THE INFLUENCE OF CONVECTION ON THE HOMOGENEITY OF LASER-APPLIED COATINGS

During laser alloying, a melt pool is created at the passage of a laser beam in which mixing occurs by convection because of surface tension gradients. This mixing process in the melt bath is reported here in different alloying elements on aluminium (manganese, nickel, cobalt) and steel (nickel) substrates and a homogeneous distribution did not appear to be evident. It is concluded that density differences, interface tensions and diffusion are the main factors affecting the mixing process.</p

AL-SIC INTERFACE STRUCTURE STUDIED BY HREM

A comparison is made between the two well-known aluminium alloys 2014 and 6061, cold pressed from powder and subsequently extruded, with and without a reinforcement of 30 wt% alpha-SiC particulates. The former one has a strength of 550 MPa and a strain at fracture of 1% while the latter one has a more moderate strength of 415 MPa but a fracture strain of 4%. A high resolution electron microscopy study of the Al SiC interface indicates that proper wetting is achieved in both alloys. A preferred orientation relationship is observed in the 6061 SiC combination: (0001)SiC//{111}Al; [2110BARBAR]SiC//[110]Al. When the (0001)SiC is not parallel to the interface, a stepped interface is observed with the 6061 alloy, with one part of the step parallel to the SiC basal plane and one type of the Al octahedral planes and the other part parallel to another type of Al octahedral planes. In the 2014 alloy the steps seem to be less pronounced probably due the processing route

MECHANICAL STRENGTH OF HIGHLY POROUS CERAMICS

This paper reports on the mechanical strength of highly porous ceramics in terms of the Weibull and Duxbury-Leath distributions. More than 1000 side-crushing strength tests on silica-catalyst carriers of various particle sizes have been performed in series. Within a series, preparation conditions were kept constant. Analysis of the fluctuations of the failure pressure around its expectation value proves that the length dependence of the mechanical strength is well described by both distributions. Focusing upon the failure pressure dependence, the µ = 1 Duxbury-Leath distribution appears to be the more appropriate.

METAL-CERAMIC INTERFACES PRODUCED BY LASER MELT INJECTION PROCESSING

This paper concentrates on the mechanical performance of various ceramic coatings of Cr2O3 on steel (SAF2205), as produced by CO2 laser processing. It is concluded that a firmly bonded coating of Cr2O3 on steel could be produced by high power laser processing. The actual interface strength of a (Fe,Cr)-spinel applied to stainless steel by laser coating depends strongly on the composition of the substrate and coating materials. The energy release rate was extremely high and delamination occurred by fracture through the coating and partially along the interface, indicating that the interface strength is similar to or higher than the fracture strength of (Fe,Cr)-spinel