Browsing by Author "Ahmad, Abdulrahaman Shuaibu"
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Item Open Access Comparative analysis of cold and warm rolling on tensile properties and microstructure of additive manufactured Inconel 718(Springer, 2022-01-14) Zhang, Tao; Li, Huigui; Gong, Hai; Wu, Yunxin; Ahmad, Abdulrahaman Shuaibu; Chen, Xin; Zhang, XiaoyongDespite the high efficiency and low cost of wire + arc additive manufacture (WAAM), the epitaxial grown columnar dendrites of WAAM deposited Inconel 718 cause inferior properties and severe anisotropy compared to the wrought components. Fundamental studies on the influence of one-pass cold and warm rolling on hardness and microstructure were investigated. Then the interpass cold and warm rolling on tensile properties were also analyzed. The results show that the one-pass rolling increases the hardness and displays a heterogeneous hardness distribution compared to the as-deposited material, and the warm rolling exhibits a larger and deeper strain compared to cold rolling. The columnar dendrites gradually change to cell dendrites under the rolling process and then change to equiaxed grains with the subsequent new layer deposition. The average grain size is 16.8 μm and 23.5 μm for the warm and cold rolling, respectively. The strongly textured columnar dendrites with preferred < 001 > orientation transform to equiaxed grains with random orientation after rolling process. The grain refinement contributes to the dispersive distributed strengthening phases and the increase in its fraction with heat treatment. The as-deposited samples show superior tensile properties compared to the cast material but inferior compared to the wrought components, while the warm-rolled samples show superior tensile properties to wrought material. Isotropic tensile properties are obtained in warm rolling compared to cold rolling. The rolling process and heat treatment both decrease the elongation and lead to a transgranular ductile fracture mode. Finally, the rolling-induced strengthening mechanism was discussed.Item Open Access Effect of rolling force on tensile properties of additively manufactured Inconel 718 at ambient and elevated temperatures(Elsevier, 2021-07-03) Zhang, Tao; Li, Huigui; Gong, Hai; Wu, Yunxin; Ahmad, Abdulrahaman Shuaibu; Chen, XinInferior mechanical properties and severe anisotropy behavior of wire + arc additive manufactured (WAAM) Inconel 718 due to the large epitaxial grown columnar dendrites restrict the industrial application of WAAM deposition. Cold rolling was integrated into the WAAM deposition process and the effect of rolling force on microstructure, precipitatation distribution and tensile properties at ambient and elevated temperatures were investigated. The results show that the hardness of cold-rolled samples is much larger than that of the as-deposited and it increases with the increase in the rolling force. The columnar dendrites of the as-deposited sample changed to finer equiaxed grains of 26.5 and 14.7 μm after cold rolling with the force of 50 kN and 75 kN, respectively. Meanwhile, more uniformly distributed grains and less δ phase appear for 75 kN rolled sample. The stress-strain curves are smooth for the tensile tests at ambient temperature, while there are serrations at elevated temperature due to the dynamic strain aging behavior. The as-deposited sample shows inferior tensile properties to the wrought material at ambient and elevated temperatures. The cold-rolled samples both exceed the wrought material at ambient temperature; however, they show higher strength but lower elongation compared to the wrought material. The 75 kN cold rolled sample shows much higher strength and similar elongation to the wrought material for the test at elevated temperature. The grain morphology and recrystallization, as well as the strengthening mechanism of hybrid deposition and cold rolling process were discussed.