Phase Transformation in Granular Alloys of Cu2S-Ni3S2-Na2S System

The effect of Na2S on the phase composition and microstructure of tempered Cu2S-Ni3S2 alloys was studied by X-ray diffraction, optical microscopy and electron probe microanalysis (EPMA). It was found that quick crystallization of the sulfide melt leads to separation into two phases - Ni3S2 and a solid solution of Cu2S with Na2Cu4S5, moreover, nickel is concentrated in large particles and copper – in small ones. In contrast to the fine dendrite solidification of granular Cu2S-Ni3S2 alloys, in the ternary system there is a well-defined two-phase microstructure with rounded borders of the interface. Friability and a low microhardness of Cu2S - Na2Cu4S5 solid solution provide an autodecomposition of the sulfides melt by quenching into water (granulation). The degree of separation of copper and nickel depends on the overheating temperature and a quantity of Na2S in melt. The results can be used to hydrometallurgical processing of copper-nickel convert matt.

Hot Deformation and Ductility Analysis of Continuous Cast C40 Steel by Means of Tensile and Compression Tests

The steel production from scrap using continuous cast technology has increased in last decades. Sometimes, steels processed via this route display poor ductility at high temperature. This feature is associated to cooling conditions and chemical composition, which in turns affect the segregation pattern and vary the transformation temperatures and the phase transformation kinetics. The material under study was a C40 steel with a dendrite solidification microstructure coming from an industrial continuous casting plant. The high temperature ductility was evaluated by means of tensile tests up to fracture at strain rate of 0.001 s-1 in a temperature range of 1100 to 710°C. The reduction in area at fracture as a function of temperature graphs show a clear reduction of the steel ductility in the intercritical region, but also after the pearlite transformation. Single deformation compression tests were also carried out on the steel in the austenitic temperature domain, 900 to 1100°C, and at strain rate of 0.001 to 1 s-1. A modification of the Garofalo hyperbolic sine equation has been employed to derive the peak and steady stresses of the flow curve. The work hardening, U, and dynamic recovery, Ω, parameters which describe the flow curve before dynamic recrystallization takes place and the k and t50 parameters, based on the JMAK model, to describe the recrystallization kinetics were also calculated for every test and expressed as a function of the Zener Hollomon parameter, Z.

Prediction of Microstructure and Distribution of Solute in Al-Zn-Mg Non-Dilute Alloys

The microstructure of directional solidified Al-Zn-Mg alloys is characterized and predicted by means of thermal analysis data, multicomponent equations for dendrite growth and data from ternary AlZnMg phase diagram. The resulting microstructure consists of α-Al dendrites with τ precipitates and eutectic in interdendritic regions. Predictions show that at growth velocities up to 9 x 10-4 m/s, the α-Al and τ intermetallic grew simultaneously. Predictions for solute concentration according to the model for dendrite solidification of multicomponent alloys with unequal liquid diffusion coefficients show a good agreement with experimental results.

Modelling of Phase Transformation During Homogenization of Ternary Aluminum Alloys

ABSTRACTThe microstructure determines for the most part mechanical properties of castings. This is the case especially with age-hardening aluminum alloys. To predict the phase transformation in cast parts during and after solidification a sophisticated approach to a coupled modeling of various simulation phenomena is presented. This approach couples a diffusion equation solver which considers the online estimation of thermodynamic equilibria with a macroscopic model for temperature calculation. The coupled micro-model predicts the dendrite solidification of ternary alloys. To simulate the phase transformation in temperature zones below solidification a homogenization model is added. Permanent mould casting experiments with ternary aluminum alloys are used to validate these models.