Process Window Research Articles

Influence of Steel Recycling on Phase Transformation in Medium‐Manganese Third‐Generation Advanced High‐Strength Steels

Due to the ensuing shift toward adoption of increased levels of scrap during steel production to reduce the carbon footprint, it is essential that the effects of tramp elements entering the produced steel from the scrap are understood. In this context, effects of four major tramp elements (Ni, Cu, Cr, and Mo) on the phase transformation and the microstructure evolution of medium‐manganese steels are studied by theoretical predictions. The results indicate that Cu and Ni are beneficial, whereas Cr and Mo have mixed effects due to the formation of different equilibrium metal carbides. The Cu and Ni concentrations of 0.1–0.5 wt% marginally increase the maximum retained austenite content by 2 vol%. Cr reduces the achievable maximum amount of retained austenite more strongly (decrease by 8 vol% for 0.5 wt% Cr) than Mo (decrease by 4 vol% with 0.5 wt% Mo), and Cr gives a wider processing window for achieving a microstructure with a lower variation than Mo. Combined effects of the elements are to decrease the maximum retained austenite by 8 vol% with lowering of processing temperature by 20 °C. This work provides a guideline for the selection of the optimum processing window of medium‐manganese steels in a circular economy.

Molecular Design for Dual Circularity: Polyester with Complementary Mechanical and Chemical Recyclability under Mild Conditions.

The plastic waste accumulation requires facile yet effective solutions. Currently mechanical recycling typically leads to downcycling, while the environmental footprint of chemical recycling is often unacceptable. Here, we introduce a dual circularity concept, where rational molecular design paves the way for complementary closed-loop mechanical and chemical recyclability under mild conditions. Very small changes in macromolecular structures, thermal and mechanical properties were observed, after as many as six repeated mechanical recycling cycles, showing that a wide processing window could be the key for closing the mechanical recycling loop. Facile, time and energy efficient closed-loop chemical recycling into products with identical performance to original ones was also realized, thanks to the abundant free volume and accessible ester-functionalities. With these design criteria at hand, dual circulation in recyclability can be realized; proceeding with mechanical recycling when we can, and switching to chemical recycling when we must.

Molecular Design for Dual Circularity: Polyester with Complementary Mechanical and Chemical Recyclability under Mild Conditions

The plastic waste accumulation requires facile yet effective solutions. Currently mechanical recycling typically leads to downcycling, while the environmental footprint of chemical recycling is often unacceptable. Here, we introduce a dual circularity concept, where rational molecular design paves the way for complementary closed‐loop mechanical and chemical recyclability under mild conditions. Very small changes in macromolecular structures, thermal and mechanical properties were observed, after as many as six repeated mechanical recycling cycles, showing that a wide processing window could be the key for closing the mechanical recycling loop. Facile, time and energy efficient closed‐loop chemical recycling into products with identical performance to original ones was also realized, thanks to the abundant free volume and accessible ester‐functionalities. With these design criteria at hand, dual circulation in recyclability can be realized; proceeding with mechanical recycling when we can, and switching to chemical recycling when we must.

Microstructure evolution and dynamic recrystallization mechanism of tantalum-tungsten alloys under hot compression

Ta-W alloys exhibit outstanding comprehensive properties at high temperatures, allowing them to have great application prospects in the high-temperature field. High-temperature compression tests (1573~1873 K) were conducted to evaluate the high-temperature mechanical properties of Ta-12W alloy, and the strain-compensated Arrhenius-Type model and hot processing map were developed to predict the optimal processing window. The electron backscatter diffraction, Transmission electron microscope, and DEFORM-3D software were performed to investigate the microstructure evolution and distributions of strain. The results demonstrated that the flow stress of Ta-12W alloy presented apparent negative temperature sensitivity and positive strain rate sensitivity. Based on the thermal processing diagrams and EBSD analysis, the results show that the low deformation temperature and high strain rate introduce stress concentration and deformation instability in the Ta-12W alloy. The optimized processing temperature and strain rate are at 1800 ~1873 K/0.001 s-1~0.05 s-1, and the microstructure at 1873 K/0.001 s-1 is more uniform and exhibits a low residual stress level. As the temperature increases, dynamic recovery and dynamic recrystallization cause significant softening effects, and continuous dynamic recrystallization dominates the high-temperature deformation behavior. Moreover, multiple continuous dynamic recrystallizations occur simultaneously, including sub-grain nucleation inside large grains, sub-grain nucleation at grain boundaries, and grain fragmentation accompanied by grain rotation. This study revealed the mechanisms of microstructural evolution during hot deformation of Ta-12W alloy, providing important guidance for optimizing the thermomechanical processing parameters.

Metal transfer and forming behavior of bypass-coupled variable polarity plasma arc additive manufacturing

This study proposes a novel bypass-coupled variable-polarity plasma arc additive manufacturing process. This process enables independent control of the main current, bypass current, and their polarities, thereby achieving decoupled control of thermal input to the deposited layers and wire melting. Additionally, the variable polarity effectively removes the oxide film on the surface of aluminum alloys, improving defects in aluminum alloy additive manufacturing. The research results indicate that the bypass-coupled variable-polarity plasma arc additive manufacturing presents different metal transfer forms compared to conventional arc additive manufacturing (MIG/TIG arc heat sources). The droplet transfer behavior manifests in various forms at different wire heights, including droplet transfer, Intermittent bridging transfer, and complete bridging transfer. Notably, the complete bridging transfer results in short metal bridge, which weakens the influence of the coupled arc magnetic field and provides a wider process window for shaping. A detailed analysis of the effects of main and bypass EN/EP currents on the formation morphology reveals that the influence of the main EN current on the width of the deposited layer is twice that of the bypass EN current. By adjusting the main EN current, the remelting depth can be effectively controlled, allowing for precise control over the morphology of the deposited layers. This study demonstrates the potential of this process to enhance deposition efficiency, reduce thermal input, and achieve effective shaping control.

In-Volume Glass Modification Using a Femtosecond Laser: Comparison Between Repetitive Single-Pulse, MHz Burst, and GHz Burst Regimes.

In this study, we report, for the first time, to the best of our knowledge, on in-volume glass modifications produced by GHz bursts of femtosecond pulses. We compare three distinct methods of energy deposition in glass, i.e., the single-pulse, MHz burst, and GHz burst regimes, and evaluate the resulting modifications. Specifically, we investigate in-volume modifications produced by each regime under varying parameters such as the pulse/burst energy, the scanning velocity, and the number of pulses in the burst, with the aim of establishing welding process windows for both sodalime and fused silica.

Research on the Weldability and Service Performance of 7075 Aluminum Alloy Welding Wire Prepared by Spray Forming–Extrusion–Drawing

A large number of MIG welding tests were carried out on a 3 mm thick 7075 aluminum alloy plate prepared by the self-developed jet forming–extrusion–drawing process of 7075 high-strength aluminum alloy welding wire, and the welding process of the welding wire and the change in the performance of the welded joint after T6 heat treatment were studied. The results show that the self-developed wire has a good forming joint and a wide welding process window: the welding speed is 5–7 mm/s, and the welding current is 100–150 A. The main precipitated phases in the joint were η(MgZn2), S(CuMgAl2), Mg2Si, and Al13Fe4, which were continuously distributed at the grain boundaries in the form of coarse networks or long strips, which was an important reason for the weak performance of the joints. After the heat treatment of T6, the precipitated phase in the joint was greatly reduced, the element segregation phenomenon was improved, and the residual precipitated phase was mainly Al13Fe4 and a small amount of insoluble phase Fe and Si, and the recrystallization size of the heat-affected zone was refined. Through heat treatment, the average microhardness of the joint was increased from 110 HV to 150.24 HV, and the tensile strength was increased from 326 MPa to 536 MPa, reaching 97.5% of the strength of the base metal, indicating that the softening phenomenon was significantly improved after heat treatment, and the joint had excellent performance.

Dual Interfacial Design Enables Efficient and Stable Semitransparent Wide‐Bandgap Perovskite Solar Cells With Scalable‐Coated Silver Nanowire Contact for Tandem Applications

ABSTRACTSemitransparent perovskite solar cells (PSCs) hold great potential for applications in aesthetic building facades and top‐illuminated tandem devices. Indium tin oxide is currently the frequently used top transparent contact, which would degrade the underlying perovskites during sputter process. Here, we report low‐temperature, scalable solution‐processed silver nanowires (AgNWs) as top window electrodes for fabricating efficient and stable semitransparent PSCs. As a decisive step, an impermeable SnO2 thin film deposited by atomic layer deposition (ALD) is applied to prevent chemical reactions between AgNWs and halides of perovskites. In parallel, the molecular absorption of propylenediamine iodine (PDADI) on perovskite surface, instead of forming two‐dimensional (2D) perovskite capping layer, is found to effectively passivate the perovskite surface, which simultaneously leads to remarkably enhanced thermal stability, thus affording the processing window for ALD‐SnO2 deposition. Eventually, the prepared semitransparent PSCs with a bandgap of 1.71 eV achieve a champion efficiency of 17.5%, being the highest efficiency for semitransparent PSCs with AgNWs top contacts. On these bases, we constructed a four‐terminal perovskite/copper indium gallium diselenide (CIGS) tandem cell, giving a state‐of‐the‐art efficiency of 26.85%.

New constitutive model and hot processing map for A100 steel based on high-temperature flow behavior

To predict the flow behavior and identify the optimal hot processing window for A100 steel, a constitutive model and a hot processing map were established using true stress-strain data extracted from isothermal compression tests performed at temperatures ranging from 1073 to 1353 K and strain rates varying between 0.01 and 10 s−1. The results indicate a strong linear trend between the logarithmic stress and the reciprocal of temperature, along with a significant quadratic relationship between the logarithmic stress and logarithmic strain rate. With a correlation coefficient of 0.9913, the new constitutive model demonstrates an excellent predictive capability for the flow behavior of A100 steel. A significant dynamic recrystallization occurs when the energy dissipation rate exceeds 25 %, resulting in a uniform equiaxed grain structure after deformation. The unstable regions primarily occur in high strain rate and low-temperature zones, where the microstructures are typically coarse and elongated. This structural characteristic adversely affects the mechanical properties. Avoiding these conditions during hot forming of A100 steel is crucial. The optimal hot forming windows for A100 steel are achieved within a temperature range of 1153–1353K and a strain rate range of 0.01–10 s−1, where complete dynamic recrystallization occurs.

Optimized battery electrodes with primer layers by simultaneous two-layer slot-die coating

AbstractMulti-layer coating is a promising method for optimizing the properties of battery electrodes. This study examines the simultaneous coating of anodes with a primer layer without the necessity of a second coating and drying step, as it is the case for sequential coating processes. The primer layer is used to concentrate the binder in proximity to the substrate, thereby enhancing the adhesion strength of the electrode. Two systems comprising anode and primer, differing in rheological properties, are selected for coating investigation. It is demonstrated that the viscosity ratio of the multi-layer coating has a pronounced effect on coating suitability. In a two-layer system, the viscosity ratio also changes with shear rate due to the possibly different shear thinning properties. This results in the observation that combinations with strong viscosity ratios might only be stable in specific coating speed ranges. In contrast, combinations with moderate viscosity ratios exhibit a reduction in stable process windows as the viscosity ratio between the top and bottom layer increases. A mechanical characterization of the adhesion strength of dried and calendered electrodes demonstrated a notable enhancement in adhesion strength when a primer was utilized. In addition, capacity retention tests revealed that the electrochemical properties were not adversely affected by the primer.

(Invited) Low Energy Methods for Highly Selective Etching and Surface Treatment of Advanced Nanodevices

In the pursuit of higher performance semiconductors, device length scales continue to shrink down to nanometer dimensions with emerging chip designs increasingly dependent on 3D structures to maintain scaling. Memory manufacturers have already deployed 3D NAND devices with ongoing development for 3D DRAM devices. Advanced logic manufacturers have already deployed 3D FinFET devices and are beginning to deploy more complex GAA (Gate-All-Around) 3D devices as well. Building 3D structures has increased the need for more sophisticated selective etching. As these selective etches have become critical to the formation of the device, atomic precision material loss is required with low contrast materials. We review several materials systems where insufficient selectivity control in plasma-based radical etch necessitates innovative approaches such as atomic layer passivation, low energy metastable activated radicals and plasma-less low energy thermal chemical etching.Dummy polysilicon removal requires full removal of the polysilicon with minimal film loss to dielectric films such as silicon oxide and silicon nitride. While polysilicon can be removed by either wet etch or dry etch, each approach has certain limitations that narrow the overall process window. Wet etch chemistries such as TMAH (tetramethyl ammonium hydroxide) anisotropically etch polysilicon preferentially along crystalline planes which can result in silicon residues at the bottom corners of trenches. Highly isotropic dry etch radical chemistries minimize silicon residues but have greater tendency to damage the underlying epitaxial silicon layer due to either excessive film loss or halogen radical penetration through the encapsulating film. We show that the introduction of atomic layer passivation modifies the top monolayer of an oxide encapsulation layer and consequently widens the epi damage-free window.Selective mask removal requires full removal of the organic mask with high selectivity to exposed epitaxial silicon surfaces. While plasma-generated radicals have been effectively used for some time, it has become increasingly difficult for both advanced FinFET and GAA devices as the epi film loss requirements lower to a single atomic layer. We propose the tail energy distribution of reactive species formed in the plasma region is the driving factor for epitaxial film loss. To reduce these effects, we apply MARS (Metastable Activated Radical Source) technology where reactive species are indirectly formed outside the plasma region though collisions with metastable intermediates. The result is a significant reduction in higher energy species flux to the surface corresponding to a lower epi loss than conventional radical approaches.GAA device integration relies on depositing and subsequently removing SiGe layers to form Si-nanowires or nanosheets. Fluorine radical-based chemistries have limited selectivity to silicon because the bond strength difference between Si-Si and Si-Ge is exceedingly narrow and about 0.3 eV. We show a thermal chemical etching approach that achieves substantially higher SiGe:Si selectivity than radical etching on both blanket films and test structures. In addition, we highlight the strict film loss requirements that require highly selective native oxide removal prior to removing SiGe layers. We describe a thermal chemical etching approach that applies wet etch mechanisms in a vacuum environment to achieve high selectivity to both silicon and silicon nitride.

Ultrasonic reconsolidation of separated CF-PEEK composite layers at 20 kHz — An experimental study on parameter optimization and Ex-situ characterization

Ultrasonic-assisted joining can replace the current repair strategies, such as adhesive bonding, to join the repair patches onto the damaged aerospace composite structures due to their energy and time efficiency. This work reports on the process optimization of repairing separated carbon fiber reinforced (CF)/ poly-ether-ether-ketone (PEEK) layers through ultrasonic reconsolidation at 20 kHz and its influence on the mechanical performance. The results showed that weld force and weld time dominate the temperature evolution, which was used to set the ultrasonic process window. Repairing CF-PEEK layers to different laminate architecture exhibited a 15% deviation from the reference repair. Compared with quantitative results, the ex-situ investigation showed that excessive holding force caused fiber–matrix debonding, leading to a cohesive failure inside the composite laminate. An optimal holding force, approximately 25% of the used weld force, is recommended to alleviate these damages.

Effects of Ge and B Concentration in Selective Epitaxial Growth of Si1-XGex(:B) at Low-Temperature

As two-dimensional devices approach their scaling limits, monolithic complementary field-effect transistors have emerged to meet the demands of advanced transistors. A low thermal budget process is essential to prevent damage to the underlying layers while forming upper layers. Therefore, a low-temperature approach for the selective epitaxial growth (SEG) of SiGe(:B) in source-drain formation is necessary. The cyclic deposition and etch method was employed for its high selectivity, highlighting the need for further research into the incubation characteristics of B-doped SiGe. [1] We investigated the incubation behavior of SiGe(:B) on SiO2 under varying Ge and B concentrations in an ultra-high vacuum-chemical vapor deposition (UHV-CVD) chamber. In this study, we investigated the influence of the Ge and B concentrations on the incubation time for SiGe(:B) on SiO2, comparing it with the epitaxial growth on Si(100) and Si(111). First, we analyzed the incubation properties of undoped Si1-xGex (0 < x < 0.4) layers. We then explored the effect of B concentration by varying the B flow rate. Our findings indicate the higher Ge concentrations extend the incubation time, independent of the total gas flow rate. In contrast, B doping reduces the incubation time compared to with that of undoped SiGe, and increasing B concentration further shortens the incubation time. Atomic force microscopy and scanning electron microscopy were used to examine amorphous formation on SiO2. In addition, high-resolution X-ray diffractometry and ellipsometry were used to analyze Ge and B concentrations, as well as growth thickness. Our study offers comprehensive insights into the low- temperature SEG process window for SiGe(:B). Acknowledgment This work was supported by the Technology Innovation Programs (RS-2023-00235609) funded by the Ministry of Trade, Industry & Energy (MOTIE, Korea).

Anomalous Electrodeposition of Palladium – Antimony Alloys

Electrodeposition of Pd-Sb alloy was studied in tartrate – ammoniacal electrolytes. Unlike any other known binary plating system, the resulting alloy was typically obtained with anomalously constant composition of about 30 wt.% antimony in a large process window. Factors like concentrations of Pd and Sb in solution, current density, temperature and agitation only slightly affected the Sb content in the deposit.The alloy exhibits several practical properties. As plated, it has a nanocrystalline structure and a moderate compressive stress of about 13 ksi (90 MPa). It is harder than pure palladium with typical Vickers microhardness of 550-650 HV10 and has good wear durability and corrosion resistance.The plating process produces unexpectedly uniform composition and properties on the substrates with the most intricate shapes. Meanwhile, plating thickness tracks with local current density fluctuations we expect on a complex shaped part.Cyclic voltammetry provides some insight into the unusual co-deposition of palladium and antimony. Additional data on the structure of the electrolyte and the deposit are presented.Figure 1. A part coated with Pd-Sb alloy. The Sb content (wt.%) is uniform around the surface of the part. Figure 1

Optimization of Copper Electrodeposition in High Aspect Ratio through Silicon Vias

Copper-filled through silicon vias (TSVs) are a key technology for 3D integration of microelectronic devices. 3D integration enables system miniaturization, increases bandwidth per volume, and improves device performance. In general, TSV copper filling processes are designed to be used with thinned wafers (<200 um), but some TSV last and microelectromechanical systems (MEMS) require full wafer thicknesses, where additional mass of the full wafer is advantageous. For high-power devices, large scale vias or via arrays can be used both to supply power and for thermal management. Copper (Cu) is a preferred material for TSV filling because of its high electrical and thermal conductivity and can be deposited through electrochemical deposition (ECD) to fill high aspect ratio features. Although Cu ECD has been historically performed using three additive systems, recent work has demonstrated that Cu deposition can be achieved in a simplified CuSO4-H2SO4 electrolyte with only a single suppressor additive and halide salt.1,2 The cyclic voltammetry (CV) scan for this electrolyte exhibits s-shaped negative differential resistance (S-NDR), observed as hysteresis in the CV voltage-current relationship between forward and reverse scans. Hysteretic voltammetry indicated bifurcating behavior in the electrolyte system, where bottom-up filling is possible in the vias, while the field surface remains passivated. In systems with limited suppression, performing ECD with a sustained potential leads to localized Cu deposition at specific depths within the vias. An increasingly negative potential waveform can be implemented to progressively move deposition vertically through the vias. Typically, a bottom-up, void-free fill is achieved with this additive-based electrolyte through a potentiostatic plating process with a reference electrode. Voltage-controlled ECD parameters have been developed through the S-NDR mechanism for bottom up filling of high aspect ratio vias, where potential stepping was performed from -500 mV (MSE) to -560 mV (MSE) in -10 mV increments, and each potential was held for 2 to 5 hours to ensure a void-free fill.3 Currently this is a time consuming procedure, with a 17 hour plating process excluding sample preparation.This work shows an optimization method for filling high aspect ratio through silicon vias (TSVs) that provides insights into the fluid replenishment as well as the diffusion and suppression kinetics for this superfilling electroplating chemistry. Both experimental results and computational predictions are shown to better understand the effects of applied plating potentials and the fluid mechanics of this plating process. Understanding the chemical transport of cupric ions and additives is important to both the adsorbed suppression layer formation and disruption within the feature. The S-NDR suppression/fill mechanism is sensitive to the via geometry, ion replenishment, as well as the overpotential during the electroplating process. We demonstrate a time-dependent process window where early on too high of an overpotential results in suppressor breakdown and too low of an overpotential results in complete suppression of the deposition process. Figure 1(a) shows that by controlling the voltage between -520 mV (MSE) and -560 mV (MSE), we were able to demonstrate complete fill of the TSVs in 30% of the time previously required for filling. We also hypothesize that there is a maximum void-free fill rate for suppressor only chemistries. To understand the dependence on solution replenishment and applied bias in a given electrolyte, a series of investigations were performed on samples rotated at different rates as shown in Figure 1(b). This investigation was also shown computationally to optimize void-free, bottom-up plating when changing to different via geometry and array densities. Understanding the filling kinetics and fluid dynamics provides a throughput target for microelectronic devices. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525. SAND (1) Josell, D.; Moffat, T. P. Superconformal Copper Deposition in Through Silicon Vias by Suppression-Breakdown. J. Electrochem. Soc. 2018, 165 (2), D23–D30. https://doi.org/10.1149/2.0061802jes.(2) Menk, L. A.; Josell, D.; Moffat, T. P.; Baca, E.; Blain, M. G.; Smith, A.; Dominguez, J.; McClain, J.; Yeh, P. D.; Hollowell, A. E. Bottom-Up Copper Filling of Large Scale Through Silicon Vias for MEMS Technology. J. Electrochem. Soc. 2019, 166 (1), D3066–D3071. https://doi.org/10.1149/2.0091901jes.(3) Schmitt, R. P.; Menk, L. A.; Baca, E.; Bower, J. E.; Romero, J. A.; Jordan, M. B.; Jackson, N.; Hollowell, A. E. Void-Free Copper Electrodeposition in High Aspect Ratio, Full Wafer Thickness Through-Silicon Vias with Endpoint Detection. J. Electrochem. Soc. 2021, 167 (16), 162517. Figure 1

The time course of syllable frequency effects in the visual recognition of Korean morphologically complex nouns: an ERP study

IntroductionThe syllable frequency effect refers to that during the lexical decision task, words beginning with high-frequency syllables elicit slower responses than words beginning with low-frequency ones, indicating an inhibitory effect. However, previous studies in Korean have yielded mixed results. For morphologically simple words, an inhibitory or null effect has been observed, whereas in morphologically complex words, a facilitative effect has been reported. Unfortunately, the explanations for these mixed findings remain unclear. This study employed both behavioral and electrophysiological methods to investigate the temporal dynamics of the facilitative syllable frequency effect in Korean morphologically complex nouns. A secondary aim was to explore whether syllable frequency is modulated by stem length as a factor in morphological processing, at both the behavioral and neurophysiological levels.MethodsTwenty-eight participants (mean age = 25.14, 9 female) performed a lexical decision task, responding whether visually presented stimuli were valid Korean words, while EEG data were recorded. The experimental condition included syllable frequency (2: High vs. low) and stem length (2: Long vs. Short).ResultsThe behavioral data showed that lexical decision latencies were faster for morphologically complex nouns with higher syllable frequencies compared to those with lower frequencies. The ERP data revealed a significant syllable frequency effect on the P300 component, reflecting early visual word processing. However, no significant effect was found in the N400 component. Although stem length did not significantly influence behavioral results, it did show significant differences in N250 amplitudes. Notably, an interaction between syllable frequency and stem length had a significant effect on N400, in contrast to the behavioral findings.DiscussionsThe findings suggest that, in the processing of morphologically complex words in Korean, syllable frequency serves as partial information that facilitates lexical decisions through the fast-guess mechanism, as proposed by the MROM-S model. Furthermore, the delayed time window for syllable processing may stemmed from a different stage of the processing between morphologically complex words and morphologically simple words. Lastly, stem length, as a form of morphological processing, may interact with syllable frequency during the lexical access stage.

Precise modulation of the debonding behaviours of ultra-thin wafers by laser-induced hot stamping effect and thermoelastic stress wave for advanced packaging of chips

Abstract Laser debonding technology has been widely used in advanced chip packaging, such as fan-out integration, 2.5D/3D ICs, and MEMS devices. Typically, laser debonding of bonded pairs (R/R separation) is typically achieved by completely removing the material from the ablation region within the release material layer at high energy densities. However, this R/R separation method often results in a significant amount of release material and carbonized debris remaining on the surface of the device wafer, severely reducing product yields and cleaning efficiency for ultra-thin device wafers. Here, we proposed an interfacial separation strategy based on laser-induced hot stamping effect and thermoelastic stress wave, which enables stress-free separation of wafer bonding pairs at the interface of the release layer and the adhesive layer (R/A separation). By comprehensively analyzing the micro-morphology and material composition of the release material, we elucidated the laser debonding behavior of bonded pairs under different separation modes. Additionally, we calculated the ablation threshold of the release material in the case of wafer bonding and established the processing window for different separation methods. This work offers a fresh perspective on the development and application of laser debonding technology. The proposed R/A interface separation method is versatile, controllable, and highly reliable, and does not leave release materials and carbonized debris on device wafers, demonstrating strong industrial adaptability, which greatly facilitates the application and development of advanced packaging for ultra-thin chips.

Atmosphere Effects in Laser Powder Bed Fusion: A Review.

The use of components fabricated by laser powder bed fusion (LPBF) requires the development of processing parameters that can produce high-quality material. Manipulating the most commonly identified critical build parameters (e.g., laser power, laser scan speed, and layer thickness) on LPBF equipment can generate acceptable parts for established materials and moderately intricate part geometries. The need to fabricate increasingly complex parts from unique materials drives the limited research into LPBF process control using underutilized parameters, such as atmosphere composition and pressure. As presented in this review, manipulating atmosphere composition and pressure in laser beam welding has been shown to expand processing windows and produce higher-quality welds. The similarities between laser beam welding and laser-based AM processes suggest that this atmosphere control research could be effectively adapted for LPBF, an area that has not been widely explored. Tailoring this research for LPBF has significant potential to reveal novel processing regimes. This review presents the current state of the art in atmosphere research for laser beam welding and LPBF, with a focus on studies exploring cover gas composition and pressure, and concludes with an outlook on future LPBF atmosphere control systems.

Effect of Processing Parameters on Recrystallization During Hot Isostatic Pressing of Stellite-6 Fabricated Using Laser Powder Bed Fusion Technique.

Crack-free Stellite-6 alloy was fabricated using the laser powder bed fusion technique equipped with a heating module as the first attempt. Single tracks were printed with a build plate heated to 400 °C to identify the processing window. Based on the melt pool dimensions, two combinations (sample A: 300 W/750 mm/s and sample B: 275 W/1000 mm/s) were identified to print the cubes. The as-printed microstructure comprised FCC-Co dendrites with M7C3 in the interdendritic region. W-rich M6C particles were found in the overlapping regions between the melt pools, matching the Scheil simulations. However, gas pores were observed due to the higher nitrogen and oxygen content of the feedstock requiring hot isostatic pressing (HIP) at 1250 °C and 150 MPa for 2 h. Sample A was partially recrystallized with slightly coarsened M7C3, while sample B underwent complete recrystallization followed by grain growth along with higher coarsening of the M7C3 after HIP. The varying recrystallization behavior can be attributed to the difference in residual stresses and grain aspect ratio in the as-built condition dictated by laser power and scanning speed. The microhardness after HIP was slightly higher than its wrought counterpart, indicating no severe impact of post-processing on the properties of Stellite-6 alloy.

Additive manufacturing Cr-Mo-Si-V steel: Systematic parameter assessments, precipitation behavior of in-situ VC-M23C6 and strengthening mechanisms

To obtain the H13 steel with defect-structure-performance compatibility fabricated by laser powder bed fusion (LPBF), a systematic optimisation framework was employed to get optimal process window in this paper. Subsequently, the microstructural evolutions, nanoprecipitation behaviors and strengthening mechanisms of H13 steels built at recommended parameters were in-depth analyzed. The evolutions of submicron sized cellular and columnar dendritic crystal were explained as well as the phase transformation process including lath martensite with a twin substructure and the carbon-rich residual austenite (RA) films were revealed. Two nano carbides, MC (rich in V and Mo) as well as M23C6 (rich in Cr and Mn), with diameters of 10–40 nm, were precipitated due to the intrinsic heat treatment (IHT) in LPBF process. Cr23C6 particles preferentially nucleated at the grain and subgrain boundaries due to the presence of crystalline defects such as dislocations and stacking faults caused by lattice distortion. It then grew by alloying elemental depletion while remaining semi-coherency with the α-Fe matrix. VC particles nucleated in situ within M23C6 as V atoms accumulated and replaced M atoms in the M23C6 lattice. With the growth of VC nuclei, the strain energy caused by local lattice misfit increased. This was offset by the development of self-accommodating twins featuring a long-period stacking order substructure within the VC particles. Eventually, spheroidal VC with twin structure were embedded in or adjacent to M23C6 carbides, and the orientation relationships for VC/M23C6 and VC/α-Fe were revealed. The as-built H13 steel exhibited excellent hardness and strength compared to wrought H13 steel, which was mainly attributed to dislocation strengthening and grain boundary strengthening, with precipitation strengthening playing a secondary role due to the low amount of nanoprecipitates. The low elongation (El) at fracture was closely related to the instability of RA films as well as the residual stress.