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Low costs (material, energy and time), high joint properties are the eternal pursuit of modern welding. In this paper, mechanisms of an innovative high frequency electric cooperated arc welding (HFAW) in enhancing welding productivity (joint penetration) and weld property control were comprehensively investigated. The process properties and weld mechanisms of this method were systematically compared with that of the traditional GMAW welding under typical process parameters. The results showed that 4.8 mm joint with an large aspect ratio of 4 was achieved by single pass HFAW at a high welding speed (15 mm/s) and a low welding heat input (reduced 1/3 than the traditional GMAW). The research on weld property control shows that the microstructure of weld zone and heat affected zone (HAZ) in the HFAW joint was much smaller than that in the GMAW joint under optimal parameters. The width of each zone in the HAZ, thermal cycle parameters such as elevated temperature holding time and cooling rate can be regulated independently by the high frequency electric heat input ratio. Such regulation is of great significance for high strength steel welding, which needs to control the welding thermal cycle process accurately. Combined with three-dimensional solid reconstruction of liquid filler metal, the mechanism of the HFAW in enhancing joint penetration was demonstrated. An interesting “self-tracking heating” of the high frequency current was found. The cutting-edge of the liquid metal was violently heated and more than half of the weld in thickness direction was achieved by a novel ultra-speed “interfacial tension driving penetrating” weld forming mechanism, which promises the HFAW high welding speed and large aspect ratio on the premise of satisfactory welding quality.

In this study, a high-tin-content Cu@Sn core/shell (40 wt.% Cu-60 wt.% Sn) powder was fabricated for transient liquid-phase sintering bonding of high-temperature power device packaging. Benefitting from the high tin content Cu@Sn core/shell powder, a sound joint was obtained at 260°C, 300°C, and 340°C with a bonding pressure of 0.2 MPa. The effect of parameters on microstructure and shear strength of the bonding layer was researched. The results demonstrated that the bonding layer consisted of Cu6Sn5, Cu3Sn, and residual Cu particles when Sn was consumed. The differential scanning calorimetry curves showed that the resultant bonding layer could sustain high temperatures up to 400°C. The shear strength of the joint was enhanced with the increase of bonding time and bonding temperature, and the highest value was 43.2 MPa. Besides, compared to the joint achieved with mixed powders, a denser joint was achieved using the Cu@Sn core/shell powders.

In this study, Ti–Si–C composite coatings were synthesized via plasma spraying of agglomerated powders prepared by a spray drying/precursor pyrolysis technology using Ti, Si, and sucrose powders. The influence of Si content, ranging from 0 wt% to 24 wt%, on the microstructure, mechanical properties, and oxidation resistance of the composite coatings was investigated. Results show that the phase composition of the Ti–Si–C composite coatings changes with the increasing Si content. The coatings without Si addition consist of TiC and Ti3O; the coatings with 6–18 wt% Si are composed of TiC, Ti5Si3, and Ti3O; the coatings with Si content of 24 wt% form only TiC and Ti5Si3 phases. As the Si content increases, the hardness of the Ti–Si–C composite coatings increases first and then decreases, depending on the intrinsic hardness of the ceramic phases, the brittleness of Ti5Si3, and the defects such as pores and cracks. The Ti–Si–C composite coatings have high wear resistance due to the in-situ synthesized high-hardness TiC and Ti5Si3. Owing to the high brittleness of Ti5Si3, the increasing Si content leads to higher wear volume loss at room temperature, which can be partially improved in high-temperature wear tests. The oxidation resistance of Ti–Si–C composite coatings increases with the increase of Si content, and the higher the oxidation temperature, the more obvious the influence of the Si addition on oxidation resistance.

That increasing temperature is beneficial for solder-wetting but not for amorphous-maintaining the state causes difficulties in joining of Zr-based bulk metallic glass (BMG). In order to solve the contradiction, this paper presents a two-step process of pre-cladding ultrasonic soldering, in which a Zn-6Al-3Cu-20Sn solder layer was firstly vacuum-cladded on surface of a Ti-6Al-4V sample, and then a Zr-14Cu-10Ti-8Ni BMG sample was ultrasonic-soldered to the solder layer without flux. Microstructures of the Zr-14Cu-10Ti-8Ni/Zn-6Al-3Cu-20Sn/Ti-6Al-4V soldering joints were studied using optical microscope, SEM, EDS, and XRD, and shear strengths were tested. Results show that shear strength ranges from 20 to 50 MPa among the joints obtained under different soldering temperatures and ultrasonic times. Shear fracture of all the experimental ultrasonic soldered joints occurred at the interface between solder and Zr-based BMG. The fracture surface shows a mixture of solder tearing and solder peeling off from the surface of the Zr-based BMG. Pits or grooves formed on surface of Zr-based BMG by ultrasonic cavitation benefit not only chemical adhesion but also mechanical adhesion by an anchoring effect. This work confirmed that ultrasonic treatment is very effective for the soldered joint of Zr-based BMG.

There is an urgent need to develop an alternative high-efficiency cooling technology that is affordable and environmentally friendly. Elastocaloric effect has attracted particular attention due to large available latent heat and large adiabatic temperature changes. The primary objective of this study is to control the deformation of NiTi solid-state cooling refrigerator simples rapidly and accurately. In the present study, coil specimens made of a pseudoelastic Ni50.8–Ti49.2 (at%) NiTi wires are utilized and elastocaloric effect behavior were studied by evaluating the temperature profiles and the tensile force characteristics during uncoiling-coiling cycle tests conducted at ambient conditions. The measured non-adiabatic temperature changes along the tested NiTi coiled wires varied with the test speed. A maximum temperature change of 13.5 °C was obtained for a speed of 1.2 mm s−1. The uncoiling-coiling test showed to be a suitable method for studying the elastocaloric effect and the mechanical behavior of NiTi alloys. From a practical point of view, pseudoelastic NiTi coiled wire can provide a NiTi wire high strain rate locally, and meanwhile provide a time long enough for heat transferring between active material and heat flow medium.

This paper aims at giving new insights into the impacts of the particle sizes of diatomite waste on the hydration properties of Portland cement from the perspective of quantitative analysis using Rietveld refinements method. XRD identification coupled with Rietveld quantitative phase analysis, as well as isothermal calorimetry and SEM observation, was performed. The results show that the cement hydration during the induction period does not show any significant differences with the decrease in the sizes of the diatomite waste particles; however, hydration during the acceleration period was significantly enhanced. Finer diatomite waste particles (d50

Sucrose, as a precursor of carbon, and titanium powders were used to prepare TiC powders by a spray-drying/precursor-pyrolysis method. Using the powders, TiC/Ti composite coatings were deposited by...

Taking advantages of reaction composite brazing, transient liquid phase bonding (TLP) and partial transient liquid phase bonding (PTLP), a novel process with the characteristics of low-temperature bonding and high-temperature resisting was developed for joining Cf/SiC composite to GH3044 alloy by using (Cu-Ti) + C + Ni mixed powder filler. Under the bonding temperature (980 °C), the reaction between the liquid Cu-Ti alloy and C particles (reaction composite mechanism), composition homogenizations between the joining layer and Ni particles (PTLP mechanism) as well as Ni-based substrate (TLP mechanism) occurred to complete the transformation (Cu,Ti)l + Cs + Nis → TiCs + (Cu,Ni)s. Thereby, a joint with high-temperature resistance and excellent mechanical properties was obtained in relatively short holding time. The melting-point of the joint (1050 °C) was obviously higher than that of Cu-Ti alloy (898 °C) in the filler. The bonded joints exhibited shear strengths of 229, 225 and 104 MPa at room temperature, 600 °C and 1000 °C, respectively.

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.

High efficiency and low heat input are the pursuit of modern welding. In this paper, an innovative high frequency electric cooperated arc welding (HFAW) was developed. The process and joint characteristics of the HFAW were compared with that of traditional arc welding (TAW). In the HFAW, a part of welding heat is generated all over the surface of weld side wall (WSW) directly and rapidly due to the skin effect and proximity effect of high frequency current. The limitation of heat conduction on the TAW was broken through. Benefited from the ultra-speed welding thermal process, the HFAW reaches 3–4 times the welding speed of the TAW, while the heat input needed in the HFAW was only about 60% that in the TAW. Meanwhile, the HFAW joint presented sound weld formation, complete penetration and finer microstructure, which made the joint possess an equal tensile strength with the base metal.

Babbitt metal cubes were prepared by means of selected laser melting (SLM) process using Sn—11% Sb—6% Cu alloy powders; their microstructures were studied using optical microscope (OM), SEM, EDS, XRD and DSC; and their mechanical properties were tested using Vickers hardness and tensile methods. The results show that fully dense Babbitt metal components can be prepared by using appropriate SLM process parameters and an interlayer staggered laser scanning strategy. Anisotropy characteristics appear in both the microstructure and mechanical properties of SLM-Babbitt cubic specimens. The average hardness was in the range of 32.5 HV0.05 to 35.3 HV0.05. Both tensile strength and elongation were somewhat higher in a direction parallel to the laser scanning speed (Y axis) than in a direction perpendicular to the laser scanning speed (X axis). The strengthening mechanism is suggested to include solid solution strengthening of oversaturated Sb in the Sn matrix, as well as dispersion strengthening of finely dispersed SnSb and Cu6Sn5 particles. The overgrown acicular Cu6Sn5 phases at low laser scanning speeds and void formation at higher laser scanning speeds seriously deteriorate the mechanical properties of the SLM-Babbitt specimens.

A kinetic model of Ni3Sn4 growth in a solid (Ni)–liquid (Sn solution saturated with Ni) interfacial reaction was established, and a kinetic equation of $$ l^{\text{IMC}} = 0.58\sqrt {\tilde{D}t} $$ was derived, which coincided with the experimental parabolic growth behavior. The Ni-Sn interdiffusion coefficient in Ni3Sn4 ( $$ \tilde{D} $$ ) was obtained as $$ \tilde{D} = 7.61 \times 10^{ - 12} \exp \left( { - \frac{{24.76\; {\text{kJ}}/{\text{mol}}}}{RT}} \right) $$ by combining the kinetic equation with kinetic experiments conducted at different temperatures. The developed model can predict the thickness of the Ni3Sn4 layer well.

Adding graphene to a polymer matrix is an effective way of fabricating advanced materials. Few-layer graphene (FLG)/polyamide-6 (PA6)/Poly (butylene terephthalate)-block-poly (tetramethylene glycol) (PBT-PTMG) ternary nanocomposites were prepared using an in situ polymerization extrusion method. Characterizations using scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy revealed a good dispersion of graphene in the composite matrix. Under the synergistic effects of a nanofiller and an elastomer, the nanocomposites showed apparent improvements in both strength and toughness. When incorporating 0.5 wt% FLG and 10 wt% PBT-PTMG, the flexural strength, impact strength, and elongation at break increased by 45%, 217%, and 390%, respectively. The reinforcing and toughening mechanisms are discussed in detail. As this method combines both the advantages of in situ polymerization and extrusion technology, it is therefore suitable for commercial production, enabling the potential applications of polymer composites.

The development of innovative methods to prepare graphene-based polymer composites with remarkable properties has become a priority due to the many practical applications of these microstructures. Herein, a new technology was used to fabricate composites by combining graphene materials and polymer microspheres. Polyamide 6 (PA6) microspheres were synthesised by reaction-induced phase separation method, and they were wrapped with few-layer graphene (FLG) or graphene oxide (GO) by exfoliated adsorption method, which allows FLG and GO sheets to form a three-dimensional network structure in the PA6 matrix. Electrical and mechanical characterisation led to a distinct improvement in the properties of PA6 composites, which were superior to traditional graphene/polymer composites. Moreover, the process proposed in this work proved to be an effective method to prepare graphene/polymer composites, suitable for industrial production, and can be extended to other kinds of composites with nanofillers.

Taking the advantages of reaction-composite brazing and transient liquid phase bonding (TLP), a novel process with the features of low-temperature bonding & high-temperature resisting was implemented to join C-SiC composite and GH4169 superalloy. In the new process, mixed powder of low-melting-point Cu85Ti15 alloy and carbon (C) was used as an interlayer. At a relatively low bonding temperature (990 °C), in-situ reaction of (Cu-Ti)l+Cs→(Cu)s+TiCs and interdiffusion between the (Cu-Ti)l liquid and the GH4169 substrate concurrently occurred to transform the interlayer into a TiC-reinforced (Cu)s matrix composite joining layer. The low-CTE reinforcement TiC helped to alleviate the high residual stress in the joint, and the (Cu)s matrix provided the high-temperature resistance for the joint. In the current work, microstructural behavior, formation mechanism, heat resistance and shear strengths of the bonded joints were investigated. Results indicated that the (Cu-Ti)l/Cs in-situ reaction had an effect of shortening the solidification time of the joining layer, thus decreasing the formation of Ti-C and Ti-Si brittle compounds at the C-SiC side interface. The bonded joints exhibited excellent comprehensive properties: melting temperature of the joining layer reached 1052 °C, which was much higher than that of Cu85Ti15 alloy (898 °C) and the bonding temperature (990 °C); the maximum shear strength at room temperature and 900 °C reached 234 MPa and 101 MPa, respectively.

In this work, quaternized nanofibrillated cellulose (Q-NFC) was isolated from bamboo bleached kraft pulp through the pre-treatment using 2, 3-epoxy-propyltrimethylammonium chloride (EPTAC) in an aqueous alkaline media and subsequent high-pressure homogenization. A series of aqueous Q-NFC dispersions with different contents of positively charged trimethylammonium groups on the surfaces of fibrils were obtained. With the amount of added EPTAC increased, the solid recovery ratio, surface charge contents, zeta potential values, and extent of nanofibrillation gradually increased for the as-obtained Q-NFCs. TEM images of Q-NFCs revealed that the incorporation of quaternary ammonium groups contributed to the defibrillation into finer nanofibrils with more uniform width distribution. With an increase in the positive charge contents, both degree of polymerization and decomposition temperature of the Q-NFC films decreased slowly. Steady-state rheological result demonstrated that the maximum shear viscosity was achieved for the Q-NFC0.6 dispersion with the medium charge content. The Q-NFC films with higher charge content displayed superior transparency and tensile strength. Furthermore, the oxygen transmission rate of PLA films was remarkably decreased dramatically from 216.0 to 10.3 mL m−2 day−1 after laminating a thin layer of Q-NFC0.6 on the one side. As compared to TEMPO-oxidized NFC from the same pulp, the surface-charged Q-NFC exhibited higher optical transmittance, shear viscosity, and thermal stability as well as comparable oxygen-barrier properties.

TC4 alloy(Ti)/304 stainless steel (SS) plates were butt joined using MIG-TIG double-sided arc welding(DSAW) with copper filler metal. Different joining modes, i.e., brazing mode, welding-brazing mode (Ti welding-SS brazing, SS welding-Ti brazing) and fusion welding mode, were achieved by regulating the welding parameters. The interfacial microstructures and mechanical properties of the joints were investigated. The results show that the interfacial microstructures and mechanical properties are strongly affected by the joining mode. For the joints with brazing mode and Ti welding-SS brazing mode, a straight Intermetallic compound(IMC) layer of Fe-Cu-Si and Ti-Fe-Cu-Si phases was respectively formed at the SS side brazing interface, resulting in the fracture at lower stress; the Ti side brazing and fusion interfaces both mainly consisted of Ti-Cu IMC layer. The joints with SS welding-Ti brazing mode and fusion welding mode led to the curved melted zone containing two phases of Fe(s,s) and Cu(s,s) at the SS side fusion interface. The tensile resistance of the interface was significantly enhanced attributed to the curved morphology and the suppression of the brittle IMCs. The fractures occurred at the Ti side interface, and the tensile strength was determined by the thickness of the reaction layer consisted of the Ti-Cu and Ti-Cu-Fe IMCs. Therefore, the SS welding-Ti brazing joint with a thinner reaction layer shows the maximum tensile strength, which is up to 319 MPa.

For high-temperature-resistant packaging of new generation power chip, a chip packaging simulation structure of Ni/Ni-Sn/Ni was bonded by a transient liquid-phase sintering process. High-temperature aging experiments were carried out to investigate joint heat stability. The microstructural evolution and mechanism during aging, and mechanical properties after aging were analyzed. The results show that the 30Ni-70Sn bonding layer as-bonded at 340°C for 240 min is mainly composed of Ni3Sn4 and residual Ni particles. When aged at 350°C, because of the difficulty of nucleation for Ni3Sn and quite slow growth of Ni3Sn2, the bonding layer is stable and the strength of that doesn’t change obviously with aging time. When aging temperature increased to 500°C, however, the residual Ni particles were gradually dissolved and the bonding layer formed a stable structure with dominated Ni3Sn2 after 36 h. Meanwhile, due to the volume shrinkage (4.43%) from Ni3Sn2 formation, a number of voids were formed. The shear strength shows an increase, resulting from Ni3Sn2 formation, but then it decreases slightly caused by voids. After aging at 500°C for 100 h, shear strength is still maintained at 29.6 MPa. In addition, the mechanism of void formation was analyzed and microstructural evolution model was also established.

Transient liquid phase sintering (TLPS) bonding process is a promising packaging process for the new generation semiconductor devices. In this paper, the dynamics of Ni-Sn TLPS bonding is researched. The melting enthalpy and the residual rate of Sn in the simulative and actual bonding process were measured by differential scanning calorimetry. Based on this, the radius of residual Ni particle and thickness of Ni3Sn4 compound were further calculated. The results show that when the initial average radius of Ni particle is 6.5 μm, after holding for 60 min and 240 min at 300 °C, the thickness of Ni3Sn4 is about 4.28 μm and 6.14 μm separately. The thickness Δr of Ni3Sn4 in the simulative bonding process shows a linear relationship as t0.308, i.e. Δr = 1.17t0.308, which is in agreement with that in the actual bonding layer.

A novel thermophysical simulation method to precisely control the reaction conditions was designed to investigate molten aluminium/solid steel interfacial reactions. The reaction layers between the materials were investigated by high-resolution transmission electron microscopy assisted by advanced focused ion beam technology. For the first time, fibrous-ordered Fe2Al5 and Fe4Al13 intermetallics induced by an order–disorder transformation appeared in the disordered substrates of Fe2Al5 and Fe4Al13, respectively. High-density planar defects composed of stacking faults and twinnings were found inside the Fe4Al13 grains. The (001) twinning as a type of growing twin was considered to be the sole operating mechanism during the solid/liquid interfacial reaction.

Weldability of a Cu-free high strength low alloy (HSLA) hull structure steel is studied. Strengthening contributions of this steel are analyzed and phase continuous cooling transformation in simulated coarse-grained heat affected zone (CGHAZ) is investigated. Indeed, strengthening contributions of simulated CGHAZs under heat input 50 and 20 kJ/cm, respectively, are estimated. It shows this Cu-free HSLA hull structure steel is dominated at grain refinement strengthening and supplemented by precipitation strengthening and phase transformation strengthening, while the simulated CGHAZ under heat input 50 or 20 kJ/cm is dominated at phase transformation strengthening and supplemented by solid solution strengthening and grain refinement strengthening. The drawn simulated heat affected zone continuous cooling transformation (SH-CCT) diagram shows this Cu-free HSLA hull structure steel can obtain main lath-like microstructures in a wide cooling rate range with low phase start temperature. Mechanical property tests of simulated CGHAZ samples indicate high strengths and good low temperature impact toughness. All results exhibit this Cu-free HSLA hull structure steel has satisfactory weldability, which suggests its wide potential applications.

A novel high frequency electric cooperated arc welding method (HFAW) was developed to join aluminium and steel of 3.0 mm thickness without groove. Owing to the skin effect and proximity effect of h...

3 mm thick Al-steel dissimilar metals were butt welded by a newly developed high frequency electric cooperated arc welding-brazing (HFAW-B) without grooves or shaping board. Microstructure characteristics and mechanical property of the joint were investigated and compared with that of the traditional single MIG joint. Results showed that sound joint with satisfactory weld appearance was achieved by the HFAW-B process under a low welding heat input (826 J/cm), while much higher heat input (1036 J/cm) was required for the traditional MIG process. The interfacial IMCs layer of the HFAW-B joint was homogeneous and thin (limited to 4.0 μm). In the traditional MIG joint, even with the same heat input, the maximum thickness of the IMCs layer exceeded 5.0 μm and massive Al-Fe brittle IMCs were found in the weld seam. When acceptable back weld appearance was obtained, a 20 μm IMCs layer was observed in the traditional MIG joint, which was extremely uneven and cracked after welding. Detailed analysis revealed that the uniform heating in thickness direction, preheating ahead of weld pool and differentiate heating of the HFAW-B process were beneficial to realize compatible regulation of interface characteristics and (back) weld appearance of Al/steel joint, i.e., to achieve not only a good weld appearance but also a thin compound layer under a low heat input. Benefitted from the sound weld appearance, thin interfacial IMCs layer and uniform stress distribution, the HFAW-B joint necked at Al side, and presented a tensile strength exceeded 90 % the strength of Al base metal.

In this paper, a novel brazing process based on in-situ alloying concept was carried out to join Cf/SiC composite to TC4 alloy at 940 °C for 20 min. Mixed powders of Ti-Zr-Cu-Ni alloy and pure Ti metal were used as interlayer. In the process, Ti-Zr-Cu-Ni alloy melted and then dissolved pure Ti metal via liquid-solid reactions, achieving in-situ alloying of the interlayer. The interfacial microstructure and formation mechanism of the brazed joints were investigated. The effect of Ti powder content on the microstructure and the mechanical properties of joints were analyzed. The results showed that: the maximum lap-shear strength of the in-situ alloying brazed joints was 283±11 MPa when using (Ti-Zr-Cu-Ni)+40 vol% Ti composite filler, and this value was 79% higher than the mechanical strength when using Ti-Zr-Cu-Ni alone. A reaction layer of (Ti,Zr)C+Ti5Si3 formed near Cf/SiC composite side, while a diffusion layer of Ti2Cu+Ti(s,s) formed near Ti-6Al-4V side. In the interlayer, lots of Ti(s,s) were distributed uniformly and few of Ti-Cu compounds were found, contributing to the plasticity of joints. Adding moderate Ti powder was beneficial for improving the interfacial reaction between Cf/SiC composite and filler material, which affected the lap-shear strength of joints.

In order to characterize the interfacial behavior of brazed joints and offer theoretical basis for the applications of TiZrCuNi-based composite fillers, Cf/SiC composite and TC4 were brazed by TiZrCuNi filler, and the microstructures of joints versus temperature and versus holding time were systematically studied in this paper. The mechanical properties of brazed joints were measured and analyzed. The results showed that Ti(Zr)C, Ti5Si3, Ti2Cu, TiNi, TiZrCu2, Ti2(Cu,Ni) and Ti(s,s) were the predominant compounds in the joints. Brazing temperature had a distinct effect on the microstructures of joints: with the increase of brazing temperature, the structure of brazed joints was reduced from four parts to three parts, and the wavy reaction layer became continuous and much thicker. While holding time had a similar but weaker effect on microstructures: with the extension of holding time, the reaction layer became thicker, but it was difficult to induce the decrease in the structural parts of joint. The thickness of reaction layer determined the mechanical properties of joints. The results were beneficial for the selection of reinforced phases and the design of composite fillers to obtain better mechanical performances. When the brazing temperature was 940 °C and the holding time was 25 min, the maximum shear strength of brazed joints attained a value of 143.2 MPa.

The effects of alkaline earth strontium (Sr) additions on the microstructure and properties of Al–Si–Ge–Zn alloys and brazed joints were investigated. The results showed that the appropriate addition of Sr changed the morphology of β-GeSi phases from coarse needle-like to fine granular shapes effectively. Sr addition prevented the growth of Si by Sr adsorbing on the Si surface and caused the formation of many twins in Si. Sr addition had little impact on the melting temperature of the filler metals, but the spreading areas of Al–Si–Ge–Zn–x Sr filler metals increased firstly and then decreased with the increase of Sr addition. In addition, the Sr addition optimized the microstructure of the brazed joints and improved the mechanical properties. Sound joints with high shear strength up to 152.4 ± 2.5 MPa could be obtained by applying Al–9.5Si–10Ge–15Zn–0.7Sr (all in wt%) filler metal.

A method for measuring peak values on the maxlength-area fraction curve and the perimeter-area fraction curve with morphological photos using Image Pro Plus 6.0 Soft for assessing grain boundary density in high-strength, high-toughness ferritic weld metals is developed. Results show the sizes of the peak values have a tough relationship with grain boundary densities in that a larger peak value stands for a larger grain boundary density. As ferrite transforms into a certain orientation relationship, this semi-empirical method provides handy references for judging the sizes of effective grain boundary densities.

A new non-isothermal phase kinetic equation which keeps the form of Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation is established. This non-isothermal JMAK type equation is expressed as X ( t ) = 1 − exp [ − ( K t ) n ] , K = K 0 exp ( − Q R T 0 ) T 0 can be given a linear relationship with transformation temperature T in relatively large parameter fluctuation ranges. The applications of non-isothermal JMAK type equation in γ→α phase process of Fe-0.002 wt%C alloy under linear cooling process and welding thermal process do show its good agreements with the experimental data.

The hardfacing (harden-surface-welding) metals without and with La 2 O 3 were prepared. The microstructures of the hardfacing metals were observed by optical microscopy. The phase structures were determined by X-ray diffraction. The morphologies and compositions of the inclusions were observed by field emission scanning electron microscope equipped with energy dispersive X-ray spectrometry. The free energies of the La-inclusions which may exist in the hardfacing molten pool were calculated according to thermodynamic theory. Subsequently, the surface properties of LaAlO 3 (100), ferrite(100) and ferrite(110) surfaces, the interfacial properties of LaAlO 3 (100)/Ferrite(100) and LaAlO 3 (100)/Ferrite(110) interfaces, and the effectiveness of LaAlO 3 as the heterogeneous nucleus of Ferrite were studied using a first-principles density functional plane-wave ultrasoft pseudopotential method. The experiment results indicate that, in the hardfacing metal, the ferrite grains can be refined and the numbers of the harmful inclusions can be reduced effectively by adding La 2 O 3 . Before the hardfacing molten pool solidification, La 2 O 3 transforms into the LaAlO 3 inclusion preferentially. The calculated results indicate that, in LaAlO 3 , most outer electrons of the Al atoms transfer to the O atoms, which means that the ionic bonds are formed between Al atoms and O atoms. Besides, because of the sp2 orbital hybridization, strong covalent bonds are formed between La atoms and O atoms with certain directionality. For LaAlO 3 (100) surface, there are two terminated structures, which are LaO terminated structure and AlO 2 terminated one. When the La chemical potential is small, surface stability of AlO 2 terminated structure is higher than that of LaO terminated one. While when the La chemical potential is large, LaO terminated structure is more stable than AlO 2 terminated one. For the LaO terminated structure, the interfacial ideal adhesion work of the LaAlO 3 (100)/Ferrite(100) interface is larger than that of the LaAlO 3 (100)/Ferrite(110) interface while the interfacial energy of the LaAlO 3 (100)/Ferrite(100) interface is smaller than that of the LaAlO 3 (100)/Ferrite(110) interface, which indicates that the interfacial binding strength and interfacial stability of LaAlO 3 (100)/Ferrite(100) interface are both higher than those of the LaAlO 3 (100)/Ferrite(110) one. For the two LaAlO 3 /Ferrite interfaces, when the La chemical potential reaches −2.447 eV and −1.009 eV, their interfacial energies are both smaller than the liquid-solid interfacial energy of Ferrite(l)/Ferrite(s), which means that LaAlO 3 can be the effective heterogeneous nucleus of Ferrite on current conditions.

Properties of γ-Fe(100) surface, RE(La,Ce)AlO3(100) surfaces and RE(La,Ce)AlO3(100)/γ-Fe(100) interfaces were investigated using a first-principles density functional plane-wave ultrasoft pseudopotential method. The results indicate that, the surface energy of γ-Fe(100) surface is stabilized gradually with the increase of the slab thickness, and it converges to 2.16 J/m2 ultimately. RE(La,Ce)AlO3(100) surface contains two terminated structures, which are REO-terminated one and AlO2-terminated one. When RE chemical potential ( Δ μ R E ) is smaller than −7.39 eV/unit cell (−2.84 eV/unit cell), AlO2-terminated surface is more stable than REO-terminated one. However, when Δ μ R E is larger than −7.39 eV/unit cell (−2.84 eV/unit cell), REO-terminated surface is more stable than AlO2-terminated one. For the RE(La,Ce)AlO3(100)/γ-Fe(100) interfaces, the binding strength of AlO2-terminated structure is larger than that of the REO-terminated one. Moreover, for the same terminated structure, the binding strength of the LaAlO3(100)/γ-Fe(100) interface is larger than that of the CeAlO3(100)/γ-Fe(100) interface. When Δ μ L a is in the range of −11.59 eV/unit cell ∼−11.22 eV/unit cell and −1.94 eV/unit cell ∼−1.56 eV/unit cell, LaAlO3 can be the heterogeneous nucleus of γ-Fe; when Δ μ C e is in the range of −6.27 eV/unit cell ∼−5.97 eV/unit cell, CeAlO3 can be the heterogeneous nucleus of γ-Fe.

The novel Al-Si-Ge-Zn filler metal was used for brazing 6061 aluminum alloy. Microstructure and properties of the filler metal and brazed joint were studied. The results showed that the main phases in the Al-Si-Ge-Zn filler metal as well as the brazed seam were α-Al, β-GeSi, and η-Zn phases. Compared with the common Al-Si-Ge and Al-Si-Zn filler metals, it had smaller and better dispersive β-GeSi solid solution phases without coarse primary Si phase. The melting temperature of Al-Si-Ge-Zn filler metal is 505.2~545.1 °C, and the narrow melting temperature interval is favorable for the brazing process. When this filler metal was used to braze the 6061 aluminum alloy, an optimized shear strength of 138.2 MPa was achieved. Observation of the fracture section showed that the brazed joints presented obvious ductile fracture characteristics.

The interfacial reaction between solid steel and liquid aluminum has been widely investigated in past decades; however, some issues, such as the solid/liquid interfacial structure, formation mechanisms of FeAl3 and Fe2Al5, and interaction between the growth and dissolution of intermetallic compounds, are still not fully understood. In this study, a hot-dipping method is designed to investigate the interfacial reaction in the temperature range between 973 K and 1273 K (700 °C 1000 °C) for 10 to 60 seconds. The intensification of the dissolution leads to the transformation of FeAl3/liquid aluminum into Fe2Al5/liquid aluminum in the solid/liquid structure with increasing reaction temperature. The formation of FeAl3 adhered to the interface depends not only on the reaction mechanism but also on precipitation at relatively low temperatures. In contrast, precipitation is the only formation mechanism for FeAl3 at relatively high temperatures. Austenitizing results in the complete transformation of the tongue-like Fe2Al5/Fe interface to a flat shape. The growth of Fe2Al5 with respect to the maximum thickness is governed by the interfacial reaction process, whereas the growth of Fe2Al5 with respect to the average thickness is governed by the diffusion process in the range of 973 K to 1173 K (700 °C to 900 °C) for 10 to 60 seconds. The dissolution of the parent metal is due to the natural dissolution of FeAl3 at low temperatures and Fe2Al5 at high temperatures.

C f /SiC composites were successfully active brazed by Ti-Zr-Be filler foil. The microstructure of the brazed joints was investigated by auger electron spectroscopy (AES) and scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS). The phase structure was determined by X-ray diffraction (XRD). The mechanical property was measured by mechanical testing machine. The results indicate that the brazed joint consisted of TiC, Ti 3 SiC 2 , ZrC, Be 2 C, Be 17 Ti 2 and Ti-based solid solution (β-Ti). TiC+Ti 3 SiC 2 /ZrC+Ti(Zr)-Si-C+Be 2 C reaction layers were formed near C f /SiC composite side while the reaction layer of β-Ti+Be 17 Ti 2 +Ti(Zr) 3 SiC 2 with a small amount of ZrC, TiSi 2 , Be 2 C particles was formed in the center of the joint. With the increase of the brazing temperature or holding time, the amount of β-Ti compound in the interlayer decreased gradually while the thickness of reaction layer increased gradually. When the brazing temperature was 1000 °C and the holding time was 15 min, the maximum room temperature shear strength of the brazed joint can be achieved, which was 136.63 MPa. The joints with the parameters of 950 °C/30 min, 1000 °C/15 min and 1050 °C/5 min could resist a pressure of 5 MPa at 1200 °C for 5 min

First-principle calculations have been performed to investigate the structural, mechanical, thermo-physical and electronic properties of η′-(CuNi)6Sn5 intermetallic compounds. The results indicated that, the doped Ni atom can not only enhance the stability of the η′-Cu6Sn5, but also improve the mechanical and thermo-physical properties, which are more dependent on the Ni atom doping number than the doping position. In all the η′-(CuNi)6Sn5, Cu3Ni3Sn5 (Cu1+Cu3 site) shows the best stability, the most excellent deformation resistance and the highest hardness. The Cu6Sn5, Cu3Ni3Sn5, Cu4Ni2Sn5, Cu1Ni5Sn5 and Ni6Sn5 are ductile while the Cu5Ni1Sn5 and Cu4Ni2Sn5 are brittle. The anisotropies of η′-(CuNi)6Sn5 are all mainly due to the uneven distribution of Young's modulus at (001) planes, moreover, the anisotropy of Cu1Ni5Sn5 (Cu1+Cu2+Cu4 site) is the strongest while that of Ni6Sn5 is the weakest. The calculated Debye temperature and heat capacity showed that Cu4Ni2Sn5 (Cu2 site) possesses the best thermal conductivity (ΘD = 356.9 K) and Cu2Ni4Sn5 (Cu1+Cu2 site) possesses the largest heat capacity. From the electronic property analysis results, the Ni s and Ni p states can replace the Cu s and Cu p states to hybridize with Sn s states at −7.98 eV. Moreover, with the increasing number of the doped Ni atom, the hybridization between Cu d states at different positions is receded, while that between Ni d states is enhanced gradually.

An overlap titanium-on-aluminum configuration based on laser penetration welding was designed to suppress the formation of intermetallic compounds. Weld surface appearance, weldgeometry, microstructure, and mechanical property of the joint were investigated. The collaps of upper liquid titanium closes keyhole filled with boiling aluminum vapor, which induces welding spatter. Optimizing processing parameters could control the welding spatter to some extent. Weld geometry is characterized by depth of the weld loss, depth of the penetration of titanium into aluminum and width of joining, which depends on processing parameters strongly. The overlap titanium-on-aluminum configuration can suppress the formation of intermetallic compounds inside Ti weld. Interfacial reaction appears between Ti weld and Al, and the reaction layers are composed of TiAl and TiAl3. The banded structures with Ti3Al were found inside Ti weld. Tensile capacity of the joint increases firstly and then decreases with increasing laser power or decreasing welding speed, depending on weld geometry and interfacial reaction. Moreover, there are two broken modes of the joints, which are fractured in interface and in Ti weld, respectively. When joints fracture in the Ti weld, the joint has the higher tensile property, up to 184 N/mm.

In this work, Boron atom adsorption, absorption and diffusion on the surface of and in the bulk of the Nickel are studied with a first-principles density functional theory approach and the climbing image nudged elastic band method. The calculated results indicate that, on the Ni (111) surface, there are three stable sites for B atom adsorption, which are Top site, Hcp-hollow site and Fcc-hollow site, and Hcp-hollow site is the most preferred one. While below the surface, the Boron atom prefers to reside at the Oct site with the absorption energy of −1.38 eV, and the energy barrier for Boron atom diffusing from Hcp-hollow site to Oct site is 1.22 eV. In bulk Ni, the Tet and Oct sites are both stable ones for solution of the B atoms, the energy barrier for B atom diffusing from Tet site to its nearest neighboring Oct site is 0.29 eV, while that for B atom diffusing between two neighboring Oct sites are 1.65 eV, which indicate that the B atom diffuses between two neighboring Oct sites is harder than that from Tet site to neighboring Oct site.

The principle of the lever rule on the dilatation curve and its application to the corresponding differential dilatation curve were introduced in a nonoverlapped two-phase continuous cooling process. The lever rule was further expanded in the case of an overlapped two-phase process. The application of the expanded lever rule was based on the approximate symmetry treatment on the differential dilatation curve, which shows reasonably both on the theoretical calculation and in the experimental results. High-strength low-alloy steels were thermal simulated with Gleeble 3500. The transformed phase volume fractions in different cooling processes were calculated by the expanded lever rule and metallography analysis. The results showed the expanded lever rule could calculate reliable phase volume fractions as metallography analysis.