Polymer Derived Ceramics from Si, B, SiB6, and Mo5SiB2 Filler-Loaded Perhydropolysilazane Precursors as Protective and Functional Coatings for Refractory Metal Alloys

Oxidation barrier coatings on the base of a perhydropolysilazane precursor with different amounts of Si, B, SiB6 and Mo5SiB2 (T2) fillers for the oxidation protection of Mo-Si-B alloys were developed. The influence of different filler compositions as well as the influence of pyrolysis conditions (temperature and atmosphere) was studied. The coating slurries were examined with respect to their rheological behavior, which allows optimization of the coating slurry. Dilatometry studies show that the coefficient of thermal expansion of the composites can be matched to refractory, especially molybdenum alloy based, substrates by varying the content and the composition of the filler. The pyrolyzed coating systems offer a low porosity, which is one of the key parameters to a high oxidation protection capability.

Coating Reactions on Vanadium and V-Si-B Alloys during Powder Pack-Cementation

Alloys in the V-Si-B system are a new and promising class of light-weight refractory metal materials for high temperature applications. Presently, the main attention is focused on three-phase alloy compositions that consist of a vanadium solid solution phase and the two intermetallic phases V3Si and V5SiB2. Similar to other refractory metal alloys, a major drawback is the poor oxidation resistance. In this study, initial pack-cementation experiments were performed on commercially available pure vanadium and a three-phase alloy V-9Si-5B to achieve an oxidation protection for this new type of high temperature material. This advance in oxidation resistance now enables the attractive mechanical properties of V-Si-B alloys to be used for high temperature structural applications.

Synthesis of Aluminum-Matrix Alloys with Al-Zr-W by Metallothermy of Oxides

The article presents the results of obtaining complex-alloyed aluminum-zirconium alloys by aluminothermy of initial metal oxides. Aluminum-matrix Al-Zr-W alloys have been obtained by a metal-thermal reduction with an excessive amount of aluminum in the initial charge of zirconium and tungsten oxides. The process of synthesis is presented as partial reduction reactions of zirconium, tungsten and synthesis of intermetallic compounds. It is shown that thermodynamic parameters of the reactions are favorable for the process of formation of refractory metal alloys. It is found that the temperature reached during the melting process makes it possible to obtain intermetallids and to synthesize alloys at the out-of-furnace process in the form of a compact ingot. The composition of the alloys obtained has been determined by an X-ray phase and an element analysis. It is established that the alloys have a composite structure: intermetallides Al3Zr and Al4W are distributed in the aluminum matrix.

Study on Recrystallization Behavior of Nb-1Zr-0.1C Alloy

The Nb-1%Zr-0.1%C (wt%) alloy is one of the most promising refractory metal alloys having an excellent combination of high temperature properties. Such a combination of properties makes it suitable for several structural applications in the Compact High Temperature Reactor (CHTR). In order to produce the alloy in different shape and sizes a new thermo-mechanical route has been established. The central idea behind the development of such thermo-mechanical route is to reduce the working temperature and provide suitable intermediate annealing treatments to develop desired microstructures. The present paper reports about the application of orientation imaging microscopy in optimizing annealing parameters like temperature and time as a function of the extent of deformation. Samples were also characterized by optical microscopy and transmission electron microscopy techniques. It has been shown that a heat treatment of 1300°C for 3 hour could produce nearly full-recrystallized microstructure. This paper also discusses about the carbide precipitation, their morphologies, chemical compositions and orientations with the matrix phase.