Numerical Study of Epitaxial Growth after Partial Remelting during Selective Electron Beam Melting in the Context of Ni–Al

In the selective electron beam melting approach an electron beam is used to partially melt the material powder. Based on the local high energy input, the solidification conditions and likewise the microstructures strongly deviate from conventional investment casting processes. The repeated energy input into the material during processing leads to the partial remelting of the already existing microstructure. To closer investigative this effect of partial remelting, in the present work the phase-field model is applied. In the first part the solidification of the referenced Ni–Al system is simulated in respect to selective electron beam melting. The model is calibrated such to reproduce the solidification kinetics of the superalloy CMSX-4. By comparison to experimental observations reported in the literature, the model is validated and is subsequently applied to study the effect of partial remelting. In the numerical approach the microstructures obtained from the solidification simulations are taken as starting condition. By systematically varying the temperature of the liquid built layer, the effect of remelting on the existing microstructure can be investigated. Based on these results, the experimental processing can be optimized further to produce parts with significantly more homogenous element distributions.

INVESTIGATION OF SUPERPLASTIC BEHAVIOR OF CERTAIN (Zn – Al) ALLOYS

Super plasticity behavior finds applications in so many fields, for example the aerospacemanufacturing that is the main bazaar for super plasticity, but automotive, medical, sports,cookware and architectural applications have their share too. "In this work a study of thesuperplastic behavior of a new Zn-Al alloy was conducted. In addition to the investigation ofthe possible superplastic behavior of Zn-0.5Al alloy. These alloys were prepared by usinggravity and chill casting techniques. Zn-0.5Al alloy was subjected to hot rolling at 250 ºCand cold rolling at room temperature, while Zn-48Al alloy was also hot rolled at 250 ºC to20% reduction in the thickness of sample followed by partial remelting at 500 ºC. Severaltests were carried out such as physical, mechanical and chemical which include (XRF, XRD,OP, SEM, Microhardness (HV) and Tensile (cold, hot) test). Results showed that the"Zn-0.5Al alloy has poor mechanical properties and may not be regarded as a superplastic alloycompared with Zn-48Al alloy. The Zn-48Al alloy generally enhanced all properties. Themaximum elongation of (450%) was obtained in Zn-48Al alloy after thermomechanicalcontrolling process and partial remelting.