Ingenieurwissenschaften und zugeordnete Tätigkeiten
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Organisationseinheit der BAM
Initially, as-cast and homogenized single crystals of nickel-base superalloy CMSX-4 are subjected to hot isostatic pressing at 1288 °C. Two series of experiments are conducted: under the same pressure of 103 MPa but with different durations, between 0.5 and 6 h, and under different pressures, between 15 and 150 MPa, but for the same time of 0.5 h. The porosity annihilation is investigated metallographically and by high-resolution synchrotron X-ray tomography. The obtained experimental results are compared with the predictions of the vacancy model proposed recently in the group. Herein, the model is further refined by coupling with X-ray tomography. The model describes the evolution of the pore arrays enclosed in the 3D synchrotron tomograms during hot isostatic pressing and properly predicts the time and stress dependences of the pore annihilation kinetics. The validated model and the obtained experimental results are used for selecting the optimal technological parameters such as applied pressure and processing time
Subsurface characterization of high-strength high-interstitial austenitic steels after impact wear
(2018)
The microstructure of the subsurface after impact wear of three high-strength high interstitial austenitic steels has been analysed using transmission electron microscopy (TEM) in alloys with C and N as interstitial elements. In all cases, a nanocrystalline region followed by a transition zone and a cold-worked area are present. Additionally, microhardness and nano-scratching tests were conducted to study the wear-related properties of the impact subsurface and the base material. The results of the microstructural analysis reveal that the following mechanisms are involved during impact wear: abrasion (ploughing), microcrack formation associated with contact fatigue, entrapment and adhesion of SiO2 particles. The analysis of the wear-related properties indicates that the subsurface acts as a self-protective layer that prevents the deterioration of the substrate.