Needle-like Intermetallic Compounds Research Articles

Interfacial Reactions of Sn-3.0Ag-0.5Cu Solder with Sputter Cu-Ti Alloy Film UBM

Herein, the influence of Ti additive on the formation of intermetallic compounds (IMC) in a SAC/Cu-Ti soldered joint and corresponding mechanical properties are systematically investigated. The Ti-to-Cu ratio under bump metallization (UBM) is adjusted by tuning the target current during magnetron sputtering. Interestingly, the needle-like IMC, which is different from the traditional scallop-like IMC, is formed in the SAC/Cu-Ti soldered joint after reflow. The growth of Cu3Sn and Kirkendall voids is significantly inhibited after thermal aging in the SAC/Cu-Ti soldered joint. Overall, the segregation of Ti at grain boundaries forms a titanium-rich layer. Also, the Ti-rich layer acts as a diffusion barrier layer and hinders the diffusion of Cu into IMC. The shear strength test results show that SAC/Cu-Ti has much stronger strength than SAC/Cu both before and after thermal aging. These results confirm that Cu-Ti UBM is beneficial to the improvement of welding reliability.

Study of Mechanical and Wear Behaviour of Hyper-Eutectic Al-Si Automotive Alloy Through Fe, Ni and Cr Addition

Effect of Fe, Ni and Cr addition on the wear behavior of hyper-eutectic Al-Si automotive alloy has been studied. Dry sliding wear tests have been conducted using pin-on-disc wear testing machine under normal loads of 20N and constant sliding speed of 0.64 ms-1. Influence of Fe addition to the base alloy increases the wear rate due to the formation of needle beta intermetallics. Ni addition to the alloy does not impede formation of needle-like intermetallic compounds and has no positive effect on the modification of microstructure. Introducing of Cr to the iron-rich alloy changes the beta intermetallics into the modified alpha phases and therefore reduced the detrimental effect of iron. As a result it recovers the strength and wear properties of the experimental alloy. Wear test surfaces were examined by SEM and have shown that Cr added alloy improves wear resistance through mild and smooth abrasive grooves filled with oxides.

Effects of Al–8.5Si–25Cu–xY filler metal foils on vacuum brazing of SiCp/Al composites

ABSTRACTRapidly solidified Al–8.5Si–25Cu–xY (wt-%, x = 0, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5) foils were used as filler metal to braze Al matrix composites with high SiC particle content (SiCp/Al-MMCs), and the filler presented fine microstructure and good wettability on the composites. The joint shear strength first increased, then decreased and a sound joint with a maximum shear strength of 135.32 MPa was achieved using Al–8.5Si–25Cu–0.3Y as the filler metal. After Y exceeded 0.3%, a needle-like intermetallic compound, Al3Y, was found in the brazing seam, resulting in a dramatic decline in the shear strength of the brazed joints. In this research, the Al–8.5Si–25Cu–0.3Y filler metal foil was found to be suitable for the brazing of SiCp/Al-MMCs with high SiC particle content.

Mechanical Properties of Al–30Si–5Fe Alloy Using Combination of Rapid Solidification and Thixoforming Processes

In this study, a combination of rapid solidification (melt-spinning) and semisolid forming (thixoforming) processes was used to refine the coarse microstructure of “as-cast” Al–30Si–5Fe alloy and improve its mechanical properties. Al–30Si–5Fe ribbons produced by the melt-spinning process were pulverized and subsequently consolidated at 300 °C in an argon atmosphere. Prepared specimens were thixoformed at temperatures ranging from 580 to 700 °C for various holding times. Some cast samples were also directly thixoformed as reference. In all thixoformed samples, microstructures were modified and needle-like intermetallic compounds as well as silicon particles in the as-cast part were changed into rounded corners or polygonal shapes with uniform distribution. Macro-hardness of up to 165 HV10 (which is almost twice as much as-cast sample) was obtained from a meltspun sample held for 5 min at 700 °C and then thixoformed. Compression strength and malleability increased 31 and 57%, respectively, and a 33% reduction in wear coefficient was obtained in this sample compared to the as-cast alloy.

Microstructural Modification of Al–30Si–5Fe Alloy Using a Combination of Rapid Solidification and Thixoforming Processes

It is commonly known that the properties of materials are strongly related to their microstructure. This paper introduces a method that is a combination of rapid solidification (melt spinning) and semisolid forming (thixoforming) processes, which are used to refine the microstructure of “as-cast” Al–30Si–5Fe alloy and improve its mechanical properties. Produced Al–30Si–5Fe ribbons by melt-spinning process, were pulverized and subsequently consolidated at 300 °C in argon atmosphere. Prepared specimens were thixoformed at temperatures ranging from 580 to 700 °C in various holding times. Some samples were also directly thixoformed from as-cast condition. Microstructure of the as-cast, meltspun, and thixoformed samples were investigated in each stage of manufacturing procedure. In all thixoformed samples, microstructures were modified, and needle-like intermetallic compounds as well as silicon particles in the as-cast part were changed into rounded corners or multifaceted structure with uniform distribution. The average size of hard particles significantly reduced from 160 μm in the as-cast condition to 3–30 μm in the meltspun-thixoformed samples. Finally, hardness test was carried out to evaluate specimens. In comparison with the as-cast condition, results showed 23–94% increase in hardness for meltspun-thixoformed samples and 12–29% for cast-thixoformed samples.

Effect of Mn addition on Fe-rich intermetallics morphology and dry sliding wear investigation of hypereutectic Al-17.5%Si alloys

The effect of Manganese addition on the iron-rich intermetallics and wear behavior of Al-17.5%Si hypereutectic alloys has been studied. Dry sliding wear tests have been conducted using a pin-on-disk machine under different normal loads of 18, 51, 74 and 100N and at a constant sliding speed of 0.3m/s. The addition of 1.2wt.% Fe to the base alloy increased the wear rate due to the formation of needle beta intermetallics. Introducing 0.6wt.% Mn to the iron-rich alloy changed the beta intermetallics into the modified alpha phases, and therefore reduced the detrimental effect of iron. Mn addition up to 0.9wt.% to the 1.8Fe alloy did not impede formation of needle-like intermetallic compounds and had no positive effect on the modification of microstructure.

Effect of Potassium Acetate on Coke Growth during Light Naphtha Thermal Cracking

Potassium acetate was used as a coking inhibitor to reduce coking during light naphtha cracking on a Cr25Ni35 alloy specimen that had already been used for 8 years. The effects of the mass concentration of potassium acetate on the morphology and structure of coke were investigated by high-resolution scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The results show that the oxide scale formed on the inner surface of the cracking tube after 8 years of service is mainly composed of (Fe, Ni, Cr) spinels and the needlelike intermetallic compound of Cr and Fe. Changes of the surface conditions accelerate catalytic coking. The amount of coke decreases with increasing mass concentration of potassium acetate in a 1-h cracking period. The amount of coke was found to decrease by about 60% when the mass concentration was 400 ppm. The diameters of filamentous coke were about 100, 60, 45, and 35 nm when the mass concentrations of potassium acetate were 0, 100, 200, and 400 ppm, respectively. However, the gasification reaction was found to have little effect on the length of catalytic coke. The gasification reaction catalyzed by potassium acetate removes the noncatalytic coke surrounding the filamentous coke, and filamentous cokes at different concentrations are carbon nanofibers with a solid structure. Coke is mainly composed of amorphous carbon.

Interfacial Reaction between Sn-3.0Ag-0.5Cu Solder/Co-P Plating and Ni-Co-P Plating

A solder joint is required to have a impact reliability for use in portable electronic products. In general, there is a correlation between the impact reliability and the morphology and thickness of the reaction layer formed at the solder/under bump metallurgy (UBM) interface. The characteristics of the reaction layer depend on the UBM. This study aims to clarify the effect of UBMs on the reaction layer formed at the solder/UBM interface. For this purpose, Sn-3.0 mass%Ag-0.5 mass%Cu was soldered on UBMs such as electroless Co-P plating (Co-P) and Ni-Co-P plating (Ni-Co-P). An electroless Ni-P plating (Ni-P) substrate was used as a reference substrate. The peak temperature of the preset reflow profile was 523 K for 60 s. Then, some of the specimens were subjected to aging at 423 K for 168-1008 h. After soldering, the spreading area of the solder on the UBMs was measured using an optical microscope (OM). The spreading area of the solder on Co-P was larger than that of the solder on Ni-Co-P and Ni-P. Therefore, the solder on Co-P had better wetting characteristics than that on Ni-Co-P and Ni-P. Further, the reaction layer at the solder/UBM interface was observed using a scanning electron microscope (SEM). A fine and a large needle-like intermetallic compound (IMC) were formed at the solder/Co-P and the solder/Ni-Co-P interfaces, respectively, whereas a layer-like IMC was formed at the solder/Ni-P interface. After aging for 1008 h, the thicknesses of the continuous IMC layers for Co-P and Ni-Co-P were approximately 10 μm and 5 μm, respectively, whereas the thickness of the continuous IMC layer for Ni-P was only approximately 3 μm.

Controlling of the Solidification Structure for Recycling by Ultrasonic Vibration

The production of aluminum scrap is expected to exceed the domestic demand in japan around the year 2010. The key to the establishment of a resource recycling-based society is the zero emission process. However, recycling materials will produce an amount of scrap that cannot be recycled and will become waste. A design that considers the intended usages and includes recycling should be incorporated into the materials development to reduce as much waste as possible. Mixing iron impurities with aluminum leads to the formation of coarse needle-shaped intermetallic compounds during solidification and hinders the recycling capacity of the finished product. The application of ultrasonic vibration during solidification was carried out in this work with the aim of controlling the morphology of the material. Experiments were performed by melting an Al-Si alloy containing 4 mass% Fe (hereafter, mass% is abbreviated by %). The primary crystals formed from the liquidus line of this alloy were intermetallic compounds identified as Al 3 Fe, α-AlSiFe (Al 7.4 SiFe 2 ) and P-AlSiFe (Al 9 Si 2 Fe 2 ). A coarse needle-like intermetallic compound was formed in the Al-6Si-4Fe and Al-12Si-4Fe alloys, but the application of ultrasonic vibration resulted in the formation of a fine grained structure. In the Al-18Si-4Fe alloy, the structure could be modified from a coarse needle-like structure into a fine grained structure.

Effect of Cu diffusion through Ni on the interfacial reactions of Sn3.5Ag0.75Cu and SnPb solders with Au/Ni/Cu substrate during aging

The effect of Cu diffusion through Ni on the interfacial reactions of Sn3.5Ag0.75Cu (SAC) and SnPb solders with Au/Ni/Cu substrate during aging was investigated in this study. AuSn4 needle-like intermetallic compound (IMC) formed at the interfaces of both SAC and SnPb solder joints after laser reflow. In SnPb solder joints, a layer-type ternary IMC, (Au,Ni)Sn4, formed over a thin layer quaternary IMC (Au,Ni,Cu)3Sn4 after aging at 150 °C for 4 days, in which Cu came from the Cu pad below the Ni layer through diffusion. This (Au,Ni,Cu)3Sn4 IMC evolved into a new kind of quaternary IMC (Au,Ni,Cu)6Sn5 with further aging at 150 °C for 8 days because more Cu diffused through Ni and was involved into the IMC formation. For SAC solder joints, needle-like binary AuSn4 IMC in as-soldered state changed into a layer-type quaternary IMC (Au,Ni,Cu)Sn4. The quaternary IMC (Au,Ni,Cu)6Sn5, which has the same composition as those found in SnPb solder joints, was developed below the (Au,Ni,Cu)Sn4 layer after aging at 150 °C for 8 days. It was found that Cu diffusion played a key role in the interfacial reaction and compound formation.

Characterization of centrifugally atomized Al-12Si-5Fe-3Cu-1Mg(wt%) alloy powder and extruded rod

The Al-12Si-5Fe-3Cu-1Mg(wt%) alloy was rapidly solidified by centrifugal atomization. The microstructural characteristics of rapidly solidified powder and the microstructure changes with heat treatment were investigated in terms and related to powder size. The microstructures of the powder consisted of dendritic α-Al, eutectic phase, Cu-rich phase, and needle-like intermetallic compounds. These phases were much finer than that of ingot cast structure and the size decreased with increasing cooling rate. The X-ray diffraction of the atomized powders revealed the presence of non-equilibrium 3-(AlFeSi) intermetallic phase. This phase appeared to transform to an equilibrium β-(AlFeSi) phase by heating at temperatures above 470°C. The extruded rod which was hot extruded at 360°C with an extrusion ratio of 40:1 also revealed the presence of the β-(AIFeSi) intermetallic phase. Using DSC, the exothermic peak due to precipitation from the supersaturated α-Al matrix was observed in the range of 200–250°C during continuous heating of atomized powder, and the size of the peaks increased with decreasing powder size.