Filler Alloy Research Articles

First-principles calculations on brazed diamond with FeCoCrNi high entropy alloys doped with strong carbide-forming elements

FeCoCrNi alloy is one of the most widely studied high-entropy alloys due to its excellent properties such as extreme hardness, excellent wear resistance, and good chemical stability. However, the feasibility of using FeCoCrNi alloy as the filler for brazing diamond and the related interfacial bonding mechanisms are unclear. In this work, the interfacial bonding behaviors between FeCoCrNi filler and diamond, and the influences of strong carbide-forming elements X (X = Mo, Mn, Ti, V, W, Zr, Nb, Hf, Ta) doping into FeCoCrNi filler on the brazed diamond were systematically investigated through first-principles calculations method. The calculated interfacial segregation work and interfacial energies show FeCoCrNi/diamond interface has a higher interfacial bonding strength and stability than Ni–Cr/diamond interface. The calculated embedding energies show that these strong carbide-forming elements X are more likely to segregate in the interfacial region close to the diamond. The doping of X, especially Hf, Zr, Ta, and Nb, significantly enhances the interfacial bonding strength and stability of the FeCoCrNi/diamond interface. Combining with further analysis of electronic structures, it is suggested that the FeCoCrNiNb is an ideal high entropy alloy filler for brazing diamond due to its dual effects on interface strengthening of FeCoCrNi/diamond and graphitization inhibiting of diamond.

Energy absorption properties of composite tubes with hexagonal and re-entrant honeycomb fillers

Compared to traditional materials, auxetic materials possess superior bending resistance and energy absorption properties due to their special deformation mechanism. To take advantage of these desirable properties, a novel composite tube with auxetic honeycomb filler was proposed in this work. The honeycomb filler of the composite tube was manufactured by 3D printing technology. The bending properties of two kinds of tubes were studied, namely aluminum tube with re-entrant honeycomb filler and aluminum tube with hexagonal honeycomb filler, respectively. The mechanical responses, deformational characteristics, and failure mechanism of the composite tube under three-point bending were studied by experimental and numerical methods. The study showed that the experiment and numerical results match well with each other. In addition, parametric analysis was carried out to examine the effects of filler and aluminum alloy tubes on the bending properties of the composite tube. Finally, kriging model and the non-dominated sorting genetic algorithm (NSGA-Ⅱ) are used to optimize the design of composite tubes, and the parameter solution with better energy absorption capacity is obtained.

Microstructure and mechanical properties of TiAl/TiAl joints brazed with a newly developed Ti–Ni–Nb–Zr quaternary filler alloy

A novel Ti–Ni–Nb–Zr quaternary filler alloy with the composition of Ti-(19∼25)Ni-(15∼25)(Nb ​+ ​Zr) (wt.%) was designed. The filler alloy was composed of (Ti,Nb)ss, (Ti,Zr,Nb)ss ​+ ​(Ti,Zr)2Ni, α-Ti and Ti2Ni phases. It was fabricated into filler foil with a thickness of about 45 ​μm by a rapid solidification technique. The results indicate that the liquidus temperature of the Ti–Ni–Nb–Zr brazing alloy was about 978 oC, and the brazing alloy presented excellent wettability on TiAl substrate. The TiAl joint mainly consisted of β/B2 phase, Ti2Al, Ti2AlNi and α2-Ti3Al phases. The diffusion of Al atom from base metal to brazed seam led to the formation of Ti2Al and Ti2AlNi. Considering that no previously references on XRD pattern of Ti2AlNi compound can be found, Ti2AlNi cast alloy specimen was specially prepared and XRD peaks were specially labeled. The micro-hardness and bending strength tests of the Ti2AlNi phase were carried out, and the results were 761 HV and 192 ​MPa, respectively. The brazing parameters of 1010 oC/10 ​min offered the joint shear strength of 280 ​MPa at room temperature, and the joints exhibited tensile strength of 372 ​MPa at room temperature and 340 ​MPa at 750 oC, indicating that the newly developed filler alloy could offer a stable high-temperature strength.

Vacuum brazing of copper and SS316L using Ni–P eutectic alloy filler for nuclear applications

Vacuum brazing of copper and SS316L using Ni–P eutectic alloy filler for nuclear applications

Interfacial strengthening mechanism of C/C/Nb0.74CoCrFeNi2/Nb brazed joints: Stress-relieving effects of the FCC phase

Joining ceramics and metals has long been a key issue for manufacturing structures that are resistant to high temperature. This study joined a carbon-fiber-reinforced carbon-matrix (C/C) composite and Nb using a Nb0.74CoCrFeNi2 eutectic high-entropy alloy filler, and the evolution mechanism of the microstructure and mechanical properties of the joints were systematically studied. The eutectic structure composed of face-centered cubic (FCC) and Laves phases gradually disappeared with the increasing temperature, while the Nb(s,s) layer thickness increased gradually. The lattice mismatch was ∼97% and ∼2.8% at the Cr23C6/C/C and FCC/C/C interfaces, respectively. Considering differences in the coefficient of thermal expansion and lattice mismatch, an increase in FCC phase content at the C/C interface is conducive to reinforcing the joint strength. At 1260 °C, the combined effects of the highly deformable FCC phase and high-strength Cr23C6 increased the strength of the mixing zone, causing fracture to occur in the Nb(s,s) layer. These results are expected to contribute to further improving the joining of dissimilar materials.

Active brazing of high entropy ceramic and Nb metal: Interfacial microstructure and brazing mechanism

To development large-size and complex high-entropy ceramic (HEC) components, the joining of (Ti0.2Zr0.2Nb0.2Ta0.2Cr0.2)C and Nb metal with nickel-based filler alloy was performed. The microstructure was characterized by SEM and the phase composition was analyzed by EDS and XRD. The brazing mechanism of the joint was mainly derived from the diffusion of Nb, which formed the NbC reaction layer in the HEC part and the diffusion zone in Nb metal part. The highest shear strength of the brazed joints at 1170 °C/10min was 139 MPa at room temperature and 117 MPa at 800 °C. In addition, the effect of brazing temperature on the microstructure and shear strength was discussed. This work provided a key method to prepare high-temperature resistant complex and large-size HEC components.

Influence of Filler Metal on Electrochemical Characteristics of a Laser-Welded CoCrMoW Alloy Used in Prosthodontics.

This paper sought to determine corrosion resistance changes in the artificial saliva of a CoCrMoW-based alloy used for dental prostheses under Nd:YAG laser welding with CoCr alloy and stainless steel wire filler metals. The paper presents the corrosion characteristics of such joints, including the next stage of porcelain-fused-to-metal (PFM) firing. Corrosion tests were performed by electrochemical methods registering anodic polarization curves and electrochemical impedance spectroscopy (EIS). The microstructures were assessed by scanning microscopy (SEM) and chemical composition analysis (EDS) at the connection and heat-affected zones. Welding CoCrMoW alloy with and without a filler material increased the open circuit potential of the samples by 40–100 mV compared to unwelded base alloy. At the same time, a potentiodynamic test showed a polarization resistance Rpol reduction in welded samples, both for CoCr and stainless steel wires, as compared to the base CoCrMoW material. On the other hand, when comparing the current density and polarization resistance between materials welded with two different filler metals, better results were obtained for samples welded with stainless steel wire. The polarization resistance Rpol for the base alloy was 402 kΩ·cm2, for the CoCr wire weld it was 436 kΩ·cm2, and the value was 452 kΩ·cm2 for stainless steel wire welds. Comparing polarization resistance Rpol from the Tafel analysis and the total charge transfer resistance from Rp(EIS) from EIS, the CoCrMoW alloy welded with a stainless steel wire after heat treatment equaled or even slightly exceeded the corrosion resistance of the base alloy and alloy welded with dedicated CoCr wire after heat treatment. These results indicated the possibility of using stainless steel wire for the laser welding of CoCrMoW alloys dental prostheses, including the next stage of PFM, without sacrificing the corrosion resistance of such connections, and this was confirmed by most electrochemical parameters.

Effect of contact time parameter on wettability and interface phenomena of B4C substrate by Ni–Cr–Si–Fe–B–C filler alloy

In the present research, the wettability of boron carbide ceramic by BNi-1 filler alloy at various contact times from 10 to 40 min has been studied. The results of sessile drop wetting tests showed that the BNi-1 filler alloy could spread well on the B4C surface at 10–40 min. With the increase of the contact time from the lowest time (10 min) to the highest time (40 min), the contact angle stably reduced, showing the enhancement of the spreading. However, by the increase of the contact time from 30 to 40 min, a slight change was observed in the wetting angle (from 21° to 19°). Overall, the appropriate spreading behavior of BNi-1 filler alloy on the B4C substrate can be attributed to the tendency of nickel for the reaction with B4C along with the simultaneous availability of silicon and chromium in the composition of this alloy. The maximum wetting angle of 48° was attained for the specimen with 10 min contact time and the minimum angle of 19° was achieved for the specimen with 40 min contact time. Due to the results, different compounds such as Ni4B3, CrB2, CrB, SiC, and Ni2Si have been observed at the system's interface. Moreover, the higher contact times can lead to the intensification of the system's interactions which can subsequently result in the higher penetration of the elements, the reacted area enlargement, and the formation of diverse microstructures and phases. The wetting experiments' results confirmed the spreading ratio calculations.

Influence of brazing temperature on interfacial reaction layer characteristics of Cu-Sn-Ti/diamond composites

Cu-Sn-Ti/diamond composites have been manufactured by cold-press forming followed by high-temperature vacuum brazing. The effects of brazing temperature on Cu-Sn-Ti/diamond wetting behaviors and associated morphologies, interfacial reaction layer products and thickness variations, elemental distribution features, as well as corresponding orientation relationships, have been systematically investigated. It has been documented that as the brazing temperature increases, diamond particles are gradually coated by the active Cu-Sn-Ti filler alloy. The interfacial reaction layer products are determined to be primarily composed of TiC, the formation of which is driven by the diffusion of dissolved Ti and reaction with C. It has been revealed that the thickness of the TiC layer shows a definitive increasing trend till reaching 1.75 μm up to 1213 K but stops afterwards. Concurrently, TiC has been confirmed to possess a semi-coherent orientation relationship ((1 1 1)TiC//(1 1 1)diamond and [1 1¯ 0]TiC//[1 1¯ 0]diamond) with the diamond matrix, boding well for a robust chemical bonding. It is suggested that the brazing temperature shall be limited under 1213 K for optimized bonding strength and grinding capability.

Titanium/steel composites were prepared by machine tool machining and composite welding mechanism

In this work, the machine tool machining and compound welding mechanism are combined to create a new processing technology. Dissimilar welds between stainless steel (SS) and Ti alloy were produced with mechanical joining and metallurgical joining technique. The mechanical joining of the Cu interlayer, CuZnSn filler and Ti alloy was connected by screws, and then the laser weld formed at the SS/Cu interface due to the good weldability of Fe and Cu. Brazing weld at Ti/CuZnSn interface formed through the SS side weld heat conduction, which realized the mechanical and metallurgical double joining of the SS/Ti joint and improved the strength of the joint. Unmelted Cu interlayer was retained by laser offset to the SS side to achieve heat transfer to the CuZnSn and Ti alloy. The CuZnSn filler was not melted, but the eutectic reaction with low melting point still occurred by atomic diffusion. The joint fractured at the Ti side interface with the maximum tensile strength of 199 MPa. This method combines the advantages of machine tool machining and metallurgical machining at the same time.

Characterization of ZTA Composite Ceramic/Ti6Al4V Alloy Joints Brazed by AgCu Filler Alloy Reinforced with One-Dimensional Al18B4O33 Single Crystal

Al18B4O33 whiskers were used as a reinforcer to study the effect of one-dimensional single crystal on the quality improvement of ZTA composite ceramic/Ti6Al4V alloy joints brazed by AgCu alloy. The microstructure of the joint with whisker additions was characterized in detail. The effects of brazing temperature on the microstructure and shear strength of the brazed joints were investigated. The results showed that the whiskers reacted with the liquid alloy during the brazing process and continuous (Cu,Al)3Ti3O layers were formed in contact with the residual whiskers. The addition of 2 wt.% Al18B4O33 whiskers into AgCu filler alloy can delay the growth of the (Cu,Al)3Ti3O layer on the ZTA side, and can significantly restrain the growth of the Ti-Cu compound region over a brazing temperature range of 800~875 °C. Because of the one-dimensional reinforcement, the temperature window for obtaining ZTA/Ti6Al4V joints with shear strength values higher than 50 MPa was extended, and the maximum shear strength of the joints reached 56 MPa.

Microstructure evolution and joining strength of diamond brazed on Ti-6Al-4V substrates using Ti-free eutectic Ag-Cu filler alloy

In this study, strong bonding of vacuum brazed synthetic diamond and Ti-6Al-4V substrates joints was achieved using a Ti-free eutectic AgCu filler alloy. It was found that the brazing temperature remarkably influenced the interfacial microstructures, and hence affected the bonding strength of brazed diamond joints. Thermodynamic calculation and TEM microstructural characterization revealed that the rapid adsorption and dissolution of Ti in molten filler alloy is responsible for the preferential precipitation of TiCu and/or Ti2Cu IMCs on the brazed diamond surface and the excessive formation of TiCu IMCs, which largely impaired the bonding strength of brazed Ti-6Al-4V/diamond joints. An evolution model exploring the microstructure and mechanical properties of the brazed joints on Ti-6Al-4V substrates was proposed, by taking the behavior of Ti adsorption into account. The underlying mechanism to gain a reliable bonding between Ti-6Al-4V substrate and diamond in this work is therefore of essential implications for the understanding of microstructure and bonding strength of other hard-to-wet materials on Ti-based substrates.

Conduction Path Formation Characteristics of Solderable Polymer Composite Filled with Low-Melting-Point and High-Melting-Point Alloy Fillers

In this study, low-melting-point alloy (LMPA) and high-melting-point alloy (HMPA) filler-filled solderable polymer composite (LH-SPC) system was proposed to enhance the mechanical and thermal properties of SPC with LMPA fillers. To identify the conduction path formation characteristics of LH-SPC according to the mixing ratio of LMPA and HMPA, four types of LH-SPC with different mixing ratios of LMPA and HMPA fillers (100:0, 80:20, 30:70, and 0:100) were formulated. Furthermore, a chip resistor interconnection test was conducted. The results indicated that LH-SPC with only HMPA did not form a conduction path because of the excessively cured polymer composite before melting HMPA. Meanwhile, LH-SPC with LMPA and HMPA fillers showed different conduction path formation mechanisms according to the mixing ratio of LMPA and HMPA fillers. In LH-SPC filled with lower HMPA content than LMPA, the conduction path was formed by the flow, coalescence, and wetting behaviors of molten LMPA containing solid-state HMPA at the melting range of the LMPA filler. On the other hand, in LH-SPC containing higher HMPA content than LMPA, the conduction path was formed by the wetting behavior of the molten HMPA at a lower temperature range than the melting temperature of HMPA because of the decreased melting temperature of HMPA owing to the chemical composition change of HMPA by the diffusion of Bi into HMPA.

Casting Welding from Magnesium Alloy Using Filler Materials That Contain Scandium.

Based on the results achieved in systematic studies of structure formation and the formation of multicomponent phases, a scandium-containing filler metal from system alloy Mg-Zr-Nd for welding of aircraft casting was developed. The influence of scandium in magnesium filler alloy on its mechanical and special properties, such as long-term strength at elevated temperatures, was studied by the authors. It is established that modification of the magnesium alloy with scandium in an amount between 0.05 and 0.07% allows a fine-grained structure to be obtained, which increases its plasticity up to 70% and heat resistance up to 1.8 times due to the formation of complex intermetallic phases and the microalloying of the solid solution. Welding of the aircraft castings made of magnesium alloy with scandium-containing filler material allows obtaining a weld with a dense homogeneous fusion zone and the surrounding area without any defects. The developed filler material for welding surface defects (cracks, chips, etc.) formed during operation on aircraft engine bodies makes it possible to restore cast body parts and reuse them. The proposed filler material composition with an improved set of properties for the welding of body castings from Mg-Zr-Nd system alloy for aircraft engines makes it possible to increase their reliability and durability in general, extend the service life of aircraft engines, and obtain a significant economic effect.

Influence of Post-Bond Heat Treatment on Microstructure and Creep Behavior of the Brazed Single-Crystal Nickel Superalloy.

Post-bond heat treatment (PBHT) is an effective way to improve the bonding quality of a brazed joint. Herein, brazing of a nickel-based single crystal superalloy is carried out using a Ni-Cr-Co-B-Si-Al-Ti-W-Mo filler alloy, and the microstructure and creep property of the brazed joint are systematically investigated using scanning electron microscopy (SEM), Thermo-Calc software, an electron probe micro-analyzer (EPMA), X-ray diffractometer, confocal scanning laser microscope (CSLM), and transmission electron microscopy (TEM). The results reveal that the as-prepared joint only consists of an isothermally solidified zone (ISZ) and an athermally solidified zone (ASZ), where the cubic γ′ phase is observed in the ISZ, and skeleton-like M3B2, γ + γ′ eutectic and reticular G phases are observed in the ASZ. Furthermore, the γ + γ′ eutectic and G phases disappear and the M3B2 alters from a skeleton-like to block-like shape in the ASZ after PBHT. Meanwhile, some lath-like M3B2 phases are precipitated at the edge of the ISZ and several M3B2 phases are precipitated in the base metal, forming a new zone in the brazed joint, namely at the diffusion affected zone (DAZ). Owing to the removal of low melting point eutectics from the as-prepared joint, the creep life also increases from 188 h to 243 h after PBHT. The current work provides a method for the optimization of brazed joints based on the Ni-based single crystal superalloy.

Features of the Transport Properties of Thermoelectric Nanocomposites Based on a Matrix from BiSbTe1.5Se1.5 Medium-Entropy Alloy and Carbon-Nanotube Filler

For the first time, thermoelectric nanocomposites consisting of a BiSbTe1.5Se1.5 medium-entropy alloy (nanocomposite matrix) and “Taunit-M”, CNT carbon nanotubes (nanocomposite filler)are obtained. All BiSbTe1.5Se1.5 + xCNT nanocomposites with different filler contents (x = 0, 0.05, 0.1, 0.5, 1.0, 1.5, and 2.0 wt %), obtained by spark plasma sintering of the initial powders of the matrix material and filler, consist of micron-sized filler inclusions formed from clusters of nanotubes. The inclusions themselves are randomly distributed within the polycrystalline matrix. In the temperature range of 290–500 K, the transport properties (electrical resistivity and total thermal conductivity, including the electronic and phonon contributions, as well as the contribution of bipolar thermal conductivity) of the nanocomposites with various filler contents are studied. It is established that the introduction of CNTs into the matrix leads to a qualitative change in the type of electrical conductivity from “metallic” (electrical resistance increases with temperature), characteristic of the nanocomposite matrix, to “semiconductor” (resistance decreases with temperature), characteristic of nanocomposites. The observed “semiconductor” behavior of the electrical conductivity is characteristic of electrically inhomogeneous systems, in which current transfer is determined by the movement of electrons through the interfaces between the inhomogeneities. For all nanocomposites with different filler contents, the temperature dependences of the total thermal conductivity are qualitatively similar. At low temperatures, they are determined by the phonon contribution; at high temperatures, by the bipolar-thermal-conductivity contribution; the electronic contribution manifests itself at all temperatures, but it gradually decreases with increasing x. The minimum thermal conductivity is observed for the nanocomposite with x = 0.5 at % CNT.

Improvement for electrical conductivity of Ti3SiC2/Cu joint brazed with a novel Sn6Ag7Ni4Co2Ti low-melting high entropy alloy filler

Reducing the interfacial electrical resistance of Ti3SiC2/Cu joint has significant value to promote its application in the field of electrical contact. In the study, a novel Sn6Ag7Ni4Co2Ti low-melting high entropy alloy (HEA) was designed and fabricated, and a sound Ti3SiC2/Cu brazed joint was obtained using above filler. The interface of Ti3SiC2/Cu joint brazed with Sn6Ag7Ni4Co2Ti filler is mainly composed of Ag(s,s), Cu(s,s) and a few (Ni, Co)2Si. Compared with Ti3SiC2/Cu joint brazed with Ag-26.7Cu-4.5Ti filler, the electrical resistance of the joint brazed with Sn6Ag7Ni4Co2Ti filler is lower at all test temperatures, which is reduced by up to 15.99% when the test temperature is 300 °C.

Microstructure and mechanical properties of ultra-high strength Al-Zn-Mg-Cu-Sc aluminum alloy fabricated by wire + arc additive manufacturing

Ultra-high strength 7xxx series aluminum alloys are widely used in aerospace applications due to their exceptional high specific strength. Wire + Arc Additive Manufacturing (WAAM) is a combination of arc and wire feeding additive manufacturing technology including either the gas tungsten arc (GTA) or the gas metal arc (GMA) process. And this technology has been applied in the aerospace manufacturing industry to reduce the time of product development and “buy-to-fly” ratios. However, the existing Al-Zn-Mg-Cu aluminum alloy filler wires are not suitable for WAAM process due to their high susceptibility to hot cracks. In this study, a novel Al-Zn-Mg-Cu-Sc aluminum alloy wire named 7A55-Sc with ultra-high strength and excellent hot-crack resistance has been successfully prepared by optimizing the composition of Al-Zn-Mg-Cu alloying elements and adding appropriate amounts of inoculants Sc and Zr elements during the smelting process. And then, thin-wall components without any hot cracks were successfully fabricated by using cold metal transfer (CMT) process. Results indicated that the microstructure of the as-deposited 7A55-Sc alloy consists of predominantly fine equiaxed grains and the average size of the grains is between 5.0 and 6.0 μm. The eutectics composed of α (Al), η phase and S phase were distributed along the grain boundaries. The Al3Sc and Al3 (Zr, Sc) particles precipitated within grains act as heterogeneous nucleation nuclei, promoting the formation of the equiaxed grains. After T6 heat treatment, most of the second phases distributed within grains and grain boundaries were dissolved into the α(Al) matrix. The distribution of alloy elements became more homogeneous. The average ultimate tensile strength, yield strength and elongation of T6 heat-treated 7A55-Sc alloy in the horizontal direction were 554 MPa, 488 MPa and 1.7% respectively, whereas 523 MPa, 469 MPa and 1.4% in the vertical direction. The lower ductility was considered due to the existence of a large number of pores in the 7A55-Sc alloy fabricated by the CMT process.

Joining of Al2O3 to Cu with Cu-Sn-Ti active brazing filler alloy

Joining of Al2O3 to Cu with Cu-Sn-Ti active brazing filler alloy

Cu-induced enhancement of interfacial bonding for brazed diamond grits with Ni[sbnd]Cr filler alloys

Restraining diamond graphitization is still the potential problem for brazed diamond tools with NiCr filler alloys. Herein, we systematically investigate the interfacial bonding and mechanical performance of brazed diamond tools with Cu-doping NiCr filler alloys through multi-scale atomistic simulations and experiments. First-principles calculations show that the Cu-doping not only inhibits the structural damage of diamond, but also enhances the metallurgical bonding between diamond and filler alloys. The tensile simulations of Ni-Cr-Cu/diamond interface further verify the strengthening effects of Cu-doping since these bonds of CC within diamond and Ni-Cr-C at interface can withstand greater tensile strains. Combined with molecular dynamics simulations, Cu-doping effectively weaken the graphitization of diamond, which is confirmed through experimental Raman spectroscopy detection. More importantly, the brazed diamond tools by NiCr filler doped with 40 wt% Cu alloy exhibit excellent mechanical grinding performance. These results shed a new light on improving the mechanical properties of brazed diamond tools.