Selective Laser Melting of 316L and Hastelloy X

Selective laser melting (SLM) is a powder bed additive manufacturing process that enables the production of functional and complex geometries by using a highly focused laser beam. The short delivery times and the ability to produce custom-made spare parts are the main advantages of this technology that oil&gas industry can benefit of, as it is the case for Engie-Laborelec.

However, the components for the energy sector are subjected to harsh environments (e.g. high temperature and corrosive atmospheres) and only a limited amount of materials that are processable by SLM stand these conditions. The limited material palette is one of the main challenge of SLM since many materials, such as high strength nickel alloys, are susceptible to cracking. Therefore, SLM of Hastelloy X, a Nickel-based superalloy, was studied in order to reduce or avoid the cracks.

Another challenge of SLM is the low production rate of the technology caused by the fine diameter lasers. Productivity is an important aspect of the technology since it affects the cost of the process. Therefore, great efforts are being taken in the industry to improve it, such as by using high power and wider laser beams, that scan bigger areas in shorter times. For that purpose, the combination of SLM and high power SLM (HP-SLM) were studied.

In this thesis, first the process and heat treatment optimisation of a well-known material, 316L and the resulting microstructure and mechanical properties were studied. Then the use of a dual-laser beam system was explored for 316L. After HP-SLM, some cracks were found that were closed by HIP.

After learning from the process on a well-known material, Hastelloy X was studied which is characterised by the cracking susceptibility. As learnt from the literature and from 316L, HIP was applied in order to close the cracks as a first option. The use of HP-SLM was also exploited and the microstructure and mechanical behaviour were investigated on a non-modified Hastelloy X variant. On the other hand, process parameters were varied in order to obtain crack-free parts. There, the experimental and numerical works were combined in order to better understand the crack mitigation obtained by the reduction of the hatch spacing on HP-SLM of Hastelloy X parts.

Lastly, a commercial Hastelloy X variant was investigated which was intentionally modified to obtain micro-crack free SLM parts. The microstructure and mechanical property evolution was studied as function of temperature.