Friction surfacing—A review

Friction surfacing (FS) is a solid state technology with increasing applications in the context of localized surface engineering. FS has been investigated mainly for producing fine grained coatings, which exhibit superior wear and corrosion properties. Since no bulk melting takes place, this process allows dissimilar joining of materials that would be otherwise incompatible or difficult to deposit by fusion based methods. Several studies also emphasize its energy efficiency and low environmental impact as key advantages when compared with other alternative technologies. Main applications include repair of worn or damaged surfaces through building up or crack sealing. It has also been applied to enhance surface properties at specific areas in the manufacturing of parts and tools. A wide range of material combinations have been deposited by FS, mainly alloy and stainless steels. Aluminium, magnesium and titanium alloys have also been investigated, including the production of metal matrix composites. Starting with a brief introduction, this review presents a detailed description of the thermo-mechanical and microstructural transformations as well as process modelling approaches. The material combinations investigated so far and the effect of process parameters are also addressed. An overview of the main technologic and equipment advances is presented, including: computational optimization models, surface preparation, gas protection, post-processing methods, pre-heating and cooling. An assessment of the material deposition rate and the specific energy consumption is also provided, comparing friction surfacing to mainstream electric arc, laser and thermal spraying based processes. Based on current process advantages and disadvantages, an outlook on future research and development is provided. Friction surfacing has a significant potential for further industrial applications and is being developed as a practicable alternative to mainstream coating processes. The present review paper provides a broad overview throughout the fundamentals of FS and the most relevant technology developments, establishing both a theoretical and technical basis for new researchers and industrial practitioners searching for new coating alternatives.