Thermal expansion coefficients in Invar processed by selective laser melting

Prior research has established that Invar, a 64Fe-36Ni alloy, is known for its low thermal expansion. This property makes it valuable in precision engineering applications. However, the impact of additive manufacturing processes on this characteristic remains unclear. Selective laser melting (SLM) is a popular technique for fabricating complex geometries from powdered metals. Yet, no prior work had resolved whether the low thermal expansion of Invar is preserved after SLM processing. This uncertainty drove the current investigation. Existing studies have not addressed the residual stress effects in SLM Invar components. The question of whether the thermal expansion behavior is altered by the SLM process remains open. This gap motivated the experimental analysis of thermal expansion coefficients in SLM-processed Invar. The study aimed to determine if the unique property of Invar is retained after additive manufacturing.

The aim of this study was to determine whether the low thermal expansion property of Invar is preserved after processing using selective laser melting (SLM). Invar is widely used in applications requiring dimensional stability under thermal fluctuations. The SLM process involves layer-by-layer melting of powdered Invar. The researchers sought to compare the thermal expansion coefficient of SLM Invar with that of conventionally processed Invar. The study also aimed to investigate the role of residual stress in influencing thermal expansion. The motivation for this work stems from the growing use of additive manufacturing in high-precision applications. Understanding the thermal behavior of SLM Invar is essential for its adoption in such contexts. The study sought to clarify whether the SLM process alters the fundamental thermal properties of Invar.

The study used selective laser melting (SLM) to process Invar powder into near-full-density components. The powder had a particle size range of 15-45 μm. Thin layers of 20 μm were melted to form the components. The resulting parts achieved a density of 99.96%. Mechanical properties of the SLM Invar were compared to those of cold-drawn Invar36®. The thermal expansion coefficient was measured using standard techniques. The researchers also analyzed residual stress in the as-deposited parts. The study focused on the thermal expansion behavior up to 100 °C to assess the impact of residual stress.

The thermal expansion coefficient of SLM Invar was found to be lower than that of conventionally processed Invar. The measured coefficient was negative up to 100 °C. This negative value was attributed to residual stress in the as-deposited parts. The mechanical properties of SLM Invar were comparable to those of cold-drawn Invar36®. The study confirmed that the low thermal expansion property of Invar is retained after SLM processing. The residual stress was identified as a key factor influencing the thermal expansion behavior. The results suggest that the SLM process does not eliminate the unique thermal property of Invar. The findings indicate that SLM Invar can still be used in applications requiring low thermal expansion.

The study concludes that the low thermal expansion property of Invar is retained after processing with SLM. The thermal expansion coefficient of SLM Invar was lower and negative up to 100 °C. The authors attribute this to residual stress in the as-deposited parts. The mechanical properties of SLM Invar were comparable to those of cold-drawn Invar36®. The findings suggest that the SLM process does not eliminate the unique thermal property of Invar. The study supports the use of SLM Invar in applications requiring dimensional stability. The results indicate that residual stress is a significant factor in the thermal expansion behavior. The authors propose that further work could explore the long-term effects of residual stress on thermal expansion.