Durability of Titanium/Dicalcium Silicate Composite Coatings in Simulated Body Fluid

Titanium/dicalcium silicate composite coatings with different ratios (weight ratios as Ca₂SiO₄: Ti = 3:7, 5:5, 7:3) were prepared by plasma spraying. Effects of titanium addition on coating properties, such as bonding strength, flexural modulus, and dissolution in simulated physiological environment, were studied. Results showed that the bonding strength between coating and Ti-6Al-4V substrate increased with increase of titanium content in the composite coatings. It was explained by the narrowed dissimilarity of thermal expansion coefficients between the coatings and substrates. Degradation of mechanical properties after immersion in simulated body fluid was also studied. The dissolution of dicalcium silicate in the composite coatings resulted in the decrease of flexural strength and flexural modulus of the coatings in the simulated physiological environment. The higher titanium content in the composite coatings, the stabler are the composite coatings in the physiological environment.     

Investigation of the grain coarsening behavior of some Aluminum alloys

Grain coarsening tests were carried out on Al-4.5 pct Cu and Al-4.5 pct Si alloys. The effects of three variables, melt composition, pour temperature, and mold temperature, were determined. It was found that the macrostructure generally coarsened with increased pour and mold temperatures. Coarsening was extreme in the unrefined alloys but was retarded by the active grain refiners like titanium and columbium. The effect of boron was spectacular in suppressing coarsening tendencies. The results of the investigation support the carbide theory of nucleation as opposed to the peritectic theory.     

Microstructure evolution during batch annealing

Design of industrial annealing cycles requires recrystallization and grain growth studies, which are typically carried out under isothermal laboratory condition. The kinetics coefficients of these phase transformations are obtained from such studies, which are subsequently used in designing the industrial nonisothermal cycles using the additivity principles. However, the strong heating rate effects on the grain growth kinetics necessitate such kinetics studies using industrial thermal profiles. In the present work, the hot and cold spot cycles of an industrial batch annealing cycle for AIK grade steel have been simulated in a programmable laboratory furnace. Subsequently, the effect of annealing temperature, soaking time, and heating rate on the microstructural features, such as grain size distribution, grain shape anisotropy, and grain orientation, have been investigated through extensive quantitative microscopy. The implications of these results on the design of industrial batch annealing cycles have been discussed.     

Determination of Active Slip/Twinning Modes in AZ31 Mg Alloy Near Room Temperature

In order to determine the deformation modes in AZ31 magnesium alloy at room temperature, computer simulations of deformation texture development and calculation of formability have been carried out. The simulation results were compared with the measured texture results. Based on agreement between the experiments and simulations the active deformation modes were determined. A Visco Plastic Self Consistent model was employed for the simulation of plastic deformation. Simulations and experiments were performed for different initial textures. The goal of the study was to develop the understanding of deformation texture evolution and its effects on mechanical properties of magnesium, with an ultimate goal of improving room temperature formability of magnesium alloys. This article was presented at Materials Science & Technology 2006, Innovations in Metal Forming symposium held in Cincinnati, OH, October 15-19, 2006.     

Effects of solid solution alloying on creep deformation of aluminum

The effects of solid solution alloying on the creep-rupture properties, deformation characteristics, ductility, and fracture of pure aluminum were studied by means of creep-rupture tests on polished specimens of three alloys each of Al-Cu (0.24, 0.79, and 2.05 pct Cu), Al-Zn (4.93, 9.89, and 19.78 pct Zn), and Al-Mg (0.94, 1.92, and 5.10 pct Mg) at 500°, 700°, and 900°F.     

Microstructure and creep behavior in AE42 magnesium die-casting alloy

The micro structural analysis of die-cast AE42 reveals a correlation between micro structure and creep strength. A lamellar-phase Al₁₁RE₃, which dominates the interdendritic microstructure of the alloy, partly decomposes above 150‡C into Al₂RE and Al (forming Mg₁₇Al₁₂). The increased solubility of aluminum in magnesium at higher temperatures may also promote the decomposition of Al₁₁RE₃. The creep strength decreases sharply with these phase changes. A mechanism for the decrease in creep strength of AE42 is proposed whereby the reduced presence of lamellar Al1₁₁RE₃ and/or the presence of Mg₁₇Al₁₂ contribute to the observed poor creep strength at higher temperatures.     

Chromium distribution between liquid iron and molten basic slags

An equilibrium study was made of the distribution of chromium and oxygen between liquid iron, containing less than 1 pct Cr, and simple slags of the CaO(MgO)-SiO₂-FeO-Cr₂O₃ type in the temperature range 1526° to 1734°C The effects of slag oxidation, temperature, and basicity were observed.     

The preparation of tantalum powder using a MR-EMR combination process

In the conventional metallothermic reduction (MR) process used to obtain tantalum powder in batch-type operation, it is difficult to control the morphology and location of the tantalum deposits. In contrast, an electronically mediated reaction (EMR) process is capable of overcoming this difficulty. It has the advantage of being a continuous process, but has the disadvantage of a poor reduction yield. A process known as the MR-EMR combination process is able to overcome the shortcomings of the MR and EMR processes. In this study, an MR-EMR combination process is applied to the production of tantalum powder via sodium reduction of K₂TaF₇. In the MR-EMR combination process, the total charge passed through an external circuit and the average particle size (FSSS) increase as the reduction temperature increases. In addition, the proportion of fine particles (−325 mesh) decreases as the reduction temperature increasess. The tantalum yield improved from 65 to 74% as the reduction temperature increased. Taking into account the charge, impurities, morphology, particle size and yield, a reduction temperature of 1123 K was found to be optimum for the MR-EMR combination process.     

Erosion testing and surface preparation using abrasive water-jetting

Erosion testing and surface preparation are studied using a 3-axis Computer Numerical Control (CNC) abrasive water jetting (AWJ) apparatus. The effects of erosion time t, impingement angle α and pressure p on the erosion rate E, average surface roughness R _a, and surface hardness Rockwell C Hardness (HRC) were investigated in detail. Compared with conventional grit blasting, AWJ can reduce grit embedment in the target material due to the action of the high-pressure water. AWJ also has the advantage of generating a higher average surface roughness R _a over water jetting (WJ) due to the action of abrasive particles. In addition, AWJ increases the surface hardness HRC of the substrate material. The obtained higher degree of average surface roughness is helpful for improving the bonding strength between the coating and the substrate material. The erosion testing and the surface preparation are numerically controlled by a 3-axis CNC system; therefore precise and detailed results for various operating parameters can be obtained.