ISO 28079:2009

Overview

ISO 28079:2009 specifies a standardized indentation method - the Palmqvist toughness test - for characterizing the toughness of hardmetals and cermets at (normally) room temperature. The method calculates Palmqvist toughness from the total length of cracks that emanate from the four corners of a Vickers hardness indentation. Tests are intended for use in a normal laboratory-air environment (not corrosive media) and can be adapted to other temperatures by agreement.

Keywords: ISO 28079:2009, Palmqvist toughness, hardmetals, cermets, Vickers indentation, fracture toughness test

Key topics and technical requirements

• Test principle: Measure crack lengths from the corners of a Vickers indentation and compute a Palmqvist toughness value (W) - often reported alongside Vickers hardness (HV).
• Indentation practice: Indentations may be made at a single load (commonly 30 kgf) or by using multiple loads and extracting toughness from the slope of crack-length vs. load.
• Sample preparation:
  • Flat, parallel faces required; remove ~0.2 mm before final polish to expose bulk material.
  • Wet grinding with metal-bonded 40 µm diamond discs; polishing sequence recommended at least 30 µm → 6 µm → 1 µm, finishing on napless cloths.
  • Surfaces should be free of residual stresses; annealing (e.g., 800 °C for 1 h in vacuum) is noted as a practice to reduce polishing-induced stresses.
  • Verify indentation geometry: diagonal measurements must agree within 1% or the test is invalid.
• Specimen size: Practical guidance suggests specimen thickness should be several times the expected crack length (some recommendations: ≥10× crack length) to avoid substrate effects.
• Environment and limitations: Designed for ambient lab air; not intended for strongly corrosive environments (acids, seawater). Palmqvist results have known variability and are sensitive to surface condition and operator measurement.
• Uncertainty and reporting: The standard includes guidance on test validity, measurement uncertainty and a recommended test-report pro forma.

Applications and users

• Quality control and production testing for cemented carbides, WC/Co hardmetals and related cermets.
• Materials development and R&D where relative toughness ranking is required.
• Failure analysis and comparative assessments where quick, low-cost toughness screening is useful.
• Typical users: materials laboratories, hardmetal manufacturers, tooling producers, and standards/verification labs.

Related standards and references

• ISO 3878 - Vickers hardness test for hardmetals (normative reference used by ISO 28079).
• ISO 28079 complements fracture toughness work and interlaboratory efforts (e.g., VAMAS studies) but is focused specifically on Palmqvist indentation measurements rather than standardized fracture-mechanics specimens.

Practical note: Palmqvist toughness provides a rapid, correlated toughness indicator together with hardness, but it is not a direct substitute for rigorous fracture-mechanics K_Ic tests; use it for comparative testing, QC and material screening.