Super duplex stainless steels (SDSS) are widely used in marine and energy industries owing to their excellent combination of strength and corrosion resistance. However, achieving both high productivity and desirable phase balance in additively manufactured SDSS remains challenging. This work establishes an in-process thermo-mechanical pathway for microstructure engineering by integrating high-productivity cold-wire gas metal arc wire-directed energy deposition with interlayer high-pressure rolling and targeted solution treatment. The coupled deformation and thermal cycles promote recovery, partial recrystallisation and the δ→γ transformation, resulting in a refined heterogeneous duplex microstructure with improved phase balance. While the as-deposited material remains slightly ferrite-rich, solution treatment restores the ferrite–austenite balance to the industrially accepted range while preserving the deformation-refined ferrite structure. Consequently, the proposed route delivers an excellent combination of strength and ductility, achieving an ultimate tensile strength of 1020 MPa in the as-deposited condition and 880 MPa, 660 MPa yield strength and 30% elongation after solution treatment. The proposed thermo-mechanical pathway provides a practical strategy for simultaneously improving productivity, microstructure control and mechanical performance in additively manufactured SDSS.

Wire-based directed energy deposition (WDED) of Invar alloys is prone to cracking due to high thermal stresses and microstructural anisotropy. In this study, in-process machine hammer peening (MHP) was integrated into WDED to mitigate cracking and control the microstructure of Invar alloy. The as-deposited material exhibited millimetre-scale columnar grains with strong build-directional alignment and severe solidification cracking along grain boundaries, indicating a dominant role of deposition-induced thermal stresses. Interlayer MHP promoted a transition from epitaxial growth to heterogeneous nucleation, producing a refined and more equiaxed grain structure with improved tolerance to thermal straining. Deformation-related FCC texture components and an increased fraction of low-energy Σ3 coincidence site lattice boundaries were observed in the MHP-treated material, contributing to enhanced grain-boundary-mediated plasticity and cracking resistance. Mechanical characterisation further revealed increased hardness and elastic modulus achieved by interlayer MHP, together with progressive build-height-dependent strengthening. In general, in-process MHP offers an effective and cost-efficient thermo-mechanical strategy for crack mitigation and is expected to contribute to microstructure-property optimisation in additively manufactured Invar alloys.

316L austenitic stainless steel manufactured by wire-direct energy deposition (w-DED) typically exhibits coarse columnar solidification microstructures and pronounced anisotropy, which significantly limits its structural performance and engineering applicability. In this work, a cold high-pressure inter-layer rolling (HPR) strategy combined with post-deposition solution heat treatment is proposed as an effective and industrially viable thermomechanical route for microstructure and property control. Cold HPR introduces a large plastic strain at a low and well-controlled inter-pass temperature. This suppresses dynamic recovery during deposition and allows substantial stored strain energy to accumulate. As a result, the as-deposited microstructure evolves from a solidification-dominated state to a deformation-controlled state. The rolled components show pronounced deformation of the gamma-austenite and fragmentation of the delta-ferrite. This deformation is accompanied by an increased fraction of low-angle grain boundaries and a higher dislocation density, which leads to significant strengthening. Subsequent heat treatment activates extensive static recrystallisation in the rolled samples. Fine equiaxed gamma-austenite grains with high fractions of high-angle and Sigma 3 boundaries are formed, together with a strongly weakened crystallographic texture. This rolling + heat treatment synergy enables a broad and continuous mechanical property window and delivers a superior strength-ductility balance. The achieved performance surpasses most reported additively manufactured and wrought counterparts. Overall, the proposed cold HPR + heat treatment route provides a practical and flexible pathway for tailoring the performance of large-scale w-DED 316L components.

Process control and quality assurance of wire + arc additive manufacturing (WAAM) and automated welding rely heavily on in-process monitoring videos to quantify variables such as melt pool geometry, location and size of droplet transfer, arc characteristics, etc. To enable feedback control based upon this information, an automatic and robust segmentation method for monitoring of videos and images is required. However, video segmentation in WAAM and welding is challenging due to constantly fluctuating arc brightness, which varies with deposition and welding configurations. Additionally, conventional computer vision algorithms based on greyscale value and gradient lack flexibility and robustness in this scenario. Deep learning offers a promising approach to WAAM video segmentation; however, the prohibitive time and cost associated with creating a well-labelled, suitably sized dataset have hindered its widespread adoption. The emergence of large computer vision models, however, has provided new solutions. In this study a semi-automatic annotation tool for WAAM videos was developed based upon the computer vision foundation model SAM and the video object tracking model XMem. The tool can enable annotation of the video frames hundreds of times faster than traditional manual annotation methods, thus making it possible to achieve rapid quantitative analysis of WAAM and welding videos with minimal user intervention. To demonstrate the effectiveness of the tool, three cases are demonstrated: online wire position closed-loop control, droplet transfer behaviour analysis, and assembling a dataset for dedicated deep learning segmentation models. This work provides a broader perspective on how to exploit large models in WAAM and weld deposits.

This austenitising bending investigation was carried out in a vacuum environment with the forming rates of 1, 10, and 100 mm/min under a certain bending temperature of 900 °C by a thermomechanical simulator. The enhanced strength at the accelerated forming rate and on the compression/tension zones throughout the thickness of the bent plates was discussed in detail in terms of dislocation pile-up, smaller prior austenite grain size, dynamic recrystallisation, smaller martensite packet, and stress-neutral layer. Since the simulation results were validated to match the experimental trend, this investigation could be applied as a valuable reference to simulate the practical manufacturing process of railway fasteners.

Strain hardening is a crucial property of metals and alloys that directly affects their mechanical processability, safe usage, and durability throughout their service life. However, titanium alloys traditionally used in structural applications often exhibit limited strain hardening, restricting their broader use. In this work, we demonstrate that by employing additive manufacturing (AM), strong strain hardening with high strength can be simultaneously achieved in a commercially available titanium alloy. These remarkable properties arise from a martensitic microstructure originated from the AM process. The microstructure is characterized by nanosized martensite plates with extremely fine triple-twinned substructures. During tensile deformation, detwinning rather than dislocation slip gradually transforms this microstructure into single-twinned lamellae with ~10 nm twin boundary spacing and internal stacking faults, necessitating progressively higher stresses and resulting in significant strain hardening.

NiTi shape memory alloy (SMA) components fabricated via additive manufacturing exhibit broad application prospects in biomedical and aerospace fields. However, directly additively manufactured NiTi SMAs often suffer from inhomogeneous phase distribution and unstable shape memory properties. Heat treatment can effectively homogenize phase distribution and enhance the stability of shape memory performance. In this study, aging treatments at varying durations and temperatures were conducted on NiTi SMAs produced by laser-directed energy deposition (L-DED) to achieve more stable and superior mechanical performance. The effects of different heat treatment regimes on microstructure evolution, elemental/phase distribution, and shape memory behavior were systematically investigated through experimental characterization and molecular dynamics (MD) simulations. Key findings include: Compared to as manufactured samples, aging at 400 degrees C to 600 degrees C minimally influenced NiTi2distribution but universally promoted an increase in phase transformation temperatures and transformation enthalpy, meanwhile, prolonged aging durations further elevated phase transformation temperatures. Aging at 500 degrees C and 600 degrees C facilitated a reduction of high angle grain boundaries in L-DED NiTi SMAs and enhanced shape memory effects, which MD simulations attributed to diminished grain boundary resistance to phase transformation. Aging at 500 degrees C and 600 degrees C also stimulated the precipitation of Ni4Ti3 phases, enabling matrix strengthening and improved shape memory performance, with extended aging times promoting precipitate coarsening. This work provides insights into optimizing aging treatments to stabilize and enhance the properties of L-DED NiTi SMAs, thereby advancing their broader industrial adoption.

Forging additive hybrid manufacturing integrated the high efficiency of forging and the great flexibility of additive manufacturing, which has significant potential in the construction of reactor pressure vessels (RPVs). In the components, the heat-affected zone (HAZ, also called as bonding zone) between the forged substrate zone and the arc deposition zone was key to the final performance of the components. In this study, the Mn-Mo-Ni welding wire was deposited on the 16MnD5 substrate with a submerged arc heat source. The in situ reheat cycle effect of the submerged arc heat source on the microstructure and mechanical properties of the HAZ were studied. The results showed that the HAZ underwent four heat treatment processes, including two full austenitizing stages, one high-temperature stage, and continuous low-temperature tempering, which formed a homogenized microstructure in the HAZ and was mainly composed of tempered sorbite (Tempered-S). The HAZ microhardness is around 278.7 HV, which is about 150 HV lower than the microhardness only conducted by one thermal cycle. Furthermore, the effects of preheating the substrate and adjusting the heat inputs on the HAZ were studied. The results indicated that the clustered cementite was precipitated, which destroys the low-temperature impact toughness of the HAZ after preheating. A suitable heat input not only homogenized the microstructure within the HAZ but also promoted the transformation of grains into equiaxed grains. The −60 °C impact toughness of the HAZ was significantly increased from 96.7 J to 113 J.

To improve the service life of agitator blades in the phosphoric-acid reactor, the NiCoCrMo0.2 medium entropy alloy (Mo0.2 MEA) was designed by cluster-plus-glue-atom model. The microstructure and erosion resistance of Mo0.2 MEA were investigated. The Mo0.2 MEA is composed of FCC solid-solution dendrites and a few tiny μ phases. The Mo0.2 MEA possesses higher microhardness (~256.4 HV0.2) compared with the Mo-free counterpart. Moreover, the lowest Icorr value and the largest impedance radius demonstrate the MEA exhibits better corrosion resistance than that of 904L steel, primarily ascribed to a dense and stable passive film comprising MoO3 and Cr2O3. The erosion resistance of Mo0.2 MEA is twice as good as that of 904L stainless steel in account of cumulative erosion mass loss. The Stacking-fault energy of Mo0 MEA (~ -105.7 mJ/m2) is lower than that of Mo0.2 MEA (~ -85.91 mJ/m2) and 904L (~251.2 mJ/m2), which suggests that Mo0 MEA is more capable of plastic deformation than Mo0.2 MEA. The related findings provide a new paradigm for the development of laser additively manufactured anti-erosion MEA by high-entropy alloying strategy using a cluster-plus-glue-atom model.

Hybrid wire-arc directed energy deposition (WDED), in which complex features are deposited onto a forged base, offers a cost-effective solution for manufacturing geometrically complex ultra-high-strength steel components, particularly for aerospace applications. However, cracking at the base forging/build interface during post-build heat treatment limits its widespread application. This study investigates the underlying causes of interfacial cracking, highlighting microstructural inhomogeneity, elemental segregation and transformation stresses as likely key contributing factors. A modified three-step post-build heat treatment incorporating a normalisation step was developed to mitigate some of these issues. The optimised process successfully suppressed cracking by refining prior-austenite grains before the application of a conventional quenching step. This enhanced tensile performance beyond AMS6419K standards, supporting the industrial implementation of hybrid WDED in aerospace structures.

Stress relaxation is key to the ultrahigh strength valve springs but has received little attention. In this work, three 55SiCr spring steels with an identical tensile strength of 2000 MPa are prepared by tailoring the wire speed in an industrial production line. The high wire speed results in the presence of undissolved Fe3C carbides and the formation of dislocation martensite in S1 steel with fine prior austenite grains, while the low wire speed and sufficient austenitization time result in the formation of carbide-free twinned martensite in S3 steel with coarse prior austenite grain. Relaxation experiment in 373 and 473 K demonstrates that the S3 steel has the lowest stress relaxation rate among the three steels. It demonstrates that the carbide-free twin martensite has the best stress relaxation resistance due to its strong barrier against the thermal activation activities of dislocations.

In this paper, the microstructure and twinning behavior of tantalum (Ta) during dynamic plastic deformation (DPD) were jointly analyzed in combination with impact experiments and molecular dynamics simulations, with a focus on the mechanism of variant selection for twinning. The results indicated that twins nucleate at grain boundaries and gradually grows with increasing deformation until it penetrates the entire grain. Due to the difference of grain boundary dislocation density, strain rate and deformation temperature have significant impacts on the quantity and distribution of twins. In addition, at room temperature, nearly half of the twin variants in DPD samples do not conform to Schmid law, and almost all the twin variants in liquid nitrogen samples do not follow to Schmid law. The activation of these non-Schmid variants is mainly affected by the strain coordination. Through this study, we have deepened our understanding of the dynamic microstructural response of Ta under high-speed deformation conditions.

This study utilized double-wire plasma arc direct energy deposition to produce functionally graded materials (FGMs) with two transition designs, abrupt (AT) and gradual (GT), from Er90s steel to Invar. The study systematically compared the transition in chemical composition, microstructure, phase evolution, thermal stress, and mechanical performance. Both FGM types exhibited a band structure in the Er90s section and coarse columnar grains in the Invar section, with the AT deposit showing a 1mm thick, defect-free interface and the GT deposit having an 18mm thick transition region with distinct boundaries. It revealed diverse microstructures across the transition zones, including fine ferrite, martensite with minor retained austenite (RA), coarse columnar austenite with martensite dendrites, and single FCC austenite. The GT sample uniquely featured a microstructure of martensite laths inside prior austenite decorated by RA semicontinuous network, with a crack detected due to dilatational stresses from martensite transformation. Hardness was similar in both FGM types, with higher values at the interfaces, especially in the GT FGM. The GT FGM demonstrated higher strength but lower ductility compared to the AT FGM, with failure occurring in the Invar portion for both. Thermal stress modelling indicated smoother stress transitions in the GT sample but no significant performance differences between Er90s and Invar. This study showcases the effectiveness of double-wire plasma arc DED in producing steel/Invar FGMs with varying composition gradients. It also underscores the importance of selecting the right mixing ratio for Er90s/Invar FGM deposits to avoid cracking and deterioration of properties in the gradient area.

The studying employed orthogonal experimental approach to optimize the laser welding process parameters for HC420LA low-alloy high-strength steel. Through metallographic analysis, microhardness testing, and tensile testing, the study assessed and contrasted the properties of laser-welded and arc-welded joints. The findings revealed that the most optimal laser welding conditions were 1.8 kW laser power, 2.5 m min-1 welding speed, and a focus distance of 1.5 mm, resulting in a well-formed 'X' shaped weld bead. Comparative analysis demonstrated that the laser-welded joint exhibited a finer microstructure, primarily composed of bainite and ferrite, whereas the arc-welded joint consisted of ferrite and martensite. Notably, the laser-welded joint exhibited superior mechanical properties, including increased microhardness and tensile strength, underscoring the distinct advantage of laser welding technology in high-strength steel welding, particularly in enhancing the weld joint's quality and performance.

Pressureless sintering is a cost-effective method to fabricate shaped Ti-Al-Nb alloy components in the aerospace industry. However, the sintering pores in the Ti-Al-Nb alloys led to inferior mechanical properties when using elemental Al powder as the raw material. By completely replacing the Al powder with the Al-Nb master alloy powder, the pores were substantially reduced in the pressurelessly sintered Ti-22Al-17.5Nb (at %) alloy, accompanied by the improvement of the tensile strength. We investigated the densification me-chanisms by implementing the isothermal quenching experiments at 500-1200 degrees C. In the Ti/Al/Nb compact, the pores originated from the melting of Al and the Kirkendall effect at the interfaces of the Ti3Al and Nb particles. The transitions of Ti + 3Al-* TiAl3 and alpha 2-* B2 determined the porosity of the sintered alloy. In the Ti/Al-Nb/Nb compact, the Kirkendall pores at the Ti/Al3Nb interfaces were reduced since the diffusion of Al in Ti was retarded. The accelerated diffusion of Nb in Ti3Al suppressed the Kirkendall effect at the Nb/Ti3Al interfaces and promoted the formation of the B2 phase. The ripening of the B2 grains further contributed to the densification of the sintered alloy.(c) 2022 Elsevier B.V. All rights reserved.

Wire-arc directed energy deposition (DED) is suitable for depositing large-scale metallic components at high deposition rates. In order to further increase productivity and efficiency by reducing overall manufacturing time, higher deposition rates are desired. However, the conventional gas metal arc (GMA) based wire-arc DED, characterised by high energy input, normally results in high remelting and reheating at relatively high deposition rates, reducing the process efficiency and deteriorating the mechanical performance. In this study, a novel wire-arc DED process with the combination of a GMA and an external cold wire, namely cold wire-gas metal arc (CW-GMA), was proposed for achieving high deposition rate and low material remelting. The maximum deposition rates at different levels of energy input were investigated, with the highest deposition rate of 14 kg/h being achieved. An industrial-scale component weighing 280 kg was built with this process at a high deposition rate of around 10 kg/h, which demonstrated the capability of the process for high productivity application. It was also found that, due to the addition of the cold wire, the remelting was reduced significantly. The working envelope and geometric process model for the CW-GMA process was developed, which can be used to avoid defects in parameter selection and predict the geometry of single-pass wall structures. Moreover, the addition of the cold wire in the CW-GMA process reduced the specific energy density, leading to a reduction in both grain size and anisotropy, which improved the mechanical properties with increased strength and reduced anisotropy.

A functionally graded AlxCoCrFeNi high entropy alloy with a variation in Al concentration along the building direction was in-situ produced using a hybrid powder-bed wire-based direct energy deposition process. A continuous transition from a single FCC structure to a major BCC+minor FCC dual-phase structure was achieved, benefiting from the remelting and reheating process during the deposition. In the FCC→BCC transition zone, the dendritic core region is identified as an FCC matrix decorated by AlNi-rich ordered B2 precipitates. The interdendritic area shows B2 precipitating in the FeCr-rich disordered A2 matrix. Additionally, the interface between the two regions shows that the A2 phase and ordered Cr3Fe intermetallic phase precipitate at the B2 phase. The mechanical properties show a tendency for higher strength and hardening rate but lower plasticity corresponding to the areas with higher Al content. Through quantitative estimation of different strengthening mechanisms, the contribution from precipitation strengthening became increasingly apparent as Al content increased. Other strengthening modes, including solid solution and dislocations, also contribute to the total strength. This investigation realises a novel additive manufacturing method combining powder bed and wire feeding, which can produce a more convenient and cost-effective gradient material with a complex composition.

The embrittlement and softening behavior in simulated heat-affected zones (HAZ) of a newly designed dual-phase DP680 steel for wheel rim applications with different flash allowances were investigated to determine weldability, and offer valuable information for the steel design and its subsequent flash butt welding (FBW). The characterization of microstructure and mechanical performance for the simulated HAZ was conducted by means of optical microscopy, scanning electron microscopy, electron backscatter diffraction, hardness distribution, and Charpy V-notch (CVN) values at selected temperatures. The investigation demonstrates that the toughness of coarse-grained HAZ was kept at an average level of 25.3 J when the prior austenite grain size was controlled to 60.54 μ m at a flash allowance of 14 mm (equivalent to heat input of 15.14 kJ/cm based on real welding process), which exhibits the worst toughness when the flash allowance was changed from 4 to 14 mm. Further, with a higher martensite fraction (> 30 pct) in base material (BM), the softening occurs in inter-critical HAZ (ICHAZ) instead of sub-critical HAZ since most of martensite in ICHAZ has decomposed, and the rest ferrite and newly formed bainite with remaining martensite reduce the hardness to a larger extent compared to SCHAZ, whose martensite has only partly decomposed. Even if the softening degree is up to 21.6 pct compared to the BM (average 233 HV 0.5 ), the work hardening during a series of forming processes after FBW has alleviated the softening evidently (work hardening degree > 10 pct). However, the failure location is still in ICHAZ after forming extension which has been confirmed in practical applications of DP680 FBW and subsequent forming processes.

In this study, the microstructure and performance of newly designed dual-phase steel (DP590) after joining by flash butt welding (FBW) for vehicle wheel rims was analysed and compared by two simulations, i.e., physical simulation and numerical simulation, due to the high acceptance of these two methodologies. Physical simulation is regarded as a thermal–mechanical solution conducted by the Gleeble 3500 simulator and which can distribute the heat-affected zone (HAZ) of the obtained weld joint into four typical HAZs. These are coarse-grained HAZ, fine-grained HAZ, inter-critical HAZ and sub-critical HAZ. A combination of ferrite and tempered martensite leads to the softening behaviour at the sub-critical HAZ of DP590, which is verified to be the weakest area, and influences the final performance due to ~9% reduction of hardness and tensile strength. The numerical simulation, relying on finite element method (FEM) analysis, can distinguish the temperature distribution, which helps us to understand the relationship between the temperature distribution and real microstructure/performance. Based on this study, the combination of physical and numerical simulations can be used to optimise the flash butt welding parameters (flash and butt processes) from the points of temperature distribution (varied areas), microstructure and performance, which are guidelines for the investigation of flash butt welding for innovative materials.