Manuscript Information Figures

0Mo = Cr-3Si (at.%)

5Mo = Cr-5Mo-3Si (at.%)

15Mo = Cr-15Mo-3Si (at.%)

25Mo = Cr-25Mo-3Si (at.%)

36Mo = Cr-36Mo-3Si (at.%)

50Mo = Cr-50Mo-3Si (at.%)

60Mo = Cr-60Mo-3Si (at.%)

Compositions are given in at.% and impurities in wt.ppm

Temperatures are provided in °C or K

Size is provided in µm and mm

Densities are provided in g/cm³

lattice parameter in Å

Stresses are given in GPa, MPa

Deformation twinning datasets are consistently indicated in blue, whereas dislocation-slip datasets are consistently indicated in red.

Fig. 1: Grain-size dependence of the normalized critical stresses for deformation twinning (blue) and no twinning (dislocation slip, red data points) in BCC metals and alloys. The grain-size and normalized critical-stress data underlying the graph are provided as *.txt files in ASCII format, with header information describing the data.

Fig. 2: Lattice parameters  of the (Cr,Mo,Si)_SS as a function of Mo content  in comparison to literature results on binary (Cr,Mo)_SS alloys. The lattice-parameter data underlying the graph are provided as *.txt files in ASCII format, with header information describing the data.

Fig. 3(a-g): SEM-BSE micrographs of the alloys after homogenization heat treatment. The raw, unedited SEM-BSE micrographs presented in the manuscript are provided as *.tif files.

Fig. 4: Representative true stress–true strain curves obtained from compression tests conducted at RT at an initial strain rate of . The data underlying the plotted stress–strain curves are provided as *.txt files in ASCII format, with header information describing the data.

Fig. 5a: Mechanical properties as a function of Mo concentration at RT. The raw data from the compression tests are provided in *.tra files. The data underlying the graph are provided as *.txt files in ASCII format, with header information describing the data.

Fig. 5b: Mechanical properties as a function of Mo concentration at RT: b) Vickers hardness () (left axis) and nanohardness () (right axis). The Vickers hardness and nanohardness datasets are provided as *.xlsx files, while the data underlying the graph are provided as *.txt files in ASCII format, with header information describing the data.

Fig. 6: SEM-EBSD orientation imaging microscopy of compression test samples at  (except 0Mo): (a) 0Mo at , (b) 5Mo, (c) 25Mo, and (d) 60Mo. The raw, unedited SEM-EBSD IPF and IQ images presented in the manuscript are provided as *.tif files, while the corresponding SEM-EBSD datasets are provided as *.osc files.

Fig.7: TEM analysis of the compression-tested 36Mo sample subjected to 5% at RT. The raw, unedited TEM-BF images and TEM-SAED patterns presented in the manuscript are provided as *.tif files.

Fig. 8: SEM-BSE micrograph of indents after HV1 and  testing inside grains: (a) 0Mo and (b) 60Mo. The insets show FIB cross sections beneath the indents. The raw, unedited SEM-BSE micrographs and FIB cross-section images presented in the manuscript are provided as *.tif files.

Fig. 9(a-e): SEM-BSE micrographs of 50Mo after Vickers testing  on positions with grain boundaries. The raw, unedited SEM-BSE micrographs and FIB cross-section images presented in the manuscript are provided as *.tif files.

Fig. 10: Mechanistic origin of slip–twinning competition in (Cr,Mo,Si)_SS alloys. The data underlying the graph are provided as *.txt files in ASCII format, with header information describing the data.

Fig. 11: Mechanistic origin of slip–twinning competition in (Cr,Mo,Si)_SS alloys. The raw DFT datasets are provided as *.csv files, while the corresponding DFT atomic configurations are provided as *.cif files. The data underlying the graph are provided as *.txt files in ASCII format, with header information describing the data.

Fig. 12: Mechanistic origin of slip–twinning competition in (Cr,Mo,Si)_SS alloys. The data underlying the graph are provided as *.txt files in ASCII format, with header information describing the data.

Supplementary Information Figures

Fig. S1: Grain-size dependence of the normalized critical stresses for deformation twinning (blue) and no twinning (dislocation slip, red data points) in BCC metals and alloys.  The data underlying the graph are provided as *.txt files in ASCII format, with header information describing the data.

Fig. S2: XRD patterns confirming the single-phase BCC crystal structure of all investigated alloys. The raw XRD data are provided in *.xy format.

Fig. S3: a) Correlation between Vickers hardness (horizontal axis) and  (vertical axis). (b) Correlation between Vickers hardness  (horizontal axis) and  (vertical axis). The data underlying the graph are provided as *.txt files in ASCII format, with header information describing the data.

Fig. S4: SEM–EBSD analysis of the active twinning modes in the 5Mo, 25Mo, and 60Mo alloys after compression at RT to .  The raw, unedited SEM-BSE micrographs presented in the manuscript are provided as *.tif files.

Fig. S5: SEM-BSE micrographs of the macroscopic compression test specimens subjected to plastic deformation at RT up to  showing deformation twinning. The raw, unedited SEM-BSE micrographs presented in the manuscript are provided as *.tif files.

Fig. S6: SEM-BSE micrographs of the macroscopic compression test specimens at RT at the 1^st load drop showing deformation twinning. The raw, unedited SEM-BSE micrographs presented in the manuscript are provided as *.tif files.

Fig. S7: SEM-EBSD-guided FIB preparation of a TEM lamella containing deformation twins after  = 5%. The raw, unedited SEM-BSE micrographs presented in the manuscript are provided as *.tif files. The SEM-EBSD datasets are provided as *.osc files.

Fig. S8: SEM-BSE/EBSD micrographs of the alloys following HV1 and HV10 indentation. The raw, unedited SEM-EBSD IPF/IQ and SEM-BSE images presented in the manuscript are provided as *.tif files, while the corresponding SEM-EBSD datasets are provided as *.osc files.

Fig. S9: Lattice misfit parameters,  for (Cr,Mo)_SS, derived from a quadratic fit of the lattice parameter.  from nanoindentation (blue symbols) compared with calculated values (blue dashed line) based on concentration-weighted single-crystal elastic constants of Mo and Cr. The data underlying the graph are provided as *.txt files in ASCII format, with header information describing the data.

Fig. S10: Equivalent flow stress as a function of Mo content across the (Cr,Mo,Si)ss series, comparing the measured slip and twinning responses with the edge-dislocation strengthening model. The data underlying the graph are provided as *.txt files in ASCII format, with header information describing the data.

Fig. S11: and for various binary BCC alloys reported in literature and the present study. The data underlying the graph are provided as *.txt files in ASCII format, with header information describing the data.

Fig. S12: Unrelaxed for various supercell sizes represented by their number of   layers. The raw data are provided in .csv format. The data underlying the graph are provided as *.txt files in ASCII format, with header information describing the data.

Acknowledgements

We gratefully acknowledge financial support by the Deutsche Forschungsgemeinschaft (DFG) within the framework of GRK 2561 MatCom-ComMat. This work was partly carried out with the support of the Karlsruhe Nano Micro Facility (KNMFi, www.knmf.kit.edu), a Helmholtz Research Infrastructure at Karlsruhe Institute of Technology (KIT, www.kit.edu). We acknowledge the chemical analysis by HCGE at the Institute for Applied Materials (IAM-AWP) by Dr. Bergfeldt, Karlsruhe Institute of Technology (KIT). The authors gratefully acknowledge the computing time provided to them at the NHR Center NHR4CES at TU Darmstadt (project number p0024417) and at RWTH Aachen University (project number p0025202). This is funded by the Federal Ministry of Research, Technology and Space, and the state governments participating on the basis of the resolutions of the GWK for national high-performance computing at universities (www.nhr-verein.de/unsere-partner). VT acknowledges the support by the Alexander von Humboldt Foundation.  The authors further thank Marcel Münch for valuable scientific discussions and input concerning the TEM and SEM-FIB analyses. We gratefully acknowledge Dr. Georg Winkens for his scientific input and analytical support. We also thank Cole Rabe for his experimental support.