Nuclear technique helps validate theoretical model for optimised laser material deposition in additive manufacturing

October 8, 2018, Australian Nuclear Science and Technology Organisation (ANSTO)
Dr Anna Paradowska and Dr Mark Reid stand near the Kowari strain scanner. Credit: Australian Nuclear Science and Technology Organisation (ANSTO)

Neutron diffraction strain scanning measurements at ANSTO have validated a new theoretical model that successfully predicts the residual stresses and critical deposition heights for laser additive manufacturing.

The model, which was developed by Prof Ramesh Singh's group from the Indian Institute of Technology Bombay in association with Prof Wenyi Yan from Monash University, accounts for both thermomechanical behaviour and metallurgical transformation that takes place by direct energy techniques, such as laser cladding.

"To collaborate with ANSTO and use the world-class facilities there can definitely enhance our research quality. This work, just published in Scientific Reports, is just one good example," said Yan.

''This research was completed through a joint Ph.D. training program between the Indian Institute of Technology Bombay and Monash University. The first author Santanu Paul has finished his Ph.D. study and is now working in an international company to develop software for additive manufacturing, ''said Yan.

Laser cladding is used widely in the maintenance, repair and overhaul of parts and structural components in the automotive and aerospace industries because it improves material properties.

"Directed energy deposition methods have a huge potential in repair and re-manufacturing of aerospace components, dies and moulds which undergo damage due to cyclic thermomechanical loading. However, the presence of tensile residual stresses in the deposited layer will reduce the fatigue life of restored component.

Comparison of residual stress predicted by finite element models with measured using Neutron and X-ray diffraction. Credit: Australian Nuclear Science and Technology Organisation (ANSTO)

The fully coupled thermomechanical and metallurgical model developed in this collaborative work has been used to determine the critical deposition height which ensures compressive residual stresses in the deposited layer for sustainable restoration." said Singh.

"Working with ANSTO team on experimental measurements of residual stresses was a great pleasure and learning experience and this paper is just the beginning of a long term collaboration," said Singh.

In the paper, the investigators reported that variation in residual stress across a cross section of laser clad steel, predicted by their metallo-thermomechanical model, demonstrated the existence of a critical deposition height.

The critical height of deposition corresponds to the layer thickness, which, when deposited, would maximise beneficial compressive residual stresses in the deposited layer and substrate.

Deposition that is lower than the critical height would produce detrimental tensile residual stresses at the interface while deposition that is higher than the critical height would result in excessive dilution.

The research also found that at the critical height of deposition, the solidification rate was at a minimum.

The Kowari residual stress diffractometer was used to measure macroscale residual stresses in a sample of H13 steel that was laser cladded with crucible particle metallurgy steel powders with a high vanadium content.

The three-dimensional measurements of residual stresses on Kowari are highly accurate and non-destructive.

"A model is only as good as its validation. Using strain scanning instrument—Kowari we were able to identify triaxial residual stresses in the deposited layers, which verified the locations predicted by the model ," said Research Scientist and Industrial Liaison Manager Dr. Anna Paradowska, who is a co-author of the paper with Dr. Mark Reid.

Laser cladding, which involves depositing molten metal on a relatively cold substrate of steel, creates a complex residual stress profile.

Theoretical models based on thermomechanical properties, which are commonly used, were shown to overestimate tensile residual stresses and underestimates compressive residual stresses in the substrate and interface.

The team used surface X-ray diffraction at the Indian Institute of Technology for measurements of residual stresses in one direction. However it was important to have an independent fully non-destructive bulk measurements to also validate the in-house measurements procedure.

Both diffraction techniques showed the presence of tensile residual stresses near the melt front and compressive stresses in the deposited layer and interface regions.

"Understanding the stresses and being able to predict them is very important for additive manufacturing industry. Validated model is very beneficial as further optimalisation of the manufacturing process using this model will be cost effective and saves time," said Paradowska.

"The model allows you to calculate the laser position rate to achieve a specific height of deposition while minimising the effect of detrimental stresses and maximise the beneficial compressive stresses."

The study authors suggested demonstrated a science-enable technology solution that could lead to an improvement in the quality, safety and economics of components manufactured with laser additive processes.

Explore further: All aboard the neutron train—mapping residual stresses for more robust rails

More information: Santanu Paul et al. Critical deposition height for sustainable restoration via laser additive manufacturing, Scientific Reports (2018). DOI: 10.1038/s41598-018-32842-z

Related Stories

Taking the stress out of residual stress mapping

May 11, 2018

Researchers from the University of Virginia (UVA) are using neutrons to explore fundamental work in residual stress mapping that promises more precise science down the road for Oak Ridge National Laboratory (ORNL) and similar ...

Recommended for you

Sculpting stable structures in pure liquids

February 21, 2019

Oscillating flow and light pulses can be used to create reconfigurable architecture in liquid crystals. Materials scientists can carefully engineer concerted microfluidic flows and localized optothermal fields to achieve ...

How to freeze heat conduction

February 21, 2019

Physicists have discovered a new effect, which makes it possible to create excellent thermal insulators which conduct electricity. Such materials can be used to convert waste heat into electrical energy.

Water is more homogeneous than expected

February 21, 2019

In order to explain the known anomalies in water, some researchers assume that water consists of a mixture of two phases, even under ambient conditions. However, new X-ray spectroscopic analyses at BESSY II, ESRF and Swiss ...

Correlated nucleons may solve 35-year-old mystery

February 20, 2019

A careful re-analysis of data taken at the Department of Energy's Thomas Jefferson National Accelerator Facility has revealed a possible link between correlated protons and neutrons in the nucleus and a 35-year-old mystery. ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.