Accelerated prediction of Cu-based single-atom alloy catalysts for CO_(2) reduction by machine learning

Various strategies,including controls of morphology,oxidation state,defect,and doping,have been developed to improve the performance of Cu-based catalysts for CO_(2) reduction reaction(CO_(2)RR),generating a large amount of data.However,a unified understanding of underlying mechanism for further optimization is still lacking.In this work,combining first-principles calculations and machine learning(ML)techniques,we elucidate critical factors influencing the catalytic properties,taking Cu-based single atom alloys(SAAs)as examples.Our method relies on high-throughput calculations of 2669 CO adsorption configurations on 43 types of Cu-based SAAs with various surfaces.Extensive ML analyses reveal that low generalized coordination numbers and valence electron number are key features to determine catalytic performance.Applying our ML model with cross-group learning scheme,we demonstrate the model generalizes well between Cu-based SAAs with different alloying elements.Further,electronic structure calculations suggest surface negative center could enhance CO adsorption by back donating electrons to antibonding orbitals of CO.Finally,several SAAs,including PCu,AgCu,GaCu,ZnCu,SnCu,GeCu,InCu,and SiCu,are identified as promising CO_(2)RR catalysts.Our work provides a paradigm for the rational design and fast screening of SAAs for various electrocatalytic reactions.

A Cu-based bulk amorphous alloy composite reinforced by carbon nanotube

Bulk Cu50Zr40Ti10 amorphous alloy composites reinforced with carbon nanotube （CNT） were successfully fabricated by hot pressing technique. Their density, thermal conductivity, and mechanical properties were systemically investigated. The density and the compression strength of the compacts both decrease with increasing CNT content. The thermal conductivity of the compacts decreases when the CNT content is less than 0.10% or exceeds 0.60% （mass fraction）, while increases when the CNT content is in the range of 0.1%-0.6%. The strain limit and the modulus of the compacts are obviously improved when the CNT content is less than 1.0% and then decrease significantly when the CNT content exceeds 1.00%. The optimum CNT addition is less than 0.20% at the comprehensive properties point of view.

Effect of consolidation parameters on mechanical properties of Cu-based bulk amorphous alloy consolidated by hot pressing

Cu50Zr40Ti10 bulk amorphous alloys were fabricated by hot pressing gas-atomized Cu50Zr40Ti10 amorphous powder under different consolidation conditions without vacuum and inert gas protection. The consolidation conditions of the Cu50Zr40Ti10 amorphous powder were investigated based on an L9（34） orthogonal design. The compression strength and strain limit of the Cu50Zr40Ti10 bulk amorphous alloys can reach up to 1090.4 MPa and 11.9 %, respectively. The consolidation pressure significantly influences the strain limit and compression strength of the compact. But the mechanical properties are not significantly influenced by the consolidation temperature. In addition, the preforming pressure significantly influences not the compression strength but the strain limit. The optimum consolidation condition for the Cu50Zr40Ti10 amorphous powder is first precompacted under the pressure of 150 MPa, and then consolidated under the pressure of 450 MPa and the temperature of 380 °C.

Microstructure of Cu-based Amorphous Composite Coatings on AZ91D Magnesium Alloy by Laser Cladding

To improve the sliding wear resistance of AZ91D magnesium alloy, Cu-based amorphous composite coatings made of CuaTTi34Zr11Nis and Cu47Ti34Zr11Ni8＋20 wt pct SiC powders were fabricated on AZ91D magnesium alloy by laser cladding, respectively. SEM （scanning electron microscopy）, EDS （energy dispersive X-ray spectroscopy）, XRD （X-ray diffraction） and TEM （transmission electron microscopy） techniques were employed to study the phases of the coatings. The results show that the coatings mainly consist of amorphous phase and different intermetallic compounds. The reason of formation of amorphous phase and the function of SiC particles were explained in details.

Formation Mechanism of Curved Martensite Structures in Cu-based Shape Memory Alloys

The curved martensite structures have been observed in CuZnAI-based shape memory alloys by both transmission electron microscope and optical microscope. It was found that the curved martensite structures observed in as-solution treated, as-aged and as-trained alloys usually occurred around dislocation tangles or precipitate, at the plate boundary or grain boundary, and when the growing plates collided with each other or alternate mutually.

Effect of brazing temperature on microstructure and tensile strength ofγ-TiAl joint vacuum brazed with micro-nano Ti−Cu−Ni−Nb−Al−Hf filler

A novel micro-nano Ti−10Cu−10Ni−8Al−8Nb−4Zr−1.5Hf filler was used to vacuum braze Ti−47Al−2Nb−2Cr−0.15B alloy at 1160−1220℃ for 30 min.The interfacial microstructure and formation mechanism of TiAl joints and the relationships among brazing temperature,interfacial microstructure and joint strength were emphatically investigated.Results show that the TiAl joints brazed at 1160 and 1180℃ possess three interfacial layers and mainly consist of α_(2)-Ti_(3)Al,τ_(3)-Al_(3)NiTi_(2) and Ti_(2)Ni,but the brazing seams are no longer layered and Ti_(2)Ni is completely replaced by the uniformly distributed τ_(3)-Al_(3)NiTi_(2) at 1200 and 1220℃ due to the destruction of α_(2)-Ti_(3)Al barrier layer.This transformation at 1200℃ obviously improves the tensile strength of the joint and obtains a maximum of 343 MPa.Notably,the outward diffusion of Al atoms from the dissolution of TiAl substrate dominates the microstructure evolution and tensile strength of the TiAl joint at different brazing temperatures.

Preparation and properties of novel Cu-based bulk metallic glasses Cu_(55-x)Zr_(37)Ti_8In_x

The glassy rods were successfully fabricated in the Cu-Zr-Ti-In alloy system by casting into a copper mold. The value of ATx reaches a maximum of 66 K for the BMG CusoZraTTi8In5 alloy. The reasons for enhancing glass forming ability of Cu-based BMGs with the addition of indium were discussed from atomic size and thermodynamics. Alternatively, the BMG Cu52Zra7Ti8In3 exhibits the highest compressive strength （1981 MPa） and the best plasticity among glassy Cu55-xZra7TisInx （x_〈5）. The total plastic deformation of Cu52Zr37TisIn3 before fracture approaches 1.2%.

Influences of different filler metals on electron beam welding of titanium alloy to stainless steel

Electron beam welding experiments of titanium alloy to stainless steel were carried out with different filler metals, such as Ni, V, and Cu. Microstructures of the joints were examined by optical microscopy, scanning electron microscopy and X-ray diffraction analysis. Mechanical properties of the joints were evaluated according to tensile strength and microhardness. As a result, influences of filler metals on microstructures and mechanical properties of electron beam welded titanium-stainless steel joints were discussed. The results showed that all the filler metals were helpful to restrain the Ti-Fe intermetallics. The welds with different filler metals were all characterized by solid solution and interfacial intermetallics. For each type of the filler metal, the type of solid solution and interfacial intermetallics depended on the metallurgical reactions between the filler metals and base metals. The interfacial intermetallics were Fe2Ti＋Ni3Ti＋NiTi2, TiFe, and Cu2Ti＋CuTi＋CuTi2 in the joints welded with Ni, V, and Cu filler metals, respectively. The tensile strengths of the joints were dependent on the hardness of the interfacial intermetallics. The joint welded with Ag filler metal had the highest tensile strength, which is about 310 MPa.

Microstructures of brazing zone between titanium alloy and stainless steel using various filler metals

Titanium alloy (Ti-Al-V alloy) substrate was brazed with stainless steel (STS304) using filler metal.At an optimized brazing condition,various filler metals were used.Microstructures were observed at each condition.Filler metals were titanium based 40Ti-20Zr-20Cu-20Ni,silver based Ag 5Pd,and nickel based Ni-7Cr-3.1B-4.5Si-3Fe-0.06C (BNi2) and Ni-14Cr-10P-0.06C (BNi7).To select a good filler metal for brazing process,wetting test was performed at 880-1050 °C.It was not brazed using silver based filler metals,but at the conditions using titanium and nickel based filler metals had brazed zone between titanium alloy and stainless steel.However,titanium alloy was eroded during brazing using titanium based filler metals.Nickel based filler metal has a good brazed zone between titanium alloy and stainless steel among the filler metals.

Effect of filler wire on the joint properties of AZ31 magnesium alloys using CO_2 laser welding

Laser welding with filler wire of AZ31 magnesium alloys is investigated using a CO2 laser experimental system. The effect of three different filler wires on the joint properties is researched. The results show that the weld appearance can be effectively improved when using laser welding with filler wire. The microhardness and tensile strength of joints are almost the same us those of the base metal when ER AZ31 or ER AZ61 wire is adopted. However, when the filler wire of ER 5356 aluminum alloy is used, the mechanical properties of flints become worse. For ER AZ31 and ER AZ61 filler wires, the microstructure of weld zone slws small dendrite grains. In comparison, for ER 5356 filler wire, the weld shows a structure of snowy dendrites and many intermetallic compounds and eutectic phases distribute in the dendrites. These intermetallic constituents with low melting point increase the tendency of hot crack and result in fiagile joint properties. Therefore, ER AZ31 and ER AZ61 wire are more suitable filler material than ER 5356 for CO2 laser welding of AZ31 magnesium alloys.

Brazing 6061 aluminum alloy with Al-Si-Zn filler metals containing Sr

Al-6.5Si-42Zn and Al-6.5Si-42Zn-0.09Sr filler metals were used for brazing 6061 aluminum alloy. Air cooling and water cooling were applied after brazing. Si phase morphologies in the brazing alloy and the brazed joints were investigated. It was found that zinc in the Al-Si filler metals could reduce the formation of eutectic Al-Si phase and lower the brazing temperature at about 520℃. Adding 0.09wt% Sr element into the Al-6.5Si-42Zn alloy caused a-Al phase refinement and transformed acicular Si phase into the finely fiber-like. After water cooling, Zn element dissolved into the Al-Si eutectic area, and η-Zn phase disappeared in the brazed joints. Tensile strength testing results showed that the Sr-modified filler metal could enhance the strength of the brazed joints by 13% than Al-12Si, while water-cooling further improved the strength at 144 MPa.

Interfacial microstructure and mechanical properties of tungsten carbide brazed joints using Ag-Cu-Zn + Ni/Mn filler alloy

WC-Co hard metal was furnace brazed by Ag-Cu-Zn+Ni/Mn filler alloy using a tube furnace under high-purity argon at730°C.The influence of brazing time and gap size of joints was studied.The results revealed the maximum shear strength of(156±7)MPa for samples with150μm gap size at a holding time15min.The characterization and microstructure of the brazed joints were characterized by SEM,EDS and XRD.The results showed that increasing the time from5to15min could provide a better chance for the liquid interlayer to flow towards the base metal.However,the formation of some metallic phases such as Mn3W3C at brazing time longer than15min resulted in decreased shear strength of the joint.

Microstructure and shear strength ofγ-TiAl/GH536 joints brazed with Ti-Zr-Cu-Ni-Fe-Co-Mo filler alloy

The influence of brazing temperature and brazing time on the microstructure and shear strength ofγ-TiAl/GH536 joints brazed with Ti-Zr-Cu-Ni-Fe-Co-Mo filler was investigated using SEM,EDS,XRD and universal testing machine.Results show that all the brazed joints mainly consist of four reaction layers regardless of the brazing temperature and brazing time.The thickness of the brazed seam and the average shear strength of the joint increase firstly and then decrease with brazing temperature in the range of 1090-1170℃and brazing time varying from 0 to 20 min.The maximum shear strength of 262 MPa is obtained at 1150℃for 10 min.The brittle Al3NiTi2 and TiNi3 intermetallics are the main controlling factors for the crack generation and deterioration of joint strength.The fracture surface is characterized as typical cleavage fracture and it mainly consists of massive brittle Al3NiTi2 intermetallics.

Vacuum brazing of Si/SiC ceramic composite and Invar alloy using TiSOCu-W filler metals

Si/SiC ceramic composite and lnvar alloy were successfidly joined by vacuum brazing using Ti5OCu-W filler metals into which W was added to release the thermal stress of the brazed joint. Microstructures of the brazed joints were irwestigated by scanning electron micrascope （SEM） and energy dispersive spectrometer （EDS）. The mechanical properties of the brazed joints were measured by shearing tests. The results showed that the brazed joints were composed of Ti-Cu phase, W phase and Ti-Si phase. W had no effect on the wettability and mobility of the .filler metals. The growth of Ti2 Cu phase was restrained, and the reaction between ceramic composite and filler metals was weakened. The specimen, brazed at 970°C for 5 rain, had the maximum shear strength of 108 MPa at room temperature.

Brazeability evaluation of Ti-Zr-Cu-Ni-Co-Mo filler for vacuum brazing TiAl-based alloy

Ti-47Al-2Nb-2Cr-0.15B(mole fraction,%)alloy was vacuum brazed with amorphous and crystalline Ti.25Zr-12.5Cu-12.5Ni-3.0Co-2.0Mo(mass fraction,%)filler alloys,and the melting,spreading and gap filling behaviors of the amorphous and crystalline filler alloys as well as the joints brazed with them were investigated in details.Results showed that the amorphous filler alloy possessed narrower melting temperature interval,lower liquidus temperature and melting active energy compared with the crystalline filler alloy,and it also exhibited better brazeability on the surface of the Ti.47Al.2Nb.2Cr.0.15B alloy.The TiAl joints brazed with crystalline and amorphous filler alloys were composed of two interfacial reaction layers and a central brazed layer.Under the same conditions,the tensile strength of the joint brazed with the amorphous filler alloy was always higher than that with the crystalline filler alloy.The maxmium tensile strength of the joint brazed at 1273 K with the amorphous filler alloy reached 254 MPa.

Joint performance in laser welding Al alloy with filler wire

CO2 laser welding aluminum alloy with filler wire was studied. The results indicate that the problems in CO2 laser welding of Al alloy, such as bad appearance of weld, easily excessive penetration and low strength, can be improved effectively by using laser welding with filler wire, and the maximum tensile strength of weld can reach 94% for the base metal. It also can be found that, the linear energy have great influence on the microstructure and mechanical properties of the joint. As the heat input increases, the cellular fir-tree crystals in the weld zone become sparse and the form of tensile fracture transforms from gliding fracture to brittle fracture.

Interfacial reaction and growth behavior of reaction layer of Si_3N_4/Si_3N_4 joint brazed by Cu-Zn-Ti filler alloy

Si3N4 ceramic was jointed to itself using a filler alloy of Cu-Zn-Ti by the reaction between Ti and Si3N4. The microstructure of the interface in the joint is found to be Si3N4 ceramic/TiN reaction layer/Ti5Si3 reaction layer. The grain size of the TiN and Ti5Si3 reaction layer is 0.1μm and 1-2μm, respectively. There is no crystal orientation relationship between TiN reaction layer and Si3N4 ceramic or Ti5Si3 reaction layer. The kinetic equation for calculating the thickness of the reaction layer was obtained. When a （CuZn）85Ti15 alloy is used as the filler alloy, the apparent activation energy of the growth of the reaction layer is 201.69kJ/mol.

The effect of different crystal conditions of filler metal on vacuum brazing of TiAl alloy and 42CrMo

Ti-based filler metals made by transient solidification and normal crystallization were selected for the vacuum brazing of the TiAl alloy and 42CrMo under different processing parameters. The results show that the tensile strength of the joint of transient solidified filler metal is higher than that of normal crystallized filler metal under the same processing parameters. By the analysis of scanning electron microscope（SEM） and X-ray diffracting （XRD） , it is found that the higher strength maybe caused by the generating of TiAl , TiNi and TiCu at the interface of joint made by transient solidified filler metal.

Effects of Rare Earths on Properties of Ti-Zr-Cu-Ni Base Brazing Filler Alloys

The effects of the addition of rare earths on the properties of Ti-Zr-Cu-Ni base brazing filler alloys and the mechanical microstructure and properties were studied for the brazed-joints in the vacuum brazing of TC4 by comparing synthetical properties of two kinds of filler metals.The results indicate that the filler metals added with rare earths have lower melting point, better wettability and higher mechanical properties in the brazing joints.

Microstructure and mechanical properties of Cu/Al joints brazed using(Cu,Ni,Zr,Er)-modified Al−Si filler alloys

To design a promising Al−Si filler alloy with a relatively low melting-point,good strength and plasticity for the Cu/Al joint,the Cu,Ni,Zr and Er elements were innovatively added to modify the traditional Al−Si eutectic filler.The microstructure and mechanical properties of filler alloys and Cu/Al joints were investigated.The result indicated that the Al−Si−Ni−Cu filler alloys mainly consisted of Al(s,s),Al_(2)(Cu,Ni)and Si(s,s).The Al−10Si−2Ni−6Cu filler alloy exhibited relatively low solidus(521℃)and liquidus(577℃)temperature,good tensile strength(305.8 MPa)and fracture elongation(8.5%).The corresponding Cu/Al joint brazed using Al−10Si−2Ni−6Cu filler was mainly composed of Al_(8)(Mn,Fe)_(2)Si,Al_(2)(Cu,Ni)3,Al(Cu,Ni),Al_(2)(Cu,Ni)and Al(s,s),yielding a shear strength of(90.3±10.7)MPa.The joint strength was further improved to(94.6±2.5)MPa when the joint was brazed using the Al−10Si−2Ni−6Cu−0.2Er−0.2Zr filler alloy.Consequently,the(Cu,Ni,Zr,Er)-modified Al−Si filler alloy was suitable for obtaining high-quality Cu/Al brazed joints.