H. Yuan

Bio: H. Yuan is an academic researcher from Yanshan University. The author has contributed to research in topics: Recrystallization (metallurgy) & Strain rate. The author has an hindex of 8, co-authored 9 publications receiving 251 citations.

Effect of the δ phase on the hot deformation behavior of Inconel 718

Abstract: Hot compression tests at different temperatures and strain rates were performed on Inconel 718 solution treated as well as solution treated and then aged at 900 °C for 1–24 h in order to investigate the effect of the δ phase on hot deformation behavior. A hyperbolic-sine Arrhenius-type equation was used to characterize the dependence of the peak stress on deformation temperature and strain rate. In the case of Inconel 718 with a large amount of the δ phase, the apparent activation energy was determined to be 458 kJ/mol, which was slightly higher than the activation energy of 443 kJ/mol for solution treated Inconel 718. The γ″/γ′ phases present in Inconel 718 prior to hot deformation enhanced the peak stress, but did not affect the peak strain. The δ phase present in Inconel 718 not only decreased the peak strain and the peak stress, but also promoted the flow softening after the peak stress.

Microstructure, texture and mechanical properties of Al/Al laminated composites fabricated by hot rolling

Abstract: AA 1060/3003/1060 laminated composites were fabricated by hot-roll bonding. The effect of rolling temperature on the microstructure, texture and mechanical properties of AA 1060/3003/1060 laminated composites was investigated. The results show that the development of microstructure and texture through the thickness of Al layers was inhomogeneous in the Al/Al laminated composites. Initial grains were elongated along the direction of about 15° to the RD in the region near the surface layer of AA 1060 aluminum alloy, and the incline angle gradually decreased as the measured position moved towards the interface of 1060/3003 from the surface layer. The rolling texture of 1060 layer consisted of the r-cube and γ-fiber shear textures and the remaining cube component. The r-cube shear texture weakened gradually as the measured position moved towards the interface of 1060/3003 from the surface layer, whereas the center layer of AA 1060 aluminum alloy had the strongest γ-fiber shear texture. The interface layer of AA 3003 aluminum alloy had a completely different texture from the center layer. For the Al/Al laminated composites, the YS and UTS first increased to a maximum value at about 200 °C and then decreased with increasing rolling temperature.

Evolution of microstructures in severely deformed AA 3104 aluminum alloy by multiple constrained compression

Abstract: AA 3104 aluminum alloy was severely deformed by multiple constrained compression in a channel die set-up. The evolution of microstructures during deformation was investigated by transmission electron microscopy. The flow stress in multiple constrained compression initially increases markedly with strain and then increases gradually. Large scale shear bands and the evidence for strain localization are observed. The microstructure consists of dislocation cells and extended boundaries after two passes to a strain of 0.86, while a cell block structure with high-angle lamellar boundaries is formed after eight passes to a strain of 3.56.

Microstructure and texture evolution in commercial-purity Zr 702 during cold rolling and annealing

Abstract: Microstructure and texture evolution in commercial-purity Zr 702 during cold rolling and annealing was investigated by optical microscopy, transmission electron microscopy, and X-ray diffraction. The results showed that crystallographic slip was the predominant deformation mechanism in the early stage of deformation. Deformation twins started to form when the rolling reduction was larger than 38.9%; both the dislocation density and the number of twins increased with increasing rolling reduction. The initial texture of the Zr 702 plate consisted of the basal fiber component. During cold rolling the strength of the basal fiber first decreased and then increased with increasing rolling reduction. The cold-rolled sheets were fully recrystallized after being annealed at 550°C. The recrystallization temperature and the size of recrystallized grains decreased with increasing rolling reduction. A larger rolling reduction resulted in a higher grain growth rate when the annealing temperature increased from 550°C to 700°C. The recrystallization texture was characterized by a major basal fiber and a minor \(\{ 01\bar 13\} \) component. The strength of the recrystallization texture increased with increasing rolling reduction.

On the Phenomenon of Stress Drop During Hot Deformation of ZrTiAlV Alloy

Abstract: Hot deformation behaviors of 47Zr-45Ti-5Al-3V alloys with different grain sizes were investigated by compression tests The flow curves exhibited a pronounced stress drop at the very beginning of deformation The magnitude of the stress drop increased with the decreasing deformation temperature and the increasing strain rate The sudden stress drop may be associated with the disappearance of mobile dislocations in the grain boundaries Larger initial grain size increased the flow stress, promoted the stress drop, and enhanced the activation energy of deformation

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Flow behavior and microstructures of superalloy 718 during high temperature deformation

Abstract: Flow behavior and microstructures of superalloy 718 were investigated by hot compression tests performed at temperatures ranging from 950 to 1100 °C with strain rates of 10−3 to 1 s−1. The dependence of the peak stress on deformation temperature and strain rate can be expressed by a hyperbolic-sine type equation. The activation energy for superalloy 718 is determined to be 443.2 kJ mol−1. A power exponent relationship between the peak strain and the Z parameter is obtained. Microstructure analysis shows that the dynamically recrystallized grain size is inversely proportional to the Z parameter. The nucleation mechanisms of DRX are closely related to the value of Z parameter. Under low Z conditions, DRX nucleation and development are mainly assisted by the formation of twins near the original grain boundaries.

Review on powder-bed laser additive manufacturing of Inconel 718 parts

Abstract: This study presents a thorough literature review on the powder-bed laser additive manufacturing processes such as selective laser melting of Inconel 718 parts. This article first introduces the gen...

The influence of Laves phases on the high-cycle fatigue behavior of laser additive manufactured Inconel 718

Abstract: In this paper, a comparative study of high-cycle fatigue tests (T=650 °C, f=110 Hz, R=0.1, Kt=1) were carried out with wrought Inconel 718 and LAMed Inconel 718. The results show that the influences of the Laves phases on high-cycle fatigue properties are based on the applied stress amplitudes. At a low stress amplitude, most of the Laves phases held their original morphologies. The fatigue cracks stopped in front or detoured around them, which means that the unbroken Laves phases play an important role in hindering crack propagation. In this way, the high-cycle fatigue life of LAMed Inconel 718 was superior to that of wrought Inconel 718. However, at a high stress amplitude almost all of the Laves phases in the crack propagation region splintered into smaller fragments, parts of which separated from the austenite matrix. Microscopic holes or cracks were formed at the interface, which provided passages for the fatigue cracks to propagate. In this case, the Laves phases were harmful, leading to the degradation of fatigue performance in LAMed Inconel 718 compared with wrought Inconel 718.

Effect of heat treatment on microstructure evolution of Inconel 718 alloy fabricated by selective laser melting

Abstract: Inconel 718 superalloy was fabricated by selective laser melting (SLM) and subsequently subjected to different heat treatments. Microstructure evolution was examined by X-ray diffraction, optical microscopy, scanning and transmission electron microscopies. In the horizontal section (normal to the building direction) of the as-built sample, columnar and cellular sub-structures formed in the overlapping area, while only cellular sub-structures existed in the central fusion area. Columnar structures were observed in the vertical section (parallel to the building direction). In the as-built condition, austenite γ and Laves phases predominated, almost to the exclusion of all other phases. When treated by the direct double aging (DA) process, δ-Ni3Nb phases precipitated mainly in the interdendritic regions where Nb preferentially segregated. Homogenization plus double aging (HA), and solution plus double aging (SA) treatments significantly eliminated microsegregation and Laves phases owing to the diffusion of Nb and Ti to the γ matrix. The δ phase dissolved in the HA-treated sample but precipitated in the SA-treated sample. The γ′-Ni3(Al,Ti) phase was prone to precipitate when treated by HA, while γ″-Ni3Nb phase tended to precipitate in the SA sample. Due to the precipitation of the higher fraction of the major strengthening γ″ phases, the SA sample showed the highest hardness value among the as-built, DA, HA, and SA samples. The morphology, distribution and crystallography of precipitates and their formation mechanisms are discussed and analyzed.