Brittle Intermetallic Compounds Research Articles

Microstructure of the interface between aluminum alloy and galvannealed steel plates jointed by FSSW multi-step loading process

When joining between GA980 and A6061 plates by the FSSW, brittle intermetallic compounds and Zn-contained region are formed at the joint interface. These local reaction products determine the strength of the joint. Therefore, the bonding interface microstructure analysis is crucial to control the process and improve strength. This study performed microstructural analysis near the joint interface on GA980/A6061 joints bonded by the FSSW. The detailed variation of the IMC thickness along with the bonded interface and the microstructure of the Zn-contained region in A6061 plate was clarified. In the A6061 plate, a simple shear texture was observed with the Al <110> direction in the tool rotational direction and the Al {111} plane perpendicular to the direction of the elongated grains. In elongated Al grains surrounded by high-angle grain boundaries, the grains were divided by the low-angle grain boundaries.

Influences of solution treatments on the microstructure and mechanical properties of TiCx-Cu (x = 0.5, 0.6, 0.7) cermets prepared by infiltration method

In this study, TiCx-Cu (x = 0.5, 0.6, 0.7) cermets were prepared combined with subsequent solution treatment, and the influences of solution treatment on the microstructures and mechanical properties were analyzed. The fracture mechanisms of cermets before and after solution treatment were mainly observed and analyzed. The results show that solution treatment can significantly improve the comprehensive mechanical properties of TiCx-Cu cermets. The fracture toughness KIC of TiC0.5-Cu and TiC0.7-Cu cermets increased by 28% and 11%, respectively. The improvements of the comprehensive properties of TiCx-Cu cermets were benefited by the reduction of the content of hard brittle intermetallic compound Cu4Ti and the refinements of the grain size of Cu.

Effect of Nb interlayer on microstructure and property of Ti-6Al-4V/690 MPa grade steel clad plate by vacuum rolling

Ti alloy clad plate is of great interest for marine and petrochemical industry applications. However, high interfacial bonding is hardly obtained in the Ti alloy clad plate due to the brittle intermetallic compounds (IMCs) forming at the interface. In this study, a Ti-6Al-4V alloy/EH690 steel clad plate was fabricated by vacuum rolling and subsequently tempered to control the mechanical property of the steel substrate. The tempered sorbite appeared in the EH690 steel after quenching and tempering (QT). A decarburized zone, Fe2Ti + TiC mixed phases layer, and β-Ti layer were formed at the interface between steel and Ti. The brittle IMCs with high lattice mismatch resulted in a low interfacial strength of 108 MPa. To improve bonding strength, Nb was inserted between Ti and steel as an interlayer, which effectively inhibited the inter-diffusion of Ti, Fe, and C without brittle TiC or Fe-Ti IMCs. A (Ti, Nb) solid solution layer with high plasticity was present at the Nb/Ti interface. Fe2Nb and Fe7Nb6 phases were detected at the steel/Nb interface, exhibiting less brittleness and hardness compared to Fe-Ti IMCs. The interfacial shear strength was up to 265 MPa after adding the Nb interlayer, showing a mixed fracture mode of brittleness and ductility.

Study on Laser Overlap Welding of Titanium/Aluminum Dissimilar Metals Based on Niobium Microalloying

Brittle intermetallic compounds, formed during the welding process of titanium/aluminum (Ti/Al), lead to a significant reduction in joint mechanical properties. The purpose of this study is to mitigate the formation of brittle phases during the laser welding of dissimilar Ti/Al metals, thereby enhancing the mechanical properties of the joints. In this investigation, an innovative approach is adopted, utilizing Nb foil as an interlayer to effectively minimize the formation of brittle intermetallic phases during dissimilar welding. A comprehensive analysis of the microstructure of the transition layer was conducted using material characterization methods, including scanning electron microscope equipped with an energy dispersive X-ray spectrometer. The mechanical performance of the welded joints was assessed using tensile testing. The results indicate that the effective welding width and joint penetration depth at the joint interface were reduced in Ti/Al dissimilar metals when Nb was added as an intermediate layer, under the same welding process parameters, when compared to unalloyed weld seams. Furthermore, the utilization of a 0.05 mm Nb foil as the intermediate layer results in a significant 25% increase in the average shear strength compared to the other condition, with the average shear strength of the joint reaching its peak value at 192 N/mm. The unalloyed Ti/Al weld joint usually fractured along the melting zone, displaying complete brittle fracture characteristics. After Nb microalloying, the joint typically fractures along the transition zone and interface, exhibiting both cleavage and ductile fracture characteristics, indicating the combination of a brittle and toughness fracture. This study provides experimental evidence and new insights for welding Ti/Al composite structures, with significant theoretical and practical applications.

Revealing microstructural evolution and mechanical properties of resistance spot welded NiTi-stainless steel with Ni or Nb interlayer

Dissimilar welding of NiTi and stainless steel (SS) for multifunctional device fabrication is challenging due to the brittle nature of intermetallic compounds (IMCs) that are formed in the weld zone. In this work, Ni and Nb interlayers were applied for the resistance spot welding (RSW) of NiTi and SS to replace the harmful Fe2Ti phase and to restrict the mixing of dissimilar molten metals, respectively. Microstructural evolution and mechanical properties of the joints were investigated. It was shown that a conventional weld nugget was created in the absence of any interlayer in the welded joint suffering from traversed cracks due to the formation of brittle IMCs network in the fusion zone (FZ). By the addition of Ni from the interlayer, Fe2Ti dominated weld nugget was efficaciously replaced by Ni3Ti phase; however, the presence of the large pore and cracks reduced the effective joining area. The use of a Nb interlayer resulted in a fundamentally different joint, in which FZs at NiTi and SS sides separated by the unmolten Nb would suppress the mixing of dissimilar molten metals. Nb-containing eutectic structures with low brittleness formed at the interfaces, contributing to the enhancement of joint strength (increased by 38% on fracture load and 460% on energy absorption). A high-melting-point interlayer showed great potential to realize a reliable and high-performing RSWed NiTi-SS joint.

High-speed hot-wire laser brazing technology for steel/aluminum alloy dissimilar joint using twin beam irradiation

The demand for steel/aluminum alloy dissimilar joints has increased for light-weighting the automobile body. However, it is well known that joining both metals by conventional welding methods, the brittle intermetallic compound (IMC) is generated at the interface, and it significantly deteriorates the joint strength. In this paper, the hot-wire laser brazing process using the twin-spot irradiation was proposed and its conditions were optimized to achieve the high brazing speed and the high joint strength on a lap-fillet joint of the steel/aluminum alloy dissimilar combination. The twin spots of a circle (ϕ5) and rectangular (5 × 11) laser beams aligned at spot ends achieved the high brazing speed up to 6 m/min, stable brazing phenomena and sound bead appearance. The joints fabricated using the optimized conditions realized the very thin IMC thickness under 2 μm and high joint strength over the yield strength of the base steel sheet.

Microstructure and mechanical properties of Ti-6Al-4V/316L dissimilar materials with FeCrCuV medium-entropy alloy transition layer by laser metal deposition

To avoid brittle intermetallic compounds during direct connection of the Ti-6Al-4V alloy and 316L stainless steel, the FeCrCuV medium entropy alloy (MEA) is designed as the transition layer, and the 316L/FeCrCuV/Ti-6Al-4V dissimilar materials are fabricated by laser metal deposition (LMD). The heterogeneous interfaces of 316L/FeCrCuV and FeCrCuV/Ti-6Al-4V are investigated by a scanning electron microscope (SEM), an energy dispersive spectroscope, and electron backscatter diffraction. The results indicate that common brittle intermetallic compounds TiFe and TiFe2 at Ti-6Al-4V/316L heterogeneous interfaces disappear, and the BCC/FCC dual-phase solid solution structure is obtained due to the solid solution effect of the FeCrCuV transition layer. Refined grains appear at heterogeneous interfaces of 316L/FeCrCuV and FeCrCuV/Ti-6Al-4V for the rapid cooling rate during LMD, which results in fine grain strengthening. The microhardness near heterogeneous interfaces increases the solution strength and fine grain strengthening. Furthermore, the design of the FeCrCuV transition layer with a dual-phase structure improves the coordinated deformation ability of 316L/FeCrCuV/Ti-6Al-4V and results in higher tensile strength.

Optimizing multi-interlayered additive manufacturing for high strength robust joints in Inconel 718 and Ti–6Al–4V alloys

The fabrication of a robust joint of Ti–6Al–4V and Inconel 718 is indispensable for numerous industries including aerospace, space, and biomedical industries, and to date not achieved without intermetallic compounds (IMCs) and microcracks. In this study, the additive manufacturing of a dissimilar functionally graded joint of Ti–6Al–4V and Inconel 718 alloy was achieved by employing V, Cr, and Ni multi-interlayers. Interlayer materials were carefully selected to mitigate the limitations of brittle IMC formation. Microstructure characterization, EBSD, and elemental analysis confirmed that all joints of Ti–6Al–4V/V, V/Cr, Cr/Ni, and Ni/Inconel 718 were crack and IMC-free, despite substantial elemental diffusion throughout the fabrication route. The as-built specimen exhibited a tensile strength of 210 MPa, which increased to 250 MPa after stress-relief heat treatment and is 40% higher than the reported tensile strength of 150 MPa for a laser welded Ti–6Al–4V/Inconel 718 specimen. The maximum hardness of the entire fabrication was 380 VHN, a typical solid-solution hardness value, indicating no detrimental brittle IMC formation. Furthermore, the finite elemental analysis predicted a moderate stress level of 90 MPa at the interface, indicating robust fabrication.

Microstructural and mechanical characterisation of reinforced aluminium foam sandwich panels made by one-step squeeze casting method

ABSTRACT In just one step, a squeeze casting process was applied to produce aluminium foam sandwich panels. NaCl particles with mean sizes of 4.75 and 6.35 mm were used as space holders in different proportions. In-situ face sheet manufacturing was conducted through previously placed steel meshes in the mould. The effect of NaCl particle sizes and the proportion of each size on porosity, microstructure, and mechanical properties were investigated. Results showed a decline from 59.8% to 43.8% in the porosity amount of samples with increasing the proportion of larger NaCl particles. Accordingly, an increase in compression yield stress (from 3.2 to 6.1 kgf/mm2) and the absorbed energy were observed. Also, at the elevated densities of the sandwich panel core, the plateau stress was enhanced. The presence of Cu, Ni, Fe, and Si elements leads to the formation of brittle intermetallic compounds in the microstructure of cell walls.

Improvement in effectiveness of diamond in strengthening the porous aluminium composite

In this study, an aluminum (Al) alloy matrix reinforced with uncoated and titanium (Ti) -coated diamond were developed using powder metallurgy technique where polymethylmethacrylate (PMMA) particles were employed as space holders. The weight % of uncoated and coated diamond varied as (0, 6, 9, 12, 15, and 20 wt.%). Microstructural and elemental analysis was examined using scanning electron microscopy and energy dispersive spectroscope, respectively. The relative density and porosity that were in the range of 0.72–0.92 and 31–44% respectively, were measured using Archimedes principle. The compressive properties were measured and correlated with microstructure observations. The microstructure of the composite samples revealed presence of well-defined macro pores with good interfacial integrity. The X-ray diffraction revealed the presence of strengthening phases such as Al2Ti, Mg2Sn, AlB12, Cu5Sn6, Al12Mg17 and MgB2 phases formed as a result of addition of metal additives in Al matrix. Further improvement in the strength was obtained by using Ti-coated diamond particles as reinforcement. As Ti formed a good interface between the Al alloy matrix and the diamond thereby preventing the formation of undesirable carbide phases. There was an improvement in plateau stress and energy absorption capacity of 82 and 88% as compared to unreinforced porous sample. The maximum values obtained for the plateau stress and energy absorption capacity were 45.12 MPa and 13.68 MJ/m3 respectively for 9 wt.% of Ti-coated diamond reinforced composites. Uncoated diamond reinforced composites, on the other hand, reduced the strength of porous Al alloy matrix due to the formation of brittle intermetallic compound such as carbides (Al2C3) at the interface. As a result, the coated diamond particle surface modifies and improves the wettability of the Al alloy matrix and diamond interface.

Compositive role of refractory element Mo in improving strength and ductility of face-centered-cubic complex concentrated alloys

Complex concentrated alloys (CCAs) with a face-centered-cubic (FCC) structure exhibit remarkable mechanical properties, introducing the expansion of compositional space in alloy design for structural materials. The formation of a single solid-solution phase is enabled by configuring various 3d-transition elements, while doping other elements even of a small portion generally leads to the formation of brittle intermetallic compounds. Herein, we demonstrate through a systematic investigation of single FCC (CoNi)100-xMox alloys that a wide range of refractory element Mo can simultaneously improve the strength and ductility while sustaining the solid-solution structure. The addition of Mo with a larger atomic size than those of 3d-transition elements introduces severe lattice distortion in the FCC lattice and causes grain-boundary segregation enriched by Mo atoms. In addition, increasing Mo content effectively reduces the stacking fault energy (SFE). The increased lattice distortion with Mo content enhances the solid-solution strengthening of the alloys. Besides, along with reduced SFE and stabilization of the dislocation emission site by grain-boundary segregation, this elevated solid-solution strengthening increases grain-boundary strengthening, reaching a yield strength of ∼1 GPa. Moreover, the reduction of SFE with increasing Mo results in the transition of dislocation substructures and the refinement of deformation twins, allowing for enhanced strain-hardening capability and thus ∼1.3 GPa tensile strength and ∼50% ductility. Such compositive and synergetic effects of refractory element Mo enable the CCAs with a single FCC solid solution to overcome the strength and ductility trade-off.

Microstructural evolutions and mechanical characteristics of roll-bonding Mg/Al clad plate regulated by cold spraying micron particle interlayer

A new process of “cold spraying interlayer + roll-bonding” (CSIR) was put forward for the preparation of Mg/Al clad plates. First, the micron Ni and Al powders (including some Zn particles) were cold sprayed to form an ultrathin coating on Al or Mg substrate slabs. Then roll-bonding was performed at 400 °C. The influence of cold sprayed coating on slab surfaces, interfacial microstructures, texture evolutions, mechanical properties and the related mechanism were systematically investigated. The results show that the average shear strength of the as-rolled Mg/Al clad plate assisted by cold spraying Al and Ni micron powders interlayer on the substrate slabs was nearly twice (35.58 MPa) than that of conventional rolling under the same conditions (single pass, reduction ratio was 35%). For as-rolled Mg/Al clad plates, almost no reaction diffusion layers are generated, and the mechanical interlocking between cold sprayed coatings and substrate slabs is the main mechanism for improving the shear strength. The interface between the Al coating and the Ni coating is weakest of the as-rolled Mg/Al clad plates. As the reduction rate increases from 27.5% to 47.5%, the function of the mechanical interlocking of cold sprayed coatings will first increase and then weaken. After annealing at 400 °C for 1 h, the interface between the Al coating and the Mg substrate slab will form thick mixed brittle intermetallic compounds, including Al3Mg2, Mg17Al12, MgZn2 and AlMg4Zn11, and cause local gaps, holes, and cracks around the Zn-rich Ni coating. The fracture path after annealing starts from the vicinity of the defective Ni particles, and eventually enlarges along the mixed intermetallic compounds layer between the Al coating and the Mg substrate slab. The research indicates that the CSIR process has great potential in cooperating the metallurgical bonding with the mechanical interlocking of clad plates.

Acoustic effect on the joint quality and process of friction stir lap welding of aluminum to steel

To gain a high strength-to-weight ratio and economic viability for multiple industrial applications, the Al and steel need to be joined successfully. In the present work, we used conventional friction stir welding (FSW) and ultrasonic vibration enhanced friction stir welding (UVeFSW) techniques to obtain high-strength industrial-grade dissimilar joints of Al and steel. The effects of acoustic energy on the joint quality and welding process were investigated. Macrographs of the joints revealed that ultrasonic vibrations could effectively promote the material flow and increase the mixing degree and width of the Al/steel interface. Steel strips' fragmentation and intermixing with the Al substrate were enhanced under ultrasonic effects. The tool torque, axial force, and spindle power were significantly decreased with ultrasonic vibration. Acoustic assistance was found beneficial to increase the joints’ failure load and change the fracture mechanism. The microhardness of acoustically treated regions was found to be higher compared to its counterparts. The thinning of the brittle intermetallic compounds (IMCs) layer at the interface of the UVeFSW joint was caused by decreased peak temperature during welding. In UVeFSW, when the welding speed was 50 mm/min, the maximum failure load of the joint was obtained under the joint action of the macro interlocks (interface zone), the thinner IMCs layer, and the micro interlocks (laminated structure). When the welding speed was 100 mm/min, the failure load of the joint was improved by 25.8% compared with conventional FSW.

Design and mechanical properties of body-centered cubic AlVCr medium-entropy aluminum alloys

The formation of brittle intermetallic compounds and the poor solubility of other metallic elements in Al alloys render the design of high- and medium-entropy Al alloys (HEAls and MEAls, respectively) challenging. Herein, new AlVCr MEAls were developed based on a reverse approach, which involved starting from an equiatomic V–Cr alloy. Al20VCr, Al33VCr, and Al50VCr were synthesized as MEAls using a vacuum induction-based melting process. The microstructural evolution and mechanical properties of the synthesized MEAls were carefully investigated. Body-centered cubic single-phases formed in Al20VCr and Al33VCr MEAls, in keeping with thermodynamic calculation results as well as multiple phase-prediction parameters. While Al33VCr exhibited brittle fracturing owing to chemical ordering, Al20VCr MEAl exhibited a compressive strain and yield strength of ∼9.4% and ∼1.0 GPa, respectively. Thus, the reverse approach, which is based on the use of an Al-free system initially, should aid the development of a new class of lightweight HEAls and MEAls.

Joining of SiC ceramics using high-silicon aluminum alloy fillers assisted by laser cladding

A Si–40Al joining transition layer was prepared via laser cladding, followed by brazing of SiC ceramics using Si–60Al alloy as the joint filler. The microstructure, composition, and flexural strength of the brazed joints were investigated under different brazing temperatures and holding times. The corrosion resistance of the joints was evaluated using a hydrochloric acid immersion test. The laser cladding layer effectively reduced interfacial stress, enhanced interfacial bonding, and suppressed the formation of brittle intermetallic compounds. The main constituents of the brazed joint were Si, Al2O3, and SiC, with newly formed SiC at the interface promoting interfacial bonding. The flexural strength of the brazed joint held at 900 °C for 30 min exceeded 279 ± 13 MPa, equivalent to that of the SiC substrate. Compared to direct brazing of SiC using Si–60Al alloy filler and Si–40Al alloy filler, the strengths were increased by 49% and 94%, respectively. Furthermore, the joints exhibited excellent corrosion resistance, with a flexural strength of 177 ± 11 MPa after 10 h of hydrochloric acid immersion.

Influence of welding parameters on the interface temperature field of TC4 titanium alloys/304 stainless steel friction stir lap joints

Abstract The welding parameters optimization of TC4 titanium alloys/304 stainless steel (TC4/304 SS) by friction stir lap welding (FSLW) based on orthogonal test was researched. The results show that when the rotating speed was constant, the area of the high temperature zone and the peak temperature decreased with the increase of the traversing speed; when the traversing speed was constant, the area of the high temperature zone and the peak temperature increased with the increasing rotating speed. Among them, under the condition of low heat input, the interface temperature was about 912 °C, the material at the interface cannot fully react, and there was no formation of a large amount of brittle and hard intermetallic compounds; under the condition of medium heat input, the interface temperature was about 930 °C, this temperature caused a large amount of brittle and hard intermetallic compounds at the interface; under high heat input, the interface temperature was about 975 °C, a large number of intermetallic compounds were not formed at the interface.

Nickel Nanoparticle/Carbon Films as an Interlayer To Improve the Stability of Solder Joints

The growth of brittle intermetallic compounds (IMCs) generated between a solder and a substrate is crucial for the reliability of solder joints. Therefore, it is necessary to control the growth of IMCs at the interface. Herein, we propose a strategy with the nickel nanoparticle/carbon (Ni&C) films as an interlayer to improve the stability of the solder joint. After adding the interface with the Ni&C film and reflowing for 450 s, the growth of IMCs decreased by 41.05%. After reflowing for 450 and 2100 s, the grain size in the 300 s-Ni&C/Cu substrate decreased by 14.34 and 20.50%, respectively, compared with the pure Cu substrate. Furthermore, the Ni&C film changes the microstructure of the interface and the diffusion pattern of elements, thus reducing the number of Kirkendall voids. As the reflow time increases, the scalloped IMCs are transformed to be prismatic, which can be well explained by the Gibbs–Thomson effect. The synergistic effect between Ni and carbon in Ni&C can jointly control the interface reaction and the growth of IMCs, with the Ni&C film acting as an inert barrier to inhibit the growth of IMCs.

Interface characterization and intermetallic compounds formation mechanism of V-4Cr-4Ti/316SS laser welded joints

In fusion reactors, the efficient connection of V-4Cr-4Ti and 316 stainless steel (316SS) is critical for heat transfer between blankets and heat exchangers. However, the presence of brittle intermetallic compounds (IMCs) can degrade the properties of welded joints, so it is necessary to investigate the formation and their mechanism of IMCs. In this study, the morphology, microstructure, hardness of the welded joint between V-4Cr-4Ti and 316SS, were analyzed after laser welding with a Cu interlayer. No significant defects (e.g., pores, macrocracks, or microcracks) were observed in the welded joints after welding, indicating good weldability. Three interfaces are formed according to the analysis of the morphology: V-4Cr-4Ti and the heat affected zone (HAZ), the HAZ and the weld, and the weld and 316SS. According to the microstructural analysis, the CuTi2 with a structure of face-centered cubic (FCC) is formed at the interface between the IMC layer and the weld, while TiFe with a structure of body-centered cubic (BCC) is formed at the weld and 316SS interface. The σ phase is formed at all three characteristic interfaces. The results of nanoindentation test show that the hardness and elastic modulus of HAZ and weld are higher than that of base metal, which may be due to the formation of IMCs. In addition, the sequence and mechanism of IMCs formation in V-4Cr-4Ti/316SS laser welded joints with Cu interlayers are discussed.

The effect of small additions of Nb and Ti on the sliding wear behavior of a Co–30Cr–5Mo alloy

This work studies the addition of 0.5%Nb and 0.5%Ti in a Co–30Cr–5Mo alloy as well as the increase of carbon from 0.1 to 0.3%. The main goal is to increase the wear resistance of the alloy with such additions due to the formation of primary carbides (TiC and NbC). The additions of carbon, niobium and titanium were as ferroalloys, which implies the addition of iron into the chemistry of the alloy. Microstructural prediction studies by JMatPro indicate that the addition of all of these elements promotes an increase in the amount of the sigma phase, an undesirable phase because it is a hard brittle intermetallic compound. However, this undesirable phase could be eliminated from the structure by means of a solubilization heat treatment undertaken at 1200 °C for 2 h; this heat treatment lowered the values of hardness of the alloys. An additional aging heat treatment promoted the precipitation of chromium carbides of the type M23C6 as dispersed elongated bars within the cobalt matrix, which notably increased the hardness of the alloys. Each alloy was wear tested under two loads 52 and 78 N and under dry sliding and also under lubricated sliding using Hank solution as lubricant; the tests were undertaken at a sliding speed of 0.5 m/s. Results indicate that the addition of Ti and Nb produced small amounts of TiC and NbC in addition to a light increase in the amount of the sigma phase which increased hardness in the as-cast conditions. These alloys, with Ti and Nb additions, shown the higher hardness values in the as-aged conditions. The wear resistance of the alloys are in agreement with the hardness results particularly for the dry sliding tests. Wear resistance was higher for the harder alloys (those with Nb and Ti additions in the as-aged conditions) and it is lower for the higher applied load. For the case of the lubricated wear tests, such a trend is also observed but not so clearly as for the unlubricated tests. However, friction and wear for the lubricated experiments shown values extremely low compared to these observed for the unlubricated sliding wear tests.

Studies on Metallic Glasses in Utsunomiya University

Studies on dissimilar metal welding and mechanical fastening using metallic glasses in Utsunomiya University have been introduced. Metallic glass ribbons placed between the two dissimilar metal plates become supercooled liquid with low viscosity by resistance welding and promote supercooling at the nuggets. As a consequence, the residual stress at the welding boundary and the formation of brittle intermetallic compounds are suppressed, resulting in excellent dissimilar resistance welding with high joint strength and high reproducibility. Mechanical fastening of two metal plates is also demonstrated by resistance heating and viscous flow forming of metallic glass rivets. Producing metallic glass rivets using bulk metallic glasses by a resistance heating is now under examination.