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

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