Integrity of Additively Manufactured Alloys and Component to Environmental Degradation

The corrosion behavior of metals/alloys depends on composition, microstructure, defects of varied length scale, and state of the outermost surface besides environmental factors. The undesirable microstructure consisting of dendritic/columnar structure, high residual strain, dislocation density, solute segregation, secondary phases such as carbides, nitrides, sigma, and chi-phase, grain size, and porosity present in the additively manufactured component change its corrosion characteristics significantly as compared to their conventional wrought or cast form. The aluminum alloys, austenitic stainless steels, Ti-6Al-4 V, Inconel 625 and 718 are few which have been progressively fabricated by the different additive manufacturing (AM) processes and have been subjected to a fundamental understanding with respect to mechanical, corrosion, and metallurgical properties. While a large segment of additive manufacturing research is directed toward the study of the design, process optimization, instrumentation, and evaluation of the mechanical properties, the least attention has been paid to exploring corrosion resistance and its response to various environments. While the corrosion properties of AM components are widely different across geometrical locations as compared to their cast and wrought counterpart, these are further modified by the types of the AM process in use and precursor powders. Various features culminated from the AM can be linked to a specific type of corrosion as they can produce conditions conducive to respective corrosion form. This review analyzed various defects that evolved from the AM process and how they influence corrosion. The manuscript further discusses the susceptibility of AM-processed components to specific forms of corrosion including hot corrosion with emphasis on corrosion protocol developments for AM components.