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3622 |
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Influence of cold sprayed Al/Ti deposition on high-temperature oxidation and mechanical properties deterioration of Ti-Al-Nb intermetallic substrates |
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Jan Cizek* / Institute of Materials Science and Engineering,
Brno University of Technology, Czech Republic Ondrej Man / Institute of Materials Science and Engineering, Brno University of Technology, Czech Republic Ivo Dlouhy/ Institute of Materials Science and Engineering, Brno University of Technology, Czech Republic |
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In the study, four powder blends of Al (oval, 1477 µm) doped with various Ti (angular, 1150 µm) content were prepared as feedstock material for cold spray deposition: Al, Al5Ti, Al15Ti, Al30Ti. Protective layers of the blends designated for deliberate oxidation were then deposited onto Ti-46Al-8Nb intermetallic substrates at 300°C, while preserving their initial chemical composition and retaining their original Al:Ti ratio. No oxidation of the materials during deposition was detected. A two-stage heat-treatment in an inert argon atmosphere (480°C/2hrs + 520°C/3hrs) was then carried out in order to induce desirable diffusion-driven processes to aid the anti-oxidizing performance indicators for the subsequent high temperature testing. Following the treatment, the specimens were subjected to 950°C air exposure for 100, 250 and 500hrs, respectively. It was found that the oxidation of the specimens was substantially reduced for the low-Ti content coatings (an increase in oxide content of 1.37 mg/cm2 and 2.06 mg/cm2 after 500hrs for Al and Al5Ti protected specimens, respectively vs. 1.21 mg/cm2 after 50hrs for non-coated specimens) and that the samples with an increased Ti content in the coatings were more susceptible to oxidation. To obtain information on the influence of coatings deposition on the mechanical properties, four-point bend experiments were performed. The flexural strength of the coated samples reached 630 MPa, slightly lower than 767 MPa of the non-coated specimens. This difference could be possibly attributed to the accumulation of stresses below a coating crack initiation site in the surface-sensitive intermetallic materials. It was found that the reduction of oxidation in the specimens due to the layers deposition did not prevent the deterioration of the mechanical properties as the flexural strength levels dropped to ~350 MPa after the 500hrs exposition (compared to ~460 MPa after 47hrs for non-coated specimens). |