[EN] The effect of high-energy ball-milling on the magnetostructural properties of a Ni45Co5Mn35Sn15 alloy in austenitic phase at room temperature has been analyzed by neutron and high-resolution X-ray diffraction. The ball milling promotes a mechanically-induced martensitic transformation as well as the appearance of amorphous-like non-transforming regions, following a double stage; for short milling times (below 30 min), a strong size reduction and martensite induction occur. On the opposite, for longer times, the increase of strains predominates and consequently a larger amount of non-transforming regions appears. The effect of the microstructural defects brought by milling (as dislocations) on both the enthalpy change at the martensitic transformation and the high field magnetization of the austenite has been quantitatively estimated and correlated to the internal strains. Contrary to what occurs in ternary Ni-Mn-Sn alloys, the mechanically induced defects do not change the ferromagnetic coupling between Mn atoms, but just cause a net reduction on the magnetic moments.This work has been carried out with the financial support of the Spanish “Ministerio de Economía y Competitividad” (Projects number MAT2015-65165-C2-R) “Agencia Estatal de Investigación (AEI), Ministerio de Ciencia, Innovación y Universidades” (Projects number RTI2018-094683-B-C54 (MCIU/AEI/FEDER, UE)), Navarra Government (Project number PC017-018 AMELEC) and Basque Government Grant No. IT-1005-16. We acknowledge ILL and ALBA for the beam time allocations: (http://doi.org/10.5291/ILL-DATA. INTER-411), CRG-2352, and ALBA BL04_MPSD beamline at ALBA Synchrotron with the collaboration of ALBA staff. PLR has received funding from “la Caixa” and "Caja Navarra" Foundations, under agreement LCF/PR/PR13/51080004
