Wear performance of Al/TiN dispersion strengthened surface composite produced through friction stir process: A comparison of tool geometries and number of passes

The Al7075-T651 alloy is extensively used as structural material in the aircraft industry and as mold material in the plastics industry. However, it experiences wear during service which consequently reduces the service life of component. With an aim to improve its wear resistance, a surface composite employing friction stir processing (FSP) is fabricated in the present study. The TiN particles of nano scale are mixed into Al7075-T651 substrate using 3 different tool geometries (i.e., threaded taper, square and triangular) and varying the number of passes over 2 levels of severity (i.e., 2 and 4). The results show that both the tool shape and the number of passes affect the distribution of reinforcing particles, which in turn influence the composite characteristics like grain size, hardness and wear resistance. The most wear resistant composite is realized when the processing is carried out using the combination of threaded tool and four passes. Further, the wear resistance and friction coefficient of this composite is respectively found to be 60% higher and 45% lower than the respective properties of parent metal (i.e., Al7075-T651). This is due to a fact that the said composite sample exhibits the highest hardness and contains the finest grains. Moreover, the formation of Al2O3 film and Fe3O4 particles is observed on the worn surfaces. These also reduce the composite wear by preventing the direct contact of sliding surfaces during wear test. This finding reveals that the tribo growth (s), in addition to hardness, is also important factor affecting the wear resistance of Al/TiN composite. This study is the first report on the wear characteristics of Al/TiN composite produced through FSP route.