Microstructure Evolution and Shear Strength of Tin-Indium-xCu/Cu Joints

The low melting temperature In-48Sn alloy is a promising candidate for flexible devices. However, the joint strength of the In-48Sn alloy on the Cu substrate was low due to the rapid diffusion of Cu into the In-rich alloy. In this study, the effect of the addition of xCu (x = 2.0 and 8.0 wt.%) on wettability, interfacial reaction, and mechanical strength of the In-Sn-xCu/Cu joint is analyzed. The results demonstrate that both the In-48Sn and In-Sn-xCu alloys exhibit good wettability on the Cu substrate and that the contact angle increases with an increase in the Cu content. Furthermore, fine grains are observed in the alloy matrix of the In-Sn-xCu/Cu joint and the interfacial intermetallic compound (IMC) comprising the Cu-rich Cu6(In,Sn)5 near the Cu substrate and the Cu-deficient Cu(In,Sn)2 near the solder side. The In-Sn-2.0Cu/Cu joint with fine microstructure and a small amount of IMC in the alloy matrix shows the highest average shear strength of 16.5 MPa. Although the In-Sn-8.0Cu/Cu joint also exhibits fine grains, the presence of large number of voids and rough interfacial IMC layer causes the formation of additional stress concentration points, thereby reducing the average shear strength of the joint.

On the Zr Electrochemical Conversion of Additively Manufactured AlSi10Mg: The Role of the Microstructure

Additively manufactured (AM) AlSi10Mg is one of the most studied AM aluminium alloys to date. While several studies have focused on investigating its mechanical properties and corrosion performance, very little work has been dedicated to study corrosion protection mechanisms and surface treatments applicable for this material. This work presents for the first time an analysis of the mechanism of Zr electrochemical conversion on AM AlSi10Mg parts. A comparison with the conventional cast alloy was also conducted. An analysis of the specimens using SEM/EDS provided interesting insights concerning the effect of the microstructure on the deposition of the Zr conversion layer. This work demonstrates that due to the very fine microstructure and distribution of alloying elements in AM AlSi10Mg, a homogeneous deposition of the Zr conversion layer is promoted. Conversely, the cast alloy is characterized by a very heterogeneous deposition of the Zr conversion layer due to the presence of relatively large Fe-containing intermetallic particles. The influence of the conversion coating on the corrosion performance of these materials was also studied. The results show that while the conversion treatment has no impact on the corrosion resistance of the cast alloy, it greatly improves the passivity of the AM AlSi10Mg samples.

Microstructure and Microsegregation Characterization of Laser Surfaced Remelted Al-3wt%Cu Alloys

Solidification rates during laser remelting of solid metals occur under solidification conditions that are far from equilibrium conditions. The microstructural evolution and microsegregation behaviors are affected by these conditions. This study comprised an experimental characterization of the ultra-fine microstructure and microsegregation in laser surface remelted regions of a hypoeutectic Al-Cu alloy. The laser scan speed, which controls the cooling rate within the remelted region, was observed to have a significant effect on microstructural features and microsegregation. Dendrite arm spacing was determined to decrease with increasing scan speed and depended on location within the melt pool. A transition of the dendrite morphology was also observed in the melt pools. This transition, which is attributed to the grain orientation change influenced by the laser beam movement, was experimentally characterized. The measured microsegregation profiles show decreasing microsegregation as cooling rate increases which is typically of increasing undercooling and non-equilibrium solidification.

Effect of Y2O3 Dispersion Method on the Microstructure Characteristic of Ni-Base Superalloy

An optimum route to fabricate the Ni-base superalloys with homogeneous dispersion of oxide nanoparticles is investigated. Two methods for developing a uniform dispersion of oxide nanopar-ticles are compared on the basis of the resulting microstructure. Microstructural analysis reveals that the calcined powder from polymeric additive solution with yttrium nitrate and polyvinyl alcohol represented more fine and uniform distribution of Ni, Y and O elements. The densified specimen by spark plasma sintering at 1000 °C using calcined powder exhibits fine microstructure with oxide nanoparticles compared with that using mechanically alloyed powder, presumably by the particle growth or agglomeration prevention from chelating reaction during the calcination step. The oxide particles in the sintered specimen is identified as Y–Al–O phase, formed by the reaction of Y2O3 with Al during calcination and sintering.

Microstructure and Sintering Behaviors of Al–Cr–xSi (at.%) System Alloys Processed by Spark Plasma Sintering

In this study, microstructure and sintering behaviors of the gas-atomized Al-(25 or 30) Cr–xSi alloy (x = 5, 10 and 20 at.%) during spark plasma sintering (SPS) process were investigated. Gas-atomized alloy powders were manufactured using Ar gas atomizer process. These alloy powders were consolidated using SPS process at different temperature under pressure 60 MPa in vacuum. Microstructures of the gas-atomized powders and sintered alloys were analyzed using scanning electron microscopy (SEM) with energy–dispersive X-ray spectrometer (EDS), and transmission electron microscopy (TEM). Hardness of the SPS sintered alloys was measured using micro Vickers hardness tester. The Al–Cr–Si bulks with high Cr and Si content were produced successfully using SPS sintering process without crack and obtained fully dense specimens close to nearly 100% T. D. (Theoretical Density). The maximum values of the hardness were 834 Hv for the sintered specimen of the gas atomized Al–30Cr–20Si alloy. Enhancement of hardness value was resulted from the formation of the multi-intermetallic compound with the hard and thermally stable phases and fine microstructure by the addition of high Cr and Si.

The Wear Behavior of the Laser Cladded Ti-Al-Si Composite Coatings on Ti-6Al-4V Alloy with Additional TiC

In this study, the Ti-Al-Si + xTiC (x = 0, 2, 6, 10 wt.%) composite coatings, each with a different content of TiC were fabricated on a Ti-6Al-4V alloy by laser surface cladding. The microstructure of the prepared coatings was analyzed by the scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The microhardness and the wear resistance of these coatings were also evaluated. The results show that α-Ti, Ti3Al, Ti5Si3, TiAl3, TiAl, Ti3AlC2 and TiC particles can be found in the composites. The microstructure can obviously be refined by increasing the content of TiC particles, while the microhardness increases and the coefficient of friction decreases. The Ti-Al-Si-6TiC composite shows the best wear resistance, owing to its relatively fine microstructure and high content of TiC particles. The microhardness of this coating is 5.3 times that of the substrate, while the wear rate is only 0.43 times. However, when the content of TiC was up to 10 wt.%, the original TiC could not be dissolved completely during the laser cladding process, leading to formation of cracks on the coatings.

Use of Different Process Gases for Manufacturing Isolating Alumina Coatings by Flame Spraying with Cords

This study assesses the quality of flame-sprayed alumina coatings produced from recently developed alumina cord using argon and compressed air as atomizing gases. Coatings of different thicknesses were deposited on aluminum substrates and then analyzed using optical microscopy, X-ray diffraction, and resistivity measurements. The coatings, particularly those sprayed with argon, had fine microstructure and higher surface and volume resistivity than flame-spray coatings made from alumina cord in the past. They were also found to have higher alpha phase content than plasma-sprayed coatings, regardless of the atomizing gas used. The effect of humidity and the possible formation of aluminum hydroxides are also addressed.

MICROSTRUCTURE EVOLUTION OF IN SITU COMPOSITE COATINGS FABRICATED BY LASER CLADDING WITH DIFFERENT POWERS

In situ reaction-synthesized TiB-reinforced titanium-matrix composite coatings were fabricated using the rapid, non-equilibrium synthesis technique of laser cladding. The Ti and B mixture was the original powders, while the Ti-matrix composite coatings enhanced with TiB were treated on a Ti-6Al-4V surface with different laser scan powers of 2.5 kW, 3.0 kW and 3.5 kW. The phase composition, microstructure evaluation, and microhardness of the cladding coatings were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and microhardness. The composite coatings mainly consist of black fishbone-shaped -Ti dendrites and white needle-like TiB phases. The microstructure evolution from the top to the bottom of the coatings was investigated. The TiB reinforcement dispersed homogeneously in the composite coatings and a fine microstructure was obtained in a sample fabricated with a laser power of 3.0 kW. The microhardness of the cladding coatings fabricated by different powders was over 2-fold greater than that of the Ti-6Al-4V titanium alloy substrate and achieved a maximum average of 792.2 HV with the laser power of 3.0 kW. The microstructures and properties of the coatings were changed by adjusting of the laser cladding power. The effects of the laser scan power on the microstructure, hardness and friction and wear properties of the laser cladding coatings were investigated and discussed.