Influence of technological parameters on nitriding behavior of spray formed Al alloys
Despite their typical high Si content of up to 30 ma.-％, spray-formed Al alloys have an excellent nitridability in plasma processes. This results from the exclusive primary solidified and homogeneously dispersed small Si precipitations in the base material due to the specific production process. Former studies reported on the influence of the general technological parameters during plasma nitriding, such as temperature, time and gas composition, as well as chemical composition of spray-formed Al alloys on their nitriding behavior. However, in connection with efforts of automatization process control, like in case of steels for example, a significant influence of the adaptive control of the plasma duty cycle has been detected. In the case where the specific nitriding technology of direct current (DC) plasma nitriding is used with in-situ sputter cleaning, the plasma duty cycle determines different processes subsiding on the sample surface. These are, on the one hand, the surface activation by means of oxide layer removal and immediate nitride nucleation as well as growth. On the other hand, there is the partial re-sputtering of the newly formed nitride layer. Very complex physical procedures and chemical reactions, which are not yet understood in detail, take place during the plasma process. The scope of this report covers both the influence of the duty plasma cycle, as well as the initial surface characteristics including the specimen shape. In spite of equal general nitriding conditions (temperature, time, voltage) over time the plasma duty cycle and the target value of plasma duty lead to different thicknesses and coverage of the nitride layer. For a better understanding of the nitriding mechanism, analyses on interrupted nitriding tests were carried out. Thereby, color changes of the sample surrounding transition zone served as criterion for selected interruption times. The results of plasma nitriding have been characterized by examining metallographic cross sections with optical microscopy, surface coverage by scanning electron microscopy (SEM) and measuring aluminium nitride layer thickness as well. Composition and structure of the nitride layers were investigated using glow discharge optical emission spectroscopy (GDOES) and X-ray diffractometry (XRD). Mechanical properties were studied using microindentation. Adhesion was tested by scratch tests.
plasma nitriding aluminum alloys aluminum nitride hypoeutectic aluminum
Anja Buchwalder Anke Dalke Heinz-Joachim Spies Rolf Zenker
TU Bergakademie Freiberg, Institute of Materials Engineering, Freiberg, Germany TU Bergakademie Freiberg, Institute of Materials Engineering, Freiberg, Germany Zenker Consult, Mitt
国际会议
北京
英文
252-257
2012-10-23（万方平台首次上网日期，不代表论文的发表时间）