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The purpose of this paper is to investigate the resistivity of geopolymer cement with nano-silica additive toward acid exposure for oil well cement application.

An experimental study was conducted to assess the acid resistance of fly ash-based geopolymer cement with nano-silica additive at a concentration of 0 and 1 wt.% to understand its effect on the strength and microstructural development. Geopolymer cement of Class C fly ash and API Class G cement were used. The alkaline activator was prepared by mixing the proportion of sodium hydroxide (NaOH) solutions of 8 M and sodium silicate (Na₂SiO₃) using ratio of 1:2.5 by weight. After casting, the specimens were subjected to elevated curing condition at 3,500 psi and 130°C for 24 h. Durability of cement samples was assessed by immersing them in 15 wt.% of hydrochloric acid and 15 wt.% sulfuric acid for a period of 14 days. Evaluation of its resistance in terms of compressive strength and microstructural behavior were carried out by using ELE ADR 3000 and SEM, respectively.

The paper shows that geopolymer cement with 1 wt.% addition of nano-silica were highly resistant to sulfuric and hydrochloric acid. The strength increase was contributed by the densification of the microstructure with the addition of nano-silica.

This paper investigates the mechanical property and microstructure behavior of emerging geopolymer cement due to hydrochloric and sulfuric acids exposure. The results provide potential application of fly ash-based geopolymer cement as oil well cementing.

The purpose of this paper is to study the wear behaviour of eutectic and hypoeutectic Al‐Si‐Mg‐Ce alloys.

The eutectic and hypoeutectic alloys were prepared using permanent mould casting process by varied cerium (Ce) addition in the alloy from 1 to 3 wt%. Dry sliding wear tests were performed against a hardened carbon steel (Fe‐2.3%Cr‐0.9%C) using a pin‐on‐disc configuration with fixed sliding speed of 1 m/s and load 50 N at room temperature of ∼25 degree. Morphologies of both worn surfaces and collected debris were characterised by a scanning electron microscope (SEM) equipped with an energy dispersive X‐ray spectrometer (EDS).

It was revealed that following the addition of cerium, intermetallic Al4Ce needle‐like structure was present in eutectic alloys whereas CeMg2Si2 blocky phase was present in the hypoeutectic alloys. The increasing of Ce addition up to 3.0 wt% in hypoeutectic alloy led to formation of AlCe3 intermetallic phase. The increase in cerium content up to 2 wt% led to higher wear resistance behaviour for both as‐cast alloys. Formation of craters and localised plastic deformation were observed on the worn surface of both as‐cast alloys, resulting fine particulate and sheet‐like wear debris. The wear resistance was found to be higher for hypoeutectic alloy compared to the eutectic alloy containing Ce.

An attempt has been made to study the influence of intermetallic compound containing Ce in the Al‐Si‐Mg alloys on wear behaviour of both as‐cast alloys.

The microstructure of the Sn‐3.5wt%Ag/Cu and Sn‐9.0wt%Zn/Cu interfaces after soldering at 250°C was evaluated. The cross‐sections were investigated using a scanning electron microscope and energy dispersive X‐ray to determine the interface layer structure and composition. Even though the cooling rate from soldering temperature to room temperature is rapid, this study indicates that the intermetallic compound is formed at the interface between the solder and the copper substrate for both the Sn‐3.5wt%Ag and the Sn‐9.0wt%Zn lead‐free solders.

The purpose of this paper is to investigate the thermal fatigue endurance of two lead‐free solders used in composite solder joints consisting of plastic core solder balls (PCSB) and different solder materials, in order to assess their feasibility in low‐temperature cofired ceramic (LTCC)/printed wiring board (PWB) assemblies.

The characteristic lifetime of these joints was determined in a thermal cycling test (TCT) over a temperature range of −40‐125°C. Their failure mechanisms were analyzed after the TCT using scanning acoustic and optical microscopy, scanning electronic microscope, and field emission scanning electronic microscope investigation.

The results showed that four different failure mechanisms existed in the test assemblies cracking in the mixed ceramic/metallization zone; or a mixed transgranular/intergranular failure occurred at the low temperature extreme; whereas an intergranular failure within the solder matrix; or separation of the intermetallic layer and the solder matrix occurred at the high temperature extreme. Sn3Ag0.5Cu0.5In0.05Ni was more resistant to mixed transgranular/intergranular failure, but had poor adhesion with the Ag3Sn layer. On the other hand, cracking in the mixed ceramic/metallization zone typically existed in the joints with Sn2.5Ag0.8Cu0.5Sb solder, whereas the joints with Sn3Ag0.5Cu0.5In0.05Ni were practically free of these cracks. The characteristic lifetimes of both test joint configurations were at the same level (800‐1,000) compared with joints consisted of Sn4Ag0.5Cu solder and PCSB studied earlier.

The study investigated in detail the failure mechanisms of the Sn3Ag0.5Cu0.5In0.05Ni and Sn2.5Ag0.8Cu0.5Sb solders under harsh accelerated test conditions. It was proved that these solders behaved similarly to the ternary SnAgCu solders in these conditions and no improvement can be achieved by utilizing these solders in the non‐collpasible solder joints of LTCC/PWB assemblies.

This paper aims to address the numerical simulation of additive manufacturing (AM) processes. The numerical results are compared with the experimental campaign carried out at State Key Laboratory of Solidification Processing laboratories, where a laser solid forming machine, also referred to as laser engineered net shaping, is used to fabricate metal parts directly from computer-aided design models. Ti-6Al-4V metal powder is injected into the molten pool created by a focused, high-energy laser beam and a layer of added material is sinterized according to the laser scanning pattern specified by the user.

The numerical model adopts an apropos finite element (FE) activation technology, which reproduces the same scanning pattern set for the numerical control system of the AM machine. This consists of a complex sequence of polylines, used to define the contour of the component, and hatches patterns to fill the inner section. The full sequence is given through the common layer interface format, a standard format for different manufacturing processes such as rapid prototyping, shape metal deposition or machining processes, among others. The result is a layer-by-layer metal deposition which can be used to build-up complex structures for components such as turbine blades, aircraft stiffeners, cooling systems or medical implants, among others.

Ad hoc FE framework for the numerical simulation of the AM process by metal deposition is introduced. Description of the calibration procedure adopted is presented.

The objectives of this paper are twofold: firstly, this work is intended to calibrate the software for the numerical simulation of the AM process, to achieve high accuracy. Secondly, the sensitivity of the numerical model to the process parameters and modeling data is analyzed.

The purpose of this paper is to compare corrosion behavior of a modified multilayer material with Cu before and after brazing process.

Sea water acidified accelerated tests (SWAATs), potentiodynamic polarization tests and scanning electron microscopy were used to study the corrosion behavior and macro/micro structures. Results indicate that the corrosion mechanisms of the sheets before and after brazing process are completely different.

The un-brazed material is uniform corrosion, while the brazed material has a high sensitivity to localized corrosion and loses cathodic protection to the core. It is found that brazing process causes copper transition from the core alloy into eutectic phases in the cladding, leading to higher E_corr and different potential distribution compared with those of un-brazed materials.

For the modified multilayer material after brazing, there are two stages of corrosion. First, corrosion attack takes place along eutectic phases in the cladding material, and then core alloy dissolves by forming a galvanic couple with the nobler residual cladding.