Wear depth Vs. Weight loss
Solid particles in dusty environments can damage materials and affect dimensional tolerances in variety of industries ranging from gas turbines, helicopter rotor system (aerospace applications), boiler tubes (coal power plants) and wind turbines (renewable energy). Erosion of certain components can reduce operational efficiency of systems and have economic impact.
In the recent days, significant advances In the area of coatings, composites and alloys have been made. A lot of this effort is geared towards reducing damage due to solid particle erosion. Advances in erosion resistant materials technologies, has also brought along the need for erosion testers that allow accurate characterization of these materials by enabling users to induce erosive wear and quantify damage caused by it.
In this article we demonstrate the use of such a technique, using the Ducom Gas Jet Erosion Tester configured with a high temperature module. We use the “ASTM G76 – Erosion Tests by Solid Particle Impingement Using Gas Jets” test standard as a broad guideline to investigate the failure behavior (ductile or brittle) of Inconel 600. Tests were conducted over a range of temperatures ranging from ambient to 800 Deg C. Samples were evaluated by measuring wear depth and weight loss for evaluating scale of erosion damage and comparison of material performance.
The evaluation of Inconel 600 for its erosive wear resistance was done using Alumina particles as the erodent. Average particle diameter was 50 microns. Particle velocity used for the test was of 150 m/s. (particle velocity is measured using our standard Double Rotating Disc Velocity Meter (referenced in the ASTM G211 – Elevated Temperature Erosion Tests by Solid Particle Impingement Using Gas Jets). The solid particle impingement angles we set at 15 degree and 90 degree angles. Tests were carried out at 28 deg C (room temperature), 600 deg C and 800 deg C.
Weight loss data was plotted as a function of temperature, for tests with 15 degree and 90 degree impingement angles. It is seen that weight loss at ambient temperature (28 deg C) is not very different between angles of 15 and 90 degrees. However, when samples are subjected to high temperatures during gas jet erosion, a considerable difference in weight loss is observed between the two angles.
The above image shows a surface image of samples after they underwent erosion tests. Using these surface scans, wear depth data was extracted and plotted as a function of temperature. It can be seen that the maximum wear depth of samples tested at 15 and 90 degrees is not significant. When the temperature of the test is varied from ambient to 600 deg C, the difference between samples tested at 15 and 90 degree remains insignificant. When the temperature is further increased to 800 deg C, it is seen that the maximum wear depth of the sample tested under a 90 degree impingement angle rises sharply, creating a considerable difference between the two angles under study. This observation does not correlate with the weight loss data obtained for tests at 800 deg C under a 15 and 90 degree angle of impact.
High erosion at an angle of 15 degrees is generally attributed to ductile failures when testing materials like Inconel 600. Under elevated temperature conditions like 800 deg C, the wear depth data suggests brittle failure in the Inconel 600 sample.
Gravimetric technique is often used evaluate erosion resistance of materials when subject to solid particle impingement. While this approach is sufficient for some applications, it proves greatly inadequate in others. Certain applications like boiler tubes in power plants, place greater importance on wear depth behavior of materials as opposed to weight loss over an area.
Our study showed that Inconel 600 samples show increased wear when subjected to erosion at high temperatures. It also shows that material behavior at 800 deg C, when assessed using weight loss portrays a very different story when compared to assessments based on wear depth data. Neither of these two approaches is sufficient by themselves. It is therefore recommended to use both gravimetric (weight loss) and surface profiling (wear depth) for evaluating wear behavior of materials.