Effect of Filler Metals on Creep Properties of 2.25Cr-1Mo Steel Weld Joints Prepared by GTAW Process

This research aims at comparing creep properties at elevated temperatures obtained on welding 2.25Cr-1Mo steel using gas tungsten arc welding (GTAW) with ER90S-G and ERNiCrMo-3 filler metals. The high temperature accelerated creep rupture test of 2.25Cr-1Mo welded samples was investigated over 139 to 315 MPa stress range at temperatures of 550 °C, 600 °C, and 650 °C. The samples were preheated at 250 °C for 0.5 hours and post-weld heat-treated at 690 °C for 1 hour. The results showed that the accelerated creep rupture lives of lower applied stress specimens were much longer than those of higher applied stress, when both welded materials were tested under same temperature conditions. The service lifetime of the welded materials can be predicted using the extrapolation of the Larson-Miller parameter. Creep surface fractures were investigated using SEM fractography that indicated the weldment fracture modes consisted of dimple ruptures and micro-voids coalescence in the fibrous matrix of the intercritical region of HAZ. Similar high-temperature creeps service lives were found in both welded materials

Production of fine calcium powders by centrifugal atomization with rotating quench bath

Recently, a novel Al/Ca composite was produced by severe plastic deformation of Al powders and Ca granules for possible use as a high-voltage power transmission conductor. Since the strength of such composites is inversely proportional to the Ca filament size, fine Ca powders (less than ~ 250 μm) are needed to achieve the desired high strength for the powder metallurgy production of an Al-matrix composite reinforced by nano-scale Ca filaments. However, fine Ca powders are not commercially available. Therefore, we have developed a method to produce fine Ca powders via centrifugal atomization to supply Ca powder for prototype development of Al/Ca composite conductor. A secondary goal of the project was to demonstrate that Ca powder can be safely prepared, stored, and handled and could potentially be scaled for commercial production. Our results showed that centrifugal atomization can yield as much as 83 vol.% Ca powder particles smaller than 250 μm. The mean particle size sometimes matches, sometimes deviates substantially from the predictions of the Champagne & Anger equation likely due to unexpected secondary atomization. The particle size distribution is typical for a ligament-disintegration atomization mode. Scanning electron micrographs showed that the morphology of these Ca powders varied with powder size. Spark testing and auto-ignition tests indicated that the atomized powders were difficult to ignite, providing confidence that this material can be handled safely in air

Introduction to Surface-Mount Technology

In chapter 1, the surface-mount technology and reflow soldering technology are overviewed. A brief introduction is presented into the type of electronic components, including through-hole- and surface-mounted ones. Steps of reflow soldering technology are outlined, and details are given regarding the properties of solder material in this technology. The rheological behavior of solder pastes is detailed, and some recent advancements in addressing the thixotropic behavior of this material are summarized. The process of stencil printing is detailed next, which is the most crucial step in reflow soldering technology; since even 60–70% of the soldering failures can be traced back to this process. The topic includes the structures of stencils, discussion of the primary process parameters, and process optimization possibilities by numerical modeling. Process issues of component placement are presented. The critical parameter (process and machines capability), which is used extensively for characterizing the placement process is studied. In connection with the measurement of process capability, the method of Gage R&R (repeatability and reproducibility) is detailed, including the estimation of respective variances. Process of the reflow soldering itself is detailed, including the two main phenomena taking place when the solder is in the molten state, namely: wetting of the liquid solder due to surface tension, and intermetallic compound formation due to diffusion. Solder profile calculation and component movements during the soldering (e.g., self-alignment of passive components) are presented too. Lastly, the pin-in-paste technology (reflow solder of through-hole components) is detailed, including some recent advancements in the optimization of this technology by utilizing machine learning techniques

Effects of Operating Parameters on the Cut Size of Turbo Air Classifier for Particle Size Classification of SAC305 Lead-Free Solder Powder

In the present study, the effects of operating parameters, namely, rotor speed, feed rate, and inlet air velocity, on the cut diameter of a cage-type separator were studied. The design of experiments (DOE) method was used to investigate the relationship between the operating parameters and the cut size. The experimental results were statistically analyzed using MINITAB 16 software. Both the rotor speed and air inlet velocity had significant main effects on the cut size. The feed rate was also significant but had a weak effect with respect to the rotor speed and inlet air velocity effects. The cut size decreased with an increase in rotor speed and increased with an increase in air inlet velocity. However, the cut size slightly decreased with an increase in feed rate. An empirical multiple-variable linear model for predicting the cut size of the classification was created and presented. The results derived from the statistical analysis were in good agreement with those from the experiments, additionally extended from the DOE. The optimal conditions for classification of SAC305 powder with size range 25–40 μm were obtained when the turbo air classifier was operated at rotor speed 406 RPM, the feed rate 4 kg/h, and the air velocity 5 m/s. The smallest cut size of the classifier was about 27.8 μm

Synthesis and characterization of Porous titanium

Porous titanium with good strength and three-dimension pore structure was fabricated by using TiH2 as vesicantfoaming titanium powder. This kind of porous titanium with good bio-mechanical compatibility may have the potential toalleviate the problems caused by the mismatch of the strength and Youngs modulus between implant (110 GPa for titanium)and bone. Moreover, the pores (mainly in 100-700 µm) are all interconnected. This porous structure would endow thematerials with better activity between bone and porous implant matrix. Furthermore, biocompatible porous titanium with aporosity of 33.51-49.09 vol.%, a compressive strength of 156.19-173.34 MPa and a hardness of 438.51-461.40 is known tobe a good candidate material for use as bone implants. In the present study, porous titanium was fabricated by using apowder metallurgical process. The effects of process variables, such as the size of the foaming agent and the sinteringtemperature, on the pore structure and the mechanical properties were investigated. The relationships between the porestructure and the mechanical properties were also studied

Effect of Aging Condition on Semisolid Cast 2024 Aluminum Alloy

2024 Aluminium alloy was squeezed cast by the Gas Induced Semi Solid (GISS) process. Effect of artificial aging on microstructure and mechanical properties of this alloy was studied in the present work. The solutionized specimens were aged hardened at temperatures of 175°C, 200°C, and 225°C under various time durations. The highest hardness of about 77.7 HRE was attained from specimen aged at the temperature of 175 °C for 36 h. Upon investigation the microstructure by using Transmission Electron Microscopy (TEM), the phase was mainly attributed to the strengthening effect in the aged alloy. The apparent activation energy for precipitation hardening of the alloy was calculated as 133,805 J/mol