| Burn-resistant titanium alloys of Ti-V-Cr system are structural materials for aero-engine, which have excellent performance in both burn-resistant and mechanical properties. Laser solid forming(LSF) has the advantages including short lead time, integrated control of the forming process and the microstructure and performance of the metallic components and high flexibility, and it has great prosperity in designing titanium alloys and engineering practice. Ti-25V-15 Cr alloy were deposited by using LSF from blended elemental Ti, V and Cr powders, and the microstructure evolution and burn-resistant of as-deposited samples were investigated. The main research results are as follows:1. Under the condition of typical process parameters, the microstructure of laser solid forming of Ti-25V-15 Cr alloy were composed by columnar grains and near-equiaxed grains growing alternately, which indicate that the solidification parameters and laser process parameters have significant impact on the microstructure.2. LSF Ti-25V-15 Cr alloy exhibited similar morphology characteristics of prior-? grains with increasing laser power under certain processing parameters, which were mainly composed of near-equiaxed grains with aspect ratio a little higher than 1 or small bamboo-like columnar grains, and the grain size and the gas porosity increased with increasing laser power. With the decrease of scanning speed under certain processing parameters, the morphology of prior-? grains of LSF Ti-25V-15 Cr alloy turned from small near-equiaxed grains to large columnar grains growing epitaxially, and the grain size increased while the gas porosity decreased significantly. In addition, the formation mechanism of the prior-? grains under different processing parameters was revealed combining the columnar to equiaxed transition(CET) model and the thermal behavior analysis during the process of deposition.3. The burn-properties of LSF Ti-25V-15 Cr alloy and forging Ti40 alloy were evaluated by DCSB method, and the burn-resistant properties, the microstructure of burning products, the element distribution after combustion and the burning mechanism were investigated by SEM, EDS and XRD analyses. Results showed that: the burning resistant property of LSF Ti-25V-15 Cr alloy was a little better than of forging Ti40 alloy. The burned Ti-25V-15 Cr sample and Ti40 sample were composed by heat-affected zone(HAZ) and combustion product zone from the substrate to the burned surface. In the heat-affected zone, V and Cr clustered at the β grain boundary, but the average content of the element was the same as that of the substrate. According to element distribution, the combustion product zone can be divided into inner surface and outer surface. In the inner surface, the content of V element and that of Cr element increased gradually from heat-affected zone to combustion product zone, with the oxygen content relatively lower. In the outer surface, the content of V element and that of Cr element were nearly the same as the substrate or slightly lower than the substrate, but the oxygen content increased significantly. The products in the burning zone of LSF Ti-25V-15 Cr and forging Ti40 were all composed of mixed oxides of Ti and V, and there was little oxides of Cr. It can be deducted that the generated mixed oxides in the outer surface of the burning product zone and the enrichment of V, Cr in the inner surface prevented the diffusion of oxygen to the substrate together, and thus the two alloys all exhibited the excellent burn-resistant. |
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