Metallurgical Reactions Research Articles

Microstructures and Crack Propagation in the Joint of Solidified TiC-TiB<sub>2</sub> to Ti-6Al-4V Prepared by Reactive Fusion Bonding in Ultrahigh Gravity Field

By taking combustion synthesis in ultrahigh gravity field to prepare solidified TiC-TiB2 composite ceramic, laminated composite of the ceramic to Ti-6Al-4V was achieved by fusion bonding and atomic inter-diffusion, and within the joint there formed the unique microstructure of multiscale (micrometer-micro/nanometer-nanometer) and multilevel characterized by size and distribution of TiB2 and TiB due to the presence of a series of metallurgical reaction including peritectic reaction of solidified and Ti liquid, direct growth of TiB solids from liquid Ti and subsequent eutectic reaction of TiB solids and liquid Ti. FEMSEM images of crack propagation paths at the joint showed despite the contribution from crack bridging of micro-nanometer TiB2 and TiB platelets to crack propagation resistance, residual stress toughening and subsequent crack pinning by micro-nanometer TiB2 ,TiB platelets and needle-like nanometer TiB grains as well as ductile phase toughening and bridging toughening by Ti metallic phases became the primary resistances to crack propagation, thereby presenting the delayed fracture behavior in the joint, so that shear fracture usually occurred at the solidified Ti alloy rather than the joint, and shear strength of 375 ± 55 MPa was achieved between the solidified ceramic and Ti alloy.

Microstructures and Mechanical Properties of Electron Beam-Welded Titanium-Steel Joints with Vanadium, Nickel, Copper and Silver Filler Metals

Electron beam welding experiments of titanium alloy to stainless steel with V, Ni, Cu and Ag filler metals were carried out. The interfacial microstructures of the joints were examined by optical microscopy, scanning electron microscopy, and x-ray diffraction analysis. Mechanical properties of the joints were evaluated according to tensile strength and microhardness. The results showed that all the filler metals were helpful to restrain the Ti-Fe intermetallics formed in the Ti/Fe joint. The welds with different filler metals were all characterized by solid solution and interfacial intermetallics. And the type of solid solution and interfacial intermetallics were depended on the metallurgical reactions between the filler metals and base metals. The interfacial intermetallics were Fe2Ti + Ni3Ti + NiTi2, TiFe, Ti2Ag, and Cu2Ti + CuTi + CuTi2 in the joints welded with Ni, V, Ag, and Cu filler metals, respectively. The tensile strengths of the joints were primarily determined by the hardness of the interfacial intermetallics. The highest tensile strength was obtained in the joint welded with silver filler metal, which is about 310 MPa.

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

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

Selection of vacuum pump system for steel degassing

Steam ejector vacuum pumps (SVPs) are mainly used on larger melt sizes up to 350 t in integrated steel plants because of the availability of steam. The use of dry operating mechanical vacuum pumps (MVPs) for steel degassing has made a tremendous step forward in the past 10 years but is still confined to melts below 150 t while its progress towards larger melt sizes is not completed. Besides the consideration of investment and operating costs there is no restriction in using any type of modern vacuum pump system for all vacuum processes and plant designs. Both systems fulfil all metallurgical requirements. Considering the significant savings in operating cost offered by MVP systems it is worth reconsidering the efforts for reducing air leaks, the use of protective gases and pressure losses between the pump set and the metallurgical reaction vessel. Both systems have made progress in energy optimising but the MVPs have a striking energy advantage. Only the overall costs should be considered, including those necessary to meet emission constraints and safety standards, and only the pressure prevailing at the reaction vessel is to be considered when comparing vacuum pump systems. Also, the means and use of dust abatement systems should be reconsidered since they offer cost savings by reducing the frequency of cleaning, less wear, little sludge handling and the significantly lower design suction capacity of SVP systems. The SVP mass flow need is to be corrected by a special coefficient before being applied to the volume conveying MVPs. Depending on the operational pressure required for the pump design, MVP systems can reach the same performance at the reaction vessel with much less mass flow capacity than that needed by a SVP system.

Comparative study of the dry sliding wear behaviour of HVOF-sprayed WC–(W,Cr)2C–Ni and WC–CoCr hardmetal coatings

Recent studies of HVOF-sprayed WC–(W,Cr)2C–Ni coatings indicated an applicability at temperatures above 600°C. Therefore, in the present paper the dry sliding wear behaviour of coatings prepared from one selected feedstock powder was studied up to 750°C and compared to a WC–10%Co–4%Cr coating as reference.Coatings were prepared onto stainless steel substrates by a liquid-fueled high velocity oxygen-fuel (HVOF) spray process. A Cr–W–Ni–C “mixed” matrix phase and chromium-rich large (W,Cr)2C grains were formed as a result of metallurgical reactions between the components WC, Cr3C2 and Ni during spraying; therefore, the resulting coating can be better designated as WC–(W,Cr)2C–Ni.The dry unidirectional sliding wear behaviour of the coatings, studied according to ASTM G99 against Al2O3 counterbodies at four different temperatures (25°C, 400°C, 600°C, 750°C) and at two sliding speeds, was interpreted on the basis of their microstructure, micromechanical properties and oxidation behaviour. The morphology and composition inside the wear scars were also studied by SEM and micro-Raman spectroscopy. The results show that the WC–(W,Cr)2C–Ni coating exhibits good wear resistance up to 750°C, whereas WC–CoCr, in spite of its very mild wear at low temperature, suffers from catastrophic oxidation at 750°C.

Multiscale and Multilevel Composite of Solidified TiC-TiB<sub>2</sub> with Ti-6Al-4V Achieved by Fusion Bonding in High-Gravity Field

By putting Ti-6Al-4V plate at the bottom of the blend of (Ti+B4C) and the high-energy thermit, a novel laminated composite of TiC-TiB2 ceramic to Ti alloy is achieved by combustion synthesis in high-gravity field, and within the joint there presents multiscale and multilevel microstructures characterized by size and distribution of TiB2 and TiB phases, thereby showing microstructure evolution rather than a clear interface from the ceramic to Ti alloy. The reasons for the unique microstructures in the joint came is considered a result of fusion bonding and atomic interdiffusion between liquid TiC-TiB2 and liquid Ti in thermal vacuum circumstances, followed by a series of metallurgical reaction including peritectic reaction of TiB2 solid and Ti liquid, direct growth of TiB from Ti liquid and subsequent eutectic reaction of TiB and Ti, so a continuously-graded microstructure consisting of the multiphases in size from micrometer to nanometer is eatablieshed in the joint.

Neutron irradiation effects on gallium nitride-based Schottky diodes

Depth-resolved cathodoluminescence spectroscopy (DRCLS), time-resolved surface photovoltage spectroscopy, X-ray photoemission spectroscopy (XPS), and current-voltage measurements together show that fast versus thermal neutrons differ strongly in their electronic and morphological effects on metal-GaN Schottky diodes. Fast and thermal neutrons introduce GaN displacement damage and native point defects, while thermal neutrons also drive metallurgical reactions at metal/GaN interfaces. Defect densities exhibit a threshold neutron fluence below which thermal neutrons preferentially heal versus create new native point defects. Scanning XPS and DRCLS reveal strong fluence- and metal-dependent electronic and chemical changes near the free surface and metal interfaces that impact diode properties.

Microstructure and physical properties of laser Zn modified amorphous–nanocrystalline coating on a titanium alloy

A Zn modified amorphous–nanocrystalline coating was fabricated on a Ti–6Al–4V alloy by laser cladding of the Co–Ti–B4C–Zn–Y2O3 mixed powders. Such coating was researched by means of a scanning electron microscope (SEM) and a high resolution transmission electron microscope (HRTEM), etc. Experimental results indicated that the Co5Zn21 and TiB2 nanocrystalline phases were produced through in situ metallurgical reactions, which blocked the motion of dislocation, and TiB2 grew along (010), (111) and (024). The Co5Zn21 nanocrystals were produced attached to the ceramics, which mainly consisted of the Co nanoparticles embedded in a heterogeneous zinc, and had varied crystalline orientations.

Microstructure and joining mechanism of Ti/Al dissimilar joint by pulsed gas metal arc welding

Butt joining of titanium alloy Ti–2Al–Mn to aluminum 1060 using AlSi5 filler wire was conducted using pulsed gas metal arc welding. Joining mechanism of Ti–2Al–Mn/Al 1060 dissimilar joint with different welding heat input was investigated. Formations of precipitation and Ti/Al interface were discussed in detail. Fusion zone near aluminum is composed of α-Al dendrites and Al–Si hypoeutectic structures. A few TiAl3 precipitations appear in the weld metal owing to metallurgical reactions of Al with dissolved Ti. When the welding heat input was in the range of 1.87–2.10 kJ/cm, titanium alloy Ti–2Al–Mn and Al 1060 were joined together by the formation of a complex Ti/Al interface. With a low welding heat input, a serrate TiAl3 interfacial reaction layer was formed near Ti/Al interface. With the increasing of the welding heat input, α-Ti, Ti7Al5Si12, and TiAl3 layers were formed orderly from Ti–2Al–Mn to weld metal.

Effect of Melting and Refining with DC-Arc on the Yield of Alloy Element

In order to know what effect on the yield of alloy elements will be if the steel is melted/refined with the DC arc furnace, the effect of melting and refining with DC-arc on the yield of alloy element has been investigated by a melting experiment, in which the melting/refining is switched to continuous melting/refining with DC-arc after the molten metal is contact with the molten slag for 41 minutes without DC-arc, and by a contrast experiment of melting/refining with DC-arc and with an AC-arc. When DC current passes through the slag-metal interface and the slag-gas interface, the existence of the electrolysis phenomenon during the DC-arc steel melting/refining has been confirmed. Electrolysis participates in the metallurgical reaction. The phenomenon of two or more electrode reactions taking place simultaneously at both the slag-metal interface and the slag-gas interface has also been observed. The two phenomena cause the accelerating loss of the alloy-elements in the molten metal and the decreasing of concentrations of the corresponding oxides in the molten slag. The electrochemical transfer of oxygen from the molten slag to the molten metal ((O2-)=[+2e and (O2-)=1/2O2+2e) at the slag-metal interface has been observed, and causes the increasing of oxygen content in the molten metal.

Characteristics of reactively sputtered niobium nitride thin films as diffusion barriers for Cu metallization

NbN films were prepared by radio frequency reactive magnetron sputtering and then employed as diffusion barriers between Cu and Si. The microstructure of the NbN films was an assembly of very small columnar crystallites with a cubic structure. To investigate the properties as diffusion barriers, we performed metallurgical reactions of Cu/NbN0.8/Si, Cu/Nb/Si and Cu/TaN0.7/Si for comparisons. The sheet resistance increased dramatically after annealing above 750°C for Cu/NbN0.80/Si, and above 500°C for both Cu/Nb/Si and Cu/TaN0.7/Si. The interfaces were deteriorated seriously and formation of Cu3Si was observed when the sheet resistance was significantly increased. The diffusion coefficient of Cu in NbN barrier films was estimated by using the change of resistance (ΔR s /R s %). Compared with TaN0.7, NbN0.8 films possess larger grain size and lower Cu diffusion coefficient. Our results suggest that the NbN film can be used as a diffusion barrier for Cu metallization as compared to the well-known TaN film.

SPS Method for Manufacturing Carbide Materials

Due the rapid heating rate combined with high pressure by the Spark Plasma Sintering (SPS) technologies possible manufacture a wide range of novel materials with exceptional properties that cannot be achieved using conventional sintering techniques. Hard metals are, from a technical point of view, one of the most successful composite materials. An overview of the metallurgical reactions during the SPS sintering process of powder mixtures for the manufacture of hard metals is presented. The relatively complex phase reactions in the multi-component system TiC-Mo-W-Ni are discussed. There were elaborated a new technology for the fabrication of nanocrystalline hard metals of a new class assigned for the production of articles with high different characteristics. Elaborated materials are characterized by high melting temperature, hardness, wear-resistance, and satisfactory strength at high temperature and corrosive resistance. Through the use of developed technology and the appropriate structural condition gives possibility to achieve high physical-mechanical characteristics. Obtaining of composite materials via elaborated technology is available from the corresponding complex compounds and directly consisting elements too. In this case High-temperature Self-propagation Synthesis (SHS) and spark plasma sintering/synthesis (SPS) process are united and during a single operation it is possible to get not only the powder materials but at the same time obtain required details.

Microstructure of Fe-Based Alloy Composite Coatings Reinforced by Ti (C0.3 N0.7) Particles Through Laser Cladding Technology

Fc-bascd alloy layer reinforced by Ti(C, N) particles was produced on the surface of cast steel. X-ray diffraction (XRD) was used for phase identification in the composite coating. The microstructure of laser cladding layer was analyzed by means of optical microscope (OM), electron probe microscope analyzer (EPMA), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that Ti(C0.3 N0.7) particle is introduced by an in-situ metallurgical reaction of TiN particle and graphite powder in the process of laser cladding. The shape of lots of Ti(C0.3 N0.7) particle is irregular. The sizes of Ti(C0.3 N0.7) particles range from 0.1 to 6.0 μm, and they arc dispersed evenly in the matrix, which is fine dendritic or cellular crystal. A new kind of phase named Ti(C0.3 N0.7) particles arc tightly bonded with α-Fe microstructure, and there is a clean and smooth phase interface between ceramic reinforcement phase and the matrix.

Subsurface characteristics of a Fe–0.4 wt%C martenstic steel abraded with nanoindentation and cross-sectional TEM techniques

The present investigation examined the unidirectional abraded surfaces of a martensitic (0.4wt%C) steel with silicon (1.5wt%Si), chromium (1.5wt%Cr) and molybdenum (1.9wt%Mo) additions in order to elucidate the work hardening and softening near the surface layer caused by abrasion, particularly its relation to wear behavior. The abrasion testing was performed on a pin-abrasion apparatus, and a small pin of the specimen was ground on silica abrasive paper at an applied load of 2.1N and a sliding speed of 0.66m/s. The abraded surfaces were examined on a nanometer scale with a nanoindentation apparatus to evaluate the changes in nanohardness as the sliding time progressed. A cross-sectional transmission electron microscope (TEM) technique was also employed to clarify the structural changes in the region close to the abraded surface. The abrasion-induced work hardening with sliding time was observed in the case of chromium and molybdenum addition steels. A fine dispersion of molybdenum carbide (Mo2C) was observed in the surface of the molybdenum steel after abrasion. Mo2C precipitates at approximately 550°C, indicating that surface and near-surface temperatures exceeded the carbide formation temperature after abrasion-induced frictional heating. In contrast, the silicon addition steel softened, which seems to be caused by abrasion heating that leads to some tempering effects. Work hardening and softening, which are caused by abrasion-induced subsurface deformation and frictional heating, respectively, seem to take place simultaneously and thus counteract each other's effect. Metallurgical reaction, such as precipitation and temper by frictional heating, has been found to play an important role in controlling the wear characteristics of steels. The present article discusses the influence of the alloying element addition on the wear response of the martensitic steel.

Liquid-phase sintering of Ti(C,N)-based cermets. The effects of binder nature and content on the solubility and wettability of hard ceramic phases

Different commercial TiC–TiN/Co/Ni mixtures were used as raw materials for Ti(C,N) cermets, and the effects of the sintering parameters (binder content, binder nature, sintering time and additives) on the final hard ceramic phase were studied at the sintering temperature of 1400°C. When Co is used as the binder medium, it is possible to completely convert the starting commercial TiC–TiN mixture into TiCxN1−x. When Ni is used, which exhibits lower solubilising capacity than Co, the total conversion can never be reached and the metallurgical reactions between TiC and TiN during the liquid-phase sintering are more dependent on the sintering time than on the binder content. However, the use of Co–Ni mixtures, showing a synergic effect between the wettability capacity of Ni and the solubilising capacity of Co, enhances the metallurgical reactions at short sintering times.

Effect of Cooling Rate on the Microstructure of Al-Zn Alloys with Addition of Silicon as Nanocomposite

Al-43.5Zn-1.5Si (wt%) alloys are widely used as coatings on steel substrates. This kind of coatings is manufactured by hot-dip process, in which Si is added as solid particles or master alloy. The role of Si during formation of the coating is to control the metallurgical reactions between solid steel and liquid Al-Zn-Si alloy initially forming an AlZnFeSi intermetallic layer and next the excess of Si forms intermetallic compounds, which grows over this alloy layer, segregates into the Zn rich interdendritic regions, and solidifies as eutectic reaction product as massive particles with needle like morphology. Therefore, during the experimental procedure is very difficult to control the final morphology and distribution of the silicon phase. The acicular morphology of this phase greatly affects the mechanical properties of the alloy because it acts as stress concentrators. When the coated steel sheet is subjected to bending, the coating presents huge cracks due to the presence of silicon phase. Therefore, the aim of the paper was to propose a new methodology to control the silicon phase through its addition to Al-Zn alloy as nanocomposite and additionally determine the effect of cooling rate (between 10 and 50°Cs−1) on the solidification microstructure and mechanical properties of Al-Zn alloy.

On the bonding strength in thermally sprayed Fe-based amorphous coatings

Bonding strength is one of the most important properties in thermally sprayed coatings as it plays crucial roles in the performance and lifetime of the coatings. This study aims to explore different factors that affect the bonding strength of the Fe48Mo14Cr15Y2C15B6 amorphous coating prepared by high velocity oxygen fuel (HVOF) thermal spraying. The results demonstrate that the substrate roughness and the coating thickness have significant influence on the bonding strength of the amorphous coating, e.g. the bonding strength increases when the substrate roughness is above a certain threshold, and decreases with the increasing coating thickness. In addition, the bond strength can be effectively enhanced via the addition of an intermediate NiCrAl layer between the substrate and the amorphous coating due to the occurrence of metallurgical reaction and the improved interfacial structure. Finally, the fracture mechanism of the coatings was also discussed.

Microstructure performance of the ceramics-reinforced laser alloying composite coating on titanium

Abstract This work was based on the dry sliding wear of Al-Cu-Sn matrix composite coating deposited on titanium using laser alloying technique, the parameters of which were such as to provide almost crack-free coatings with minimum dilution and very low porosity. To our knowledge, it is the first time that Al-Cu-Sn+B4C mixed powders were deposited as hard coating by laser alloying technique. Scanning electron microscopy results indicated that a laser alloying coating with metallurgical joint to the substrate was formed, and hard fine particles were produced in the matrix of the upper coating due to the in situ metallurgical reactions. Compared with titanium substrate, improvement of the microhardness and wear resistance were observed for such composite coating.

Preparation and Characterization of Thermal Spray Coating of Glass Microspheres on Metal Substrate

Plasma spray technology utilizes the exotic properties of the plasma medium to effect physical, chemical or metallurgical reactions to produce new materials or impart new functional properties to conventional materials. It is in fact a process that includes melting, rapid solidification and quenching taking place simultaneously. As for the coating materials, it is well understood that for a number of unique application, spherical particles are preferred over irregular ones due to low surface area to volume ratio, high density, free flowing ability and close sizing etc. In view of this, the present paper reports on the preparation of glass microspheres coatings on mild steel substrate using plasma spray technology. An 80 kW atmospheric plasma spray set up is used for spraying purpose. Solid glass micro-spheres of average sized 100 micron are used as the coating materials which are deposited at four different power levels on mild steel substrate. The coatings are characterized in terms of their thickness, hardness, density and porosity. The coatability of glass micro-spheres on mild steel is assessed by evaluating the coating deposition efficiency. Different phases present in the coating are ascertained using X-ray diffractography.

Physical properties and microstructural performance of Sn modified laser amorphous-nanocrystals reinforced coating

An amorphous-nanocrystals reinforced composite coating was fabricated on TA15 titanium alloy substrate by laser alloying of Al–Sn–B4C–SiC–TiN–Y2O3 mixed powders, which greatly improved the wear resistance of substrate. Experimental results indicated that Al–Sn nanocrystalline phases were produced through in situ metallurgical reactions, which blocked the motion of dislocation. The productions of the eutectics, such as Ti–Si greatly promoted the formation of amorphous phases in such coating. Compared with the substrate, higher wear resistance of laser alloying coating was mainly ascribed to the hard phase, amorphous-nanocrystalline phases and fine grain strengthening. This research provided essential theoretical and experimental basis to promote the application of laser alloying technique in modern aviation industry.