Vibromet

In order to illustrate the microstructure of the investigated materials, pseudo-3D figures were prepared using electron channeling contrast (ECCI) images captured using JEOL IT-500HR (JEOL, Tokyo, Japan) scanning electron microscope (SEM). The metallographic cross-sections were prepared using standard techniques with a final polishing stage of 8 h polishing in colloidal silica using Vibromet (Buehler, Lake Bluff, IL, USA) vibratory polisher. Chemical composition was studied by Octane Elite (Ametek EDAX, Pleasanton, CA, USA) energy dispersive X-ray analysis (EDX) system.

For the analysis of the initial pin microstructure, samples were cut with the cutting machine Accutom-50 (Struers GmbH, Willich, Germany) from the deposited material (friction surfacing), as well as from the material in as-cast state. The cut-outs were embedded, ground, and polished by standard metallographic methods. A final polishing step with $0.05$   $\mathsf{\mu }$ $\mathrm{m}$ colloidal silica suspension (Masterprep Polishing Suspension, Buehler, Düsseldorf, Germany) and vibratory polishing (Vibromet, Buehler, Düsseldorf, Germany) was necessary for optical light microscopy. For the color-etched microstructures, the samples were anodized in Barker reagent ( 5 $\mathrm{m}$ $\mathrm{L}$ HBF4 (48%) in 200 $\mathrm{m}$ $\mathrm{L}$ aqua dest.) at 22 ${}^{\circ }\mathrm{C}$ for 120 $\mathrm{s}$ at a voltage of 20 $\mathrm{V}$ using the electrochemical etching device LectroPol-5 (Struers GmbH, Willich, Germany). The samples were analyzed by light microscopy under crossed polarized light and a sensitive tint filter (BX-10, Olympus, Duesseldorf, Germany).

The phase purity and crystal structure of products were investigated by X-ray diffraction (XRD) using a diffractometer (D8 Advance, Bruker AXS GmbH) with Cu-Kα radiation (40 kV and 40 mA, $\lambda$ = $0.154$ nm) and a step size of 0.01° in the 2 $\theta$ range from 10° to 85°. Rietveld refinements of XRD patterns were performed on the software TOPAS (Version 6, Bruker AXS GmbH). PrCrO₃ ( $Pnma$ , ICSD 251098) and SrCrO₄ ( $P{2}_1/n$ , ICSD 40922) were used as starting structures. The elemental composition and microstructure of membranes were examined by two field-emission scanning electron microscopes (FE-SEM): JEOL JSM-6700F equipped with an energy-dispersive X-ray spectrometer (EDXS, Oxford Instruments INCA-300) and JEOL JSM-7610FPlus with twin EDXS (Bruker XFlash 6|60). Before measurements, the cross-sections of membranes were vibratory-polished by VibroMet (Buehler). The backscattered electron channeling contrast images were captured at an acceleration voltage of 15 kV.