Effect of annealing on microstructures and mechanical properties of PA-12 lattice structures proceeded by multi jet fusion technology

Abstract

Polymer based additive manufacturing is a robust manufacturing paradigm and facilitates production of highly customized parts with substantially improved mechanical properties. Therefore, the aim of this research is to investigate seven polymeric lattice structures namely: Diamond, Gyroid, Kelvin, Split-P, SUP, Primitive, and Octet. The annealing heat-treatment was used at two different tempartures:110 °C and 130 °C for a constant time period (2 h). In total, five specimens were investigated for each sample (such as for each case of annealed and as built samples). The SEM images show greater smoothness of microstructure with application of heat treatment. However, a higher temperature can have an adverse effect. For example, the roughness of Gyroid, Octet, and SUP is decreased compared to the As-built sample. In addition, it is shown that surface roughness is directly proportional to the mechanical strength. Among all the structures, Diamond and SUP structures (As-built) demonstrate higher performance in terms of load-bearing capacity (at densification point) and lower flexibility compared to their counter-part. For instance, Diamond and Octet structures’ strength is increased by 22% and 20% whereas flexibility is decreased by 12% and 8%, respectively. Maximum energy absorption is achieved by the Diamond structure followed by the Gyroid, Split-P, Kelvin, SUP, and Primitive. Apparently, the heat treatment has induced brittleness in the structure making it prone to cracks. A newly designed SUP structure has demonstrated the maximum strength among all the tested structures whereas the Octet structure exhibited the least strength. In return, this increase in the strength of the SUP structure is achieved at a cost of a decrease in flexibility.