Application framework for selection and method discussions; not a customer test report.
Purpose
Alloy structures, coating sections and substrate interfaces.
Preparation route
Prepare an oriented section from the relevant region. Protect coatings and interfaces and match grinding and polishing to material hardness and brittleness.
Checkpoints
Inspect coating edges, pores and interfaces. Repeatability depends on controlled sampling, preparation records and evaluation methods.
Equipment stages
Cutting → Mounting → Grinding and polishing → appropriate microscopy and testing.
Record sampling position, consumables, actual settings and images. Evaluate using the agreed method.
Typical inspection scenarios
Plasma-sprayed 8YSZ thermal barrier coating on a nickel-base superalloy substrate
- Challenge
- The ceramic top coat is brittle and contains genuine pores; mechanical stress from cutting and grinding can spall the coating or introduce artificial cracks, while quantitative analysis of porosity and interface integrity requires preparation that leaves the original pore structure unchanged.
- Preparation & method
- Section perpendicular to the coating surface on a low-speed precision saw with a diamond blade at very low feed and ample coolant. Cold mount with low-viscosity epoxy under vacuum impregnation so the resin infiltrates pores and microcracks to consolidate the coating. Grind gently with SiC papers from P400 to P1200; rough polish with 3 μm diamond, then chemo-mechanically finish with 0.05 μm colloidal silica. Examine unetched and quantify coating porosity by image analysis while inspecting the bond coat/top coat interface.
- Reference standards
- ASTM E2109 Standard Test Methods for Determining Area Percentage Porosity in Thermal Sprayed Coatings; ASTM E3 Standard Guide for Preparation of Metallographic Specimens; GB/T 13298 Metallographic examination methods for metals
7075-T6 high-strength aluminum alloy friction stir welded (FSW) butt joint
- Challenge
- The nugget, thermo-mechanically affected zone (TMAZ), HAZ and base metal differ in strengthening-phase (η′) distribution, and the differences are too subtle for a single etch to reveal all zones clearly; soft aluminum traps abrasive and polishing media, and second-phase particles pull out; a hardness traverse is needed to map HAZ softening.
- Preparation & method
- Take a transverse section perpendicular to the weld on a low-speed precision saw with a diamond blade and ample coolant; cold mount. Grind with SiC papers from P400 to P2000 under light pressure with frequent rinsing to prevent abrasive embedment; polish with 3 μm then 1 μm diamond and finish with 0.05 μm colloidal silica. Etch with Keller's reagent to reveal grain boundaries in each zone (anodizing plus polarized light for grain contrast where needed); examine at 100×–500× under bright field for equiaxed fine grains in the nugget, bent deformed grains in the TMAZ and HAZ grain coarsening, checking for tunnel voids and lack of bonding; scan micro-Vickers hardness (HV0.5) point by point across the section to plot the hardness curve and determine the width of the softened zone and the minimum-hardness location.
- Reference standards
- GB/T 3246.1 Inspection method for structure of wrought aluminium and aluminium alloy products — Part 1: Microstructure; ISO 25239-5 Friction stir welding — Aluminium — Quality and inspection requirements; GB/T 4340.1 Metallic materials — Vickers hardness test
Scenarios are method examples, not customer test reports; confirm the process per specimen.
MICROCRE learning notes · confirm the method for the specimen.