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Powder Bed Fusion is a promising metal additive manufacturing technology based on layer by layer powder spreading, and particle uniformity has a great influence on the forming quality. By Discrete Element Method, the interaction and movement between particles were studied during powder spreading, including powder jamming, rebound, splash, eddy and empty powder area. Additionally, five kinds of powder spreading schemes were explored, and the new process of one-way reciprocating with tri-splint blade was designed to change the motion state of powder spreading from "blade pushing powder" to "blade holding powder". The results showed that by adjusting the spacing between the blade and the working platform, the optimized powder spreading process decreased the defects such as powder splash and empty powder, and achieve the uniform powder bed of aluminum alloy powder.

The electronic structure, cohesive energy and interfacial energy of ferrite (100)/NbC (100) and TiC (100)/NbC (100) interfaces have been investigated by the first-principles calculation. Moreover, the heterogeneous nuclei mechanism of NbC particle was also analyzed. The results showed that the stacking sequences have a great influence on the cohesive energy and equilibrium interfacial separation of the above-mentioned interfaces. Compared with C-terminated interfaces, the cohesive energy of Nb-terminated ones is lower while the equilibrium interface distance is larger. Among the two C-terminated interface structures, the interfacial energy between the NbC and ferrite is 4.54 J/m2, which is larger than that of NbC/TiC interface (1.80 J/m2). Therefore, NbC particles prefer heterogeneous nucleation on TiC particles surface rather than the ferrite matrix, which agrees well with the experimental result.

The nucleation potential of transition metal (TM) carbides formed in steel can be predicted by the behavior of iron adsorption on their surface. Therefore, Fe adsorption on the (001) surface of (A1-xmx)C (A = Nb, Ti, m = Mo, V) was investigated by the first-principles method to reveal the initialization of Fe nucleation. The Mulliken population and partial density of state (PDOS) were also calculated and analyzed in this work. The results show that Fe adsorption depends on the composition and configuration of the composite carbides. The adsorption energy (Wads) of Fe on most of (A1-xmx)C is larger than that of Fe on pure TiC or NbC. The maximum Wads is found for Fe on (Nb0.5Mo0.5)C complex carbide, indicating that this carbide has the high nucleation capacity at early stage. The Fe adsorption could be improved by the segregation of Cr and Mn atoms on the surfaces of (Nb0.5Mo0.5)C and (Ti0.5Mo0.5)C. The PDOS analysis of (Cr, Mn)-doped systems further explains the strong interactions between Fe and Cr or Mn atoms.

Nine Cu(I)-cyanide metal–organic frameworks (MOFs), namely, [Cu4(CN)2(4-bpt)2]n (1), {[Cu3(CN)2(4-bpt)]·H2O}n (2), [Cu2(CN)(3-bpt)]n (3), [Cu2(CN)2(3-Hptz)]n (4), [Cu3(CN)2(3-ptz)]n (5), [Cu7(CN)7(3-tpt)2]n (6), {[Cu9(CN)9(btb)2]·btb}n (7), [Cu2(CN)2(4-azpy)]n (8), and [Cu3(CN)3(bpp)]n (9) (4/3-Hbpt = 3,5-bis(4/3-pyridyl)-1,2,4-triazole; 3-Hptz = 3-pyridyl-tetrazole; 3-tpt = 2,4,6-tris(3-pyridyl)-1,3,5-triazine; btb = 1,4-bis(1,2,4-triazol-4-yl)benzene; 4-azpy = 4,4′-azobispyridine; bpp = 1,3-bis(4-pyridyl)propane), were synthesized under hydrothermal conditions and structurally characterized. The 4-bpt, 3-bpt, and 3-Hptz ligands in 1–4 were in situ generated by cycloaddition reactions. Their structural features vary from two-dimensional (2D) (3), three-dimensional (3D) (4, 5, 6), 3D 2-fold interpenetration (1, 2, 8), to 3D 3-fold interpenetration (7, 9). Complex 1 is an intriguing 3D metal–organic framework (MOF) with a nanosized rectangular channel. Complex 3 exhibits a chiral 2D double-layered network ...

Interfacial models of SiC/ZrB2 composite coating were studied by first-principles calculations based on density functional theory (DFT). The cubic SiC and hexagonal ZrB2 were selected in our work, and twelve types of SiC (111)/ZrB2 (0001) interface structures were investigated in consideration of four different terminations and three stacking sequences. The cohesive energy (Wad), interfacial energy (γint), and electronic structure of the SiC/ZrB2 interfaces were all calculated. The results show that the ZrB2 (0001) surface with 9 layers exhibits bulk-like interior characteristic. Among the interfaces of C/Zr terminated hcp-stacked (CZH), Si/Zr terminated hcp-stacked (SZH), C/B terminated center-stacked (CBC) and Si/B terminated center-stacked (SBT), the CZH interface has the largest Wad (6.28 J/m2) and thus is of the best stability. Over the range of zirconium chemical potential, the γint of CZH, SZH, CBC and SBT interfaces are −0.31–2.50 J/m2, 1.07–3.88 J/m2, 2.85–5.66 J/m2 and 2.32–5.13 J/m2, respectively. The calculated electronic properties reveal that, the CZH, CBC and SBT interfaces mainly contain covalent bonding, while the SZH one primarily consists of metallic bonding.

The segregation behavior of alloying elements X (X=Zr, V, Cr, Mn, Mo, W, Nb, Y) on the ferrite (100)/TiC(100) interface has been investigated using first principles method, and the work of separation and interface energy of ferrite/TiC interfaces alloyed by these elements were also analyzed. The results indicated that all these alloying additives except Y were thermodynamically favorable because of the negative segregation energy, showing that they have the tendency to segregate to the ferrite/TiC interface. When the Fe atom in the ferrite/TiC interface is replaced by Y, Zr, or Nb, the adhesive strength of the interface will be weakened due to the lower separation work, larger interfacial energy, and weaker electron effects. However, the introduction of Cr, Mo, W, Mn and V will improve the stability of the ferrite/TiC interface through strong interaction between these elements and C, and Cr-doped interface is the most stable structure. Therefore, the Cr, Mo, W, Mn and V in ferrite side of the interface can effectively promote ferrite heterogeneous nucleation on TiC surface to form fine ferrite grain.

Three Cu(I)-cyanide coordination polymers based on trigonal 1,3,5-tris(1H-imidazol-1-yl)benzene (tib) ligand, namely [Cu 3 (CN) 3 (tib)] n ( 1 ), [Cu 4 (CN) 4 (tib)] n ( 2 ), and [Cu 2 (CN) 2 (tib)] n ( 3 ), have been prepared and characterized by elemental analysis, IR, PXRD, thermogravimetry and single-crystal X-ray diffraction analysis. Complex 1 displays a 3D metal-organic framework with nanosized pores. Complex 2 is a 3D coordination polymer assembled by three μ 2 -cyanides and a μ 3 -cyanide with a very short Cu(I)···Cu(I) metal bond(2.5206 A). Complex 3 is a 2D coordination polymer constructing from 1D Cu(I)-cyanide zigzag chain and bidentate tib spacer. Three Cu(I) complexes are thermally stable up to 250–350 °C. Complexes 1 – 3 show similar orange emission band at 602 nm originating from LMCT mechanism.

In order to eliminating the banded structure in SAE8620H gear steel,an isothermal annealing process and its mechanism has been studied in this paper. Results showed that isothermal annealing process can effectively eliminate banded structure in SAE8620H gear steel.With isothermal temperature 640°C-a certain low temperature indeed high undercooling,and for high nucleation at this temperature resulting in the decrease of nucleation rate difference in all areas,banded structure level decreased to 1 level.When isothermal temperature decreased to 610°C and 590°C,although the undercooling is so high that various regions began to nucleate at the same time,the transition temperature is so low that alloy elements in the regions previously occupied by pearlite bands diffuse faster than other regions,thus proeutectoid ferrite grains in these regions grow faster,regenerating the banded structure .

By adding Mn into SAE8620 gear steel, the effect of Mn on the microstructure and hardness of steel treated by quenching and partitioning process is investigated in this research. Microstructure is observed. Hardness is measured, after that it is converted into tensile strength. And the content of austenite is determined by X-ray diffraction analysis. It is found that higher content of Mn increases the content of martensite and reduces that of blocky ferrite and also leads to higher hardness of steel. In addition, XRD pattern shows obvious existence and enhancement of retained austenite.

Material cutting properties can be judged by turning temperature and chip shape. A new method that can measure turning temperature more accurately was discussed in this paper. Compared with the traditional method, results show that turning temperature can be accurately measured through a new method in turning process. Turning temperature become stable and will not jump after 20s later. In addition, the higher the hardness, the higher the energy is needed, leading to the higher turning temperature. The average turning temperature of the quenched specimen, normalized specimen and annealed specimen measured through the new method is 100°C,70°Cand 60°C, respectively. And the chip morphologies of quenched specimen, normalized specimen and annealed specimen are irregular band chips, spiral debris chips and C-shaped chips, respectively.

Hydrothermal reactions of AgNO3, K3[Fe(CN)6] with N-heterocyclic ligands afforded three novel Ag(I)–cyanide coordination polymers, [Ag2(CN)2(tpt)]n (1), {[Ag(CN)(bpe)0.5][Ag(CN)]}n (2) and [Ag(CN)(btmb)0.5]n (3) (tpt = 2,4,6-tris(4-pyridyl)-1,3,5-triazine, bpe = 1,2-bis(4-pyridyl)ethane, btmb = 1,2-bis(1,2,4-triazol-1-ylmethyl)benzene). In complex 1, two Ag(CN) linear chains are bridged by bidentate tpt ligand to form a ladder-like structure, which are further connected by Ag Ag metal bond to generate a 2D polymeric network. Complex 2 is an interesting 3D supramolecular architecture assembled by 2D [Ag1(CN)(bpe)0.5]n network and linear [Ag2(CN)]n chain combined by strong Ag Ag metal bond. Complex 3 is a 1D ladder-like double-chain polymer constructed from Ag–cyanide linear chains and btmb spacer, which is further extended to a 2D supramolecular network by Ag–Ag weak interaction. The Ag–Ag metal interactions play important roles in the construction of three coordination polymers. Complexes 1 and 2 are respectively thermally stable at 300 and 180 °C. Complexes 1 and 3 emit strong blue luminescence.

A numerical model of recrystallization taking the deformation and the inhomogeneous distribution of stored energy into account were proposed in this paper. Here the deformed microstructure is obtained by a lattice deformation model and the microstructure evolution during recrystallization is simulated by a multi-state free energy phase field method. According to the characteristics of the different deformation zone and the inhomogeneous distribution of the stored energy, the weight factor reflected the distribution of the stored energy in the deformed zones is introduced in this work. As for the density of dislocation, the stored energy in the grain boundary and the triple junctions are double and 2.5 times higher than that within the grain, respectively. We utilize the multi-state free energy function to simulate the recrystallization process of the 0.11C-0.21Si-1.40Mn-0.04Nb steel. The results of simulation match very well with the experiments in the 0.11C-0.21Si-1.40Mn-0.04Nb steel. Therefore, through these models, it provides an excellent resolution to the problem that the deformation and nucleation affection on the process of the recrystallization. It is confirmed that recrystallization simulation depending on the lattice deformation model and taking the inhomogeneous distribution of the store energy into account can be successfully proposed to simulate practical situation.

Non-isothermal resistance heating in the hot stamping of quenchable steel sheets was developed to produce ultra-high strength steel formed parts with tailored properties. The heating temperature of parts is related with width of samples heated by resistance heating. With the same input energy, the strength in the narrow portions is high owing to the high energy density and that in the wide portions is low owing to the low energy density. Hat-shaped products having a tensile strength arrange from 600 MPA to 1800 MPa were formed. The tempering treatment on the directly hot-stamped boron steel resulted in better mechanical properties and higher formability index. The SEM figures indicates that the nano-carbide formation during the tempering treatment were suggested as the evident reasons for the occurrence of the mentioned robust properties. Finally the combination of temperature 250 ℃ and holding time 45 min can achieve the best comprehensive mechanical properties.

In this study, a improved mathematical model was developed for Nb-Ti microalloyed steel during hot rolling simulation. Using the compression test, the dynamic and static recrystallization characteristics of Nb-Ti microalloyed steel were studied. Though multi-pass hot rolling simulation, it is found that the recrystallization during hot rolling can play an important role, it can make the mean flow stress lower and refine the grains. And respective comparison between calculated and measured data of microstructure showed some of the validation of the built model. Meanwhile, the evolution characteristic of average austenite grain size during hot rolling can be achieved by theoretical model and experiment.

Technology and defect in the low-pressure semi-solid die casting of aluminum wheel hub under different process has been studied. The simulation software ADSTEFAN 2012 is used to analyze the solidification in different die temperature. Stereomicroscope, digital camera and optical microscope (OM) are used to study defect in the casting. The result shows that the low slurry temperature (606°C) will result in higher viscosity, and the low preheated die temperature will increase the cooling rate so that shrinkage is formed in the isolate solidification area. In the technology of casting wheels, the optimum temperature of the slurry is 614°C, preheated temperature of die is 400°C.

Austenitic continuous heating transformation dynamics, microstructural evolution and quenching properties of 22MnB5 steel during resistance heating were investigated. Steel sheets with thickness of 1.6 mm were heated to various temperatures (800~1200 °C) either by resistance heating at two heating rates of 100 and 300 °C/s or furnace heating. The increment of superheat degree was parabolic relationship with increasing heating rate. Samples heated above Ac3 of respective heating rates exhibited a full martensite microstructure and a hardness of above 490 HV. Austenitic coarsening rate of resistance heating samples was much lower than those by furnace heating. Austenite grain size by resistance heating was smaller than 38 μm while these by furnace heating reached 74 μm at 1200 °C. Samples heated by resistance heating at 300 °C/s had a good performance of 1800 MPa tensile strength and 5.6 % elongation, and product of strength and elongation reaches 10080 MPa%. The good combination of tensile strength and elongation by resistance heating might result from the finer austenite grain size and smaller martensite plate.

Based on a improved mathematic model of predicting austenite grain size of hot rolled Nb-Ti micro-alloyed steel, a module for calculating microstructure evolution in the steel during hot-forming process was developed. To evaluate the recrystallization behavior according to the proposed model during plate multi-pass hot rolling, the multi-pass hot compression and its FE analysis in couple with the newly determined model were conducted. It indicated that the present models were capable of simulating the multi-pass hot compression and the actual multi-pass rolling process. After simulating an actual rolling process in factory by using the above models, evolution laws of microstructure were analyzed. Simulation results of microstructure had a good agreement with the measured ones.

Six complexes based on a new rigid V-shaped ligand, 2,6-bis(3-(pyrid-4-yl)-1,2,4-triazolyl)pyridine (2,6-H2bptp), namely, [Cd4(2,6-bptp)2(d-cam)(l-cam)(H2O)2]n·4nH2O (1), [Cd2(2,6-Hbptp)2(Hbtc)]n·4nH2O (2), [Zn(2,6-bptp)(H2O)]n·nH2O (3), [(Mo8O26)Cu2(2,6-H2bptp)2]n (4), [Co(2,6-H2bptp)2][Mo8O26]0.5·5H2O (5), and [(PMo12O40)Ag(2,6-H4bptp)]·2H2O (6) (d/l-H2cam = d/l-camphoric acid; H3btc = 1,3,5-benzenetricarboxylic acid), have been synthesized under hydrothermal conditions. Among these complexes, 2,6-H2bptp adopts seven types of coordination modes; all display a central tridentate chelating plane. Complex 1 possesses a 3D porous metal–organic framework that exhibits an intriguing sandwich-like motif. Complex 2 is a 1D nanorod-like coordination polymer with a square section of 1.11 × 1.06 nm2. Complex 3 exhibits a 1D zigzag chain structure, which is extended to a supramolecular double-chain by hydrogen bonding. In complex 4, polyoxometalate β-Mo8O264– links Cu2(2,6-H2bptp)24+ dimer to form a 1D linear chain...

Rolling force and temperature field are important parameters in the hot rolling process of plate steel. Most researchers use ANSYS/LS-DYNA and MSC.Marc to simulate the hot rolling process, however, software DEFORM-3D is not used widely in this field. Therefore, in this study, the commercially available finite element analysis software DEFORM-3D is used to simulate the distribution of rolling force, stress-effective, strain-effective and temperature field during the hot rolling process of plate steel with the size of 0.220m×2.070m×1.904m. Both the simulated rolling force and temperature of the multi-pass are compared with the measured results. It is shown that the simulated values by the finite element method are approximate to the measured values in the hot rolling of plate steel. So the simulation can provide an important reference and optimization to make rolling process and parameters in steel factory.

The hypoeutectic Al-Si alloy billet with non-dendrite was reheated to meet the needs of the semi-solid thixoforming microstructure by four kinds of reheating power, achieving the same final temperature of 851 K. Subsequently, under the same condition of thixoforming, the microstructure, surface hardness and tensile properties were observed. Afterwards, quantitative analysis was made for the microstructures of the reheated semi-solid of billet and the thixoforming parts. The results show that when the induction reheating power is 90 kW, the average grain size of the semi-solid billet is the minimum, the microstructures of the thixoforming samples also are the finest, and the mechanical properties of the relevant thixoforming samples are the best. Furthermore, after studying on the relationship between the microstructures of the semi-solid billet of aluminum alloy and the mechanical properties of the thixoforming samples, the reverse design of microstructure is primarily achieved. Finally, the effectiveness of the reverse design for semi-solid microstructure is confirmed by an actual automobile part with complex shape.

It is shown from experiment that the pure B contained salt exhibits little refining effect, while the pure Ti contained salt, especially the salt containing 5Ti/1B, shows obvious refining effect on the pure aluminum. Crystallographic study indicates that Al 3 Ti particle is a more suitable nucleation site for the aluminum matrix than (Ti, Al)B 2 type particles (TiB 2 , AlB 2 and (Ti, Al)B 2 ), because there exist more coherent planes with aluminum matrix in the former. Thermodynamics estimation, X-ray diffraction (XRD) and SEM detection show that the refining mechanism of (Ti, B)-contained refiners is mainly contributed to the heterogeneous nuclei of fine Al 3 Ti particles dispersed in the melting, which comes from the reaction between the Ti and aluminum. (Al, Ti)B 2 type particle shows little or no direct refining effect, but it will reduce the size of Al 3 Ti since the Al 3 Ti nucleates and grows along the (Al, Ti)B 2 type particle interface.

The relationship between structure morphology of semi-solid aluminum alloy die-casting sample and filling condition was studied. By systematical structure analysis and computer simulation of the filling process, the quantitative relationship between microscopic morphology (such as solid fraction, grain size and shape) and formation state was studied. The results showed that the billet microstructure must have fine and round grains for the die-casting of complex shapes. It is necessary to optimize injection speeds to escape the non-uniform distribution of the solid fraction in complex and changeable mold cavity.

To enhance the comprehension on the internal rule of microstructure evolvement and quality-controlled relativity, the microstructure during the induction reheating of billets and die casting of parts was systematically investigated. According to general structure observation and aided analysis of some computer simulations, the quantitative relationships between microscopic morphology (including solid fraction and grain shape) and formation state was minutely discussed. The experimental results showed that liquid and solid phase in semi-solid slurry had different filling tendency, fluid velocity of liquid phase in the area of high filling speed was relative quick and easy to flow into far area and corner. Solid particles far from gate possessed fine and round grain. Moreover, the structure configuration of original billets markedly affected forming process; billets with fine and round grain were required for the die-castings of complex shape and thin thickness. In the case of the big change in shape and thickness of die-castings, the design of gating system and the control of plunger speed should be so properly carried out as to avoid unequal distribution of solid and liquid phase in die-casting part as soon as possible.

The morphology of semi-solid alloy is one of the key influence factors on the rheological behavior of slurry during die filling and the mechanical properties of formed parts. However, it is difficult to study such effect due to hard controlling of morphology in semi-solid state. In this paper, a self-developed Searle-type viscometer was used to determine the rheological behavior of A356 aluminum alloy in different morphology, which was refined with the salts mixture of K2TiF6 and KBF4. The results indicated that the flow behavior of refined A356 alloy in the semi-solid state possesses obviously thixotropic behavior under isothermal shearing condition with less time to reach steady state and lower steady apparent viscosity as compared to that of the A356 alloy. During continuous cooling at a constant shearing rate, the apparent viscosity of refined A356 slurry in the same solid fraction decreased with the content of Ti. It is shown from quantitative image analysis that the primary α-Al grain in the refined alloy evolves from dendrites to rosettes or sphericitys, and then tends to be rounder and finer in higher Ti content. The mechanism of the influence of morphology on rheological behavior was also discussed in this paper.

To aid the optimizing design of filling system, computer simulation technique is introduced to predict injection-forming process and to protect defects during trial manufacture of automotive parts by using semi-solid die cast process. By comparing formed appearance of parts in experiments and that in simulations, and observing the relationship between internal defects inspected by X-ray and flow field obtained in simulation, it is indicated that there are quite good agreements between simulation and experiment, right predictions for cast defects resulting from filling process can be made and improving direction is proposed. The realization of numerical visualization for filling process of high speed during semi-solid die cast process will play an important role in optimizing technology plan and process.

Hydrogen content in pure aluminum melting was increased through inserting fresh branches and measured by decompression solidification method and density method. Resistivity of pure aluminum casting was measured by means of the electrical resistance method, and physical model of resistivity measuring method was established. Combined with experimental data, the mathematical relationship between resistivity of pure aluminum casting and hydrogen content was derived. To further verify the feasibility of resistivity measurement model on the hydrogen content in aluminum melting, this paper also has carried on the hydrogen evolution experiment.