Volume 55, Issue 1

From ancient times to the present, copper alloys, brasses and bronzes are used for marine applications due to their high resistance to sea water. In time, numerous of copper alloys have been developed and manganese (Mn) and aluminium (Al) bronzes are the well-known members of this large family. They have superior properties and are used to produce some critical components of boats. These alloys are in competition with each other. For this reason, C86500 Mn bronze and C95800 Al bronze were evaluated in this study. Mechanical and corrosion tests were carried out on specimens which were taken from sand castings. Tensile, impact and hardness tests were applied to determine mechanical properties. Corrosion behaviour of the alloys was characterized in HCl, NaCl, and H 2 SO 4 solutions. Additionally, microstructure observations and a definition of phases were realized. According to mechanical tests results, Al bronze has better properties than Mn bronze. Moreover, Mn bronze provides lower corrosion rates in HCl solution as Al bronze in H 2 SO 4 . Intergranular corrosion was detected in HCl solutions. Moreover, some micro shrinkage zones were seen on an Al bronze specimen after corrosion tests.

The present work describes a method for the temperature measurement in furnaces or test rigs for the range 750 – 1000°C by means of the selective oxidation of nickel in palladium-gold-nickel alloys in a constant oxygen atmosphere (p O2 = 2.1 · 10 4 Pa). For this method, extensive aging tests using alloys of different compositions (PdAu x Ni2, x = 0; 10; 15; 20; 30 wt. %) were performed and the alloy-dependent material constants ln( A ) and B of the Arrhenius equation were determined. These values allowed for the spatially resolved evaluation of the temperature load by means of a metallographic analysis of the oxidation depth. It is furthermore shown that the oxygen diffusion rate in PdAu x Ni2 as well as the activation energy needed decrease with increasing gold content x , while the lattice constant a increases. In addition to that, a geometric derivation for the determination of the layer thickness is presented aiming at simplifying the preparation of the wire-shaped samples.

A check for surface cracks under application of the magnetic flux leakage method (MT testing) was performed on the turbine wheel disk of a heavy-duty turbine gas turbine engine for energy generation. It revealed unacceptable findings on the bearing surface of the sealing plate groove. In order to identify the damage-causing mechanism of the material, a metallographic examination was performed. The findings during non-destructive material testing were caused by a gaping material separation which was also easily detectable to the naked eye. The material separation is a high-cycle fatigue crack induced by fretting. Hence, the damage causing mechanism was fretting fatigue cracking.