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Item Metastable microstructures at the interface between AISI 321 steel and molten aluminum during hot-dip aluminizing(Elsevier B.V., 2018) Huilgol, P.; Udupa, K.R.; Bhat, K.U.The microstructure at the interface between AISI 321 stainless steel and molten aluminum was investigated which occurs during the process of hot-dip aluminizing. Microstructural characterization was carried out by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The study revealed the formation of metastable FeAlm and multiple twinned Al13Fe4 phases at the interface between steel and aluminum. Multiple twinned Al13Fe4 phase exhibits pseudo tenfold electron diffraction pattern. Another metastable phase Al3(NiFe) with an orthorhombic structure was formed as one of the eutectic phase mixture in the solidified aluminum topcoat. The Al3(NiFe) phase in the eutectic shares crystallographic orientation relationship with the Al matrix. Metastable intermetallic phases are being reported for the first time during hot-dip aluminizing. © 2018 Elsevier B.V.Item Microstructure and Mechanical Properties of Cast Al-5Zn-2Mg Alloy Subjected to Equal-Channel Angular Pressing(Springer New York LLC barbara.b.bertram@gsk.com, 2018) Manjunath, G.K.; Preetham Kumar, G.V.P.; Udaya Bhat, K.; Huilgol, P.In the present work, cast Al-5Zn-2Mg alloy was processed through equal-channel angular pressing (ECAP) in route BC up to four number of passes. Microstructure and mechanical properties were investigated on processed and unprocessed materials. In cast condition, the material was composed of dendritic structure. After homogenization treatment, large-sized grains were observed. After ECAP processing, significant grain refinement was observed. After ECAP processing, high-density dislocations and high degree of misorientation between the grains were observed. In cast material, rod-shaped precipitates were observed, while, after ECAP processing, spherical-shaped precipitates were observed. ECAP processing leads to a noticeable improvement in the mechanical properties of the material. After four passes, 122% improvement in the microhardness and 135% improvement in the ultimate tensile strength of the material were observed. After three passes, a slight decrease in the mechanical properties was observed. This is attributed to the dissolution of the metastable ?? phase, annihilation of dislocations, dynamic recrystallization and texturing during ECAP processing. Brittle fracture mode was observed in tensile testing cast and homogenized samples. After ECAP processing, fracture mode was changed into shear fracture mode. © 2018, ASM International.Item Precipitate evolution during severe plastic deformation of cast Al-Zn-Mg alloys and their thermal stability(Institute of Physics Publishing helen.craven@iop.org, 2019) Manjunath, G.K.; Huilgol, P.; Preetham Kumar, G.V.P.; Bhat, K.U.In the current investigation, an effort was made to understand the precipitate evolution process during equal channel angular pressing (ECAP) of an alloy composed of only aluminium, zinc and magnesium. For this purpose, three different compositions of cast Al-Zn-Mg alloys were selected and ECAP processed in route BC upto four passes. Microstructural observations indicated that, ECAP processing leads to refined structure possessing high density dislocations and large amount of grains with high angle grain boundaries. The precipitate volume in the alloys increased with increase in the zinc quantity in the alloy. Microstructural characterization through transmission electron microscope (TEM) and differential scanning calorimeter (DSC) revealed that, processing by ECAP results in structure having stable ? phase precipitates without the presence of GP zones and intermediate ?? phase precipitates. Thereby demonstrates that, ECAP process accelerates the precipitation kinetics and also shifts the morphology of the precipitates. Higher mechanical properties were noticed in the alloy containing large quantity of MgZn2 precipitates. © 2018 IOP Publishing Ltd.Item Microstructural investigations on the hot-dip aluminized AISI 321 stainless steel after diffusion treatment(Elsevier B.V., 2019) Huilgol, P.; Udupa, K.R.; Bhat, K.U.The microstructure of the hot-dip aluminized AISI 321 stainless steel was studied after diffusion treatment at 900 °C for 3 h. The microstructural characterization was carried out by scanning electron microscopy, transmission electron microscopy, and X-ray diffractometry. The microstructure of the as aluminized steel consisted of two regions, viz.; aluminum topcoat and aluminide layer. During the diffusion treatment, the coating transformed into a layered structure consisting of four layers. The Fe2Al5 phase was formed in the outermost layer and the presence of Al13Fe4 quasicrystalline approximant phase was observed. The innermost layer adjacent to the base metal transformed to ferrite phase with NiAl precipitates. Next, to this layer, a disordered FeAl phase was observed. The lattice parameter of the disordered FeAl phase was found to be larger than that of the ordered B2 FeAl phase. The layer between outer Fe2Al5 phase and disordered FeAl phase consists of a mixture of three phases, namely Fe2Al5, disordered FeAl and a new phase with the simple cubic structure. The phase with simple cubic structure shares cube on cube crystallographic orientation relationship with the disordered FeAl phase. © 2019 Elsevier B.V.