Thin Compound Layer Research Articles

SnPbInBiSb high-entropy solder joints with inhibited interfacial IMC growth and high shear strength

The rapid advancements in microelectronic devices towards miniaturization and multifunctionality have led to an increasing demand for solder joints that exhibit enhanced mechanical properties and reliability. This study focuses on investigating the high-shear strength of SnPbInBiSb/Cu high-entropy solder joints. The analysis encompasses the microstructure evolution, interfacial reactions, and shear behavior of these solder joints after reflowing at 180 °C. The study reveals the formation of very thin intermetallic compound (IMC) layers, specifically Cu6Sn5 and Cu3Sn, at the SnPbInBiSb/Cu interface with an average thickness of about 1.04 μm following a 10min reflow. Transmission electron microscopy (TEM) analysis illustrates the presence of nanoscale precipitates of InSn3 or Sn3Sb phases dispersed within the Cu6Sn5 IMC. The high mixing entropy of the SnPbInBiSb solder contributes to the suppression of the interfacial IMC growth rate during the reflow process. Notably, the shear strength and fracture behavior of the SnPbInBiSb high-entropy solder joints are significantly influenced by the thickness of the interfacial IMC. In particular, solder joints reflowed at 180 °C for 10 min exhibit a high shear strength of 102.4 MPa with a ductile fracture mode.

Enhancing Interfacial Stability and Mechanical Strength of a CoSb3-Based Thermoelectric Junction Using Ti-Based Alloy Barrier Layers.

CoSb3-based filled skutterudites (SKDs) are among the most promising materials for power generation. However, the poor interfacial stability and mechanical strength severely limit their practical application when joined with Cu electrodes. In this study, we propose multiphase Ti-based alloy barrier layers for CoSb3-based thermoelectric junctions to prevent the continuous brittle TiCoSb phase formation. Following the principles of coefficient of thermal expansion matching, we designed three types of Ti80-xNbxCo20 (x = 0, 5, and 10, at.%) barrier layers with the thin intermetallic compound (IMC) layers (<20 μm). Transmission electron microscopy analysis revealed that the interfacial microstructure of the Ti75Nb5Co20/Ce-SKD junction comprises Ti5Sb3, Ti5CoSb3, TiCoSb, and TiSb2 phases, as well as unreacted TiCo, Ti2Co, and Ti(Nb)ss phases, demonstrating a uniform staggered distribution state. After aging tests, the IMC thickness increased gradually from 7 to 12 μm, and the interfacial contact resistivity increased from 7.59 to 15.46 μΩ·cm2. A Cu layer was chosen as a buffer during the brazing process to prevent the formation of cracks and holes. After aging for 360 h at 823 K, the shear strength of the brazed joints remained at ∼21 MPa. Our results demonstrate that the Cu/CuSnP/Cu/Ti75Nb5Co20/Ce-SKD brazed joint exhibits excellent interfacial stability and satisfactory mechanical strength.

Detection of the explosive nitroaromatic compound simulants with chemosensory systems based on quartz crystal microbalance and chemiresistive sensor arrays

The work is devoted to investigations of possibility of rapid detection and subsequent identification of explosive substances by using the arrays of two types of sensor elements: quartz crystal microbalances and chemiresistive electrodes. Thin layers of calixarene compounds and composites of electrically conductive polymers, respectively, were used as the sensitive coatings. Several types of nitroaromatic compounds from nitrotoluene series were chosen as simulants of explosive substances: O-Nitrotoluene (2-MNT) and Nitrobenzene (MNB), the concentration of these volatile compounds varied from 10 to 100 ppm. The observed detection threshold, depending on the type of analyzed explosive simulants, was within the range of 1 to 10 ppm for quartz crystal sensors with calixarene sensitive films, and the response time was within 10…20 s for quartz crystal sensors and up to 1 min for chemiresistive sensors. It has been shown that among the tested calixarenes there are samples with high selective sensitivity. The possibility of qualitative identification of explosives at relatively low concentrations by using the statistical methods of chemical patterns recognition (the so-called “electronic nose”) has been demonstrated.

Building Sustainable Saturated Fatty Acid-Zinc Interfacial Layer toward Ultra-Stable Zinc Metal Anodes

The commercialization pace of aqueous zinc batteries (AZBs) is seriously limited due to the uncontrolled dendrite growth and severe corrosion reaction of the zinc anode. Herein, a universal and extendable saturated fatty acid-zinc interfacial layer strategy for modulating the interfacial redox process of zinc toward ultrastable Zn metal anodes is proposed. The in situ complexing of saturated fatty acid-zinc interphases could construct an extremely thin zinc compound layer with continuously constructed zincophilic sites which kinetically regulates Zn nucleation and deposition behaviors. Furthermore, the multifunctional interfacial layer with internal hydrophobic carbon chains as a protective layer is efficient to exclude active water molecules from the surface and efficiently inhibit the surface corrosion of zinc. Consequently, the modified anode shows a long cycle life of over 4000 h at 5 mA cm-2. In addition, the assembled Zn||V2O5 full cells based on modified zinc anodes have excellent rate performance and long cycle stability.

The thermal process for hardening the nitrocarburized layers of a low-carbon steel

Undesirable microstructures, with thin or uneven compound layers, pores, pearlitic structures, vein-like nitrides, etc., are detrimental to mechanical and tribological properties of nitrocarburized components. Here, we report a novel heat process in which a thicker nanobainitic layer, consisting of γ′ lamellas and α-Fe laths with high-density α′′-phase GP-zones, is obtained by heating the undesirable nitrocarburized layer at 700 °C (austenitizing) followed by isothermal aging at 225 °C for 14 h. The total phase-transformation sequences of this process are described as: ε + γ′ → γ-N/C → γ′ + α-Fe + GP-zones. The thicker nanobainitic layer exhibits much higher hardness, load-bearing capacity, fracture toughness and wear resistance as compared to the nitrocarburized layer, and corresponding mechanisms for strengthening and toughening are shown.

Interfacial characteristics and mechanical properties of aluminum / steel butt joints fabricated by a newly developed high-frequency electric cooperated arc welding-brazing process

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.

Micromechanical tensile test investigation to identify elastic and toughness properties of thin nitride compound layers

The measurement of thin-layer mechanical properties, like compounds generated by thermo-chemical nitriding process, is a key issue to optimize and predict the endurance of surface treatment against contact fatigue and wear. An original FIB micro-tensile test strategy involving plain and micro-notched tensile specimens is proposed. These specimens were FIB machined in a thin ε(50%)- γ’(50%) compound layer resulting from a common low pressure gaseous nitriding process (Allnit ©) and tested using a dedicated micro-testing system. Combined with DIC analysis, such micro-tensile test strategy allows extracting both the elastic modulus and the Poisson's ratio. Additionally, testing micro-notched specimens underlines the necessity to include FE simulations in order to take into account the radius of the micro-notch tip as well as the surface roughness induced by the FIB machining process. The investigation of this ε - γ’ compound layer suggests a Young's modulus E = 200 GPa, a Poisson's ratio ν =0.31 and a rather low fracture toughness KIC = 0.55 MPam. This methodology involving FIB machining, DIC analysis, test procedures and FE post processing simulations is fully detailed and the given results are discussed regarding literature.

Investigations on the Micro-Pitting and Wear Behavior of Nitrided Internal Gears

Nitriding processes can significantly increase the load carrying capacity of gears, compared e.g. to through hardened gears. Nitrided gears are generally characterized by a thin and hard compound layer on the surface and an adjacent diffusion layer that extends deeper into the material. Structure and properties of the compound layer significantly determine especially the tribologically dominated load carrying capacity characteristics of the tooth flank surface such as micro-pitting and wear. Previous investigations on nitrided gears were mainly focused on fatigue limits for the surface durability against pitting and tooth root bending strength. Furthermore, mostly external nitrided gears were investigated. Results of systematic investigations on the wear and micro-pitting behavior of nitrided internal gears are scarcely available. Based on the investigations in the research project FVA 482 IV, experimental test results confirm that nitrided internal gears in the material pairing “case hardened/nitrided” provide a significantly better performance regarding wear compared to through hardened or case hardened internal gears. Furthermore, it was shown that nitriding can have a positive influence on the micro-pitting behavior. A detailed analysis of the microstructure shows that the properties of the compound layer are primarily responsible for both, the micro-pitting and wear behavior.

Effects of Extreme Thermal Shock on Microstructure and Mechanical Properties of Au-12Ge/Au/Ni/Cu Solder Joint

Extreme temperature change has generally been the great challenge to spacecraft electronic components, particularly in long, periodic, deep-space exploration missions. Hence, researchers have paid more attention to the reliability of component packaging materials. In this study, the microstructure evolution on the interface of Cu/Ni/Au/Au-12Ge/Au/Ni/Cu joints, as well as the effects of extreme thermal shock on mechanical properties and the fracture mode in the course of extreme thermal changes between −196 and 150 °C, have been investigated. Results revealed that the interface layers comprised of two thin layers of NiGe and Ni5Ge3 compounds after Au-12Ge solder alloy was soldered on the Au/Ni/Cu substrate. After extreme thermal shock tests, the microstructure morphology converted from scallop type to planar one due to the translation from NiGe to Ni5Ge3. Meanwhile, the thickness of interface layer hardly changed. The shear strength of the joints after 300 cycles of extreme thermal shock was 35.1 MPa, which decreased by 19.61%. The fracture location changed from the solder to solder/NiGe interface, and then to the interface of NiGe/Ni5Ge3 IMC layer. Moreover, the fracture type of the joints gradually transformed from ductile fracture mode to brittle mode during thermal shock test. Simultaneously, the formation and extension of defects, such as micro-voids and micro-cracks, were found during the process of thermal shock due to the different thermal expansion coefficient among the solder, interface layer and substrate.

The History of the German Association for Crystal Growth

The History of the German Association for Crystal Growth

Lithium-Silicon Compounds as Electrode Material for Lithium-Ion Batteries

The element silicon is currently considered as one of the most promising alternative electrode materials for lithium-ion batteries. During lithiation, silicon experiences a large volume increase, which often leads to material failure and significant irreversible loss of capacity. The production of amorphous thin layers of lithium-silicon compounds as pre-lithiated electrode material is a promising approach to reduce significant capacity losses and to “homogenize” volume expansion. We demonstrate that it is possible to produce stable amorphous lithium-silicon thin films with variable stoichiometry using ion beam co-sputtering. The electrochemical experiments show that the different starting compositions of the electrode material (different x for LixSi) compared to pure amorphous silicon cause significant differences in the electrochemical behavior and in the electrode kinetics. With an increasing amount of lithium in the lithium-silicon electrode, the specific charge and discharge capacity decreases, but irreversible capacity losses are reduced in the first cycle and the Coulomb efficiency stabilizes at a value of almost 100%. Thin films with a low Li concentration, such as Li0.06Si, are likely not stable to the lithiation process during long term cycling due to material failure, whereas Li0.4Si shows a much better charge/discharge stability up to 100 cycles.

A universal approach for the synthesis of two-dimensional binary compounds

Only a few of the vast range of potential two-dimensional materials (2D) have been isolated or synthesised to date. Typically, 2D materials are discovered by mechanically exfoliating naturally occurring bulk crystals to produce atomically thin layers, after which a material-specific vapour synthesis method must be developed to grow interesting candidates in a scalable manner. Here we show a general approach for synthesising thin layers of two-dimensional binary compounds. We apply the method to obtain high quality, epitaxial MoS2 films, and extend the principle to the synthesis of a wide range of other materials—both well-known and never-before isolated—including transition metal sulphides, selenides, tellurides, and nitrides. This approach greatly simplifies the synthesis of currently known materials, and provides a general framework for synthesising both predicted and unexpected new 2D compounds.

Dissolution of thin TaV2 during annealing of Ta/TaV2/V tri-layer below the order-disorder temperature

In this research, we provide first experimental evidence on the dissolution of a thin compound layer sandwiched between the parent materials when it is heated below the order-disorder temperature. The Ta(10 nm)/TaV2(6 nm)/V(30 nm) system, prepared by DC magnetron sputtering, has been chosen to prove the expected simulation results. The samples were investigated mainly by secondary neutral mass spectrometry. The about 6 nm thick TaV2 compound layer was dissolved by annealing at 1025 °C for 1 h. Then, it was reformed by increasing the annealing time to 2–3 h. These results prove our previous computer kinetic Monte Carlo and Kinetic mean field calculations. These findings are important for nanotechnologies utilizing early stages of solid state reactions.

Improving the surface characteristics of Ti-6Al-4V and Timetal 834 using PIRAC nitriding treatments

Despite the popularity of a number of techniques of thermochemical diffusion for titanium, in many cases the surface engineering processes used may not be economically viable options for industry. This work focuses on the application of Powder Immersion Reaction Assisted Coating (PIRAC), a relatively inexpensive nitriding treatment that can provide a remarkable improvement in the surface characteristics of titanium alloys. The aim of this work was to determine whether PIRAC could be successfully applied to Ti-6Al-4V and the high-performance near-α titanium alloy Timetal 834. In order to study the response of these materials to PIRAC nitriding, techniques such as X-ray diffraction, micro-indentation hardness, surface profilometry, optical and electron microscopy, nano-scratch adhesion testing and ball-on-plate reciprocating-sliding wear testing were employed. These techniques highlighted the markedly different response between the two alloys to the PIRAC treatment; namely, that Ti-6Al-4V forms a thick compound layer, while at the same processing temperature and time Timetal834 does not form any appreciable Ti2N phase instead forming a nitrogen-diffusion case with a thin TiN compound layer at the surface. This inherent difference in nitridability influences the metallurgical response of each alloy. Despite this, the surfaces of both alloys were still hardened considerably and their tribological performance in dry sliding conditions improved compared to the untreated alloys.

Copepod avoidance of thin chemical layers of harmful algal compounds

AbstractIn a physical model of a thin planktonic layer, the estuarine copepod Acartia tonsa strongly avoided weakly stratified layers of dissolved chemical compounds from the harmful dinoflagellate Karenia brevis. Chemical‐induced changes in swimming kinematics allowed copepods to effectively avoid the layer and surrounding volume, highlighting the relevance of harmful alga‐grazer interactions at a distance that involve dissolved chemical signals. Avoidance increased significantly with increasing chemical concentration representative of a range of ecologically relevant bloom conditions (1–104 cells/mL equivalent). Under mid to maximal bloom conditions, Acartia displayed visually and hydrodynamically conspicuous avoidance jumps featuring large, rapid displacements with swimming speeds near those reported for predatory escape reactions. Previous findings show K. brevis is both toxic and nutritionally inadequate to A. tonsa when ingested and that exposure to dissolved chemical compounds likely rapidly suppresses effective sampling and grazing behaviors. Thus, copepods have strong incentive to sense and avoid nearby, spatially discrete patches of toxic algae in order to improve fitness by avoiding exposure and/or ingestion and associated negative impacts. Our results suggest harmful alga not only produce deleterious physiological effects in copepod grazers, but chemical‐induced behavioral responses also likely alter grazer distributions and top‐down control via avoidance reactions (reduced harmful alga‐grazer encounter rates). Additionally, predator‐prey encounter rates at higher trophic levels are likely enhanced via significant changes in copepod swimming kinematics. These combined mechanisms could protect and sustain harmful blooms contained in subsurface thin layers until blooms reach critical mass and produce widespread impacts at the ecosystem level, the “cryptic bloom” effect.

Mechanical Properties and Tribological Behavior of In Situ NbC/Fe Surface Composites

The mechanical properties and tribological behavior of the niobium carbide (NbC)-reinforced gray cast iron surface composites prepared by in situ synthesis have been investigated. Composites are comprised of a thin compound layer and followed by a deep diffusion zone on the surface of gray cast iron. The graded distributions of the hardness and elastic modulus along the depth direction of the cross section of composites form in the ranges of 6.5-20.1 and 159.3-411.2 GPa, respectively. Meanwhile, dry wear tests for composites were implemented on pin-on-disk equipment at sliding speed of 14.7 × 10−2 m/s and under 5 or 20 N, respectively. The result indicates that tribological performances of composites are considerably dependent on the volume fraction and the grain size of the NbC as well as the mechanical properties of the matrices in different areas. The surface compound layer presents the lowest coefficient of friction and wear rate, and exhibits the highest wear resistance, in comparison with diffusion zone and substrate. Furthermore, the worn morphologies observed reveal the dominant wear mechanism is abrasive wear feature in compound layer and diffusion zone.

Shear strength and fracture behavior of reflowed Sn3.0Ag0.5Cu/Cu solder joints under various strain rates

The effects of strain rate on the shear fracture behavior of Sn3.0Ag0.5Cu/Cu solder joints with thin and thick interfacial intermetallic compound layers were investigated. A single lap-shear sample was designed to conduct the study. The Cu/Sn3.0Ag0.5Cu/Cu joints were reflowed at 250 °C and 280 °C for 10 min, respectively, resulting in formations of a thin (6.08 μm) and thick (13.25 μm) intermetallic compound layer between the solder and Cu substrate. The single lap-shear tests were performed at the shear strain rates of 5 × 10−4 s−1, 5 × 10−3 s−1, 2 × 10−2 s−1, 1 × 10−1 s−1 and 2 × 10−1 s−1 to observe the shear fracture behavior. Experimental results revealed that both the thickness of the interfacial intermetallic compound layer and strain rate had influence on the shear strength and failure mode of the solder joint. The shear strength of the solder joints increased with increasing strain rate, but decreased with thickness of the interfacial intermetallic compound layer. It was observed that the solder joints broke in a ductile manner at low strain rates (5 × 10−4 s−1, 5 × 10−3 s−1), although they exhibited a ductile-brittle mixed manner at intermediate (2 × 10−2 s−1) and a brittle manner at high strain rates (1 × 10−1 s−1, 2 × 10−1 s−1). In the case of low strain rates, the ductile fracture behavior of joints with thin and thick intermetallic compound layers were similar. Nevertheless, more cleavage and broken Cu6Sn5 grains were detected on the fracture surface of the solder joint with a thick intermetallic compound layer as the strain rate increased to 2 × 10−2 s−1, 1 × 10−1 s−1 and 2 × 10−1 s−1. Furthermore, when the strain rate of 2 × 10−1 s−1 was applied, the solder joint with a thin intermetallic compound layer was completely broken inside the Cu6Sn5 layer, but partly broken at the Cu6Sn5/Cu3Sn interface for the joints with a thick intermetallic compound layer. Four modes were proposed to explain the detailed ductile-to-brittle transition in failure behavior. In addition, the strain rate sensitivities of the solder joints with thin and thick interfacial intermetallic compound layers were also investigated. It was found that the strain rate of a solder joint with a thick interfacial intermetallic compound layer was lower than that of one with a thin interfacial intermetallic compound layer.

Evaluation of microstructure and wear properties of Ti-6Al-4V alloy plasma carbonized at different temperatures

Ti-6Al-4V (TC4) alloys were plasma carbonized at different temperatures (900, 950, and 1 000 °C) for duration of 3 h. Graphite rod was employed as carbon supplier to avoid the hydrogen brittleness which is ubiquitous in traditional gas carbonizing process. Two distinguished structures including a thin compound layer (carbides layer) and a thick layer with the mixed microstructure of TiC and the α-Ti in carburing layer were formed during carburizing. Furthermore, it was found that the microstructure and the properties of TC4 alloy were significantly related to the carbonizing temperature. The specimen plasma carbonized at 950 °C obtained maximum value both in the hardness and wear resistance.

Phenylvinyl-Substituted Carbazole Twin Compounds as Efficient Materials for the Charge-Transporting Layers of OLED Devices

Twin compounds containing two phenylvinyl-substituted carbazole rings were synthesized by multi-step synthesis. The compounds were characterized by thermogravimetric analysis, differential scanning calorimetry, and electron photoemission spectroscopy. The thermal stability of the materials was very high; initial thermal degradation temperatures were in the range 411–419°C. The glass-transition temperatures of the amorphous materials were in the range 74–119°C. Electron photoemission spectra of thin layers of the compounds revealed ionization potentials were in the range 5.05–5.45 eV. The hole-transporting properties of thin amorphous layers of the twin compounds were tested in organic light-emitting diodes with Alq3 as green emitter. The best overall performance was observed for a device based on the twin compound containing 3-[2-(4-methylphenyl)vinyl]carbazole groups; the turn-on voltage was 2.6 V, the maximum photometric efficiency 2.34 cd/A, and maximum brightness approximately 7380 cd/m2. At a brightness of 1000 cd/m2 the photometric efficiency was 23% higher than for a PEDOT:PSS-based device.

Ferritic Nitrocarburizing of SAE 1010 Plain Carbon Steel Parts

nitrocarburizing offers excellent wear, scuffing, corrosion and fatigue resistance by producing a thin compound layer and diffusion zone containing e (Fe2-3(C, N)), γ′ (Fe4N), cementite (Fe3C) and various alloy carbides and nitrides on the material surface. It is a widely accepted surface treatment process that results in smaller distortion than carburizing and carbonitriding processes. However this smaller distortion has to be further reduced to prevent the performance issues, out of tolerance distortion and post grinding work hours/cost in an automotive component. A numerical model has been developed to calculate the nitrogen and carbon composition profiles of SAE 1010 torque converter pistons during nitrocarburizing treatment. The nitrogen composition profiles are modeled against the part thickness to predict distortion. Experimental composition profiles of torque converter pistons are reported for model validation and to determine the effect of nitrogen composition on distortion. The surface residual stresses predicted by the model are also compared to the measured residual stresses. The correlations between nitrocarburizing temperature, distortion and composition profiles are discussed using the modeling results. CITATION: Manivannan, M., Stoilov, V., and Northwood, D., Ferritic Nitrocarburizing of SAE 1010 Plain Carbon Steel Parts, SAE Int. J. Mater. Manf. 8(2):2015, doi:10.4271/2015-01-0601. 2015-01-0601 Published 04/14/2015 Copyright © 2015 SAE International doi:10.4271/2015-01-0601 saematman.saejournals.org Downloaded from SAE International by Madhavan Manivannan, Tuesday, March 03, 2015