Alloy Surface Structure Research Articles

Lightweight design of lattice structure of boron steel prepared by selective laser melting

Three-cycle minimum surface structures show excellent lightweight and energy absorption capabilities, and additive manufacturing techniques provide a unique degree of freedom for lattice structure design. Therefore, in this study, three-period minimum surface (TPMS) structures of Schwarz-P boron steel alloys were prepared by Selective Laser Melting (SLM) technique. By investigating the effect of lattice structure design, we have analyzed the deformation behavior, mechanical properties and energy absorption capacity under compression. In addition, tensile properties and fracture morphology were analyzed to gain insight into the performance characteristics of these structures, and the effect of structural design on hardness was explored. The results of the study show that the structural design has a small effect on the microstructure and hardness. Under compressive loading, the P (0.5 1) structure exhibits a uniform deformation behavior, while the other four structures show a crushing deformation pattern. In particular, the P (0.5 1) structure exhibits excellent compressive performance, with an energy absorption work per unit mass as high as 296.2 J/mm^3, and its stiffness reaches 1627 MPa. Meanwhile, the P (0.35 1) structure exhibits excellent tensile performance with the tensile strength of 687 MPa. The morphological analysis of the tensile fracture reveals that the fracture mainly occurs in the strut nodes, and it mainly exhibits ductile tensile fracture.

Pt nanodendrites with a PtIr alloy surface structure exhibit excellent stability toward acidic hydrogen evolution reaction

Pt nanodendrites with a PtIr alloy surface structure exhibit excellent stability toward acidic hydrogen evolution reaction

Optimal Interfacial Model between the Alloy Surface and Electrolyte Solvation Structure for a Stable Lithium Metal Electrode

Long-term mitigation of dendrite growth is the major barrier to building practical Li metal batteries (LMBs). This issue is efficaciously addressed herein, by an advanced alloy surface with optimized interfacial kinetics regulated by the electrolyte solvation structure. By dipping brass skeleton in Ag+-containing solution, the reinforced displacement reaction driven by the large potential gap between Ag+ and Zn can promote the fast formation of a continuous alloy framework with both high lateral and longitudinal Li+ diffusivities for dendrite-free Li deposition. In addition to the displacement-reaction-reinforced alloy surface, this work deciphers exclusively the synergism between the alloy surface and the electrolyte solvation structure, where the strongly coordinated high-concentration electrolyte is revealed as the most suitable model to retain the functionality of the alloy surface. In contrast, both the low-concentration and localized high-concentration electrolytes deteriorate the functionality of the alloy surface by free or diluent-bound solvent molecules, resulting in impeding side products that reduce the active alloying areas. Based on the optimal alloy/solvation structure interfacial model, the high-rate ability and long-cycling performances of the LMBs with a practical capacity of ∼2.5 mAh cm–2 are demonstrated. This strategy is also proved effective for other metal electrodes such as zinc.

Achieving a Strong Friction‐Lap Joint of Continuous Carbon‐Fiber‐Reinforced Plastic/Aluminum Alloy via a Surface Laser‐Processing Pretreatment

It is difficult to achieve high‐strength joints of metals to carbon‐fiber‐reinforced plastics (CFRPs) with high contents of continuous fibers with the poor fluidity. Herein, a special designed laser‐processing pretreatment is conducted on the surface of 5052Al, and friction‐lap joining (FLJ) is employed to join pretreated 5052Al to the CFRP with 50%–55% fiber content. The maximal tensile shear force and strength reach 4.06 kN and 18.04 MPa, respectively, with an increment of 72% compared to the untreated sample. It is the first time to achieve the high‐strength joint of Al alloys to CFRPs with high contents of continuous fibers via FLJ. The joining area and adhesion work are quantified by theoretical calculations, and the residual stresses are visualized by finite‐element analysis. The laser‐processing pretreatment changes the plain Al alloy surface structure into the rough and porous structure, largely increasing the mechanical interlocking effect of the joint, and also changes the Al alloy surface wetting behavior and increases the adhesion work from 59.66 to 81.17 mN m−1. That largely changes the chemical reaction feature between the CFRP and Al alloy, resulting in their tight bonding. In addition, the residual stresses weaken, which further improve the tight bonding effect.

Oxidic structures on copper-gold alloy nanofacets

Bimetallic alloy catalysts often display superior performance to their monometallic counterparts in numerous chemical reactions, whose reactivity and selectivity primarily depend on their surface structures and chemical compositions under reaction environments. Predicting the structure and composition of alloy surfaces under reaction conditions is still challenging. In this work, using density-functional theory with ab initio thermodynamics, we examine the surface structures of the Cu-Au alloy system under different preparation and oxidative environments. We analyze the stability of thin copper oxide layers on various substrates, ranging from clean Au(111) to Au3Cu and their mixtures, and Cu overlayer structures. Our results show that the stability of the oxide layer structures strongly depend on the atomic configurations of the substrate. We also explore the possibility of using computational surface characterization methods to capture the atomic configurations and electronic structure of different interfacial regions of these substrates. Our electronic structure analysis demonstrates that controlling the concentration of surface Cu allows one to fine tune the surface electronic structure, and modulating the growth conditions to express the desired surface oxide phase may achieve the same effect. By providing an atomic-scale account, this study aims to capture the atomic configurations and electronic structure of different interfacial regions of these complex oxidic Cu/Au nanoalloys for selective oxidation reactions.

Unveiling the Local Structure and Electronic Properties of PdBi Surface Alloy for Selective Hydrogenation of Propyne.

Building a reliable relationship between the electronic structure of alloyed metallic catalysts and catalytic performance is important but remains challenging due to the interference from many entangled factors. Herein, a PdBi surface alloy structural model, by tuning the deposition rate of Bi atoms relative to the atomic interdiffusion rate at the interface, realizes a continuous modulation of the electronic structure of Pd. Using advanced X-ray characterization techniques, we provide a precise depiction of the electronic structure of the PdBi surface alloy. As a result, the PdBi catalysts show enhanced propene selectivity compared with the pure Pd catalyst in the selective hydrogenation of propyne. The prevented formation of saturated β-hydrides in the subsurface layers and weakened propene adsorption on the surface contribute to the high selectivity. Our work provides in-depth understanding of the electronic properties of surface alloy structure and underlies the study of the electronic structure-performance relationship in bimetallic catalysts.

Hierarchical CoNi alloys toward microwave absorption application: Chain-like versus particle-like

CoNi alloys are well known as excellent magnetic microwave absorption materials, but their various structures greatly influence electromagnetic properties, especially chains versus particles. Hierarchical CoNi chains were prepared using the solvothermal method in conjunction with an external magnetic field, and hierarchical CoNi particles were obtained in the absence of the magnetic field. Changing the reaction time from 6 to 12 h can change the surface structures of hierarchical CoNi alloys, as seen in the SEM images. The lattice parameters of samples are determined by XRD results, which include crystalline structures, lattice constants, mean crystallite sizes, and internal strain. The investigation of magnetic properties indicates that CoNi chains possess a stronger saturation magnetization and higher coercivity than CoNi particles as a result of their higher aspect ratios and larger crystalline sizes. Furthermore, CoNi chains have a higher microwave absorption capacity than CoNi particles, with a minimum reflection loss value of −42.113 dB (16.5 GHz) and an effective absorption bandwidth of 3.5 GHz (13–16.5 GHz). Conductive loss, defect-induced polarization relaxation, eddy current effect, exchange resonance, N é el relaxations, multiple reflections, and scatterings all contribute to the excellent microwave absorption performance of the CoNi chains. This research establishes that a chain-like structure outperforms a particle-like structure for hierarchical CoNi alloys as microwave absorbers, and it will provide clear guidance for designing high-performance magnetic microwave absorption materials.

Research on surface integrity optimization of TC-4 alloy surface structure processed by picosecond laser

The fabrication of microstructure on metal surface by laser processing technology will damage the surface integrity. In this research, picosecond laser was used to fabricate microstructure on the surface of TC-4 alloy, and the surface integrity was protected by adjusting parameters. The results show that using 0.6W power, 100mm/s scanning speed, 700kHz pulse frequency and 0.1ms point engraving time can avoid the influence and remodeling of the structure when the laser removes the material. In addition, the surface integrity after material removal is improved by ultra-low power and ultra-high speed laser cleaning process.

One Decade of Computational Studies on Single-Atom Alloys: Is In Silico Design within Reach?

ConspectusSingle-Atom alloys (SAAs) are an emerging class of materials consisting of a coinage metal (Cu, Ag, and Au) doped, at the single-atom limit, with another metal. As catalysts, coinage metals are rarely very active on their own, but when they are, they exhibit high selectivity. On the other hand, transition metals are usually very active but not as selective. Incorporating transition metals (guest elements) into coinage metals (host material) is therefore appealing for combining the activity and selectivity of each constituent in a balanced way. Additionally, first-principles calculations have shown that single atoms embedded in the surface of a coinage metal can exhibit emergent properties. Here, we describe how computational studies based on density functional theory (DFT) and kinetic Monte Carlo (KMC) simulations, often undertaken in close collaboration with experimental research groups, have shaped, over the past decade, the way we understand SAA catalysis.This Account reviews our contributions in elucidating the stability of SAAs, their electronic structure, and the way adsorbates interact and react on SAA catalytic surfaces. By studying in detail the processes that affect the stability of the SAA phase, we have shown that out of several bimetallic combinations of coinage metals with prominent Pt-group metals only PtCu and PdCu are stable surface alloys under vacuum. However, more surface alloy structures are possible in the presence of adsorbates because the latter can stabilize, via strong binding, dopants in the surface of the material. More interestingly, a large number of these surface alloys are resistant to the aggregation of dopant atoms into clusters, thereby favoring the SAA structure. These major results from DFT calculations serve as a guide for experimentalists to explore new SAA catalysts. Further analysis has shown that SAAs have a unique electronic structure with a very sharp d-band feature close to the Fermi level, analogous to the electronic structure of molecular entities. This is one of the reasons that SAAs are particularly sought after: although they are metallic nanoparticles, they have properties akin to those of homogeneous catalysts. In this context, we have contributed extensive screening studies, focusing on molecular fragments of catalytic relevance on a range of SAAs, which have driven the identification of new catalysts. We have also explored the rich chemistry of two-adsorbate systems via kinetic modeling, demonstrating how a spectator species with greater affinity for the dopant can modulate the reactivity of the catalyst via the so-called (punctured) molecular cork effect.Since the first experimental characterization of SAAs about a decade ago, theoretical models have been able to support and explain various experimental observations. These models have served as benchmarks for assessing the predictive capability of the underlying theoretical methods. In turn, the predictions that have been delivered have guided and continue to guide the experimental research efforts in the field. These advancements show that the in silico design of new SAA catalysts is now within reach.

Energy Absorption AZ31B using Quenching in Nano Fluid

This paper focuses on improving energy absorption through a series of heat treatment and quenching in medium, presence of nanoparticle. The characterisation of the experiment was to determine the suitable combination of composition factors: temperature, soaking time, and the medium that consist of nanoparticle on magnesium alloy surface structure to improve the energy absorption using quenching in nanofluids. The diameter and thickness of the specimen are 6 mm and 10 mm, respectively. All specimens undergo heat treatment based on the temperature of the furnace and the soaking time of the specimen in the furnace, which will be submerged into three medium distilled water, and the addition of a 0.1% wt carbon-nanotube (CNT) and 0.1% wt nano-silica. The addition of CNT and nano-silica shows an increment of 106.68%% and 59.30% for energy absorption, respectively, when compared to the controlled sample. Later microscopy has performed on the specimen to correlate the addition of nanoparticles in the heat treatment and improved energy absorption by EDS analysis on the material composition on the specimen’s surface. Therefore, this paper reveals factors of heat treatment and the presence of CNT and Nano silica effects on enhancing magnesium alloy energy absorption: UTS and yield strength using quenching method.

On the Role of Sn Segregation of Pt-Sn Catalysts for Propane Dehydrogenation

Bimetallic nanoparticle catalysts attract extensive attention for relevant catalysis processes due to their flexible structures, while the structure evolution under specific conditions is ambiguous. This paper describes the structure evolution of Pt-Sn bimetallic nanoparticles for catalytic dehydrogenation, especially Sn segregation for surface recovery of a Pt-Sn alloy. An acid etching-reduction process was adopted to investigate the migration of Sn atoms after surface Sn species loss. By acid etching, Sn atoms at the surface of Pt-Sn alloy nanoparticles were removed, leaving nanoparticles with a Pt-rich shell and an unchanged Pt3Sn alloy core. Excitedly, during the following reduction process, the Pt3Sn alloy surface was recovered due to the migration of Sn atoms from the core to the surface, as confirmed by transmission electron microscopy, quasi in situ X-ray photoelectron spectroscopy, and density functional theory calculations. Subsequent studies on the catalyst performance for propane dehydrogenation (PDH) showed that the recoverable Pt3Sn alloy surface structure contributed to the high efficiency with 92% propene selectivity even after 5 cycles of the acid etching-reduction procedure. The recovery of the Pt-Sn alloy through Sn segregation could enable catalysts to overcome component fluctuations, making an efficient catalytic process.

Janus Nanocages of Platinum-Group Metals and Their Use as Effective Dual-Electrocatalysts.

Janus nanocages with distinctive platinum-group metals on the outer and inner surfaces can naturally catalyze at least two different reactions. Here we report a general method based on successive deposition and then selective etching for the facile synthesis of such nanocages. We have fabricated 11 different types of Janus nanocages characterized by a uniform size and well-defined {100} facets, together with porous, ultrathin, asymmetric walls up to 1.6 nm thick. When tested as dual-electrocatalysts toward oxygen reduction and evolution reactions, the Janus nanocages based on Pt and Ir exhibited superior activities depending on the thickness and relative position of the metal layer. Density functional theory studies suggest that the alloy composition and surface structure of the nanocages both play important roles in enhancing the electrocatalytic activities by modulating the stability of key reaction intermediates.

Janus Nanocages of Platinum‐Group Metals and Their Use as Effective Dual‐Electrocatalysts

AbstractJanus nanocages with distinctive platinum‐group metals on the outer and inner surfaces can naturally catalyze at least two different reactions. Here we report a general method based on successive deposition and then selective etching for the facile synthesis of such nanocages. We have fabricated 11 different types of Janus nanocages characterized by a uniform size and well‐defined {100} facets, together with porous, ultrathin, asymmetric walls up to 1.6 nm thick. When tested as dual‐electrocatalysts toward oxygen reduction and evolution reactions, the Janus nanocages based on Pt and Ir exhibited superior activities depending on the thickness and relative position of the metal layer. Density functional theory studies suggest that the alloy composition and surface structure of the nanocages both play important roles in enhancing the electrocatalytic activities by modulating the stability of key reaction intermediates.

Computation of the lattice dynamics for the low-coverage Au/Cu(111) ordered metallic surface alloy system

The lattice dynamics of the ordered Au/Cu(111) surface alloy system are investigated, in particular for the low-coverage ordered Cu(111)-Au 3×3 R30° surface alloy structure. The computations are developed using the phase field matching theory (PFMT) and the Green's functions (GF) formalism. Dispersion branches for surface phonons and resonances along the directions of high symmetry ΓM‾, MK‾, and KΓ‾ of the two-dimensional (2D) surface Brillouin zone (BZ) of the system, are computed. The vibration local densities of states (LDOS) are also determined for representative atomic sites at the surface alloy boundary. The lattice dynamics of the Cu(111)-Au 3×3 R30° surface reveal novel surface phonon and resonance dispersion branches that could be of potential interest for electronic, chemical, and spintronic applications, notably via electron-phonon interactions at this surface.

Computational simulation of al-based alloy surface structure dislocation: the first-principles calculation and atomic pair-potential lattice dynamics calculation

In this paper, the first-principles calculation methods are used to obtain the generalized stacking fault (GSF) energy of Al and Al alloy surface structures. At the same time, after obtaining the atomic pair potential, GSF energy is calculated by the means of atomic simulation simultaneously. By comparison, the calculation of GSF energy at different scales is consistent and the study of GSF energy from different scale level with an acceptable accuracy is realized. For the study of surface structure dislocation defects, the calculation of antiphase boundary (APB) energy is pretty significant. By means of the atomic pair potential, we calculate the APB energy of surface structure of the NiAl, FeAl and CoAl binary Al-based alloys. Therefore, in this paper, the surface structural dislocation of Al-base binary alloys was studied on different scales.

The Effect of Ti-6Al-4V Alloy Surface Structure on the Adhesion and Morphology of Unidirectional Freeze-Coated Gelatin

The modification of a metal implant surface with a biomimetic coating of bone-like anisotropic and graded porosity structures to improve its biological anchorage with the surrounding bone tissue at implanting, is still a high challenge. In this paper, we present an innovative way of a gelatin (GEL) dip-coating on Ti-6Al-4V substrates of different square-net surface textures by the unidirectional deep-freezing process at simultaneous cross-linking using carbodiimide chemistry. Different concentrations of GEL solution were used to study the changes in morphology, density, and mechanical properties of the coatings. In addition, the surface free energy and polarity of Ti-6Al-4V substrate surfaces and GEL solutions have been evaluated to assess the wetting properties at the substrate interfaces, and to describe the adhesion of GEL macromolecules with their surfaces, being supported by mechanical pull-out testing. The results indicate that the coating’s morphology depends primarily on the Ti-6Al-4V substrate’s surface texture and second, on the concentration of GEL, which further influences their adhesion properties, orientation, morphological arrangement, as well as compression strength. The substrate with a 300 × 300 μm2 texture resulted in a highly adhered GEL coating with ≥80% porosity, interconnected and well-aligned pores of 75–200 μm, required to stimulate the bone ingrowth, mechanically and histologically.

Effects of metal dusting relevant exposures of alloy 601 surfaces on carbon formation and oxide development

Ni and Fe are excellent catalysts for carbon formation, and industrial alloys are therefore susceptible to metal dusting corrosion; a costly issue in e.g. synthesis gas manufacture. The objective of this work is to better understand the initial reaction phenomena leading to metal dusting, and thereby minimize the corrosion through optimum alloy selection and pretreatment. Pre-oxidized alloy 601 samples were subjected to carburizing gaseous environments at 750 °C, and carbon formation and surface oxide layer development were investigated by SEM, optical microscopy, AES and Raman spectroscopy. Thin (S)TEM/EDS cross-section lamellae were prepared by Focussed Ion Beam milling.Beyond the initial incubation period, less carbon is formed under 10% CO/Ar than under synthesis gas with finite low carbon activity. Cr2O3 evolves as a thin surface oxide layer with only CO reacting and more ordered carbon develops with increasing exposure time. In contrast, oxidation yields (Ni, Fe, Cr)3O4 spinel formation while the materializing carbon remains its disorder during prolonged exposure to synthesis gas. The metal dusting corrosion rate is hence lowered due to Cr2O3 stabilization, while the spinel represents an unstable redox state that continuously yields new carbon. A fine-grained alloy surface structure is also found beneficial to the Cr2O3 formation.

Water-Assisted Growth of Cobalt Oxide and Cobalt Hydroxide Overlayers on the Pt3Co(111) Surface

Bimetallic platinum–cobalt (Pt–Co) catalysts have highly enhanced performance for the oxygen reduction reaction (ORR), where this peculiar surface alloy structure contributes to efficient energy co...

Engineering the Surface Architecture of Highly Dilute Alloys: An ab Initio Monte Carlo Approach

Highly dilute alloys of platinum group metals (PGMs) - (Pt, Rh, Ir, Pd, and Ni) with coinage metals (Cu, Au and Ag) serve as highly selective and coke-resistant catalysts in a number of applications. The catalytic behaviour of these materials is governed by the size and shape of the surface “ensembles” of PGM atoms. Therefore, establishing a means of control over the topological architecture of highly dilute alloy surfaces is crucial to optimising their catalytic performance. In the present work, we use on-lattice Monte Carlo (MC) simulations that are parameterised by density functional theory (DFT) derived energetics, in order to investigate the surface aggregation of PGM atoms under vacuum conditions and in the presence of CO. We study several highly dilute alloy surfaces at various PGM loadings, including Pd/Au(111), Pd/Ag(111), Pt/Cu(111), Rh/Cu(111), Ir/Ag(111) and Ni/Cu(111). Under vacuum conditions, we observe a thermodynamic preference for dispersion of PGM as single atoms in the surface of the coinage metal host, on all examined alloy surfaces except Ir/Ag(111), where Ir atom aggregation and island formation is preferred. By evaluating the alloy surface structure in the presence of CO, we determine that the size and shape of PGM ensembles can be manipulated by tuning the partial pressure of CO (PCO) on the Pd/Au(111), Pd/Ag(111), Ir/Ag(111) and Ni/Cu(111) surfaces. In contrast, we determine that Pt/Cu(111) and Rh/Cu(111) highly dilute alloys are unresponsive to changes in PCO with Rh and Pt dispersing as isolated single atoms within the host matrix, irrespective of gaseous composition. Our findings suggest that it may be possible to fine-tune the surface architecture of highly dilute binary alloys for optimised catalytic performance.

Quasi Pd1Ni single-atom surface alloy catalyst enables hydrogenation of nitriles to secondary amines

Hydrogenation of nitriles represents as an atom-economic route to synthesize amines, crucial building blocks in fine chemicals. However, high redox potentials of nitriles render this approach to produce a mixture of amines, imines and low-value hydrogenolysis byproducts in general. Here we show that quasi atomic-dispersion of Pd within the outermost layer of Ni nanoparticles to form a Pd1Ni single-atom surface alloy structure maximizes the Pd utilization and breaks the strong metal-selectivity relations in benzonitrile hydrogenation, by prompting the yield of dibenzylamine drastically from ∼5 to 97% under mild conditions (80 °C; 0.6 MPa), and boosting an activity to about eight and four times higher than Pd and Pt standard catalysts, respectively. More importantly, the undesired carcinogenic toluene by-product is completely prohibited, rendering its practical applications, especially in pharmaceutical industry. Such strategy can be extended to a broad scope of nitriles with high yields of secondary amines under mild conditions.