Papers by Author: N. Wanderka

Abstract: Nano-crystalline-amorphous Al based alloys with minor additions of rare earth elements and transition metals are of technical interest, because of their extraordinary high mechanical strength. This strengthening effect depends strongly on the alloy composition and the pathway of crystallisation. The crystallisation behaviour of Al87Ni6La7 and of Al87Ni5La7Zr metallic glass was studied with complementary methods such as XRD, TEM and 3D-AP. The amorphous matrix of the Zr-containing glass shows fluctuations of all minor elements on the nanometer scale. It is suggested, that these fluctuations act as nucleation zones for the crystallization of the glass during annealing.

Abstract: Aluminium foam sandwich panels (AFS) made of a low-density aluminium alloy AlSi6Cu6 foam core and two dense 6082 alloy face sheets were fabricated, after which the panels were subjected to two different heat treatments. First, the AFS panels were aged to increase their strength without further solution heat treatment and fast quenching, a process which resembles a T5 treatment. Second, to define a reference point the face sheets of AFS samples were cut off the foam and subjected to a full T6 treatment. Hardness profiles were measured across the thickness of the face sheets after the two different treatments and the microstructure was investigated. The main conclusion is that mechanical performance of AFS panels can be considerably increased by heat treatment without full solution heat treatment (T5), but without reaching the level of a full T6 treatment. The potential use of an easy to apply T5 treatment is an important cost reducing factor.

Abstract: Si3N4 based ceramics that made by hot isostatic press, were implanted at room temperature with N+ - and C+ - ions with energy of 500 keV and 2 MeV, respectively. The specimens were irradiated at a fluence of 1017 ion/cm2. The microstructure changes after ionimplantation in the surface layer were investigated by transmission electron microscopy (TEM). The effect of ion-implantation on the tribological properties was also studied. After N+ and C+ ionimplantation an amorphous layer near to the surface has been formed which was observed by electron diffraction measurement. The wear tests were performed by means of a ball-on-disk configuration using commercially available Si3N4 ball. The friction coefficient was measured online, the wear coefficient was determined on the base of the wear scar sizes. The specific wear rate was reduced by N+-implantation and the coefficient of friction was lower in the initial stage in both cases.