Producing Ruthenium and Palladium Doped Stainless Steel by Field Assisted Sintering

Stainless steels are generally corrosion resistant, however, in reducing acidic environments passive film dissolution can occur. Though studies have shown alloying with platinum group metals (PGMs) benefits stainless steel corrosion resistance, cost and performance issues have limited the commercial success of this strategy. This project explored the production of stainless steel-PGM alloys via powder metallurgy to address these challenges.

Using the field assisted sintering technique, bulk alloyed and functionally graded materials (FGMs) were successfully produced using water atomised 316L and 17-4PH stainless steel doped with 0.5 wt.\% Ru and Pd, respectively. Sintering optimisation was carried out by varying the processing temperature and time. Corrosion performance was evaluated by electrochemical testing in H2SO4 and immersion testing in NaCl. The performance of cast and sintered PGM-doped 316L was also compared.

Increasing the sintering temperature enhanced the density of the 17-4PH samples but had little effect on the 316L specimens. In contrast, increasing the sintering time had minimal impact on either alloy's density. Regarding the effect of PGM doping on corrosion performance, no clear trend emerged in H2SO4. In NaCl, however, immersion testing revealed PGM doping benefitted the corrosion resistance of 316L. The cast samples outperformed the sintered samples exhibiting wider passive regions and a greater ease of passivation. In the FGMs, it was observed that PGM presence had a positive effect on pitting resistance in a chloride environment.

This study demonstrated the feasibility of powder metallurgical PGM-doped stainless steels. While mixed corrosion performances were observed, further research could render more consistency. Future studies should focus on investigating the effect of different atomisation techniques or sintering conditions.