Cyclic oxidation tests

Cyclic oxidation tests were conducted al 800°C in static laboratory air for up to 1500 cycles. Each temperature cycle consisted of exposure for one hour at reaction... 

The prequalification of these materials was carried out by static and cyclic oxidation tests at 1200-1300 °C. First test components (80 x 30 x 3 mm) were produced (Fig.2) and successfully tested on the high pressure sector test rig at DLR. The test conditions chosen - 20 cycles at 20 bar, approximately 1200 °C, in air for a total duration of 4 hours - are representative for operating conditions. 

In some cases a measure of the reaction kinetics is not as useful as a measure of the useful life under a given set of experimental conditions. Cyclic oxidation tests using weight-change versus time measurements and visual examination of exposed specimens can be useful to determine times beyond which protective scales, such as alumina, are no longer formed on alloy test coupons. 

Lance, Accelerated cyclic oxidation testing protocols for thermal barrier coatings and alumina-forming alloys and coatings. Mater. Corrosion, 57 (2006), 1-13. 

Standard guide for high temperature Oxidation testing of nonoxide advanced ceramics at atmospheric pressures and low gas velocities Test method for continuous oxidation test at elevated temperatures for metallic materials Method of cyclic oxidation testing at elevated temperatures for metallic materials... 

The objective of the project was to create the technical basis that will permit the comprehensive definition of all the test-related aspects of the cyclic oxidation test. In order to achieve these objectives the following work packages and tasks were undertaken in two phases ... 

Evaluation of the presently used test procedures and experimental facilities for cyclic oxidation testing. 

Development of a draft code of practice for three types of cyclic oxidation testing based on the outcome of phase 1. 

In the joint European COTEST project a solid basis has been developed for a reliable and meaningful standard for high temperature cyclic oxidation testing. This basis combines scientific approaches with industrial needs and for the first time allows an intercomparison of data from different laboratories. The draft standard developed in the frame of COTEST can be found on the internet [4]. In the following chapters and in [5], details of the work within the COTEST project and the results are reported. 

The current version of the code of practice for thermal cyclic oxidation testing can be found on the internet under http //cotest.dechema.de/Code of Practice.html. 

Variation in cyclic oxidation testing practice and data The European situation before... 

Cyclic oxidation testing is a key method to aid material selection and to predict service lifetime of components. However, it is a complex procedure that has many possible variables. Hence it is often difficult to compare data from different laboratories unless either (i) the procedures in each laboratory are similar, or (ii) the influence of any differences in procedure on the resultant data is known. 

Schematic representation of cyclic oxidation test facility in... 

At this stage it was also decided to classify cyclic oxidation testing into three classes based upon the time at temperature during each cycle. The definitions were agreed to be as follows ... 

Where closed systems are used, the laboratories utilised bottled gas mixtures, and the reported gas flow rates in such cases are summarised in Table 17.10. As with temperature stability, the recommendations developed in the TESTCORR project should be adopted directly for cyclic oxidation testing, i.e. a linear flow rate of 1-10 mm s". Where the tests are carried out in laboratory air in open furnace systems, the atmosphere is static apart from convection effects. 

The results of these surveys underline the necessity of the COTEST project because little of the reported data from different sources is amenable to intercomparison. The role of testing variables on the outcome of cyclic oxidation testing at the time was not sufficiently clear, thus demonstrating the need for standardisation of testing procedures. 

Designing experiments for maximum information from cyclic oxidation tests and their statistical analysis using half normal plots (COTEST)... 

Cyclic oxidation testing at elevated temperatures requires careful experimental design and the adoption of standard procedures if reliable data are to result. This is a major aim of the COTEST research programme. Further, as such tests are both time consuming and costly, in terms of human effort, to take measurements over a large number of cycles, it is important to gain maximum information from a minimum number of tests (trials). This search for standardisation of cyclic oxidation conditions leads to a series of tests to determine the relative effects of cyclic parameters on the oxidation process. Standard oxidation conditions are required to develop a code of practice for the characterisation of high temperature materials performance. 

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