Investigating Multi-Material Additive Manufacturing as a Method to Join Previously “Un-weldable” Material Combinations

The bonding of dissimilar metals is a powerful and important part of modern manufacturing. Being able to combine the capabilities of many different alloys in one coherent structure is of great interest to designers, engineers, and manufacturers. However, many alloy combinations are deemed “un-weldable” for a variety of reasons, such as large differences in physical properties or the formation of deleterious material phases at the compositional gradient between the materials. Additive manufacturing presents an array of unique advantages over other multi-material fabrication techniques that may allow for the development of successful bonds in alloys that have in the past failed. Assessment of a material junction using a wide range of tools such as thermal and thermodynamic simulation – accompanied by thorough experimental analysis – is the key to overcoming these challenges. 

In the current work, a variety of computational tools are employed alongside experimental methods to assess whether past fabrication failures can be made into successes. Out-of-the-box solutions include CALPHAD (Calculation of phase diagrams) and material kinetics simulations to assess the range of material properties and phase formations that can occur and nearly and alloy composition. A thermal simulation program specifically developed for additive manufacturing process development is also detailed, including its comparison to conventional computational tools and the range of its possible applications. 

Several case studies are detailed involving the development of multi-material bonds with additive manufacturing. The first involves the avoidance of brittle carbide formation at the interface between 304 stainless steel and Inconel 625 nickel superalloy. In the second study, AL-6XN super-austenitic stainless steel is bonded with Invar 36 to assess whether this steel has potential for use as a highly corrosion-resistant option for additive manufacturing. The last study details the bonding of Inconel 718 nickel superalloy with GRCop-84, a high-strength copper alloy; the possibility of using a Ni interface layer is posited as a method to avoid severe intermetallic formation at the interface between these two alloys. In each study, simulation techniques are combined with experimental validation to assess the efficacy of additive manufacturing as a tool for the development of these multi-metal combinations. The principles behind the avoidance of bond failure in each study may have applications for the further identification of alloys and alloy combinations for multi-material fabrication, even when said alloys have previously been discounted by traditional manufacturing techniques.