Browsing by Author "Zhang, Xiaoyong"

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    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, Xiaoyong
    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.
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    Element partitioning and electron backscatter diffraction analysis from feeding wire to as-deposited microstructure of wire and arc additive manufacturing with super duplex stainless steel
    (Elsevier, 2019-12-24) Zhang, Xiaoyong; Wang, Kehong; Zhou, Qi; Kong, Jian; Peng, Yong; Ding, Jialuo; Diao, Chenglei; Yang, Dongqing; Huang, Yong; Zhang, Tao; Williams, Stewart W.
    The redistribution of alloying elements and the crystallographic characterizations in wire and arc additive manufactured (WAAM) super duplex stainless steel (SDSS) was investigated from the wire to the final as-deposited structure. The results showed that elemental partitioning between austenite and ferrite was suppressed in the last layer and the solidified droplet. The high Ni content but low Cr and N contents in the initial state of the intragranular austenite (IGA) confirmed the predominance of the chromium nitrides acted as the nucleation sites. Gathering of nitrogen was found more distinct in the coarsening IGA, Widmanstätten austenite (WA) than the grain boundary austenite (GBA). The columnar epitaxial ferrite presented a strong <001> texture in the deposition direction, while the <001> and <101> orientations was found in the austenite. Random orientations of the intragranular secondary austenite was revealed. The Rotated Cube texture of the austenite grains were consumed by the “recrystallization” textures (Brass, Rotated Brass, Cu, R, E, and F) caused by the austenite reformation. The low-angle interphase boundaries between austenite and ferrite were predominated in the as-deposited wall, and, at which, the K–S orientation took the crucial part. A Taylor factor analysis revealed that through fabrication via additive process, the austenite became oriented “harder” and contributed most to good mechanical properties. The textured microstructure contributed about a 2.6% higher engineering strain in the Z direction and a 27.8 MPa higher yield strength in the X direction.
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    Hybrid wire - arc additive manufacture and effect of rolling process on microstructure and tensile properties of Inconel 718
    (Elsevier, 2021-09-08) Zhang, Tao; Li, Huigui; Gong, Hai; Wu, Yunxin; Diao, Chenglei; Zhang, Xiaoyong; Williams, Stewart
    Wire - arc additive manufacture (WAAM) is suitable for Inconel 718 components due to its high deposition efficiency. However, large columnar dendrites decrease the mechanical properties and can cause severe mechanical anisotropy. Cold rolling and warm rolling through flame heating have been investigated to analyze their effects on microstructure and tensile properties compared to as-deposited WAAM material. Standard solution and double aging (SA), as well as homogenization followed by solution and aging (HSA) heat treatments were compared. The results show that the large columnar dendrites change to finer equiaxed grains 16.4 μm and 26.2 μm in size for warm and cold rolled alloy, respectively. This increases to 22.5 μm and 30.1 μm after HSA treatment. The microhardness and strength of rolled material increase significantly and the warm rolled material after HSA treatment exceeds that of the wrought alloy. While the as-deposited and cold rolled samples both show significant anisotropy, isotropic tensile properties are obtained for warm rolled plus HSA heat treated samples. Finer equiaxed grains with more dispersive distributions of γ' and γ" strengthening precipitation contribute to the superior mechanical properties for warm rolled material. For both the cold and warm rolled material, there was an elongation decrease due to precipitated particles, which also led to a trans-granular ductile fracture mode. The strengthening mechanism of the hybrid rolling process was analyzed and found to be related to work hardening, grain boundary strengthening, precipitated strengthening phases and the δ phase.
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    Microstructure and mechanical properties of TOP-TIG-wire and arc additive manufactured super duplex stainless steel (ER2594)
    (Elsevier, 2019-07-02) Zhang, Xiaoyong; Wang, Kehong; Zhou, Qi; Ding, Jialuo; Ganguly, Supriyo; Marzio, Grasso; Yang, Dongqing; Xu, Xiangfang; Dirisu, Philip; Williams, Stewart W.
    As the excellent combination of mechanical properties and corrosion resistance for super duplex stainless steel, a prospective method – Wire and Arc Additive Manufacturing – for fabricating this material was proposed, and a wall component was deposited in this study. The microstructure of the as-deposited wall was carefully analyzed along with the variation of mechanical properties. The results revealed that, in the wall-body, the austenite/ferrite phase balance was broken by the overgrowing the austenite phase. During this process, the intergranular secondary austenite leading the increase of austenite phase together with some contributions made by the precipitation of intragranular secondary austenite. Propagation of the intermetallic phases, chi and sigma phase, was not the major reason for the low impact toughness in the last layer area and the root region. Instead, the presence of CrN and “inclusions” (Cr2N and impurities) took the main responsibility not only in the impact toughness but also the ductility. The anisotropic analysis revealed that the UTS and elongation appeared distinct difference in vertical and horizontal direction samples. The varieties in YS were eliminated by the nitrogen work hardening effect to a large extent.
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    Study on location-related thermal cycles and microstructure variation of additively manufactured Inconel 718
    (Elsevier, 2022-04-04) Zhang, Tao; Li, Huigui; Gong, Hai; Wu, Yunxin; Chen, Xin; Zhang, Xiaoyong
    The complicated thermal history of wire + arc additive manufacturing (WAAM) will affect the microstructure variation and mechanical properties of the as-deposited material. Numerial models of Inconel 718 in WAAM deposition were established and the location-related thermal history and temperature distribution were analyzed. A hybrid method of WAAM and cold rolling was investigated and its effect on the microstructure distribution and texture was investigated compared to that in as-deposited condition. The results show that WAAM deposition features repeated thermal cycles, high heating rate and low cooling rate. The trough values of the thermal cycles first increases and then decreases, while the peak temperature always decreases with the proceeding of the deposition process. The as-deposited samples show columnar dendrites and its average dendrite arm spacing increases with the increased build height due to the location-related heat accumulation. The strongly textured columnar dendrites with preferred <001> orientation transform to equiaxed grains with random orientation in heat-affected zone after cold rolling process, and its average size decreases with the increased rolling force. The as-deposited samples show the strongest intensity of 7.609 for the {100} family of grains oriented along the transverse direction; while it decreases to 3.629 and 2.057 for the cold rolled conditions with the force of 50 kN and 75 kN, respectively. The relationship between thermal history and the microstructure distribution was discussed. The mechanism of hybrid WAAM and cold rolling method consisted of spatially and temporally heterogeneous work hardening and recrystallization.
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    Study on microstructure and tensile properties of high nitrogen Cr-Mn steel processed by CMT wire and arc additive manufacturing
    (Elsevier, 2019-01-23) Zhang, Xiaoyong; Zhou, Qi; Wang, Kehong; Peng, Yong; Ding, Jialuo; Kong, Jian; Williams, Stewart W.
    A designed Cr-Mn-N wire with 0.99 wt% of nitrogen content (HNS0.99) was used to make high nitrogen austenite stainless steel parts by introducing CMT wire and arc additive manufacturing (CMT-WAAM) method. The solidification behaviour, microstructure evolution, inclusions and tension properties were studied both in the as-built and post heat treatment conditions. Excellent tension properties parts with high nitrogen content were successfully produced. Ferrite-austenite (FA) and austenite-ferrite (AF) solidification models were revealed in the as-built microstructure of two different areas, inner layer area (ILA) and partial melting area (PMA), respectively, and the former predominated the microstructure. Amorphous inclusion islands and microspherical inclusions made by MnO were found. The increasing density of the latter in 0.1-1 μm diameters was detrimental to the tensile properties because the matrix-inclusion surfaces acted as the preferred nucleation sites for Cr2N during heat treatment. Due to the stable austenite and the nitrogen work hardening effect, planer dislocation-arrays predominated the dislocation slip model which, to some extent, diminished the strength anisotropy in different directions. However, the ferrite dendrites caused the diversity of UTS and elongation by acting as tunnels for cracks in the horizontal direction samples.