Effect of interface microstructure on the bond strength of the diffusion welded joints between titanium and stainless steel

Diffusion bonding between commercially pure titanium and 304 stainless steel was carried out at a temperature of 950 °C for 30–120 min under uniaxial load in a vacuum. The diffusion bonds were characterized by optical and scanning electron microscopy. The diffusion zone contained different reaction bands and their chemical composition was determined using energy dispersive X-ray spectroscopy. The concentration of chemical species indicated the presence of σ, λ, χ, FeTi, β-Ti and Fe₂Ti₄O phases in the reaction zone and their existence was confirmed by X-ray diffraction. A maximum bond strength of 71% of that of titanium along with 5.8% ductility were obtained for the diffusion couple processed for 30 min due to formation of finer size intermetallics. A rise in joining time increases void generation and growth of intermetallic compounds, which are responsible for a drastic fall in the strength value.     

Interface structure of diffusion bonded duplex stainless steel and medium carbon steel couple

Diffusion bonding of duplex stainless steel to medium carbon steel was carried out with different temperatures for sound bonds. In the bonding process, relatively intermediate temperatures such as 750, 800, 850 and 900 °C were used with a bonding time of 30 min. In this study, microstructural changes and mechanical properties in the interface region of duplex stainless steel and medium carbon steel couples were determined. The results showed that, in interface region, Cr₂₃C₆ was formed on the stainless steel side, while ferrite formation was observed on the carbon steel side as a result of mutual diffusion of C and Cr.     

Structure and properties of solid state diffusion bonding of 17-4PH stainless steel and titanium

Abstract

Solid state diffusion bonded joint between titanium and 17-4 precipitation hardening stainless steel was carried out in the temperature range of 800–1050°C in steps of 50°C for 30 min and also at 950°C for 30–180 min in steps of 30 min under a uniaxial pressure of 3·5 MPa in vacuum. Bonded samples were characterised using light microscopy, field emission scanning electron microscopy and X-ray diffraction technique. Up to 850°C for 30 min, FeTi phase was formed at the diffusion interface; however, α-Fe+λ, χ, Fe₂Ti and FeTi phases and phase mixtures were formed above 850°C for 30 min and at 950°C for all bonding times. Maximum tensile strength of ～326 MPa, shear strength of ～254 MPa and impact toughness of ～24 J were obtained for the diffusion couple processed at 1000°C for 30 min and 30–180 min time interval at 950°C, and maximum tensile strength ～323 MPa, shear strength ～243 MPa and impact toughness of ～22 J were achieved when bonding was processed for 120 min. The residual stress of the bonded joints increases with the increase in bonding temperatures and times.     

Effects of temperature on interface microstructure and strength properties of titanium–niobium stainless steel diffusion bonded joints

Abstract

The effects of temperature on interface microstructure and strength properties of Ti/stainless diffusion bonded joint using Nb interlayer, processed in the temperature range 800–950°C for 1·5 h in vacuum were investigated. The stainless steel/Nb interface is free from intermetallic phase up to 900°C; however, Fe₂Nb+Fe₇Nb₆ phase mixture has been observed at 950°C processing temperature. The Nb/Ti interface is free from intermetallic for all processing temperatures. The maximum tensile strength of ～287 MPa (～90% of Ti) and shear strength ～222 MPa (～75% of Ti) along with 6·9% ductility have been achieved in the diffusion bonded joints, when processed at 900°C. The bonded samples failure takes place through the stainless steel/Nb interface for all processing temperatures during the loading.     

Effect of fretting conditions on the wear of silicon nitride against bearing steel

Lubricated and unlubricated wear tests were conducted with silicon nitride against bearing steel couples under fretting conditions. The effect of fretting amplitude (5–50 μm), test duration at constant frequency and load on the tribological behaviour was evaluated according to wear volume, coefficient of friction, as well as the wear mechanisms involved. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were employed to determine the detailed nature of the friction and wear processes. It is suggested that wear under lubricated conditions is primarily related to the tribochemical reaction between silicon nitride and iron, which is the main cause of cratering on the steel counterpart, while wear of the ceramic part is relatively low. The wear rate is controlled by the nature of the tribolayer which is created, and this is a function of the sliding speed which influences the temperature at contact. At lower amplitudes the layer is brittle, while above 25 μm it becomes more plastic which hinders the wear process. Under unlubricated conditions, the wear is much more severe and increases exponentially with amplitude.     

Determination of pigments in colour layers on walls of some selected historical buildings using optical and scanning electron microscopy

For successful restoration of painted walls and painted coloured finishing coats it is necessary to determine the composition of the original colour layers. Identification of the pigments used in The Cistercian Abbey of Stična and The Manor of Novo Celje was carried out using optical and scanning electron microscopy. Selected samples of wall paintings were inspected by the combined application of an optical microscope and a low-vacuum Scanning Electron Microscope to determine their colour and structural features and to identify the position of individual pigment grains. Energy dispersive spectroscopy was used to determine the elemental distribution on selected surfaces and elemental composition of individual pigments. It was found that the most abundantly used pigments were iron oxide red, cinnabar, green earth, umber, calcium carbonate white, ultramarine, yellow ochre and carbon black. These identifications have allowed us to compare the use of various pigments in buildings from different historical periods.     

Evaluation of interface microstructure and mechanical properties of the diffusion bonded joints of Ti-6Al-4V alloy to micro-duplex stainless steel

In the present investigation, Ti-6Al-4V and micro-duplex stainless steel was diffusion bonded in vacuum. The layer wise σ phase and λ + FeTi phase mixture were observed at the bond interface when bonded joints was processed at and above 850 °C for 90 min and at 800 °C for 120 min and longer bonding time. Effect of bonding temperature and time on the strength properties at room temperature were evaluated. The maximum tensile strength of ∼510.1 MPa and shear strength of ∼397.5 MPa along with 6.5% elongation were obtained for the diffusion couple processed at 850 °C for 90 min. Fracture surface observation in SEM using EDS demonstrates that, failure takes place through λ + FeTi phase when bonding was processed at 850 °C for 90 min and at 800 °C for 120 min, however, failure takes place through σ phase for the diffusion couples processed at and above 900 °C for 90 min and at 800 °C for 120 min and longer bonding time.     

Investigations on TlBa2Ca2Cu3Ox superconducting thin films formation on LaAlO3 substrate

Investigations on pure superconducting phase TlBa₂Ca₂Cu₃O_x (Tl-1223) thin films formation, of about 100-125 nm in thickness, on (001) LaAlO₃ single crystal substrate, were made using radio-frequency sputtering deposition of Ba₂Ca₂Cu₃O_x precursor films and ex-situ thallination in sealed quartz tube. The precursor films were thallinated under different conditions of partial oxygen pressure, temperature, time and y thallium source content using unreacted pellets of composition Tl_yBa₂Ca₂Cu₃O_x. In all cases, strongly c-oriented multiphase films were obtained. A correlation between the Tl-1223 phase purity and the precursor film conditions of thallination is established. Temperature and time of thallination as well as the thallium source content and the partial pressure of oxygen play a key role in the quality of the obtained film. The films' onset temperature of the superconducting transition ranges between 90 and 103 K. It is shown that the best samples can be obtained from a dense precursor film and relatively medium thallination time.     

Ti2Al(O,N) formation by solid-state reaction between substoichiometric TiN thin films and Al2O3 (0001) substrates

Titanium nitride TiN_x (0.1 ≤ x ≤ 1) thin films were deposited onto Al₂O₃(0001) substrates using reactive magnetron sputtering at substrate temperatures (T_s) ranging from 800 to 1000 °C and N₂ partial pressures (pN₂) between 13.3 and 133 mPa. It is found that Al and O from the substrates diffuse into the substoichiometric TiN_x films during deposition. Solid-state reactions between the film and substrate result in the formation of Ti₂O and Ti₃Al domains at low N₂ partial pressures, while for increasing pN₂, the Ti₂AlN MAX phase nucleates and grows together with TiN_x. Depositions at increasingly stoichiometric conditions result in a decreasing incorporation of substrate species into the growing film. Eventually, a stoichiometric deposition gives a stable TiN(111) || Al₂O₃(0001) structure without the incorporation of substrate species. Growth at T_s 1000 °C yields Ti₂AlN(0001), leading to a reduced incorporation of substrate species compared to films grown at 900 °C, which contain also Ti₂AlN(101?3) grains. Finally, the Ti₂AlN domains incorporate O, likely on the N site, such that a MAX phase oxynitride Ti₂Al(O,N) is formed. The results were obtained by a combination of structural methods, including X-ray diffraction and (scanning) transmission electron microscopy, together with spectroscopy methods, which comprise elastic recoil detection analysis, energy dispersive X-ray spectroscopy, and electron energy loss spectroscopy.     

Nanoindentation and nanoscratch behaviour of reactive sputtered deposited W–S–C film

Transition metal dichalcogenides having layered structure are promising self lubricating film and can be considered as substitute for carbon based films in several varieties of environmental conditions. The macrotribological properties of these films are studied extensively and are fairly well understood. However, mechanical and tribological behaviour of these films in millinewton load range have hardly been reported. Study of mechanical and tribological properties at applied load in the millinewton range is useful for possible application related to microelectro mechanical systems or micromechanical assemblies. In view of the above, the present work is undertaken to understand the indentation behaviour and scratch behaviour under constant and low applied load of reactive sputtered deposited W–S–C thin films. Towards that purpose, W–S films containing various amount of C are deposited on 100Cr6 steel using a radio frequency magnetron sputtering unit. The load vs. displacement curves of all these films are generated for four different loads to assess the load effect, substrate effect and size effect on the hardness and the load displacement curves of these films. Curves showing the variation of load as a function of the square of displacement are also evaluated in order to understand deformation and fracture mechanisms of these films and the interface between various microstructures of these films. The scratch behaviour of these films under constant load is determined to examine the friction and wear performance. The results show that the film containing 54 at.% carbon has the maximum hardness and the minimum scratch depth. In contrast, the minimum friction coefficient is exhibited by the film containing the maximum carbon.     

Characterization of Al/Ni multilayers and their application in diffusion bonding of TiAl to TiC cermet

The Al/Ni multilayers were characterized and diffusion bonding of TiAl intermetallics to TiC cermets was carried out using the multilayers. The microstructure of Al/Ni multilayers and TiAl/TiC cermet joint was investigated. The layered structures consisting of a Ni₃(AlTi) layer, a Ni₂AlTi layer, a (Ni,Al,Ti) layer and a Ni diffusion layer were observed from the interlayer to the TiAl substrate. Only one AlNi₃ layer formed at the multilayer/TiC cermet interface. The reaction behaviour of Al/Ni multilayers was characterized by means of differential scanning calorimeter (DSC) and X-ray diffraction. The initial exothermic peak of the DSC curve was formed due to the formation of Al₃Ni and Al₃Ni₂ phases. The reaction sequence of the Al/Ni multilayers was Al₃Ni → Al₃Ni₂ → AlNi → AlNi₃ and the final products were AlNi and AlNi₃ phases. The shear strength of the joint was tested and the experimental results suggested that the application of Al/Ni multilayers improved the joining quality.     

Effect of post-weld heat treatment on the interface microstructure of explosively welded titanium–stainless steel composite

In this study, the interface microstructure evolutions of the explosively welded cp-Titanium/AISI 304 stainless steel composites due to heat treatment are presented. The composites were subjected to heat treatment process at temperature ranges of 650–950 °C in argon atmosphere for 1 h. The investigations were carried out by using optical microscopy (OM), scanning electron microscopy (SEM). The results reveal the presence of reaction layers in the diffusion zone. The compositions of the reaction products were determined by energy dispersive spectroscopy (EDS). Furthermore, the composition–penetration plots for Ti, Fe, Cr and Ni across the interface were obtained from EDS microanalysis. Concentration of discontinuities in the profiles indicating the formation of intermetallics in the diffusion zone that were also detected by X-ray diffraction (XRD) method, on the Ti-side of fractured surfaces. The results show that post-heating of the composite layers in these temperatures causes to form different intermetallic phases at the joint interface. Moreover, post-heating increases the width of interfacial layers of the composite.     

Element distribution and phase constitution of Al2O3-TiC/W18Cr4V vacuum diffusion bonded joint

Vacuum diffusion bonding between Al₂O₃-TiC ceramic composites and W18Cr4V tungsten-based tool alloy has been carried out by using Ti/Cu/Ti multi-interlayer. Element distribution near the Al₂O₃-TiC/W18Cr4V interface was discussed and fracture morphology was analyzed using electron probe microanalysis. Additionally, phase constitutions of the Al₂O₃-TiC/W18Cr4V joint were determined by X-ray diffraction. The results indicate that Ti-rich layers are formed near both Al₂O₃-TiC and W18Cr4V. The Ti-rich layer near Al₂O₃-TiC helps to wet the Al₂O₃-TiC surface. The Ti-rich layer near W18Cr4V can restrain the formation of Fe-Ti intermetallic compounds in the diffusion transition zone. Residual Cu in the diffusion transition zone can act as a stress releasing zone. The structures of interfacial phases are identified as follows: Al₂O₃-TiC/TiO + Ti₃Al/Cu + CuTi/TiC layer/mixed layer of Fe₃W₃C, Cr₂₃C₆ and α-Fe/W18Cr4V. The fracture morphology of Al₂O₃-TiC/W18Cr4V joint appears brittle features and the failure occurs within the Al₂O₃-TiC ceramic.     

Influence of the common varistor dopants (CoO, Cr2O3 and Nb2O5) on the structural properties of SnO2 ceramics

The influence of dopants commonly used in SnO₂ varistor ceramics, such as CoO, Cr₂O₃ or Nb₂O₅, on the structural properties of SnO₂ was investigated. Several SnO₂-based ceramics containing only one of the dopants were prepared and characterized. Spectroscopic investigations [visible, near infrared (IR) and IR region] were performed to obtain information about dopants valence states inside the ceramics, as well as about their influence on electronic structure of the material. Structural properties were investigated by X-ray diffraction analysis and mechanisms of dopant incorporation were proposed. Obtained results were confirmed with results of the electrical measurements. Microstructural changes in doped ceramics were investigated by scanning electron microscopy (SEM) analysis that showed great differences in densities, grain size, and morphology of the SnO₂ ceramics depending on type of dopants and their distribution.     

Synthesis and structural characterization of mesoporous V2O5 thin films for electrochromic applications

Mesoporous vanadium pentoxide (V₂O₅) films have been synthesized by hydrolysis of vanadium tri-isopropoxide (VO(OC₃H₇)₃) in the presence of polyethylene glycol (PEG) as a structure-directing agent. The structure, the stoichiometry and the morphology of the films have been studied as a function of the thermal annealing by X-ray diffraction (XRD), micro-Raman spectroscopy, optical microscopy, scanning electron microscopy and atomic force microscopy. XRD patterns and Raman spectra show the presence of two previously unreported crystalline phases. The PEG:V₂O₅ molar ratio affects the temperature of phase formation, the amount and even the order in which the phases appear. The morphological characterization underlines the role of the surfactant to promote porous networks, formed by micrometric clusters of controlled shapes and patterns embedded in a homogeneous host matrix.     

Understanding the galvanic corrosion of the Q-phase/Al couple using SVET and SIET

The galvanic corrosion of the Q-phase/Al couple in 0.1 M NaCl solutions has been studied using the scanning vibrating electrode technique (SVET), the scanning ion-selective electrode technique (SIET) and energy dispersive X-ray spectroscopy (EDX). The galvanic corrosion of the Q-phase/Al couple was found to be dependent on pH and immersion time. Current density maps obtained by SVET shows that the anodic oxidation processes emerge from Al in a localized manner in pH 2 and 6 solutions but is initiated in a uniform manner in pH 13 solution, whereas, the cathodic processes are more homogeneously distributed over the Q-phase at pH 2, 6 and 13. It is seen that the Q-phase remains cathodic in the Q-phase/Al couple in acidic, neutral and alkaline solutions indicating that the galvanic polarity of the Q-phase is independent of pH. The effect of the galvanic corrosion was largest at pH 2 and 13 compared to pH 6. The pH map obtained by SIET indicates that the galvanic activity of the Q-phase/Al couple proceeds via heavy alkalization of the Q-phase surface with the generation of appreciable amounts of OH⁻ ions. The enrichment of Cu indicated by EDX is responsible for the observed cathodic activity of the Q-phase in the Q-phase/Al couple.     

Fabrication and characterization of magnesium–fluorapatite nanocomposite for biomedical applications

Recent studies indicate that there is a high demand for magnesium alloys with adjustable corrosion rates, suitable mechanical properties, and the ability for precipitation of a bone-like apatite layer on the surface of magnesium alloys in the body. An approach to this challenge might be the application of metal matrix composites based on magnesium alloys. The aim of this work was to fabricate and characterize a nanocomposite made of AZ91 magnesium alloy as the matrix and fluorapatite nano particles as reinforcement. A magnesium–fluorapatite nanocomposite was made via a blending–pressing–sintering method. Mechanical, metallurgical and in vitro corrosion measurements were performed for characterization of both the initial materials and the composite structure. The results showed that the addition of fluorapatite nano particle reinforcements to magnesium alloys can improve the mechanical properties, reduce the corrosion rate, and accelerate the formation of an apatite layer on the surface, which provides improved protection for the AZ91 matrix. It is suggested that the formation of an apatite layer on the surface of magnesium alloys can contribute to the improved osteoconductivity of magnesium alloys for biomedical applications.     

The effect of arsenic thermal diffusion on the morphology and photoluminescence properties of sub-micron ZnO rods

As-doped sub-micron ZnO rods were realized by a simple thermal diffusion process using a GaAs wafer as an arsenic resource. The surface of the sub-micron ZnO rods became rough and the morphology of As-doped sub-micron ZnO rods changed markedly with increasing diffusion temperature. From the results of energy-dispersive X-ray spectroscopy, X-ray diffraction and photoluminescence, arsenic elements were confirmed to be introduced into the sub-micron ZnO rods. The acceptor ionization energy was deduced to be about 110 meV based on the temperature-dependent PL spectra.     

Scanning transmission electron microscopy (STEM)-transmission electron microscopy (TEM) analysis of nitrogen ion implanted austenitic 302 stainless steel

The microstructure of nitrogen implanted AISI 302 austenitic stainless steel and the effect of long-term room temperature ageing on it have been studied. Samples were implanted in 1992 with 2.5×10²¹ N₂⁺ m⁻² at 130 keV. The characteristics of the implanted layer and the depth profile have been investigated by scanning transmission electron microscope combined with energy dispersive X-ray spectrometry. Electron diffraction patterns recorded in the implanted layer using transmission electron microscopy confirm the formation of CrN along with the presence of Cr₂N. The identification of phases by glancing angle X-ray diffraction also indicates the formation of Cr₂N and nitrogen solid solutions. The effects of ageing on the microstructure are observed to be small.     

Influence of sputtering parameters and nitrogen on the microstructure of chromium nitride thin films deposited on steel substrate by direct-current reactive magnetron sputtering

Chromium nitride thin films were deposited on SA-304 stainless steel substrates by using direct-current reactive magnetron sputtering. The influence of process conditions such as nitrogen content in the fed gas, substrate temperature, and different sputtering gases on microstructural characteristics of the films was investigated. The films showed (200) preferred orientation at low nitrogen content (< 30%) in the fed gas. The formation of Cr₂N and CrN phases was observed when 30% and 40% N₂ were used, with a balance of Ar, respectively. Field emission scanning electron microscopy and atomic force microscopy were used to characterize the morphology and surface topography of the thin films, respectively. Microhardness tests showed a maximum hardness of 16.95 GPa for the 30% nitrogen content.