In-situ synthesized Al2O3 reinforced metal-ceramic composite coating was fabricated on lowalloyed carbon steel surface by laser cladding. Injection of the ceramic powder into the melted surface can be difficult due to the effect of surface tension and to the lower density of the Al2O3 particles, compared to that of the steel matrix. These difficulties can be avoided by the in-situ synthesis of Al2O3 particles in the liquid steel matrix. In this paper, the results of experiments performed by laser beam will be introduced, together with the interpretation of these results. Experiments proved that the Al2O3 ceramic phase can be created in-situ in the steel matrix.
In the present study the analysis of 5 different mechanisms of porosity formation during laser melt
injection (LMI) technology were performed. Experiments were supported by thermodynamic and
fluid-flow analysis. Special attention should be paid to i. clean the surface of the substrate, ii. use
inert shielding gas, iii. use proper particle size and gas velocity, iv. use proper laser power and laser
beam velocity to control bath temperature and v. deoxidize the surface of the added particles.
Gravity induced stresses in terrestrial laboratory specimens comprising of relatively weak and soft granular materials, are often of the same magnitude as the external tractions that are applied during investigations of constitutive behavior especially at low intergranular stress levels. The presence of heterogeneous strain and stress fields within such a specimen makes it difficult if not impossible to obtain objective and unambiguous constitutive properties and to devise relevant constitutive equations. To fill this technological gap, microgravity experiments are now planned which will be performed during future flights of the Space Shuttle, in conjunction with ground-based tests. This paper deals with analytical and experimental issues related to constitutive modeling of granular materials.
Small batches of two oxide powders falling in the particle size range of about 30-230 μm were received from industrial sources and were electroless nickel (EN) coated in order to prepare properly modified reinforcing particles for further laboratory experiments with the Laser Melt Injection (LMI) technique to produce particle reinforced steel composite surface layers. The partially calcined alumina (Al2O3) as well as the hydrothermally recycled crystalline iron(III) oxide precipitate were characterized first to check their exact size ranges, specific surface areas and major chemical contaminants so that the best possible EN plating technique would be selected and applied. It was revealed soon that the sensitization and activation pre-treatment steps could not be omitted and after their proper adjustment, also the composition and pH of a relatively commonly used hypophosphite reducing type bath had to be modified to the given purpose. Eventually a slightly alkaline EN bath was successfully prepared with which both industrial oxide powders surface could be nickel coated soundly, which final result was demonstrated also by several metallographic testing techniques showing the microstructure of the quite evenly and fully coated oxide particles.
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