G. Madhusudhana Reddy

Bio: G. Madhusudhana Reddy is an academic researcher from Defence Metallurgical Research Laboratory. The author has contributed to research in topics: Beam (structure) & Welding. The author has an hindex of 3, co-authored 3 publications receiving 163 citations.

Improvement of mechanical properties of Inconel 718 electron beam welds—influence of welding techniques and postweld heat treatment

Abstract: Effects of electron beam oscillation techniques (sinusoidal, square, triangular, ramp, circle, and elliptical) in controlling Nb segregation, Laves formation, and tensile behavior of Inconel 718 electron beam welds were studied. Effects of various postweld heat treatments on tensile behavior were compared. Elliptical beam oscillation technique resulted in less Nb segregation and discontinuous finer Laves in the interdendritic regions compared to that of unoscillated beam weld. Response to aging was better for welds made with elliptical oscillated beam compared with welds made with unoscillated beam. Oscillated beam welds exhibited better mechanical properties than unoscillated beam welds in both solution-treated and aged and directly aged conditions.

Grain refinement through arc manipulation techniques in Al–Cu alloy GTA welds

Abstract: Effect of three arc manipulation processes pulsed current welding, magnetic arc oscillation and the simultaneous application of pulsed current and arc oscillation, on the weld metal grain structure and tensile properties of the welds were investigated. Initial studies were conducted on autogenous welds made on 3.5 mm thick 2219-T6 plates, to identify and optimize, welding parameters resulting in fine equiaxed grains in the weld metal. Welds were made on 8.5 mm thick 2219-T87 plates using the optimized parameters and tested for tensile properties. All three techniques resulted in fine equiaxed grains in weld metals and optimum parameters were suggested based on the extent of refinement. Fine-grained weld metals exhibited better yield and ultimate tensile strengths and significant improvement in percent elongation. The reasons for the same were explained with the help of TEM and EPMA studies.

Effects of electron beam oscillation techniques on solidification behaviour and stress rupture properties of Inconel 718 welds

Abstract: Effects of electron beam oscillation techniques (sinusoidal, square, triangular, ramp, circle and elliptical) in controlling Nb segregation, Laves formation and stress rupture behaviour of Inconel 718 electron beam welds are studied. Effects of various post-weld heat treatments on stress rupture behaviour are compared. Elliptical beam oscillation technique resulted in less Nb segregation and discontinuous and fine Laves in the interdendritic regions compared with other welds and unoscillated beam weld. Response to aging was better for welds made with elliptical oscillated beam compared with welds made with unoscillated beam. Oscillated beam welds exhibited longer rupture life than unoscillated beam welds in both solution treated and aged and directly aged conditions.

Effect of standard heat treatment on the microstructure and mechanical properties of selective laser melting manufactured Inconel 718 superalloy

Abstract: Inconel 718 superalloy has been fabricated by selective laser melting technology (SLM). Its microstructure and mechanical properties were studied under solution+aging (SA) standard heat treatment, homogenization+solution+aging (HSA) standard heat treatment and as-fabricated conditions. Precipitated phases and microstructures were examined using OM, SEM, TEM and X-ray analysis methods. The fine dendrite structures with an average dendrite arm spacing of approximately 698 nm accompanying some interdendritic Laves phases and carbide particles can be observed in the as-fabricated materials. After standard heat treatments, dendrite microstructures are substituted by recrystallization grains, and Laves phases also dissolve into the matrix to precipitate strengthening phases and δ particles. The test values of all specimens meet Aerospace Material Specification for cast Inconel 718 alloy, and the transgranular ductile fracture mode exists for the three conditions. The strength and hardness of heat-treated SLM materials increase and are comparable with wrought Inconel 718 alloy, whereas their ductility decreases significantly compared with the as-fabricated material. This is because of the precipitation of fine γˊ and γ〞strengthening phases and needle-like δ phases. For the as-fabricated alloy, the formation of finer dislocated cellular structures that develop into a ductile dimple fracture shows excellent ductility. Due to dislocation pinning from γˊ and γ〞strengthening phases and the impediment of dislocation motion caused by the needle-like δ phases, the ductility of the SA materials decreases and causes a transgranular fracture, compared with the as-fabricated samples.