A new process for design and manufacture of tailor-made functionally graded composites through friction stir additive manufacturing

Motivated by the recent use of friction stirring in the manufacture of in-situ composites, a new additive manufacturing method for the design and manufacture of tailor-made functionally graded composites is presented. The existing literature on the subject matter is limited to creating functional grades in the vicinity of the weld nugget without direct control on composition and property gradients. A mathematical model is developed for achieving a compositional gradient over a predefined length in a metal matrix composite and subsequently demonstrated through the manufacture of aluminum + TiC functionally graded composite. Progressive gradients are observed in hardness and local mechanical properties, namely, Young's modulus, stain hardening exponent, and yield stress obtained using the digital image correlation technique. The process mechanism is elucidated by correlating results of mechanical tests and electron backscatter diffraction analysis. A specific process condition vis-à-vis the number of passes, volume faction, and particle size combination may promote one or more phenomena such as continuous dynamic recrystallization, particle fragmentation, and breaking of initial matrix grains, which eventually affect particle mixing and matrix grain size and thus cause property gradients. The findings are expected to enable the manufacture of functionally graded composites products of larger size