Formation Of Brittle Intermetallic Compounds Research Articles

Predicting and controlling interfacial microstructure of magnesium/aluminum bimetallic structures for improved interfacial bonding

Abstract In this study, an overcasting process followed by a low-temperature (200°C) annealing schedule has been developed to bond magnesium to aluminum alloys. ProCAST software was used to optimize the process parameters during the overcasting process which lead to Mg/Al bimetallic structures to be successfully produced without formation of Mg-Al intermetallic phases. Detailed microstructure evolution during annealing, including the formation and growth of Al-Mg interdiffusion layer and intermetallic phases (Al12Mg17 and Al3Mg2), was experimentally observed for the first time with direct evidence, and predicted using Calculation of Phase Diagrams (CALPHAD) modeling. Maximum interfacial strength was achieved when the interdiffusion layer formed at the Mg/Al interface reached a maximum thickness the without formation of brittle intermetallic compounds. The precise diffusion modeling of the Mg/Al interface provides an efficient way to optimize and control the interfacial microstructure of Mg/Al bimetallic structures for improved interfacial bonding.

Peculiarities of Pressure Welding of Pd Foil to Stainless Steel

The peculiarities of joining a palladium alloy foil to 12Cr18Ni10Ti stainless steel by diffusion and resistance welding are considered. It is shown that both technologies can be realized only using an intermediate nickel layer with a thickness of 0.1 mm, which provides uniform strength and joint tightness and also prevents the formation of brittle intermetallic compounds. Diffusion welding allows one to obtain high-quality joints of palladium alloy to stainless steel, but this process proceeds at relatively high (950°C) temperatures and takes a long time. Resistance welding does not have these disadvantages, but the outcome significantly depends on the correct choice of welding conditions, upon which the spot weld nugget must be displaced as much as possible toward the stainless steel and the intermediate nickel layer. The connection of the palladium alloy to the intermediate layer occurs owing to mutual diffusion occurring during the passage of the welding pulse.

Strong and reliable dissimilar brazing titanium to copper using niobium diffusion barrier

Dissimilar brazing of titanium (Ti) and copper (Cu) using Ag-based braze and niobium (Nb) diffusion barrier was investigated. It was found that the addition of a Nb interlayer can effectively block the interaction between Ti substrate and molten braze, thus completely eradicate the formation of brittle intermetallic compounds (IMCs). This leads to a brazed joint consisting of Ti-Nb solid solution, remnant Nb interlayer and Ag-Cu braze. The resultant IMCs free joint exhibits superior structural integrity with bonding strength exceeding that of the Cu substrate. Meanwhile, negligible dissolution of Nb into molten braze and sluggish solid-state diffusion at the Ti/Nb interface keep the Nb interlayer intact, enabling excellent reliability of the joint.

Application of pulse plasma MIG welding process to Al/steel dissimilar joining

Arc welding of aluminium and steel joins are commonly inundated by the formation of brittle intermetallic compounds (IMC) at the aluminium-steel interface. As the formation of IMC is closely related to the heat input into the base metals, it is hypothesised that the ability to regulate the heat input would enable the control of the thickness of IMC. This paper proposes the use of a pulse plasma MIGW system to regulate the heat input during the welding process. A shadowgraph method was used to compare the weld droplet stability of the pulse plasma MIGW with a pulse MIGW system. It was found that the plasma MIGW generated a regular heat input into the base metal due to the smoothness of the droplet detachment and resulted in the formation of IMC with uniform thickness. Al/steel joining was then conducted using both pulsed plasma MIGW and pulse MIGW systems, and the resulting IMC formations and thicknesses were evaluated. It was found that the formation and thickness of IMC in Al/steel dissimilar welding can be controlled by using pulse plasma MIGW. Its lower droplet temperature and decreased cooling rate during welding would suppress the formation of Fe2Al5 and FeAl3, and thus decreasing the overall thickness of IMC at the joining interface.

Influence of interlayer on microstructure and mechanical properties of friction stir welded dissimilar joints: A review

The study of joining dissimilar materials through Friction Stir Welding process is a trending issue because of increasing application in marine, aerospace, automobile, high speed train and ship industry. FSW process is becoming popular as an energy efficient green technology as it is free from shielding gas and harmful emissions. Joining of dissimilar materials plates is more challenging task in many techniques due to the formation of brittle intermetallic compound (IMC) and large residual stress. To reduce these problems interlayers were used in many welding processes. FSW is a modern technique which can reduce the above stated defects to a minimum effect, by considering few operating parameters. The main aim of this review paper is to discuss about the selection of dissimilar aluminium and magnesium alloys and many criteria for the selection of interlayer materials to insert between the dissimilar materials such as thickness of interlayer and physical properties. This paper also focuses on the corresponding effects of positioning the Mg and Al alloy during the process, to get sound weld joint. The main advantage of using interlayers in FSW is to improve the microstructure and mechanical properties with enhance the corrosion resistance.

Feasibility study of different filler metals on MIG-TIG double-sided arc brazing of titanium alloy-stainless steel

The feasibility of Cu, Cu-Si and Cu-Ni based filler metals on MIG-TIG double-sided arc brazing (DSAB) of TC4-304ss (Ti-SS) was studied. The microstructures and mechanical properties of the joints were investigated and compared. Defect-free Ti-SS brazing joints with double-sided sound forming were achieved using different filler metals. Thin reaction layers with the thickness of 75 μm and 50 μm were respectively formed at the Ti-side interfaces in the Cu filled joint and the Cu-Si filled joint, which mainly consisted of various Ti-Cu phases. The reaction layer with a width of 115 μm formed in the Cu-Ni filled joint showed complex phases of β-Ti, Ti2Cu, TiNi, Ti(Cu1-xNix)2 (x = 0.20–0.82), (Cu1-x Nix)1-y Tiy (x = 0–1; y = 0–0.14), TiCu4, Cu (s,s) phases. The Ti-Fe brittle phases formed at the SS side interface and weld zone in Cu-filled joint were replaced by the Ti-Si-containing phases in Cu-Si filled joint and Cu-Ni-containing phases in Cu-Ni filled joint. The tensile strength of the joints was 256 MPa, 273 MPa and 276 MPa, respectively. The Cu filled and Cu-Si filled joints fractured at the SS side interface due to the presence of the flat interface and the formation of brittle intermetallic compounds (IMCs). The Cu-Ni filled joint fractured at the thick Ti side interface, which induced by Ti(Cu1-xNix)2 phase with high brittleness.

Effects of Boron Addition on the Microstructure and Mechanical Properties of (Ti,Ta)(C,N)-Co Based Cermets

In this work, a titanium–tantalum carbonitride based cermet, with cobalt as the binder phase and boron as a sintering additive, was developed by a mechanically induced self-sustaining reaction process using two different methodologies. The boron additive was added to prevent the formation of brittle intermetallic compounds generally formed during the liquid phase sintering step due to the excessive ceramic dissolution into the molten binder phase. A systematic study was carried out to understand the effects of boron addition on the nature of the phases, microstructure, and mechanical properties of cermets. With the boron addition, the formation of two different boride solid solutions, i.e., (Ti,Ta)B2 and (Ti,Ta)3B4, was observed. Moreover, the nature of the binder was also modified, from the (Ti,Ta)Co2 brittle intermetallic compound (for cermets without boron addition) to ductile and tough (Ti,Ta)Co3 and α-Co phases (for cermets with boron addition). These modifications caused, as a general trend, the increase of hardness and toughness in cermets.

Continuous laser welding with spatial beam oscillation of dissimilar thin sheet materials (Al-Cu and Cu-Al): Process optimization and characterization

Continuous laser welding with spatial beam oscillation was investigated as a method of joining combinations of thin copper and aluminum sheets. Welding of these materials is required for manufacturing of electronic components due to their physical properties. Welding of dissimilar metals such as Al-Cu with conventional manufacturing techniques is difficult due to unavoidable formation of brittle intermetallic compounds, which reduce both the mechanical and electrical properties of the joint. The aim of this work was to understand how process parameters such as laser power, welding speed and wobbling amplitude affected the weld seam, making it possible to determine which parameters were of greatest influence on the mechanical and electrical properties of the resulting joint. Both the width and penetration of the weld seam were strongly correlated to the wobbling amplitude. The ultimate tensile strength of both configurations (Al-Cu and Cu-Al) was as high as 100 kgf with optimized process parameters. Micro-hardness tests showed an increase in hardness near the molten area. The temperatures attained during welding were approximately 40 °C at 10 mm from the weld seam. Low electrical contact resistance and high tensile strengths were obtained with the same parameters.

Dissimilar metals deposition by directed energy based on powder-fed laser additive manufacturing

In this research, powder-fed laser additive manufacturing based on directed energy deposition (DED) technology is utilized for 3D printing/fabrication of dissimilar alloy walls. Three-dimensional fabrication of metallic layers (A410-L stainless steel, A316-L stainless steel, and zirconium) with different crystallographic structures such as body-centered cubic (BCC), face-centered cubic (FCC), and hexagonal close-packed (HCP) are studied. Solidification cracking of the HCP metal structure inhibits the manufacturing of a sound dissimilar wall during direct deposition of zirconium on stainless steel. Different techniques are employed to eliminate cracking during the deposition of such dissimilar walls. First, a functionally graded transition layer is employed to gradually transition from a BCC or FCC layer to a zirconium layer. However, several longitudinal and horizontal cracks are observed in the functionally graded structure, deteriorating the overall integrity of the wall. Subsequently, inter-layers are applied to reduce the metallurgical differences between the BCC, FCC, and HCP metal structures. These inter-layers are designed to suppress the formation of brittle intermetallic compounds and decrease the level of thermal stress leading to cracking. Several metallic powders including nickel, titanium, vanadium, and copper are tested and analyzed as inter-layer materials during layer by layer fabrication of the dissimilar wall. Cross-sectional examinations are performed for each case, in order to study the feasibility of fabricating a sound dissimilar wall without deleterious phases. Embrittlement and presence of nickel-rich intermetallics within the Zr matrix restricts the successful fabrication of a dissimilar alloy wall through the formation of vertical cold cracks. Samples with titanium and vanadium inter-layers demonstrate horizontal hot solidification cracking at the stainless steel interface, which is attributed to the large solidification temperature range. Nonetheless, best results are attained with the copper inter-layer due to its high compatibility with both of the stainless steel and Zr metals.

Inhibiting Brittle Intermetallic Layer in Magnesium/Aluminum Bimetallic Castings via In Situ Formation of Mg2Si Phase

A quasi-continuous Mg2Si layer is formed in situ at the magnesium/aluminum interface of bimetallic castings, by selecting a Si-containing aluminum alloy and overcasting process control. This effectively inhibits the formation of brittle intermetallic compounds (Al3Mg2, Al12Mg17) during the casting process, and the mechanisms are discussed based on phase diagram calculations and experimental validation. It is, thus, recommended to select Si-containing Al alloys as substrate for Mg/Al bimetallic castings.

Effect of Mechanical Mixing in Dissimilar Friction Stir Welding of Aluminum to Titanium with Zinc Interlayer

Welding of aluminum (Al) and titanium (Ti) is difficult and challenging due to their differences in chemical and physical properties, and the evolution of brittle intermetallic compounds. Formation of critical intermetallics can be minimized by using an interlayer material, which leads to ternary mechanical mixing in the weld nugget. In the present investigation, a zinc (Zn) interlayer has been used during friction stir welding (FSW) of Al–Ti. It has been found that tool offset position is one of the important parameters in controlling the amount of ternary mechanical mixing of materials. The mechanical mixing of Zn with Al and Ti alters the phase evolution and restricts the formation of the brittle Al3Ti intermetallic compound. The optimum tool offset exhibits a homogeneous mechanical mixing and inhibits the formation of brittle intermetallic compounds, which leads to a substantial increment in the mechanical properties of the weld.

CMT Welding of Titanium and Stainless Steel Using CuSi3 Electrode

The article deals with the possibility of a tight permanent joint of X5CrNi 18–10 austenitic steel and UNS N50400 titanium. The nuclear and chemical industries are in particular interested in solving this problem. The joining by means of fusion welding has come up against unreliability due to the formation of brittle intermetallic compounds between titanium and iron. The article deals with joining of these two heterogeneous materials by an innovative CMT welding method. CuSi3 soldering electrode was chosen as the additional material. Protective atmosphere consisting of clean argon has been chosen due to the undesirable gas absorption by titanium at temperatures over 600 °C. The results will compare different welding parameters and their impact on the quality of the weld joint. The quality of the created welds will be verified on the basis of the tensile test and the results will be graphically visualized. The microhardness in the weld and its surroundings will be measured. The microhardness measurement results will be graphically displayed. The experimental results will be supplemented by macrostructure snapshots and metallographic analysis snapshots.

Effects of process parameters on the quality aspects of weld-bead in laser welding of NiTinol sheets

ABSTRACTThe effects of process variables, like scan speed and laser power, on the quality of bead-on-plate welding of NiTinol sheets were investigated. The measured quality aspects for the weld-bead profile were bead geometry, changes in microstructure, variation of microhardness value along the weld-bead, extent of oxide contamination during welding, Ti/Ni ratio after welding, changes in tensile strength of the welded samples and corrosion behavior of the welded and parent materials. The laser weld-bead profile changed from the shape of a stemless wineglass to that with a prominent leg. Dimensional aspects of weld-bead geometry showed a decreasing trend with increasing scan speed. However, an increasing trend of the same was observed with power. The Ti/Ni ratio on the top surface after welding was found to decrease with scan speed at a particular power. Oxide contamination during welding followed the same pattern of variation as that of the Ti/Ni ratio. Microhardness values gradually increased from the weld centerline to the base metal. Formation of brittle intermetallic compounds reduced the tensile strength of the material after welding. A dual failure mode for the welded sample was observed, whereas a single mode of failure was detected for the parent material. The corrosion properties of the welded samples were better than that of the parent material.

Co-P Diffusion Barrier for p-Bi2Te3 Thermoelectric Material

(Bi0.25Te0.75)2Te3 (p-Bi2Te3) is thermoelectric material that can harvest waste heat into useful electric power. A severe reaction between p-Bi2Te3 and Sn-based solder decreases the reliability of thermoelectric modules. Sn/p-Bi2Te3 and Sn3.0Ag0.5Cu (SAC305)/p-Bi2Te3 with and without electroless Co-P at the interfaces were investigated in this study. Without a Co-P layer, brittle SnTe, Sn3Sb2, and Bi precipitates formed at the interface. A thin layer of SnTe after reflow results in growth of a layer-type Sn3Sb2 instead of a strip-like Sn3Sb2. The addition of a Co-P layer to both systems successfully inhibited the formation of brittle intermetallic compounds. Shear test results confirmed that the Co-P diffusion barrier also effectively increased the joint strength.

A Comprehensive Study of Diffusion Bonding of Mg AZ31 to Al 5754, Al 6061 and Al 7039 Alloys

In the present study, microstructural and mechanical properties of diffusion bonding of AZ31–Mg with Al 5754, Al 6061, and Al 7039 alloys were compared under same conditions. The vacuum diffusion processes were performed at a temperature of 440 °C, the pressure of 29 MPa, and a vacuum of 1 × 10−4 torr for 60 min. The microstructural characterizations were investigated using optical microscopy and scanning electron microscopy equipped with EDS analysis and linear scanner. The XRD analysis was performed to study phase figures near the interface zone. The results revealed the formation of brittle intermetallic compounds like Al12Mg17, Al3Mg2, and their other combinations at bonding interfaces of all samples. Additionally, the hardness of Al alloys seemed to play a key role in increasing diffusion rate of magnesium atoms toward the aluminum atoms, with Al 6061 alloy having the highest diffusion rate. It consequently led to an increase in diffusion rate and thus formation of a strong diffusion bonding between magnesium and aluminum alloys. The highest strength was about 42 MPa for the diffusion bonding between Mg AZ31 and Al 6061. Further investigations on surfaces indicated that the brittle phases especially Al3Mg2 caused brittle fracturing.

Parameter optimization of laser welding of steel to Al with pre-placed metal powders using the Taguchi-response surface method

Welding of steel to aluminum alloy is a difficult work due to the formation of brittle intermetallic compounds. In order to improve the quality of the dissimilar materials weld joints, metal powders are pre-placed on the surface of aluminum alloy prior to welding. In this study, laser welding technique is employed to join DC04 steel to 6016 aluminum alloy with pre-placed metal powders in a lap joint configuration. The morphology, micro-structure and elemental composition of the joints are characterized using SEM equipped with an EDS and optical micro-scope while the micro-hardness and tensile strength are measured. It is indicated that although metal powders do not form compounds directly with Fe or Al, they prevent the contact of Fe and Al. Tensile experiments show that the pre-placed metal powders can significantly improve the joints’ tensile properties. The combined Taguchi-response surface method approach is employed to optimize the laser welding parameters and the optimal condition to have a quality weld is found at laser power 1344.73 W, welding speed 30 mm/s, Defocus distance −2 mm, Shield gas flow 30 L/min. Confirmation experiment proves that the Taguchi-response surface method is an effective way to optimize welding parameters to gain higher mechanical resistance reach to 165.24 N/mm and the bead appearance of optimization joint with fish scales and without cracks.

Effect of Ni-Ti filler on brazed W-Cu/18-8 joints

W-Cu composite and 18-8 stainless steel were vacuum brazed with an improved Ni-based filler metal, with varying Ti content. The microstructure, element distribution, phase composition, and fracture mechanism of the brazed joints were investigated. The improved NiCrSiBFe-Ti quench filler metal showed good wettability on the W-Cu composite and 18-8 stainless steel. Enhanced diffusion and metallurgical reactions between the filler metal and base metal were observed. The addition of Ti not only optimized the structure, but also reduced the formation of brittle intermetallic compounds, which is important for significantly improving the brazed-joint strength. The highest brazed-joint shear strength (381 MPa) was observed when the Ti content was 1.6%.

Additive manufacturing hybrid Ni/Ti-6Al-4V structural component via selective laser melting and cold spraying

The hybrid Ni/Ti-6Al-4V structural component was fabricated by an innovative hybrid additive manufacturing (AM) process, which combines two very effective AM techniques of selective laser melting (SLM) and cold spraying (CS), and an Eulerian model was used to study the deposition behavior of Ni on Ti-6Al-4V. The influence of vacuum heat-treatment on the interfacial microstructure and adhesion strength of the hybrid structural component was examined. After vacuum heat-treatment, the annealing twins were observed accompanying the healing-up of un-bonded interfaces between the deposited Ni particles, and the platelet α phase with the intergranular β phase was in-situ decomposed to acicular α′ martensite. The abnormal coarser α and fleck β, as well the multi-layer intermetallic near the interface between Ni/Ti-6Al-4V, were investigated. In addition, a reduction in bonding strength between deposit/substrate was evaluated after vacuum heat-treatment due to the formation of brittle intermetallic compounds.

Aluminium to steel resistance spot welding with cold sprayed interlayer

ABSTRACTStudies on bonding of aluminium alloys to steels are popular because these are structural materials widely used in a variety of industries. However, joining these dissimilar materials is difficult mainly because of the formation of brittle intermetallic compounds. This paper presents a study on welding aluminium to steel by resistance spot welding. Before the welding, steel surface was covered by cold spraying with the layer of aluminium, nickel and nickel–aluminium. This way, instead of the welding of dissimilar materials, the welding of aluminium to aluminium (or nickel) layer pre-deposited on the steel sample was performed. The feasibility of using interlayers for improving the welding of dissimilar materials was tested using SEM, EDX and XRD. Mechanical properties of welds were investigated by microhardness and shear strength tests. The results showed that the coating allowed to decrease hardness in the welding zone and to increase the shear strength of the weld.

Improving Mechanical Properties of Dissimilar Material Friction Welds

Friction welding of stainless steel to titanium with aluminum insert metal was investigated to improve the mechanical properties of the joints. Two different methods were used to insert the aluminum as a barrier between to substrates. The process parameters were found to be different for these two methods to obtain the sound welds. The friction welds between stainless steel and titanium with aluminum insert prevented the formation of brittle intermetallic compounds in the weld interface. A new intermetallic compounds such as AlTi and Al3Ti were formed between titanium and aluminum insert metal interface which are more ductile than the FeTi and CrTi intermetallic compounds. The joints characterized that the aluminum insert metal improved the metallurgical reaction at the weld interfaces thus indicates the results of decrease in microhardness of the intermetallic compounds which have major influence on the strength of the joints. The tensile strength of the aluminum insert welds was higher than the direct joints between the stainless steel and titanium. Higher tensile properties were attained at higher upset pressure condition due to the effect of higher force upon the welded materials and the remnant narrower thickness of insert metal.