A Review of Portable Low-Pressure and Medium-Pressure Cold Spray Repairs: Process Window, Deposition Behaviour, and Deposit Integrity

Low-pressure cold spray (LPCS) and medium-pressure cold spray (MPCS) provide field-deployable alternatives to stationary high-pressure cold spray (HPCS) for lightweight metallic component repair, although lower particle velocities and narrower process windows restrict the range of compatible repair materials. This review evaluates portable LPCS and MPCS repair as a distinct class of cold spray application using HPCS as the reference baseline. The article synthesises evidence on process windows, critical velocity, particle velocity ratio, deposition efficiency, deposit build-up capability, substrate preparation, porosity, oxide disruption, ceramic-assisted densification, interfacial bonding mechanisms, adhesion strength, hardness, residual stress, tensile behaviour, and fatigue performance. Attention is given to repair geometry, including blend-out depth, taper angle, aspect ratio, spray angle, and stand-off distance, because these factors govern particle impact conditions and interfacial integrity across practical repair geometries. Available evidence indicates that LPCS can achieve dimensional restoration, surface protection, and, in some cases, fatigue performance comparable with that of the substrate. However, structural qualification remains constrained by limited portable system fatigue data, few direct LPCS–MPCS comparisons under equivalent conditions, and inconsistent reporting of powder characteristics, surface preparation, porosity, and repair geometry. MPCS may extend the range of compatible repair materials while maintaining field deployability, but its peer-reviewed evidence base remains limited. Future work should prioritise controlled LPCS–MPCS comparisons, geometry-sensitive fatigue testing, standardised deposit quality metrics, and qualification procedures linking process window control with repair integrity.