D. Bergner

Investigations of nitrogen diffusion in austenitic CrNi steels

Parameters of the diffusion of N (up to 0.3 wt.%) in austenitic stainless steels (12 to 19 wt.% Cr, 12 to 16 wt.% Ni, up to 2 wt.% Mo) were determined within the temperature range of 1283–1573K. The small concentration gradients of N were successfully investigated using (1) mechanical serial sectioning technique in combination with either chemical N analysis or X-ray precision lattice parameter determination, and (2) measurements on microsections by means of either electron probe microanalysis or Kossel technique.The diffusion coefficients of N were found to be independent of its concentration. The alloying elements Cr and Mo reduce the N diffusivity in austenitic stainless steels which on the other hand is increased by Ni.

Applicability of a Au(50 at%) Ti(50 at%)-alloy for diffusion measurements in the Au-Ti system

In connection with diffusion experiments in the Au-Ti system, a AuTi (50at%)-alloy sample has been prepared. Its homogeneity was characterized by metallography, EPMA and X-Ray phase analysis. Three phases were found: mainly TiAu (α.-, β-allotropic forms) together with Ti3Au and TiAu2.Diffusion couples of Au-AuTi50-Ti were used to study formation and growth of the intermetallic phases TiAu4 and TiAu2 between Au and AuTi50 and Ti3Au between AuTi50 and Ti, respectively. At 800 °C parabolic layer growth was observed and the growth constants were determined.

Short circuit diffusion in CuSn6/Ni/Au planar tricouples

To investigate processes of short circuit and uphill diffusion, low-temperature diffusion experiments were carried out with sandwich samples of CuSn6/Ni/Au in the kinetic regimeB after Harrison. Two kinds of base material CuSn6 with different grain sizes were chosen. The first material was cold rolled CuSn6 with a mean grain size of 3–4 μm. The second was annealed CuSn6 with a mean grain size of 40 μm. The Ni and Au layers with thicknesses in the μm range were deposited by galvanization. The sheets were prepared by ion beam slope cutting, characterized by scanning electron microscopy and transmission electron microscopy. After annealing at 576 K up to 120 d, the samples were investigated with glow discharge spectroscopy and scanning electron microscopy. Concentration penetration plots made with glow discharge spectroscopy showed a different diffusion behaviour dependent on the CuSn6 material. The diffusion processes in the samples of cold rolled CuSn6 are more extensive than in the annealed CuSn6 samples. To find out causes of this phenomenon, a model of short circuit diffusion was developed and concentration penetration curves were calculated numerically with the finite difference method. Images of an ion beam slope cut sample show grain growth in the Au layer.

Investigations of precipitates in heat treated AgPd30/CuSn6 layers

The subject of the investigations are precipitation zones, which grew as a result of chemical diffusion in AgPd30/CuSn6 bimetals. These precipitation zones have been characterized by metallography, electron probe microanalysis and x-ray diffraction. The growth of precipitation zones in the plating layer and in the substrate layer in dependence on time have been determined. The use of x-ray diffraction alone for the identification of the precipitates could not supply satisfying results in every case. This problem was solved by the application of electron probe microanalysis using a correction method, which allows the estimation of the chemical composition of small particles.