LAMELLATED – Laser Additive Manufacturing for novEL Large scAle ThermoElectric Devices

Aim: To develop a pilot scale selective laser melting (SLM) process to deliver cost-effective fully densified thermoelectric legs with superior microstructure & properties.

Challenges: Thermo-electric generator (TEG) manufacturing processes are inherently wasteful & expensive due to the necessity to grow high purity thermo-electric (TE) crystals & then slice & dice them into small TE legs (~dimensions 1.2mm2x0.8mm), losing >50% of the raw material. state-of-the-art BiTe TE processing involves an energy-intensive zone melting with the following limitations:

• Crystals are sliced & diced into legs wasting > 50% of the material.
• TE composition is limited to stoichiometries that readily grow crystals.
• Materials exhibit poor physical properties leading to breakages & failure during use.
• TE legs are limited to cubes or cuboids reducing design freedom & creating stress concentrators causing cracking & failure.

Spark plasma sintering (SPS) has enhanced TE performance & enable a powder metallurgy route. However, SPS does not enable net shape manufacture, also requires slicing and dicing & the process is not industrially scalable. TE legs & metallisation account for up to 70% of the TEG module cost today. Conventional SLM has been applied to powder beds of bismuth telluride, however, the conventional beam energy distribution has led to tellurium volatilisation & overall poor TE properties.

Benefits: LAMELLATED integrates novel material processing technologies for the large-scale manufacture of thermoelectric devices. It will deliver novel devices with TE legs with geometries not commercially available today & capable of delivering outstanding performance and providing cost leadership in the sector. The thermoelectric sector will benefit from a manufacturing process that enables complete material compositional choice, including the addition of sintering aids, 2D materials and grain growth inhibitors.

Activities & Present achievements: SLM has been applied to selected materials and whilst densification has been achieved, non-uniform temperature gradients have been produced creating material loss and non-optimal grain structures. The process combines bespoke diffractive optic elements (DOEs) to tailor the beam shape and heat zone utilising a cost-effective 35 W 808 nm diode laser.

Current Status: Both deliverables for the technology development phase was completed on time and passed the acceptance criteria. Diffractive optical element (DOE) production, covering the thermal modelling of the TE legs and Hologram design was completed.