Dynamic high-temperature erosion testing is an accelerated laboratory method that evaluates how metals, ceramics, and protective coatings withstand the combined attack of elevated temperature and high-velocity, particle-laden gas flow. The technique is widely used to qualify thermal barrier coatings, superalloys, and hot-section components for gas turbines, aerospace engines, and power generation equipment. This article explains the test principle, sample requirements, key parameters, evaluation criteria, and typical industrial applications.
Technical Overview
Dynamic high-temperature erosion testing reproduces one of the most aggressive service conditions encountered in modern engineering: a material surface bombarded by hard solid particles entrained in a hot gas stream while simultaneously exposed to thermal activation and, in many cases, a through-thickness temperature gradient. In service, this combination drives erosion–oxidation interaction, in which the protective oxide scale that forms at high temperature is repeatedly fractured and removed by particle impact, exposing fresh material and accelerating degradation far beyond what either pure oxidation or pure erosion alone would cause.
The word dynamic distinguishes this test from static isothermal exposure. The specimen is subjected to a continuously moving erosive jet—frequently combined with programmed thermal cycling, back-side substrate cooling, or varying impingement angles—so that time-dependent mechanisms such as coating densification, thermally grown oxide growth, and interfacial degradation are captured together with impact wear. Because of this coupling, the method is far more representative of field behavior than separate furnace oxidation or room-temperature erosion tests.
Established reference methods include ASTM G76 (solid particle erosion by gas jet, commonly adapted to elevated temperature), ISO 13123 (cyclic heating–erosion testing of thermal barrier coatings under a temperature gradient), and ASTM C633 for measuring coating adhesion strength before and after exposure. National specifications aligned with the GB, EN, and JIS frameworks are often applied to sector-specific components, and testing is typically carried out by accredited third-party laboratories.
Testing Samples
Thermal Barrier Coatings (TBCs)
Air-plasma-sprayed (APS) or electron-beam physical-vapor-deposited (EB-PVD) yttria-stabilized zirconia top coats on superalloy substrates with MCrAlY bond coats are the most frequently tested material system. Testing quantifies the erosion durability of the ceramic top coat and the resistance of the full coating system to spallation under combined thermal and mechanical loading.
Superalloy and Hot-Section Metallic Components
Nickel- or cobalt-based superalloy coupons—including directionally solidified and single-crystal variants—can be tested as flat specimens, while actual hardware such as blade segments, vane airfoils, and combustor liners can be sectioned to rank alloys and protective coatings at representative service temperatures.
High-Temperature Protective Coatings
Aluminide diffusion coatings, MCrAlY overlay coatings, slurry aluminides, ceramic-based exhaust coatings, and as-built or post-treated additive-manufactured surfaces are evaluated to compare erosion resistance and coating integrity after hot exposure.
Ceramics and Refractory Materials
Structural ceramics, silicon carbide and silicon nitride hot-gas filter elements, refractory linings, and catalyst support materials are tested where ash-laden flue gas or fluidized-bed particles cause high-temperature erosion.
Testing Items
Common measured outputs include:
- Erosion rate, expressed as volume or mass loss per unit mass of erodent (typically mm³/g)
- Incubation behavior and steady-state mass-loss curves as a function of exposure time
- Angle dependence of erosion, comparing ductile and brittle response at 30°, 45°, 60°, and 90° impingement angles
- Coating thickness reduction and remaining top-coat thickness after exposure
- Adhesion and cohesion strength retention, measured by pull-off testing before and after exposure
- Surface and cross-sectional morphology by SEM/EDS, including crater geometry, embedded erodent particles, and thermally grown oxide thickness
- Microhardness and elastic modulus profiles across the coating cross-section
- Spallation area, delamination depth, and crack density after cyclic exposure
Testing Methods
Test Apparatus
A representative rig combines a high-temperature tube or chamber furnace, a metered particle feeder, a converging acceleration nozzle, and a motorized specimen holder with adjustable impact angle and standoff distance. For temperature-gradient testing, the specimen is heated on the top surface by radiation or plasma heating while the rear face is cooled by compressed air or a water-cooled block, producing through-thickness gradients representative of engine service conditions.
Test Parameters
Typical parameter windows are:
- Gas and specimen temperature: ambient up to approximately 1,100–1,400 °C, depending on furnace and fixture materials
- Particle impact velocity: approximately 30–250 m/s, verified by double-disk or optical diagnostic methods
- Erodent: angular alumina or silica sand with median particle sizes of 50–250 µm, delivered at feed rates of roughly 2–20 g/min
- Impingement angle: 20° to 90°
- Standoff distance: typically 10–20 mm from nozzle exit to specimen surface
- Exposure mode: single continuous runs or programmed thermal cycles (for example, 5–60 minutes hot with forced-air cooling between cycles)
Test Procedure
- Specimens are cleaned ultrasonically, dried, dimensioned, and weighed on an analytical balance.
- Baseline characterization, including thickness, roughness, adhesion strength, and microstructure, is recorded.
- The furnace is stabilized at the set point, the particle feed is calibrated, and the particle velocity is confirmed.
- The specimen is exposed to the heated erosive jet for the defined duration or number of cycles.
- After cooling in a desiccator, specimens are reweighed, with loose debris and embedded particles handled according to the agreed reporting protocol.
- Erosion rate, thickness loss, and morphology data are compiled, and repeat runs establish measurement scatter.
Evaluation and Acceptance Criteria
Erosion rate is normally reported as volume loss divided by the mass of erodent delivered, normalized to a reference velocity, angle, and particle size so that results can be compared across laboratories and materials. Acceptance limits are material- and program-specific. Typical qualification criteria for thermal barrier coatings specify a maximum steady-state erosion rate, no gross spallation after a defined number of thermal cycles, and retention of a minimum fraction of the as-coated adhesion strength.
Applications
- Aerospace propulsion: erosion qualification of thermal barrier coatings on high-pressure turbine blades and vanes, combustor heat shields, and seal runners operating in ash- or sand-laden environments
- Industrial gas turbines and power generation: burner nozzles, transition pieces, boiler tubes, and fluidized-bed components exposed to fly ash and bed material
- Automotive engineering: turbocharger housings and wheels, exhaust manifolds, heat shields, and coated substrates subjected to hot pulsating gas carrying particulates
- Petrochemical and process furnaces: reformer tubes and radiant-section hardware exposed to catalyst fines and flue-gas particulates
- Materials development: ranking of new coating chemistries, additive-manufactured surfaces, ceramic composites, and repair coatings under realistic combined thermal and mechanical loading
FAQ
What is the difference between dynamic and static high-temperature testing?
Static isothermal exposure holds a specimen at temperature in a furnace without mechanical loading and primarily reveals oxidation behavior. A dynamic high-temperature erosion test superimposes a moving, particle-laden hot gas jet—often with thermal cycling—so that impact damage, erosion–oxidation synergy, and coating spallation are reproduced together.
Which standards are commonly referenced?
ASTM G76 defines the gas-jet solid particle erosion baseline and is routinely adapted to elevated temperature; ISO 13123 specifies cyclic heating–erosion testing of thermal barrier coatings under a temperature gradient; ASTM C633 is used to measure adhesion strength before and after exposure. Sector specifications within the GB, EN, and JIS frameworks may add component-specific requirements.
How is erosion rate calculated?
Erosion rate equals the volume of material removed, calculated as mass loss divided by material density, divided by the mass of erodent delivered, and is reported in mm³/g. Normalizing to standard velocity, angle, and particle size allows comparison across laboratories and material systems.
What temperatures and particle velocities can be achieved?
Conventional rigs operate from ambient up to approximately 1,100–1,400 °C with particle velocities from roughly 30 to 250 m/s. Temperature-gradient configurations add back-side cooling to create through-thickness gradients typical of engine hardware.
What sample size and preparation are required?
Flat coupons of roughly 25 mm × 25 mm or discs of 25–30 mm diameter and 3–6 mm thickness are standard; actual components can be sectioned if flat reference areas are available. All specimens must be cleaned, dried, weighed, and documented for coating thickness and surface condition before testing.
How long does a typical test take?
Single continuous exposures typically run from a few minutes to several hours, depending on the target material loss. Cyclic programs that include heating, erosion, and cooling segments may span one to several days, with test plans designed to balance acceleration and representativeness of real service conditions.