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Dissimilar metal welds (DMWs) made between ferritic steels and austenitic alloys are used extensively in high-temperature power plant components. These DMWs experience premature creep failure in the ferritic steel’s heat affected zone (HAZ), close to the weld interface. Steep variations in microstructure and chemical composition across the dissimilar weld interface have been the contributing factors for the failure. Graded transition joints (GTJs), developed by functionally grading the chemical composition in layers, have been proposed as potential candidates to replace DMWs. In this research, GTJ coupons were fabricated between 2.25Cr-1Mo steel and Alloy 800H base material using two filler materials: (i) Inconel 82 and (ii) P87. These samples were aged at 600°C for 2000h to accelerate high-temperature microstructural evolution seen in service conditions, before subjecting them to short-term (~1 month) creep tests. Surface strains were measured using digital image correlation (DIC) technique to extract creep strain rates at different locations within GTJs. Both the GTJs exhibited heterogeneous creep strain distribution. Creep strain accumulated in the FGHAZ of 2.25Cr-1Mo steel, similar to type IV failure associated with Cr-Mo steel weldments. Microstructure based creep model framework was developed to describe the discrete creep strain rates observed in various 2.25Cr-1Mo steel regions of GTJs.

ABSTRACTDriven by the interest to weld steel and aluminium in the solid state to prevent intermetallic formation, 9 kW ultrasonic additive manufacturing (UAM) has been used to fabricate Al 6061-4130 steel dissimilar metal builds. In addition, Al 6061-Al-6061 builds were fabricated using similar techniques to provide a baseline for mechanical property measurement. Mechanical testing performed using pushpin testing shows that steel–aluminium dissimilar metal welds fail across multiple layers while Al–Al welds delaminate from the substrate. Multi-scale characterisation indicates that the change in failure morphology is due to the formation of metallurgical bonds in the Al–steel builds. Texture analysis shows identical textures at the interface of Al–steel, Al–Al and Al–Ti joints; showing that the bond formation in all cases relies extensively on plastic deformation across multiple materials. In addition, no changes to the bonding mechanism occurred when the materials used as foils and substrate were swapped.

Driven by the interest to weld steel and aluminium in the solid state to prevent intermetallic formation, 9 kW ultrasonic additive manufacturing (UAM) has been used to fabricate Al 6061-4130 steel dissimilar metal builds. In addition, Al 6061-Al-6061 builds were fabricated using similar techniques to provide a baseline for mechanical property measurement. Mechanical testing performed using pushpin testing shows that steel–aluminium dissimilar metal welds fail across multiple layers while Al–Al welds delaminate from the substrate. Multi-scale characterisation indicates that the change in failure morphology is due to the formation of metallurgical bonds in the Al–steel builds. Texture analysis shows identical textures at the interface of Al–steel, Al–Al and Al–Ti joints; showing that the bond formation in all cases relies extensively on plastic deformation across multiple materials. In addition, no changes to the bonding mechanism occurred when the materials used as foils and substrate were swapped.

Complex geometries and topology optimisations for weight and materials savings are leading drivers for the additive manufacturing of Ni-based superalloys through electron beam powder bed fusion (PBF-EB). However, there is a marked departure in these geometrically complex components with respect to the thermal signatures understood in commonly studied prismatic PBF-EB test coupons. This often results in unaccounted site-specific microstructure-property variations in complex PBF-EB builds. Here, the effects of topological changes, such as intentionally engineered internal voids, on the mechanical performance of an as-fabricated Haynes 282 monolith is revealed. The internal voids serve as representative physical models for changing thermal boundary conditions with build height. Complementary local nanoindentations, multi-scale microscopy, and residual stress measurements were used to understand the mechanisms behind geometry-structure-property relationships. The results highlight the effectiveness and influence of changing thermal conditions on the local mechanical property response of PBF-EB Haynes 282.

Magnitude and distribution of residual stresses in additively manufactured Ni-based superalloys may impact the mechanical performance of as-fabricated parts. Though electron beam powder bed fusion (E-PBF) can produce components with minimal defects and residual stresses compared to laser powder bed fusion and directed energy deposition, variations of them may occur within the complex geometry of a component, due to inherent variations of thermal signatures and the evolution of section modulus along the build direction. This work reveals the residual stress distribution, characterised from neutron diffraction, of an as-fabricated Haynes 282 monolith containing internal cube voids and thin wall struts of varying thicknesses. Complementary local hardness measurements and multi-scale microscopy were used to investigate the geometry-structure-property relationships. Observed variations in hardness were attributed to a combination of type I macro-scale residual stresses and variations in bimodal γ′ precipitation behaviour. The results highlight the influence of residual stresses and microstructure on the mechanical properties of E-PBF Haynes 282.

In this overview paper, the possibility of qualifying welded components by integrating software and hardware tools that are capable of describing physical processes that occur during welding is explored. The existing and emerging tools to define geometrical boundary conditions, process parameters, heat and mass transfer, solidification, solid-state transformation, plastic deformation, distortion, residual stress, and performance of welded components are reviewed. Existing challenges relevant to the fundamental understanding of complex alloying, processing environment, and transients in energy deposition are discussed with reference to microstructure evolution. Approaches to address these challenges were articulated with published case studies relevant to welding and additive manufacturing. [ABSTRACT FROM AUTHOR]

Electron beam powder bed fusion (E-PBF) can produce nickel-based superalloy components with minimal cracking and post-processing. This is due to the reduced thermal gradients and high print temperatures accessible through innovative beam scanning strategies compared to other AM processes. However, variations in thermal signature along the build direction inherent in alloys printed using E-PBF can drive significant changes in the microstructure and associated mechanical properties. In this work, through complementary local property measurements we observed a 127 – 145% increase in mean elastic modulus and 7–9% increase in mean hardness, as a function of build height, of an as-fabricated non-weldable Ni-based superalloy, Inconel 738. These properties were attributed primarily to variations in the γ′ character with build height, revealed through a multi-scale microstructural characterisation. The results highlight the influence of the thermal signatures on the microstructural-property relationships of E-PBF Inconel 738.

The article focuses on the use of advanced materials for wide range of applications integrated with computational weld mechanics (CWM) standards. It states that CWM minimizes welding distortion in heavy-section joint and to minimize fabrication costs through multiple gas metal arc welding. In addition, CWM reduces welding-induced distortion in an electron beam welded gear for higher flexibility in the weld and generated by heat sources and single electron beam.