ADDITIVE MANUFACTURING OF APPLICATION-BASED MULTI-MATERIAL STRUCTURES VIA LENS(TM) PROCESS: BUILD STRATEGIES AND  UNDERSTANDING PROCESSING CHALLENGES

Bonny Onuike

Multi-material structures provide unique solutions to many engineering problems through enhanced-property capabilities to achieve site-specific functionalities in engineering systems. Among structures made of multi-materials, bimetallics comprise largely of two different metals joined together to benefit from the distinct properties of the base materials, or to selectively improve the overall performance of one of the components. But, bimetallic-joint’s processing suffers immensely from bonding compatibility issues due to mismatch in metallurgical and thermal properties of the base-metals. Four different build-strategies: direct bonding, compositional gradation, intermediate and compositional bond layers were employed to fabricate different bimetallic joints through laser engineered net shaping (LENSTM) process. These bonding techniques applied to specific materials’ combinations stem the four research projects. In the first instance, titanium alloy (Ti64) and niobium (Nb) materials were bonded together via direct deposition due to metallurgical compatibility, single-phase solid solution, of the base-elements. Directly bonded structures are mostly characterized with well-defined interface with sharp properties’ variation. Compositional gradation approach minimizes such interfacial properties’ mismatch. Hence, the second research project involved using this strategy to fabricate a bimetallic joint of Inconel 718 and GRCop-84 materials. In the third research project, a concept suitable for bonding immiscible materials was employed. Ti64 and SS410 are dissimilar metals with incompatible metallurgical properties. An intermediate layer material, Nb, was used to join these materials. A proof-of-concept part for the direct application of the bimetallic structure was demonstrated. The final project involved use of compositional bond layer (CBL) (a mixture of VC + the base-materials) to fabricate a bimetallic structure of metallurgically incompatible alloys, Inconel 718 and Ti64. In all the four projects, a crack-free joint with no delamination or de-bonding features at the interfaces of the bimetallic joints were observed. In addition, the bimetallic joints, especially Ti64/Nb, Inconel 718/GRCop-84 and Ti64/SS410 showed strong interfacial bond strength in comparison to the base-materials. Thermal diffusivity of Ti64 and Inconel 718 materials were enhanced, as well. Hence, to manufacture a mechanically reliable joint of dissimilar materials with tailored/enhanced properties requires understanding the process-property relationships. It holds promise of next generation multi-materials metal additive manufacturing for hi-tech applications in engineering structures.

ADDITIVE MANUFACTURING OF APPLICATION-BASED MULTI-MATERIAL STRUCTURES VIA LENS(TM) PROCESS: BUILD STRATEGIES AND UNDERSTANDING PROCESSING CHALLENGES

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