Thermodynamic Conditions for Consolidation of Dissimilar Materials in Bimetal and Functional Graded Structures

Abstract

Functional Graded Structures and Functional Graded parts, made using dissimilar materials, are designed to provide specific properties to the final product. One of the most promising methods for manufacturing 3D Functional Graded objects is 3D laser cladding and/or direct energy deposition. However, the construction of graded and especially layered graded structures in the process of joining materials with different thermophysical properties under certain conditions is accompanied by the formation of cracks along the phase boundaries, which are a consequence of residual stresses and/or chemical segregations. The conditions for phase consolidation are macroscopic balancing of residual stresses in the region of the interface. In a broader sense, in the field of the interface, it is necessary to consider the thermodynamic equilibrium of the phases in connection with mechanical equilibrium. In this regard, the article proposed criteria for the thermodynamic affinity of phases in the area of the Functional Graded Structures interface, including the coefficients of thermal expansion and isobaric and isochoric heat capacities of the phases. Examples of cracking and the use of the obtained criteria are provided.

Research on Cracked Conditions in Nickel Chrome Alloy Ni50Cr33W4.5Mo2.8TiAlNb, Obtained by Direct Laser Deposition

“…In previous works [58,59], the authors of the article showed that the heat balance equation at the interface between two phases can serve as a basis for identifying the energy of discontinuity and identifying the conditions for the initiation of cracks, given the possible displacement of the phases relative to each other. Without taking into account heat transfers to the external environment, the heat balance equation near the phase boundary or an area with a large gradient in the change in chemical composition takes the following form:…”

Design and Fabrication of Extremely Lightweight Truss-Structured Metal Mirrors

“…As shown by the red circle in Figure 11, there were unmolten particles and micropores on the mirror surfaces, which not only degraded the surface quality but also reduced the surface densification. It is known that the mirrors used in visible and infrared systems have to be plated with a NiP layer to increase the surface roughness, but this may lead to bimetal effects because of the different thermal coefficients between NiP and the mirror blanks [15].…”