Effect of prolonged isothermal heat treatment on the mechanical behavior of advanced NANOBAIN steel

The microstructural evolution and consequent changes in strength and ductility of advanced NANOBAIN steel during prolonged isothermal heat-treatment stages were investigated. The microstructure and mechanical properties of nanostructured bainite were not expected to be influenced by extending the heat-treatment time beyond the optimum value because of the autotempering phenomenon and high tempering resistance. However, experimental results indicated that the microstructure was thermodynamically unstable and that prolonged austempering resulted in carbon depletion from high-carbon retained austenite and carbide precipitations. Therefore, austenite became thermally less stable and partially transformed into martensite during cooling to room temperature. Prolonged austempering did not lead to the typical tempering sequence of bainite, and the sizes of the microstructural constituents were independent of the extended heat-treatment times. This independence, in turn, resulted in almost constant ultimate tensile strength values. However, microstructural variations enhanced the yield strength and the hardness of the material at extended isothermal heat-treatment stages. Finally, although microstructural changes decreased the total elongation and impact toughness, considerable combinations of mechanical properties could still be achieved.     

Design and Manufacture of a Wax Injection Tool for Investment Casting Using Rapid Tooling

A rapid wax injection tool of a gearbox shift fork was designed, simulated, and manufactured using rapid prototyping and rapid tooling technology to save time and cost of producing wax models used for the investment casting process. CAE simulation softwares, in particular, MoldFlow, are used to get wax injection moulding parameters such as filling parameters, temperature profiles, freeze time, speed, and pressure. The results of this research were compared with conventional wax model production methods. The criteria of such comparison were based upon parameters such as time, cost, and other related characteristics, which resulted in saving of 50% in time and 60% in cost. In this research, design, assembly, and wax injection operation of the wax tool took 10 days. Considering the fact that wax melting temperature is as low as 70℃ and injection pressure of 0.5 MPa, the tool suffers no damage due to the thermal and pressure stresses, leading to the mass production of wax models.     

Estimation of froth flotation recovery and collision probability based on operational parameters using an artificial neural network

An artificial neural network and regression procedures were used to predict the recovery and collision probability of quartz flotation concentrate in different operational conditions. Flotation parameters, such as dimensionless numbers (Froude, Reynolds, and Weber), particle size, air flow rate, bubble diameter, and bubble rise velocity, were used as inputs to both methods. The linear regression method shows that the relationships between flotation parameters and the recovery and collision probability of flotation can achieve correlation coefficients (R2) of 0.54 and 0.87, respectively. A feed-forward artificial neural network with 3-3-3-2 arrangement is able to simultaneously estimate the recovery and collision probability as the outputs. In testing stages, the quite satisfactory correlation coefficient of 0.98 was achieved for both outputs. It shows that the proposed neural network models can be used to determine the most advantageous operational conditions for the expected recovery and collision probability in the froth flotation process.     

Rapid synthesis of MoSi2-Si3N4 nanocomposite via reaction milling of Si and Mo powder mixture

The nanocomposite of MoSi2-SiaN4 （molybdenum disilicide-silicon nitride） was synthesized by reaction milling of the Mo and Si powder mixture. Changing the processing parameters led to the formation of different products such as a- and B-MoSi2, SiaN4, Mo2N, and M05Si3 at various milling times. A thermodynamic appraisal showed that the milling of Moa2Siss powder mixture was associated with highly exothermic mechanically induced self-sustaining reaction （MSR） between Mo and Si. The MSR took place around 5 h of milling led to the formation of a-MoSi2 and the reaction between Si and N2 to produce Si3N4 under a nitrogen pressure of 1 MPa. By increasing the nitrogen pressure to 5 MPa, more heat is released, resulting in the dissociation of Si3N4 and the transformation of a-MoSi2 to β-MoSi2. Heat treatment was also performed on the milled samples and led to the formation of Mo2N and the transformation of a-MoSi2 to β-MoSi2 at the milling times of 10 and 40 h, respectively.