Xu Cheng

Bio: Xu Cheng is an academic researcher from Beihang University. The author has contributed to research in topics: Microstructure & Alloy. The author has an hindex of 18, co-authored 47 publications receiving 930 citations. Previous affiliations of Xu Cheng include Chinese Ministry of Education.

Microstructure and mechanical properties of the austenitic stainless steel 316L fabricated by gas metal arc additive manufacturing

Abstract: The austenitic stainless steel 316L was fabricated by gas metal arc additive manufacturing (GMA-AM) and its microstructure and room temperature tensile properties were investigated. Results show that in the GMA-AM 316L plate, a large number of well-aligned austenitic dendrites vertically orient, forming large columnar grains in the middle and some dendrites bent toward the plate surfaces, forming small columnar grains near the edges. The microstructure of GMA-AM 316L consists of δ, γ and σ phases. After one layer was deposited, the δ phase exhibited reticular morphology within austenitic dendrites. The δ phase redissolved in austenite with the intermetallic σ phases forming at γ/δ interfaces under the thermal cycles influence of subsequent three deposition layers. And under the thermal influence after the fourth layers, both δ and σ phases turned into fine vermicular morphologies within austenitic dendrites. The tensile properties of GMA-AM 316L steel are comparable to wrought 316L and exceed the industry requirements for 316L. Its fracture type is ductile fracture due to the obvious fracture surface dimples. The microcracks initiate at the interior of σ phases and grow into large cracks leading to materials failure.

Effect of heat treatment on microstructure, mechanical and corrosion properties of austenitic stainless steel 316 L using arc additive manufacturing

Abstract: The mechanical and corrosion properties of gas metal arc additive manufacturing (GMA-AM) 316L could be optimized by modifying the volume fractions of sigma (σ) and delta-ferrite (δ) phases through heat treatment. Results show that the heat treatment at 1000 °C to 1200 °C for one hour will not obvious influence the morphology of grains in steel but largely influence the contents of σ and δ phases. The heat treatment at 1000 °C effectively increases the amount of σ phase in steel, causing both increase of UTS and YS but decrease of El and RA. The heat treatment at 1100 °C to 1200 °C completely eliminates σ phase, leading to the decrease of UTS and YS but increase of El and RA. The σ phase has better strengthening effect than δ phase, but which may degrade ductility and increase the possibility for cracks generation in steel. Meanwhile, limiting the number of both σ and δ phases through heat treatment can improve the corrosion resistance of steel. And σ phase appears more detrimental impact on degradation the corrosion resistance of steel than δ phase.

Additive manufacturing of steels: a review of achievements and challenges

Abstract: Metal additive manufacturing (AM), also known as 3D printing, is a disruptive manufacturing technology in which complex engineering parts are produced in a layer-by-layer manner, using a high-energy heating source and powder, wire or sheet as feeding material. The current paper aims to review the achievements in AM of steels in its ability to obtain superior properties that cannot be achieved through conventional manufacturing routes, thanks to the unique microstructural evolution in AM. The challenges that AM encounters are also reviewed, and suggestions for overcoming these challenges are provided if applicable. We focus on laser powder bed fusion and directed energy deposition as these two methods are currently the most common AM methods to process steels. The main foci are on austenitic stainless steels and maraging/precipitation-hardened (PH) steels, the two so far most widely used classes of steels in AM, before summarising the state-of-the-art of AM of other classes of steels. Our comprehensive review highlights that a wide range of steels can be processed by AM. The unique microstructural features including hierarchical (sub)grains and fine precipitates induced by AM result in enhancements of strength, wear resistance and corrosion resistance of AM steels when compared to their conventional counterparts. Achieving an acceptable ductility and fatigue performance remains a challenge in AM steels. AM also acts as an intrinsic heat treatment, triggering ‘in situ’ phase transformations including tempering and other precipitation phenomena in different grades of steels such as PH steels and tool steels. A thorough discussion of the performance of AM steels as a function of these unique microstructural features is presented in this review.

Additive manufacturing of structural materials

Abstract: Additive manufacturing (AM), also known as three-dimensional (3D) printing, has boomed over the last 30 years, and its use has accelerated during the last 5 years AM is a materials-oriented manufacturing technology, and printing resolution versus printing scalability/speed trade-off exists among various types of materials, including polymers, metals, ceramics, glasses, and composite materials Four-dimensional (4D) printing, together with versatile transformation systems, drives researchers to achieve and utilize high dimensional AM Multiple perspectives of the AM of structural materials have been raised and illustrated in this review, including multi-material AM (MMa-AM), multi-modulus AM (MMo-AM), multi-scale AM (MSc-AM), multi-system AM (MSy-AM), multi-dimensional AM (MD-AM), and multi-function AM (MF-AM) The rapid and tremendous development of AM materials and methods offers great potential for structural applications, such as in the aerospace field, the biomedical field, electronic devices, nuclear industry, flexible and wearable devices, soft sensors, actuators, and robotics, jewelry and art decorations, land transportation, underwater devices, and porous structures