Ultrasonic cavitation erosion of gas nitrided Ti-6Al-4V alloys.
Ultrasonic cavitation erosion experiments were performed on Ti-6Al-4V alloys samples in annealed, nitrided and nitrided and subsequently heat treated state. The protective oxide layer formed as a result of annealing and heat treatment after nitriding is eliminated after less than 30 min cavitation time, while the nitride layer lasts up to 90 min cavitation time. Once the protective layer is removed, the cavitation process develops by grain boundary erosion, leading to the expulsion of grains from the surface. The gas nitrided Ti-6Al-4V alloy, forming a TixN surface layer, proved to be a better solution to improve the cavitation erosion resistance, compared to the annealed and nitrided and heat treated state, respectively. The analysis of the mean depth of erosion rate at 165 min cavitation time showed an improvement of the cavitation erosion resistance of the nitrided samples of up to 77% higher compared to the one of the annealed samples.
D.c. diode ion nitriding behavior of titanium and Ti-6Al-4V
What determines the propagation of the surface layer if nitriding parameters or alloy composition were changed? By adjusting nitriding temperature and nitrogen partial pressure, the surface layers grown on titanium and Ti-6Al-4V were characterized in this study to reveal the propagation of each layer. Ion nitriding was carried out in a d.c. glow discharge. The nitrided specimens were characterized by a number of techniques including optical microscopy, scanning electron microscopy, wavelength dispersive spectroscopy and X-ray diffraction. Surface microhardness measurements were conducted in order to evaluate the effect of the processing parameters on the surface layers. 
 
The results show that the aluminum segregated layer forming between the compound layer and diffusion layer hinders the diffusion of nitrogen toward the core of Ti-6Al-4V and reduces the growth rate of the compound layer without affecting diffusion layer thickness. The change in plasma conditions such as H2 gas concentration can only have the effect on a nitrided compound layer. The most efficient ionization occurs at the H2 gas concentration of 17.5% in our case. The activation energy measured is lower than those obtained at higher nitriding temperature. This is believed to be the result of the changes in diffusion path that are affected by the compound layer texture and internal stress.
Magnetic properties of Lu2Fe17 crystals
Abstract We present the results of crystal structure and magnetization studies of three single crystals grown from melts of different nominal compositions in the vicinity of the Lu2Fe17 stoichiometry. The ferromagnetic state of the crystals is strongly dependent on the real sample composition and the local atomic ordering. A drastic difference is observed in the behaviour of the ferro–antiferromagnetic transition, even in crystals for which almost identical composition and crystal parameters were determined by microprobe and X-ray analysis.