scratches. Care should be taken to avoid particle pull-out, which could lead to misinterpretation of the microstructure.

Note: Begin with careful coarse grinding to ensure sufficient material removal to reveal the true microstructure. After grinding with fine diamond wheels, polish on fine plastic, felt, or paper discs using diamond paste or powder with progressively decreasing grain size down to 1 μm.

6. Procedure

6.1 Metallographic Specimen Preparation

6.1.1 General

Proper specimen preparation yields a polished surface that, after etching, reveals the true microstructure. Safety: Specimen preparation and etching involve toxic or hazardous chemicals. Operators must be professionally trained and follow laboratory safety protocols.

6.1.2 Sectioning

Diamond tools are widely used for cutting hardmetals. Wire saws with diamond-impregnated wire are economical and produce excellent slices.

6.1.3 Mounting

Cold mounting: Epoxy, acrylic, or polyester resins. Hot mounting: Thermosetting powders (phenolic resin or polyamide) under heat and pressure. Recommended to remove specimens from mount before etching and SEM observation.

6.1.4 Grinding

Typically, at least 200 μm of material should be removed to obtain a representative microstructure.

6.1.5 Fine Grinding

Fine grinding on glass, metal, plastic, or composite plates with diamond abrasive produces flat surfaces.

6.1.6 Polishing

Polishing on short-nap or nap-free cloths using progressively smaller diamond abrasives: 15 μm → 9 μm → 3 μm → 1 μm.

Lubricant: Alcohol-based lubricants serve as both coolant and cleaning agent.

6.1.7 Cleaning

Ultrasonic cleaning with warm water and detergent, or acetone for unmounted specimens. Acetone cleaning before SEM is strongly recommended.

6.2 Etching

6.2.1 Murakami Reagent

Murakami reagent (potassium ferricyanide + sodium/potassium hydroxide) is commonly used to reveal the microstructure.

Recommended solution: Equal volumes of 10-20% potassium ferricyanide and sodium/potassium hydroxide in water (10-20 g per 100 mL). At 20°C, etching time: 0.5 to 6 minutes depending on WC grain size.

6.2.2 α-phase (WC) Determination

Etch with Murakami reagent. Classify WC grain size into grades:

• Nano-grain → Ultra-fine → Sub-fine → Fine → Medium → Coarse → Extra-coarse

Note: For nano and ultra-fine grains, SEM observation is required when optical microscopy cannot clearly resolve the grain structure.

6.2.3 β-phase (Binder) Determination

Etch with concentrated hydrochloric acid. This phase appears white.

6.2.4 γ-phase Determination

Etch with Process 2 (Murakami + HCl). This phase appears light tan/brown with characteristic spherical morphology.

7. Test Report

• a) Reference to this standard (GB/T 3488.1-2014)
• b) All details necessary to identify the specimen
• c) Test results
• d) Any operations not specified in this standard
• e) Any details that may have affected the results

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Plate Descriptions

Figure 1 — α-phase (WC) nano-grain and ultra-fine grain

• a) Nano-grain — Optical (20 μm)   b) Nano-grain — SEM (3 μm)
• c) Ultra-fine grain — Optical (20 μm)   d) Ultra-fine grain — SEM (3 μm)

Figure 2 — α-phase (WC) sub-fine, fine and medium grain

• a-b) Sub-fine grain — Optical/SEM (20 μm / 10 μm)
• c-d) Fine grain — Optical/SEM (20 μm / 10 μm)
• e-f) Medium grain — Optical/SEM (20 μm / 10 μm)

Figure 3 — α-phase (WC) coarse and extra-coarse grain

• a-b) Coarse grain — Optical/SEM (20 μm / 30 μm)
• c-d) Extra-coarse grain — Optical/SEM (20 μm / 30 μm)

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Original PDF (Chinese Version)

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