Orientational growth behavior and mechanism of delta(δ)phase precipitation in cold-rolled Inconel 718 alloy during heat treatment

Due to the important role ofδphase's quantity and morphology in the mechanical and fatigue properties of Inconel 718 alloy and its components,it is necessary to renew insights into the effect of cold deformation on theδphase precipitation,especially on the morphology evolution.Therefore,the nucleation and growth behavior ofδphase in cold-rolled Inconel 718 alloy during aging were investigated.The results show that the precipitation rate and volume fraction ofδphase increase with increasing the cold rolling reduction from 10%to 50%.The volume fraction ofδphase reaches equilibrium after 5 h,remaining at 5.98%,6.52%,and 6.79%under different rolling reductions(10%,30%,and 50%),respectively.The nucleation ofδphase mainly occurs on different sites(grain boundaries,new twin boundaries and old twin boundaries)under 10%rolling reduction,whileδphase mainly nucleates on the new grain boundaries of static recrystallization due to 50%rolling reduction.And the growth ofδphase undergoes a process of alternate orientation growth from spherical(nucleation)→short rod(longitudinal orientation growth)→short rod(radial orientation growth)→dynamic equilib-rium.Under 10%rolling reduction,δphase tends to grow into the matrix,while under 50%rolling reduction,the orientation grows faster and is easily affected by the grain boundary curvature.

Effect of δ Phase on Mechanical Properties of GH4169 Alloy at Room Temperature

Tensile tests of GH4169 alloy were performed at room temperature. Different fractions, distributions and shapes of δ phase was prepared by aging treated at 880 ℃, 930 ℃ and 980 ℃ for 5 h or 10 h. The effect of δ phase on the mechanical pro- perties of GH4169 alloy was investigated. The results show that 0.2% yield strength and ultimate tensile strength of GH4169 alloy increase by 61 MPa and 78 MPa respectively when the fraction of δ phase increases from 2.20% to 5.21%. Then, the ultimate tensile strength remains at 1 012 MPa even when the fraction of δ phase reaches 7.56%. The fraction effect of δ phase on the strength improvement of GH4169 alloy is more significant than morphology, and the critical fraction value is 5.21%. In addition, the elongation decreases by 14.1% when the fraction of δ phase increases from 2.20% to 7.56%. Excessive needle or short rod shaped 8 ohase is resoonsible for the reduction of eloneation.

Influence of delta phase precipitation on static recrystallization of cold-rolled Inconel 718 alloy in solid solution treatment

Due to the improvement in fatigue strength of cold-rolled blades,the static recrystallization behavior of cold-rolled Inconel 718 alloy in the solid solution treatment was investigated with the methods of optical microscopy and electron backscattered diffraction.The effect ofδphase precipitation on the static recrystallization process was also analyzed.The results show thatδphase preferentially precipitates comparing to static recrystallization.Affecting by theδphase preferential precipitation process,sub-grain migration is the main nucleation mechanism in the static recrystallization of coldrolled Inconel 718 alloy at 980°C.Meanwhile,strain-induced boundary migration also exists as an aided nucleation mechanism when the rolling reduction is less than 30%.

Effect of Cold Rolling Parameters on the Longitudinal Residual Stress Distribution of GH4169 Alloy Sheet

For plastic deformed parts, the dimensional accuracy is significantly affected by residual stresses and so does the performance in service. Therefore, the rolling process of GH4169 alloy sheet at room temperature was investigated by finite element method. The effects of rolling reduction, friction coefficient, rolling velocity and initial stress on the longitudinal residual stress distribution over the thickness of GH4169 alloy sheet were analyzed. The results show that the values of longitudinal residual stress can be slightly reduced by increasing the rolling reduction and velocity. The longitudinal residual stress over the thickness distributes as ‘‘V＇＇ type or weak ‘‘W＇＇ type. The initial stress mainly has an effect on the longitudinal stress in the backward slip area. But the friction coefficient has remarkable influence on longitudinal residual stress. With the friction coefficient increasing from 0.1 to 0.5, the value of longitudinal residual stress on the sheet surface is reduced by 282 MPa. Simultaneously, the tensile stress turns into compressive stress with a strong‘‘W＇＇ type distribution.

Twinning and detwinning during compression–tension loading measured by quasi in situ electron backscatter diffraction tracing in Mg–3Al–Zn rolled sheet

Twinning and detwinning are the important deformation modes in magnesium alloys during cyclic loading at room temperature. To analyze these two deformation mechanism, cyclic compression–tension experiments were performed on Mg–3Al–1Zn rolled sheet along the rolling direction. In these tests, the microstructure evolutions of a series of grains during deformation were traced by using quasi in situ electron backscatter diffraction(EBSD). Important quantities like the Schmid factors of twinning system, the fraction of twinning during compression, and the fraction of twinning after reverse loading were calculated on the basis of measured quantities. The influence of Schmid factor of twinning variants on detwinning upon reverse loading was analyzed. Detwinning would prefer to proceed during reverse loading if the Schmid factor of twinning in the twinning area before reverse loading is sufficiently large.