Deposition of metal-matrix Ti–NiAl composites onto substrate surface by in-situ combustion synthesis: Numerical modelingTuesday (27.09.2016) 11:15 - 11:30 Part of:
This study is focused on the in-situ deposition of cast coatings—such as those reported in —on a substrate surface for use in conditions of shock loading and intense friction.
At optimal green mix/substrate mass ratio, we managed to deposit a Ti–NiAl coating strongly joined with a substrate material. Metallographic analysis suggests that the material of the coating contains both combustion products and substrate material.
A numerical model is developed for aluminothermic reaction in porous NiO + Al mixtures containing a number of functional additives and carried out in a centrifugal machine. It is assumed that within the warm-up zone Al is melted (933 K) and the oxide (alumina) film is partially destroyed. The adopted reaction scheme involves the dissociation of NiO at 1500 K; exothermic oxidation of Al with oxygen; and somewhat slower reaction of Ni with Al yielding NiAl. At high temperatures, the initially porous mass transforms into agile melt in which the gravity-assisted phase segregation takes place under the action of centrifugal forces. Mass exchange is controlled by convection, whereas the diffusion-controlled one is neglected.
Numerical calculations gave the following results: (a) at the stage of ignition, we observed the gravity-induced shrinkage at the sample surface and (b) the reaction temperature in the combustion front can exceed the adiabatic temperature. Nowadays, we are planning the research work on experimental verification of the model predictions and optimization of process parameters.
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