Neutron Diffraction Reveals Additive Manufacturing Induced Stresses

DMTC has been progressing Australia’s industrial knowledge of four types of additive manufacturing through a detailed benchmarking program. The four additive manufacturing techniques that have been compared for application on metallic components are Selective Laser Melting (SLM), Electron Beam Melting (ARCAM), Direct Metal Deposition (DMD) and Wire and Arc Additive Layer Manufacturing (WALAM). The program has examined the evolution and character of the deposited metal for each of the four processes, and will go on to conduct a cost benefit analysis of their application.

Previous work has identified that additive manufacturing processes create residual stresses in the region in and immediately below the processed area. These stresses when tensile in nature compromise the structural integrity of the component. Due to this, understanding the tension or compression distribution and magnitudes for the different additive manufacturing technologies becomes a critical piece of information when selecting one of the four techniques for a particular application.

The Australian Nuclear Science and Technology Organisation (ANSTO) has provided access to and ‘beam time’ on their neutron strain scanner known as “KOWARI” to measure the residual stresses induced by each of the additive manufacturing techniques. Ti-6AL-4V samples were created in the shape of a wedge to imitate the effect of section thickness on residual stress formation. Strain maps of the four samples were then measured in ANSTOs neutron beam.

The results showed that that ARCAM, DMD and WALAM processes all produce a very low residual stress. SLM on the other hand was shown to produce a compressive stress state. This is exciting as compressive residual stresses are known to increase the structural integrity of metallic structures and therefore extend the fatigue life. This result makes SLM a more promising technology for future production of aerospace components.

Posted by DMTC on July 14th, 2014