Study ofof weld morphology on thin Hastelloy C-276 sheet of Study weld morphology on thin Hastelloy C-276 sheet of pulsed laser welding pulsed laser welding

AbstractIn this paper, it was indicated that the laser welding was well suitable to joining of thin Hastelloy C-276 sheet (0.5 mm thickness), and also the fine grain were observed in welding zone with invisible HAZ (heat affected zone). In addition, the smooth weld joint could be controlled by means of the laser parameter adjustment. On the other hand, it’s proposed that Ni–Cr–Co–Mo and austenite CFe15.1 cubic face-centered crystal structure should be existed in as-received and welding samples, as well as the cause of FWHM (Full Width at Half Maximum) widened and peak offset of joined samples were analyzed

Analytical model for nonlinear vibration of flexible rotor system

An analytical model is proposed to analyze a series of typical nonlinear behaviors of flexible rotor system, such as resonance, oscillation, whirl and whip. The model is constructed by introducing a defined nonlinear scale factor ε, nonlinear stiffness and nonlinear damping. Based on multi-scale method, the analytical solutions of steady-state and transient-state are derived, and the nonlinear natural frequency and Frequency Response Equation (FRE) are obtained. A transient time scale factor t1 is defined to reflect the transient-state influence on steady-state solution. The experimental result also verifies the rationality and validity of the analytical model and the analytical solutions

Laser Rapid Manufacturing of Stainless Steel 316L/Inconel718 Functionally Graded Materials: Microstructure Evolution and Mechanical Properties

Two patterns of functionally graded materials (FGMs) were successfully fabricated whose compositions gradually varied from 100% stainless steel 316L to 100% Inconel718 superalloy using laser engineered net shaping process. The microstructure characterization, composition analysis, and microhardness along the graded direction were investigated. The comparison revealed the distinctions in solidification behavior, microstructure evolution of two patterns. In the end, the abrasive wear resistance of the material was investigated

The Effects of Pulse Parameters on Weld Geometry and Microstructure of a Pulsed Laser Welding Ni-Base Alloy Thin Sheet with Filler Wire

Due to its excellent resistance to corrosive environments and its superior mechanical properties, the Ni-based Hastelloy C-276 alloy was chosen as the material of the stator and rotor cans of a nuclear main pump. In the present work, the Hastelloy C-276 thin sheet 0.5 mm in thickness was welded with filler wire by a pulsed laser. The results indicated that the weld pool geometry and microstructure were significantly affected by the duty ratio, which was determined by the pulse duration and repetition rate under a certain heat input. The fusion zone area was mainly affected by the duty ratio, and the relationship was given by a quadratic polynomial equation. The increase in the duty ratio coarsened the grain size, but did not obviously affect microhardness. The weld geometry and base metal dilution rate was manipulated by controlling pulsed parameters without causing significant change to the performance of the weld. However, it should be noted that, with a larger duty ratio, the partial molten zone is a potential weakness of the weld

Effect of layer thickness on crack suppression in laser engineered net shaping of ceramic structure

Laser engineered net shaping (LENS) has been innovatively applied to direct additive manufacturing of ceramics in recent years. Using this technique, neat ceramic powder without binders can be completely melted and solidified, obtaining compact and high-purity netshaped ceramic structures rapidly. However, existing LENS process for fabricating ceramics suffers from cracking defect due to intrinsic brittleness of ceramics and high temperature gradient in deposition. Here we reported the effect of layer thickness on cracking in LENS of ceramic structure, which indicates that cracks can be effectively suppressed by reasonably optimizing process parameters. Pure Al2O3 structures with different layer thickness were fabricated by LENS system and their microstructure were analyzed to figure out the crack suppressing mechanism of optimizing layer thickness. Results indicate that cracks of fabricated specimen decreases obviously with the increase of layer thickness. Reduction of grain boundary defects and increase of transverse grain ratio are the main mechanism of crack suppression.Published versio

Synthesis of network reduced graphene oxide in polystyrene matrix by a two-step reduction method for superior conductivity of the composite

Polymer/graphene composites have attracted much attention due to their unique organic-inorganic hybrid structure and exceptional properties. In this paper, we report the synthesis of polystyrene/reduced graphene oxide (PS/r-GO) composites by a two-step in situ reduction technique, which consists of a hydrazine hydrate reduction and a subsequent thermal reduction at 200 degrees C for 12 h. The structure and micromorphology of PS/r-GO composites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis. The results show that the GO can be efficiently reduced by the two-step in situ reduction method, and the r-GO sheets are well dispersed and ultimately form a continuous network structure in the polymer matrix. PS/r-GO composite films (5 wt% GO) are prepared by the hot press molding method, possessing a conductivity as high as 22.68 S m(-1). The superior conductivity arises from the high reduction degree of GO and its high dispersion and the formation of a network structure in the polymer matrix. These polymer/r-GO composites are expected to be applied in multiple electric devices. The techniques for preparing polymer/r-GO composite films could be further extended to other similar systems

Microstructure and Wear Property of ZrO2-Added NiCrAlY Prepared by Ultrasonic-Assisted Direct Laser Deposition

For improving the wear properties of NiCrAlY, the 10 wt %, 20 wt % and 30 wt % ZrO2-added NiCrAlY samples were prepared by ultrasonic-assisted direct laser deposition, respectively. The results showed that the ultrasonic-assisted direct laser deposition can realize the ZrO2-added NiCrAlY preparation. Furthermore, due to the cavitation effect and agitation of the ultrasound in the molten pool, ultrasonic-assisted could make the upper surface of the samples smoother and flatter, and it also improved the microstructural homogeneity. The microstructure was mainly composed of columnar dendrites, and most of ZrO2 particles were located in the intergranular regions. The principal phase constituents were found to contain γ-Ni and t-NiZr2, and the amorphous (Ni, Zr) intermetallic phase generated, because of more rapid solidification after ultrasound assisted. The microhardness was improved slightly with the increase of ZrO2 contents, rising from 407.9 HV (10% ZrO2) to 420.4 HV (30% ZrO2). Correspondingly, wear mass loss was decreased with the maximum drop 22.7% of 30% ZrO2 compared to that of 10% ZrO2, and wear mechanisms were mainly abrasive wear with slightly adhesive wear. After applying ultrasound, the oxide islands in samples disappeared, and more ceramic particles were retained. Thus, the hardness and wear performance of the samples were improved

Super Hydrophobic Mesoporous Silica With Anchored Methyl Groups On The Surface by a One-Step Synthesis Without Surfactant Template

Mesoporous silicas with methyl groups anchored on the pore wall by covalent bonds were prepared using polymethylhydrosiloxane and tetraethylorthosilicate as silica sources via a one-step synthesis approach. No surfactants were introduced in the synthesis and the pore size can be tuned readily by adjusting the amount of polymethylhydrosiloxane used in the synthesis. Generally, such a hybrid structure is achieved by two steps: synthesizing mesoporous silica substrate using surfactant as template and grafting the pore wall surface with an organic silane. The synthesis in this study is based on a nonsurfactant route and thus is distinctly different from other synthesis routes in reaction mechanism. The obtained silicas exhibit superior hydrophobicity: their contact angles with water are all beyond 150 degrees because the surface is covered by methyl groups. The hydrophobic silicas can be used as efficient adsorbents for cleaning up spills of oil or organic chemicals on the water surface and toxic organic pollutants in water, such as alkylphenols, at very low concentrations