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Comparative analysis of cold and warm rolling on tensile properties and microstructure of additive manufactured Inconel 718

Zhang Tao, Li Huigui, Gong Hai, Wu Yunxin, Ahmad Abdulrahaman Shuaibu, Chen Xin, Zhang Xiaoyong

Archives of Civil and Mechanical Engineering

2022

Vol. 22, no. 1

art. no. e44, 2022

Despite 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.

Utilization of coconut shell residual in green roof: hydraulic and thermal properties of expansive soil amended with biochar and fbre including theoretical model

Wang Hao, Garg Ankit, Zhang Xiaoyong, Xiao Yangyang, Mei Guoxiong

Acta Geophysica

2020

Vol. 68, no. 6

1803--1819

The study intends to explore hydraulic and thermal properties of expansive soils treated with fbre, biochar and biochar–fbre mix. Both fbre and biochar are derived from coconut shell, which is highly common in coastal regions around the world. Besides, benefts, limitations and engineering feasibility of these geomaterials in green roofs are explored. Theoretical framework for thermal–hydraulic analysis is proposed based on mass conservation and the frst law of thermodynamics. Heat capacity, thermal conductivity, water retention curve, crack intensity factor (CIF) and saturated and unsaturated hydraulic conductivities of four kinds of soils are evaluated and compared. Characterizations of geomaterials are also investigated via thermal mass loss, micro-structure, surface area and functional groups identifcation. Both biochar and fbre admixtures contribute to improvement in soil heat capacity and saturated and unsaturated hydraulic conductivities. Biochar enhances saturated and residual water contents of expansive soil by 10% and 8%, respectively. Also, biochar decreases soil thermal conductivity and CIF by 31% and 5%, respectively, while fbre decreases soil-saturated and residual water contents by 15% and 29%, respectively, and reduces soil thermal conductivity and CIF by 21% and 50%, respectively. Soil–biochar–fbre composite is also recommended due to low air-entry value, acceptable water-holding capacity and limited crack propagation. The study flls the knowledge gap of how soil thermal–hydraulic properties are afected due to biochar and/or fbre admixture. It is recommended to pay more attention on production and utilization of biochar derived from coconut shell currently utilized for fbre extraction.