Modeling of diffusion processes in multilayer PVD Zn-ZnMg coating and steel substrate

Samenvatting

It is recognized that ZnMg represents a new advance in metallic coatings and combines a range of especially beneficial properties. In our ongoing project we study a new coating technique, i.e. physical vapor deposition of ZnMg alloy, which is particularly promising for high speed coating applications. The next generation steels contains alloying elements such as Mn, Si and Al, which tend to segregate to the interface between coating and steel substrate upon annealing (pain baking) or welding and can form a range of intermetallic phases with Mg. Precipitates of intermetallic phases at the interface between ZnMg coating and steel substrate influence the coating adhesion. Diffusion and phase transformation rates are high enough to deteriorate coating adhesion to unacceptable levels within several hours at 175°C (typical paint baking temperature in the automotive industry). To avoid the formation of intermetallic phases we investigate a new technique: deposition of a multilayer PVD coating, which consists of a dual Zn–ZnMg layer with the Zn layer situated between the steel substrate and the ZnMg layer. The idea is to use Zn interlayer as a barrier for Mg diffusion, thereby preventing the formation of intermetallic precipitates. We need to tune the interlayer thickness and to elaborate recommendations concerning the optimum duration and temperature of various thermal treatments after the coating deposition (e.g. paint baking in automotive industry).

To achieve this goal we are going to model diffusion processes in the multilayer structure substrate – Zn interlayer – ZnMg layer. The modelling will allow us to save experimental time and resources. Theoretical investigations and modelling will be performed by Dr. Turkin.

Two visits of Dr. Turkin, each of two months duration, will be required to accomplish the tasks summarized below.

Visit 1: Study of alloying element distributions in the multilayer structure
substrate – Zn interlayer – ZnMg layer. Formulation of the model of interdiffusion and precipitate formation
The first visit will be devoted to the study of experimental data on redistribution of elements in the dual Zn-ZnMg coating and steel substrate, which will be obtained in our group. Based on this analysis a model of interdiffusion in both the coating and the substrate will be formulated. The underlying set of equations will be solved numerically, because of nonlinearity and complexity. This will require additional efforts to select and adapt corresponding numerical methods.

Visit 2: Validation of the model, comparison to experimental data and preparation of publication(s)
During the second visit, the experimental data obtained in our group will be analyzed and compared with predictions of the theoretical model. It will allow us to determine parameters, which controls diffusion of elements and formation of second phase precipitates, such as:
• coating and interlayer thicknesses;
• temperature and duration of thermal annealing,
• optimum composition of ZnMg layer
The results of the proposed investigations will be prepared for publication in peer-reviewed journals.

Kenmerken

Projectnummer

040.11.688

Hoofdaanvrager

Prof. dr. Y.T. Pei

Verbonden aan

Rijksuniversiteit Groningen, Faculty of Science and Engineering (FSE), ENgineering and TEchnology institute Groningen (ENTEG)

Looptijd

16/04/2019 tot 15/11/2019