Metallurgical Reactions Research Articles

Wetting and spreading behavior of Ti-based brazing filler on Ti64 substrate

In this work, wetting behavior of Ti–20Zr–20Cu–20Ni brazing filler on Ti–6Al–4V substrate was studied using sessile drop technique. Effects of the substrate surface roughness, Ra of ~0.40 and 0.08 µm, and heating scheme on wetting and spreading of the filler metal were evaluated. The wetting mechanism was investigated by the combination of cooling technique, thermal, compositional, and microstructural analysis. This was performed using a heat-flux DSC and an SEM equipped with EDS. The degree of wetting was evaluated by measuring the apparent dynamic contact angle between the filler drop and substrate surface and by calculating the drop spread ratio. The surface roughness of the substrate was found to have little or no effect on the final apparent contact angle. The wetting behavior of this system showed a reactive nature, because it involves dissolution of the substrate and formation of interfacial layers. Three heating schemes were used in the current study. While the high heating rate of 6.8 °C s−1 was found to limit the metallurgical reaction between the substrate and the brazing filler, in the low heating rate scheme of 1.7 °C s−1, more intense metallurgical reaction occurred between the brazing filler and the substrate. The high heating rate with soaking scheme is recommended for brazing, because it entails extensive spreading and limited metallurgical reaction between the brazing filler and the substrate.

Microstructure and mechanical behavior of friction spot welded AA6181-T4/Ti6Al4V dissimilar joints

Friction spot welding has become an excellent alternative to produce dissimilar joints in a fast and reliable way. This paper investigates the microstructure and the mechanical behavior of friction spot welded AA6181-T4/Ti6Al4V dissimilar joints produced by two different tool rotational speeds, 2500 and 3000 rpm, previously demonstrated to be the welding parameter with the most influence on the mechanical performance of these joints. Temperature profiles indicated that tool rotational speed directly affects the process temperature and, consequently, the metallurgical reaction taking place at the joint interface. Higher temperatures (3000 rpm condition) resulted in a complex and cracked Ti/Al interface because of the local melting of the aluminum plate. In contrast, by decreasing the process temperature (2500 rpm condition), a continuous thin TiAl3 layer was observed, increasing the lap shear resistance of the joints. Moreover, the local Von Mises strain distribution of a sound joint under lap shear was successfully associated with the different stages of a typical force–displacement curve and used to elucidate the fracture evolution. Lastly, the fatigue behavior of the joints indicated that FSpW dissimilar welds exhibited a better performance than FSpW aluminum similar joints.

Effect of adding powder on joint properties of laser penetration welding for dual phase steel and aluminum alloy

The experiments of laser penetration welding for dual phase steel and aluminum alloy were carried out, and the effect of adding Mn or Si powder on mechanical properties and microstructure of the weld was investigated. Some defects, such as spatter, inclusion, cracks and softening in heat affected zone (HAZ), can be avoided in welding joints, and the increased penetration depth is obtained by adding Mn or Si powder. The average tensile-shear strength of Si-added joint is 3.84% higher than that of Mn-added joint, and the strength of both joints exceeds that of no-added joint. In the case of adding Mn powder, small amount of liquid Al is mixed into steel molten pool, and the Al content increases in both sides of the weld, which leads to the increased weld width in aluminum molten pool. Thus, transverse area increases in jointing steel to aluminum, which is significant for the improved tensile-shear strength of joints. As far as adding Si powder is concerned, it is not the case, the enhancement of the joint properties benefits from improvement of metallurgical reaction.

The effect of TIG arc brazing current on interfacial structure and bonding strength of tin-based babbit

The interfacial structure of the tin-based babbit obtained by TIG arc brazing was studied through the OM, XRD, SEM and EDS and the bonding strength was investigated by the Electronic Universal Testing Machine. It can be found that interfacial layers, unequal in thickness, ranged from 10.26 to 34.27 μm and IMCs layers formed at the interface, ranged from 1.5 to 4 μm as the welding current increased from 50 to 90 A. Also, the bonding strength apparently increased from 73 to 155 Mpa and shear fractures which occurred at the interface near iron substrate side were mainly brittle cleavage fracture. On the brazed interface, the higher element concentration of Fe was helpful to promote the metallurgical reaction and ensured the bonding property. The phase constituents of IMCs were FeSn, FeSn2 and Fe3Sn2. Moreover, the FeSn layer was plate shape, FeSn2 layer and Fe3Sn2 layer were branched shape which staggered with the plastic Sn-based solid solution so that the bonding strength was improved. Physical model of the Fe–Sn IMC layers formation mechanism was proposed, the experimental results further showed that the model was scientific and effective.

The effect of alumino-thermic addition on underwater wet welding process stability

Real-time electric signal data, metal transfer images and weld appearances at different alumino-thermic additions in underwater wet flux-cored arc welding (FCAW) were obtained. The electric signal results showed that the thermite addition would improve the stability of the wet welding process while the weld appearances at larger content of thermite displayed numerous tiny spatters. The shock in weld pool due to metallurgical reaction was responsible for the tiny spatters. Two typical modes of metal transfer process, globular repelled transfer mode and surface tension transfer mode, were observed. The aluminum flux addition changed the droplet diameter, transfer time and relative proportion of metal transfer mode. When the thermite addition increased from 0 to 50%, the weld penetration depth increased from 2mm to 4mm, and the weld dilution rate increased from 22% to 37%.

Analysis of aluminium brazing sheet differential scanning calorimetry data

Differential scanning calorimetry (DSC) measurements have provided insight into metallurgical reactions which can occur during joining of Al brazing sheet. Researchers have claimed that DSC is sensitive enough to differentiate between brazing sheets with different initial conditions; however, no rigorous proof of this claim has been given. The sensitivity of DSC measurements, as measured by changes in melting peak area, to experimental factors such as DSC sample preparation, sample orientation during testing and starting sheet temper has been investigated. A 23 factorial design was used, and the results were analysed using analysis of variance. The results showed that only the sheet punching direction during sample preparation had a statistically significant influence on the DSC measurements. Microstructure analysis revealed that punching on the core layer of the sheet led to extra clad alloy on the side of the sample, which melted during heating and contributed to a greater measured melting peak area.

КИНЕТИКА ИСПАРЕНИЯ МЕТАЛЛОВ ИЗ Sb–Pb–Ag СПЛАВА ПРИ ВАКУУМНОЙ ПЕРЕГОНКЕ

Most of today's research is mostly concentrated on the thermodynamics of the separation of polymetallic alloys by vacuum distillation, as it allows you to determine whether the direction and limitation of the flow of the metallurgical reactions. While studying the kinetics of evaporation of metals it is possible to identify the effective process conditions, such as temperature, vacuum grade and duration of distillation required in the design process for the separation of the components of the alloys. The goal of the work was to determine the rate of evaporation of the metals from the Sb–Pb–Ag alloys of different composition depending on temperature and pressure, and identify the limiting stage of the process. In the making prototype models, sample source metal was welded in an induction furnace in argon atmosphere of high purity, to obtain the alloy composition, mol. %: 16–77 Sb; 75–20 Pb; Ag 9–3. It this work the kinetics of evaporation of metals from Sb–Pb–Ag alloy in temperature range 823–1073 K and a pressure of 1.33–133 Pа is defined, as described by the first order equation. Values of the apparent rate of the first order constants with the sublimation of metals from the melt depends on temperature, pressure and chemical composition of the alloy. The total mass transfer coefficients of lead, antimony, silver ( k Me , m· . s –1 ) evaporation of Sb–Pb–Ag (0,55–0,40–0,05) of the alloy is (3.718–7.852)·10 –7 , (1.194–2.436)·10 –7 , (1.859–3.790)·10 –10 at T = 823–1073 K, P = 13.3 Pa, respectively. The calculated apparent activation energy of evaporation of the metals from the Sb–Pb–Ag alloy: E = 20,93–46,41 kJ/mol. The apparent activation energy of evaporation of the metals, calculated by the Arrhenius equation leads to the conclusion of an easier evaporation of components from the composition of the Sb–Pb–Ag alloy compared to pure metal: E = 150–280 kJ/mol. It is shown that quantitative transport of lead and antimony in the gas phase does not limit the speed in vacuum distillation. The evaporation of the metals from the Sb–Pb–Ag alloy is controlled jointly by mass transfer, mainly in the liquid phase, as well as through the surface layer at the phase interface liquid–gas in the studied experimental conditions. Increasing temperatures above 823 K increases the rate constants of the evaporation k Me components Sb–Pb–Ag alloy. Reducing system pressure less than 133 Pa contributes to the sublimation of antimony, lead and silver.

Process-Structure-Property Relationships for 316L Stainless Steel Fabricated by Additive Manufacturing and Its Implication for Component Engineering

We investigate the process-structure-property relationships for 316L stainless steel prototyping utilizing 3-D laser engineered net shaping (LENS), a commercial direct energy deposition additive manufacturing process. The study concluded that the resultant physical metallurgy of 3-D LENS 316L prototypes is dictated by the interactive metallurgical reactions, during instantaneous powder feeding/melting, molten metal flow and liquid metal solidification. The study also showed 3-D LENS manufacturing is capable of building high strength and ductile 316L prototypes due to its fine cellular spacing from fast solidification cooling, and the well-fused epitaxial interfaces at metal flow trails and interpass boundaries. However, without further LENS process control and optimization, the deposits are vulnerable to localized hardness variation attributed to heterogeneous microstructure, i.e., the interpass heat-affected zone (HAZ) from repetitive thermal heating during successive layer depositions. Most significantly, the current deposits exhibit anisotropic tensile behavior, i.e., lower strain and/or premature interpass delamination parallel to build direction (axial). This anisotropic behavior is attributed to the presence of interpass HAZ, which coexists with flying feedstock inclusions and porosity from incomplete molten metal fusion. The current observations and findings contribute to the scientific basis for future process control and optimization necessary for material property control and defect mitigation.

Interface dynamics in one-dimensional nanoscale Cu/Sn couples

The isothermal metallurgical reaction in two-segmented Cu-Sn nanowires results in the formation of a Sn/Cu6Sn5/Cu3Sn/Cu sandwich structure. In-situ transmission electron microscopy is used to study how Cu6Sn5/Sn and Cu/Cu3Sn interfaces propagate and change shape during the intermetallic compound growth. The Cu6Sn5/Sn interface is observed to evolve from an inclined configuration to a vertical, edge-on configuration with the propagation of the Cu6Sn5 phase towards the Sn segment. The Cu/Cu3Sn interface also becomes less inclined as it propagates toward the Cu segment. This interface evolution is driven by the minimization of the interface energy associated with minimizing the interface area associated with the edge-on interface. The Kirkendall void growth induces the breakage of the Cu segment and results in the Cu3Sn → Cu6Sn5 transformation with the final Sn/Cu6Sn5/void/Cu sandwich structure.

Overwhelming reaction enhanced by ultrasonics during brazing of alumina to copper in air by Zn-14Al hypereutectic filler

The ultrasonic-assisted brazing of α-alumina to copper was achieved in air without flux using Zn-14wt%Al hypereutectic filler at 753K within tens of seconds. The effects of ultrasonic time on the microstructures and mechanical properties of joints were investigated. In the joint interlayer, large amounts of intermetallic phases consisted of binary CuZn5 embedded by many ternary Al4.2Cu3.2Zn0.7 particles were formed. At the ceramic interface, newly formed crystalline Al2O3 aggregated. At the Cu interface, acoustic corrosion on the copper resulted in depriving the surface oxides and forming many pits on its surface, which provided saturated Cu in the melted filler alloys during the brazing. The ultrasonic vibrations had distinct effects on the metallurgical reactions of the joints, resulting in intermetallic-phase-filled composite joints with shear strength of 66MPa. The overgrowth of intermetallic compounds, the newly formed crystalline alumina, and the acoustic pits was probably ascribed to the ultrasonic effects.

Laser cladding of 420 stainless steel with molybdenum on mild steel A36 by a high power direct diode laser

Laser cladding, as one of the most promising surface modification technologies, is being widely applied in industry to improve the wear and corrosion resistance of components. The high energy input and high cooling rate during the cladding process lead to severe metallurgical reactions that determine the microstructure and properties of the cladded layer. In this study, a 3-dimensional (3-D) finite element (FE) model was developed to study heat transfer during laser cladding of 420 stainless steel+4% molybdenum on mild steel A36. In this model, the effects of laser-powder interaction, temperature-dependent material properties, latent heat, and Marangoni flow were considered. A method based on mass balance was adopted to predict the clad geometry. The thermal results such as the temperature history, temperature gradient, and solidification rate were investigated. Based on the simulated thermal results, the microstructure and Mo distribution in the clad layer were studied. In order to verify the established model, a series of experiments was conducted by using an 8-kW high-power direct diode laser (HPDDL). Thermocouples and a CCD camera were used to monitor the temperature history and molten pool size. The predicted clad height and width showed a good agreement with the experimental results.

Pressurized metallurgy for high performance special steels and alloys

The pressure is one of the basic parameters which greatly influences the metallurgical reaction process and solidification of steels and alloys. In this paper the history and present situation of research and application of pressurized metallurgy, especially pressurized metallurgy for special steels and alloys have been briefly reviewed. In the following part the physical chemistry of pressurized metallurgy is summarized. It is shown that pressurizing may change the conditions of chemical reaction in thermodynamics and kinetics due to the pressure effect on gas volume, solubility of gas and volatile element in metal melt, activity or activity coefficient of components, and change the physical and chemical properties of metal melt, heat transfer coefficient between mould and ingot, thus greatly influencing phase transformation during the solidification process and the solidification structure, such as increasing the solidification nucleation rate, reducing the critical nucleation radius, accelerating the solidification speed and significant macro/micro-structure refinement, and eliminating shrinkage, porosity and segregation and other casting defects. In the third part the research works of pressured metallurgy performed by the Northeastern University including establishment of pressurized induction melting (PIM) and pressurized electroslag remelting (PESR) equipments and development of high nitrogen steels under pressure are described in detail. Finally, it is considered in the paper that application of pressurized metallurgy in manufacture of high performance special steels and alloys is a relatively new research area, and its application prospects will be very broad and bright.

Research and Analysis on the Physical and Chemical Properties of Molten Bath with Bottom-Blowing in EAF Steelmaking Process

Bottom-blowing technology is widely adopted in electric arc furnace (EAF) steelmaking to promote the molten bath fluid flow, accelerate the metallurgical reaction, and improve the quality of molten steel. In this study, a water model experiment and a computational fluid dynamics model were established to investigate the effects of bottom-blowing gas flow rate on the fluid flow characteristics in the EAF molten bath. The results show that the interaction among the bottom-blowing gas streams influences the molten bath flow field, and increasing the bottom-blowing gas flow rate can accelerate the fluid flow and decrease the volume of the dead zone. Based on industrial application research, the physical and chemical properties of the molten bath with bottom-blowing were analyzed. Compared with traditional melting conditions without bottom-blowing, bottom-blowing technology demonstrates obvious advantages in promoting the heat transfer and metallurgical reactions in the molten bath. With the bottom-blowing arrangement, the dephosphorization and decarburization rates are accelerated, the contents of FeO and T. Fe in endpoint slag are decreased, and the endpoint carbon-oxygen equilibrium of molten steel is improved.

Effects of zinc coating on interfacial microstructures and mechanical properties of aluminum/steel bimetallic composites

In the present work, the effects of zinc coating on interfacial microstructures and mechanical properties of the aluminum/steel bimetallic composites prepared by a solid-liquid diffusion method were investigated, and the formation mechanism of intermetallic compounds at the interface between the aluminum and the steel were also discussed. The results show that a relatively uniform and compact interface between the aluminum and the steel was formed with the application of the zinc coating. The reaction layer that was mainly composed of τ6-Al4.5FeSi, α-Al rich, α + η eutectoid, η-Zn and eutectic silicon phases, between the aluminum and the steel, had an average thickness of approximately 650 μm. The microhardnesses at the interface between the aluminum and the steel gradually decreased from the steel insert side to the aluminum base side, where the microhardnesses were obviously higher than those of the aluminum base metal. Moreover, the shear stress of the aluminum/steel bimetallic composite with the zinc coating increased by 71% compared to that of the one without the zinc coating. The zinc coating played important roles in the removal of oxidation of the steel insert and the improvement of the wettability between the aluminum and the steel, which promoted the metallurgical reaction of the aluminum with steel, resulting in a significant improvement of the bonding between the aluminum and the steel.

Co-extrusion process to produce Al–Mg eutectic clad magnesium products at elevated temperatures

A novel and effective method to co-extrude metallic alloys is described using a direct extrusion method. This co-extrusion method was used to experimentally produce Al–Mg eutectic clad rods of magnesium using a laboratory scale extruder at the University of Waterloo. In addition a mathematical model of the co-extrusion process using DEFORM 2D was developed to gain insight and a scientific understanding of the material flow and metallurgical reactions that occurred between the aluminum and magnesium during the co-extrusion process. The co-extrusion method involved, filling a feeder pocket of the extrusion die with a disc of one material (Al), whereas the billet material had a different composition (magnesium). As the ram pushes the billet into the die, it punches through the disc and the resulting extrudate is clad in a eutectic alloy of the disc and billet material. An added benefit to this process is that with the choice of the correct material compositions and process conditions, the extrusion loads can be substantially lowered as a eutectic composition is formed between the billet and disc materials such that the interface becomes molten at the extrusion temperatures while the parent billet and disc remain solid. This greatly aids in the formation of a high quality interface with respect to bonding between the eutectic clad layer and core material of the extrudate. Subsequent extrusions done using the die with an already punched disc in the feeder pocket (a donut) were also able to be clad and showed significantly lower loads (∼30% difference in peak load) during extrusion as compared to billet materials that were extruded with an empty die feeder pocket. In this research, extrusion trials were performed with a magnesium billet and aluminum disc at 350°C (below the Al–Mg eutectic point) and 450°C (about the Al–Mg eutectic point). At 350°C, no significant cladding of the aluminum on the core Mg alloy occurred, but at 450°C, the co-extrusion process was successful with an Al–Mg eutectic clad rod of magnesium being produced. Subsequent co-extrusion trials were also done using the Al-donut in the feeder pocket of the die and also resulted in significantly lower loads and an Al–Mg eutectic clad extrudate. The integrity of the interface was examined and deemed to be of high quality based on visual and microscopic examinations. Both the Finite Element Method (FEM) simulation using DEFORM 2D and extrusion load measurements showed a significant drop in extrusion pressure using this co-extrusion process.

Ultrasonic semi-solid coating soldering 6061 aluminum alloys with Sn–Pb–Zn alloys

In this paper, 6061 aluminum alloys were soldered without a flux by the ultrasonic semi-solid coating soldering at a low temperature. According to the analyses, it could be obtained that the following results. The effect of ultrasound on the coating which promoted processes of metallurgical reaction between the components of the solder and 6061 aluminum alloys due to the thermal effect. Al2Zn3 was obtained near the interface. When the solder was in semi-solid state, the connection was completed. Ultimately, the interlayer mainly composed of three kinds of microstructure zones: α-Pb solid solution phases, β-Sn phases and Sn–Pb eutectic phases. The strength of the joints was improved significantly with the minimum shear strength approaching 101MPa.

Electrospark deposition of ZrB<SUB align="right">2-TiB<SUB align="right">2 composite coating on Cu-Cr-Zr alloy electrodes

To improve electrode life during the resistance spot welding of aluminium alloy sheets, a ZrB2-TiB2 composite coating was synthesised on the surfaces of spot-welding electrodes through an electrospark deposition process. The microstructure, elemental composition, phase structure, and mechanical properties of the coating were characterised using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction analysis, and microhardness testing. It was found that extensive cracking occurred in the monolithic ZrB2-TiB2 coating and at the coating-electrode interface. When the ZrB2-TiB2 coating was deposited on electrodes precoated with Ni, the number of defects decreased significantly. Further, delamination did not occur, fewer cracks were formed, and metallurgical bonds formed at the interface. The average hardness of the multilayered ZrB2-TiB2/Ni coating was approximately HV 1050 and lower than that of the monolithic ZrB2-TiB2 coating (HV 1280). For all the investigated coating conditions, a narrow, softened zone was observed near the coating-substrate interface. The softening mechanism was different for the two cases. In the case of the monolithic ZrB2-TiB2 coating, a heat-affected zone (HAZ) with large crystallites was formed. In the case of the multilayer ZrB2-TiB2/Ni coating, the zone was formed owing to the metallurgical reaction of Ni with the substrate as well as the mixing of Ni with the substrate.

Microstructure evolution and mechanical properties of transient liquid phase bonded Ti–6Al–4V joint with copper interlayer

The microstructure evolution and mechanical properties of transient liquid phase bonded Ti–6Al–4V joint with copper interlayer was investigated by varying the bonding time at 930°C. It was revealed that intensive metallurgical reactions occurred at the Ti–6Al–4V/Cu interface and integral joint consisting of TiCu, Ti2Cu layers and eutectoid structure was obtained for a bonding duration of 1min. Prolonged holding time resulted in transformation of TiCu into Ti2Cu and subsequently progressive decomposition of the Ti2Cu phase. Ultimately, homogenized joint primarily composed of α-Ti matrix with tiny Ti2Cu platelets was obtained when bonding for 30min. Tensile tests demonstrated that the homogenized joint exhibited mechanical properties comparable with that of the Ti–6Al–4V parent alloy. These experimental results demonstrate that the transient liquid phase bonding technique employing Cu interlayer is of great potential to be used for joining titanium based alloys.

Thermal and mechanical properties of commercial MgO-C bricks

MgO-C (magnesia-carbon) refractories are widely used in several steelmaking linings. These refractories are exposed to extreme stress due to high temperatures (T > 1600 °C) required to cause the metallurgical reactions. These working conditions produced refractory wear through various related processes. The different types of degradation that the material suffers can be from thermochemical or thermomechanical origin. In this work, the Young's modulus, the fracture resistance and the thermal expansion coefficient of three commercial magnesia-carbon bricks (A, B, and C) were measured to evaluate their resistance to thermomechanical degradation. These data provided an estimation of the thermomechanical stresses that they can withstand. According to the results, the lowest fracture toughness is developed by brick C. This behavior is associated to a higher porosity and quality of the binder and magnesia used. Furthermore, while the brick B has the highest resistance to crack initiation due to thermal shock, the brick A proves to be the most suitable, taking into account the relationship between resistance to the initiation and propagation of cracks. A greater degree of strain to the level of the fracture stress is also presented in the bricks A and B. This is connected to their higher content of graphite (9-12 %) compared to brick C (~ 4 %).

In Situ Visualization of Metallurgical Reactions in Nanoscale Cu/Sn Diffusion Couples

The Cu–Sn metallurgical soldering reaction in two-segmented Cu–Sn nanowires is studied by in situ transmission electron microscopy. By varying the relative lengths of Cu and Sn segments, we show that the metallurgical reaction results in a Cu–Sn solid solution for small Sn/Cu length ratio while Cu–Sn intermetallic compounds (IMCs) for larger Sn/Cu length ratios. Upon heating the nanowires to ∼500 °C, two phase transformation pathways occur, η-Cu6Sn5 → e-Cu3Sn → δ-Cu41Sn11 for nanowires with a long Cu segment and η-Cu6Sn5 → e-Cu3Sn → γ-Cu3Sn with a short Cu segment. The evolution of Kirkendall voids in the nanowires demonstrates that Cu diffuses faster than Sn in IMCs. Void growth results in the nanowire breakage that shuts off the inter-diffusion of Cu and Sn and thus leads to changes in the phase transformation pathway in the IMCs.