Françoise Hlawka

Study of aluminium-copper-iron alloys: application for laser cladding

Abstract The modifications brought to aluminium by addition of copper and iron are investigated after rapid surface solidification by a CO 2 laser. In order to carry out an exhaustive study, the laser surface alloys are obtained using a precoating process. Samples are characterised using microscopic examination, X-ray diffraction and hardness measurement. The optimum composition (42 wt.% Cu–5 wt.% Fe) is selected for its fine and homogeneous microstructure (Al 2 Cu and Al 7 Cu 2 Fe phases) and its high hardness (370 Hv 0.2 ).

Exploring thermal spray gray alumina coating pore network architecture by combining stereological protocols and impedance electrochemical spectroscopy

Complex multiscale pore network architecture characterized by multimodal pore size distribution and connectivity develops during the manufacture of ceramic thermal spray coatings from intra- and interlamellar cracks generated when each lamella spreads and solidifies to globular pores resulting from lamella stacking defects. This network significantly affects the coating properties and their in-service behaviors. De Hoff stereological analysis permits quantification of the three-dimensional (3D) distribution of spheroids (i.e., pores) from the determination of their two-dimensional (2D) distribution estimated by image analysis when analyzing the coating structure from a polished plane. Electrochemical impedance spectroscopy electrochemically examines a material surface by frequency variable current and potential and analyzes the complex impedance. When a coating covers the material surface, the electrolyte percolates through the more or less connected pore network to locally passivate the substrate. The resistive and capacitive characteristics of the equivalent electrical circuit will depend upon the connected pore network architecture. Both protocols were implemented to quantify thermal spray coating structures. Al2O3-13TiO2 coatings were atmospherically plasma sprayed using several sets of power parameters, are current intensity, plasma gas total flow rate, and plasma gas composition in order to determine their effects on pore network architecture. Particle characteristics upon impact, especially their related dimensionless numbers, such as Reynolds, Weber, and Sommerfeld criteria, were also determined. Analyses permitted identification of (a) the major effects of power parameters upon pore architecture and (b) the related formation mechanisms.