MoSi2-based materials produced by Selective Laser Melting for corrosion/erosion components of gas turbine
| Reference number | |
| Coordinator | CHALMERS TEKNISKA HÖGSKOLA AKTIEBOLAG - Industri- och materialvetenskap |
| Funding from Vinnova | SEK 858 709 |
| Project duration | September 2018 - September 2019 |
| Status | Completed |
Purpose and goal
The project aimed to improve the resistance to high temperature oxidation of hot components through optimized coating of MoSi2 achieved with the additive manufacturing technique Selective Laser Melting (SLM). The goal was to produce MoSi2 coated samples of the nickel base alloy Hastelloy X (HX) that can withstand thermal fatigue testing (TCF) at 1100 °C for 1000 hours without deteriorating the properties of the layer. However, the project failed to avoid microcracks in the coatings to a sufficient extent that it would make sense to even move on to TCF and the goal was thus not achieved.
Expected results and effects
The results showed that thermal cracking was critical for the properties of the SLM-built MoSi2 layer on substrates of both HX and stainless steel SS420. The cracks are not only caused by hot cracking but also by cyclic thermal shocks through the repeated melting / cooling processes during SLM, which results in a Ni-enriched liquid phase at grain boundaries where solidification cracks can be induced. Layer quality and adhesion improved when a powder mixture of MoSi2 and HX was deposited with SLM. Crack sensitivity hence seem to decrease as HX content is increased, but cracks were still observed in the optimized MoSi2 layer regardless of the process parameters tested. Thus, the project failed to obtain samples of sufficient quality to undergo thermal fatigue testing according to plan and thus the continuation criterion was not met to proceed from Stage 1 to Stage 2. The project constellation concluded that there is no prerequisite for success in Stage 2 with this material concept. and therefore agreed to end the project after Stage 1.
Planned approach and implementation
The project produced MoSi2 powder for application through SLM. Process parameters were optimized with eight statistically experimentally planned trial runs in the SLM equipment. Samples with pure MoSi2 and MoSi2 + HX powders on disk and built cube substrates were coated with 220 sets of process parameters. Homogeneous layers with good adhesion were obtained with whatever parameter set, microcracks could not be avoided in the coating. Consequently, there were no conditions for it to make sense to proceed with thermal fatigue testing and the project participants therefore agreed to finish the project after the first stage.