Browsing by Author "Oluwasegun, K. M."

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The contribution of eutectic liquid film to the TMAZ microfissuring in intertia friction welded PM RR1000 superalloy
(The Nigerian Institution of Mechanical Engineers, 2010) Oluwasegun, K. M.; Olorunniwo, O. E.; Oluwole, O. O.
The microstructure of the base alloy and thermomechanical affected zone (TMAZ) of inertia friction welded powder metallurgy (PM) RR1000 were examined by the use of standard metallogrphic techniques involving optical, analytical scanning transmission electron microscopes equipped with energy dispersive spectometer and an electron probe micro analyser. It was discovered that liquation of grain boundary phases present in the pre-weld alloy resulted in the formation of eutectic type ƴ-ƴ1 solute rich liquid film predominant in the TMAZ regions whic contributed significantly to micro fissuring during welding. It was found that apart from the effect of rapid precipitation of ƴ particles on the TMAZ cracking as has been widely reported, constitutinal liquidation of ƴ particles was a notable part of liquidation process which promoted the susceptibility of TMAZ to microcracking.
The role of forging during inertia friction welding of nickel-base superalloy RR1000
(2011-12) Oluwasegun, K. M.; Adedayo, A. V.; Adeleke, A. A.; Oluwole, O. O.
The dissolution response of y’ phase to thermal and mechanical effects in an inertia friction welded turbine disk nickel base superalloy RR1000 has been investigated. The thermo-chemical affected zone (TMAZ) and heat affected zone (HAZ) microstructures around welds in a commercial PM nickel-based RR1000 superalloy were simulated using a Gleeble thermo-chemical simulation system. Detailed microstructures examination of the simulated TMAZ and HAZ and those present in actual inertial friction welded specimens showed that y’ particles persisted during heating to the welding temperatures, where they reacted in the surrounding y matrix producing liquid film by a eutectic- type reaction. However, it was observed that the compressive strain during the forging stage of welding significantly enhanced resistance to weld liquation cracking of the alloy by strain-assisted rapid isothermal re-solidification of the constitutional liquation products within 150µm of the bond line.
TMAZ microcracking in inertia friction welding of PM RR1000 superalloy: concomitant effect of constitutional liquating particles
(2010) Oluwasegun, K. M.; Ibitoye, S. A.; Oluwole, O. O.
The effect of constitution liquidation of strengthening particles in PM RR1000 superalloy in response to inertia friction welding process was investigated. The thermomechanical affected zone(TMAZ) microstructures were simulated using Gleeble® thermomechanical simulation system. The microstructural examination of the simulated TMAZs and those from the actual welded specimens showed the occurance of extensive grain boundary liquidation of the main strengthening phase ƴ and MC type carbide and consequently attendant microcracking in the TMAZ of the alloy. The existence of these particles in the temperature range well above thier solvus temperatures orchestrated the eutectic type reaction to their constitutional liquidation and subsequent cracking of the weldment.