Corrosion management concepts utilising the application and integration of corrosion predictive tools for corrosion occurrence and corrosion propagation will be a driver for new technical advances in the field of corrosion maintenance and in development of new structural designs, materials and processes for surface protection. Additional benefits can be expected by reduced time to market for new products.
The scientific and technological objectives of SICOM were:
Objective I: Definition of parameters that represent corrosion condition and in-service experience of aircraft
The definition of requirements and specifications for optimal corrosion modelling including experience of in-service findings for corrosion problems related to Al alloys was the base line for model development. This should result in formulating relevant input parameters for the other WP.
Objective II: Development of a numerical micro-scale model to simulate localised corrosion of Al- Alloys with regard to micro-structure and the micro-electrochemical condition
The dominating factors that trigger localised corrosion on aluminium alloys was analysed. The purpose was to evaluate the influence of the microstructure of an Al alloy on the onset of localised corrosion. Numerical models - a mechanistic, mass transport model and a probabilistic, cellular automaton model - were developed that allow simulating electrochemical reactions at the micrometer scale. The mass transport model was used to simulate local dissolution processes, such as those occurring during pitting and crevice corrosion. The cellular automaton model simulated the corrosion propagation path when intergranular corrosion occurs. In order to determine the required input parameters for the numerical models, different kinds of micro-electrochemical experiments were performed in combination with various types of surface analytical investigations. The input parameters required for the models include:
a) the micro-geometry of local corrosion sites;
b) the microchemistry that has been generated near corrosion sites;
c) the dissolution kinetics of active surface micro-zones. In order to validate the simulated data specific configurations were selected, that allow a quantitative classification of the computed results.
Objective III: Determine the corrosion rate of Al-Alloys in the mesoscale of occluded cells by means of numerical calculation as a function of physical and geometrical factor for given macro-environment
A basic model was developed to understand and quantify the possible chemical and electrochemical changes that occur in an occluded cell resulting from joint design (e.g. crevice). The purpose was to model the (electro) chemical evolution leading to the localised corrosion (intergranular) inside a narrow gap of electrolyte encountered in a sensitive assembly as a function of the relevant physica
The influence of surface treatment on modelling results was included with regard to inhibitor release from protection systems, role of clad layer and oxide degrading effects. A decision support tool was established to enable exploitation and implementation of the project results in scientific and technical applications. SICOM set out to provide models that will become an essential part of future predictive maintenance concepts to avoid unanticipated and unscheduled maintenance with high costs. Data from monitoring systems and non-destructive inspection can be used as model input. Models output will be utilised for the repair decision process or can supply structural integrity concepts & hereby fill the gap between monitoring or inspection and calculation of the structural impact of corrosion. Aircraft development costs will be reduced through saving on testing time and quantity. The prediction models can be combined with expert systems and databases for a more efficient and reliable development and selection of materials.
The following major results were expected:
- specification of requirements for in- and output data used in different fields of application;
- mass transport model and the evaluated, critical parameters that trigger localised corrosion;
- numerical calculation of the corrosion rate of aluminium in an occluded cell;
- advanced modified mass transport model for the impact of a clad layer that includes the relevant (complex) geometrical and chemical parameters;
- galvanic corrosion model predicting the corrosion rates for typical structural joints under varying conditions;
- a decision-support software tool will be designed and provided to enable a wide application in corrosion management.