The sensitivity of the single-phase, low thermal expansion (LTE) alloy 36 (Fe-36Ni) to intergranular cracking hinders its processability during additive manufacturing. This study investigates the effect of accelerated cooling via a CO₂ jet and the addition of TiC particles on the cracking susceptibility of the LTE36 alloy during wire-arc additive manufacturing (WAAM). Results show that accelerated cooling reduces inter-pass deposition times and the susceptibility to cracking due to increased heat dissipation. A crack-free microstructure was achieved only with the addition of TiC particles, which pinned the high-angle grain boundaries and induced tortuosity, thereby limiting grain growth and mitigating intergranular cracking. Mechanical performance was restored compared to the cracked condition, and the critical LTE property of the as-deposited LTE36 alloy was improved due to the enhanced ferromagnetic character of the alloy. Therefore, the combined approach effectively mitigated intergranular cracking while retaining the LTE behaviour during WAAM of the LTE36 alloy.

The binary Fe–Ni system offers alloys with notably low linear coefficients of thermal expansion (CTE), contingent upon their Ni content. In this respect twin-wire arc additive manufacturing (T-WAAM) presents the opportunity of in-situ alloying through the simultaneous feeding of two metal wires into a weld pool to obtain desired alloy compositions. This study aims to deposit a graded wall with Ni contents targeted at 42, 46, and 52 wt% in the building direction of the wall, along with a block comprising of 46 wt% Ni, employing the T-WAAM approach. The results show effective incorporation of additional Ni into the weld pool and geometrically stable weld beads in the continuous metal transfer mode during the T-WAAM process. This mode led to the defect-free and chemically stable deposition of the graded wall and the block with average Ni contents of 42.3 ± 1.1, 45.8 ± 1.4, 52.6 ± 0.8 wt%, and 46.4 ± 0.9 wt%, respectively. The measured Curie temperatures of the as-deposited alloys and the mean CTE values of alloy 46 were found to be comparable to the commercial alloys. In summary, this study validates the feasibility of in-situ deposition of low thermal expansion alloy compositions, thereby enabling the possibility of on-demand thermal expansion properties.

Invar alloys exhibit low thermal expansion and are useful in applications requiring dimensional stability when subject to temperature changes. Conventional production of Invar faces certain challenges that can be offset by exploiting additive manufacturing processes. This study employed pulsed gas tungsten arc welding (GTAW) to deposit Invar 36 alloy blocks at five heat inputs (HI) ranging from 200 to 550 J mm⁻¹. The results show that the microstructure comprised of columnar grains and remained in the austenitic phase regardless of the HI. Ductility dip cracking was found to prevail in all the blocks except the block deposited at the lowest HI. The decreased susceptibility to cracking with a reduction in the HI was due to the preservation of the grain boundary area, consequently leading to an improved partitioning of strain among the grain boundaries. On lowering the HI from 550 to 200 J mm⁻¹ the average yield strength, tensile strength and elongation improved by 16%, 23% and 38%, respectively. The HI had a negligible effect on the mean linear coefficient of thermal expansion (CTE) in different temperature ranges as the CTE values were nearly identical between the blocks deposited at 200 and 550 J mm⁻¹. In general, the CTE in the building direction was slightly higher than the travel direction, with a maximum difference between the CTE of the two directions being 15%. In summary, this work demonstrates the application of the cold wire GTAW process as an alternative to conventional/laser based methods for realizing the functional properties of Invar.

Laser beam shaping offers remarkable possibilities to control and optimise process stability and tailor material properties and structure in laser-based welding and additive manufacturing. However, little is known about the influence of laser beam shaping on the complex melt-pool behaviour, solidified melt-track bead profile and microstructural grain morphology in laser material processing. A simulation-based approach is utilised in the present work to study the effects of laser beam intensity profile and angle of incidence on the melt-pool behaviour in conduction-mode laser melting of stainless steel 316L plates. The present high-fidelity physics-based computational model accounts for crucial physical phenomena in laser material processing such as complex laser–matter interaction, solidification and melting, heat and fluid flow dynamics, and free-surface oscillations. Experiments were carried out using different laser beam shapes and the validity of the numerical predictions is demonstrated. The results indicate that for identical processing parameters, reshaping the laser beam leads to notable changes in the thermal and fluid flow fields in the melt pool, affecting the melt-track bead profile and solidification microstructure. The columnar-to-equiaxed transition is discussed for different laser-intensity profiles.