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1.
The influence of thermal history on the microstructures and properties of a multilayer stainless steel 410 (SS410) thin wall built by laser direct metal deposition (LDMD) process was investigated experimentally and numerically. Thermal history at two specified points in the substrate was measured by thermocouples during the process. A three-dimensional (3D) finite element model was developed to study the thermal history of the deposited material for the laser direct metal deposition of multilayer thin wall. The simulated and measured thermal history indicated that the absorption and loss of heat tended to be close to equilibrium when the deposited material reached a certain height during the LDMD process. Different microstructure regions were formed due to the different thermal history the material experienced. The hardness distribution along the height centerline of the thin wall was measured. The results indicated that thermal history had an important effect on the microstructure, and consequently on the final properties.  相似文献   

2.
The laser deposition of AISI316 powder blended with Cr3C2 over austenitic stainless steel plate was carried out as part of an investigation aimed at determining the feasibility of applying localized reinforcement to stainless steel components. The chromium carbide powder dissolved in the process to produce a range of carbides which reinforced and increased the hardness of the material. The results of optical microscope metallography and SEM/EDX and XRD analysis as well as microhardness measurements are reported. Surfaces produced by deposition of the powder blend were machine-ground and subjected to pin-on-disc and corrosion tests. The tests indicated an improvement to sliding wear resistance and a good resistance to salt spray and pitting corrosion conditions.  相似文献   

3.
Direct laser deposition (DLD) is an additive manufacturing process that builds up a part layer-by-layer by fusing metal powder to a solid substrate. A coaxial laser and powder delivery head is commonly used, and here a critical process variable is the standoff distance between the nozzle and the material deposition point. This contribution investigates the role of this variable and the effect that it has on the final part geometry. The experimental results show that good layer consistency can, in fact, be obtained with no movement of the substrate between layers for more than 20 layers, or 10 mm under tested conditions, and that poorer results are obtained by regular movement of the substrate by a badly chosen constant amount. A theoretical analysis of the situation establishes a method to estimate melt pool size using an analytically calculated temperature near the heat source. Based on this, simple heat and mass flow models are established to allow some of the results to be explained.  相似文献   

4.
The vacuum plasma spraying (VPS) process allows the production of thin solid oxide fuel cells (SOFCs) with low internal resistances. This enables the reduction of the cell operating temperature without a significant decrease in power density. Consequently, the long-term stability of the cells can be improved and low-cost materials can be used. Different material combinations and spray parameter variations were applied to develop thin-film SOFCs, which were plasma sprayed in a consecutive deposition process onto different porous metallic substrates. The use of Laval nozzles, which were developed at the German Aerospace Center (DLR), and the use of conical F4V standard nozzles enable the fabrication of thin gas tight yttria- and scandia-stabilized ZrO2 (YSZ and ScSZ) electrolyte layers and of porous electrode layers with high material deposition rates. The optimization of the VPS parameters has been supported by laser doppler anemometry (LDA) investigations. The development of the plasma-sprayed cells with a total thickness of approximately 100 μm requires an overall electrical and electrochemical characterization process of the single layers and of the completely plasma-sprayed cell assembly. The plasma-sprayed cell layers reveal high electrical conductivities. The plasma-sprayed cells show very good electrochemical performance and low internal resistances. Power densities of 300 to 400 mW/cm2 at low operating temperatures of 750 to 800 °C were achieved. These cells can be assembled to high performance SOFC stacks with active cell areas up to 400 cm2, which can be operated at reduced temperatures and good long-term stability.  相似文献   

5.
In order to protect C/C composites from oxidation, SiC-MoSi2 composite coating was synthesized by chemical vapor infiltration /reaction (CVI/CVR) technology. A porous Mo layer was prefabricated on SiC coated C/C composites, and then MoSi2 and SiC were subsequently prepared in a CVI /CVR process using methyltrichlorosilane (MTS) as precursor. The deposition and reaction mechanism of the MoSi2-SiC composite coating was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The oxidation behavior of SiC-MoSi2 coated specimens was tested. The results show that the porous Mo layer can be densified with SiC phase decomposed from MTS, and transformed into SiC-MoSi2 by reacting with MTS as well. A dense composite coating was prepared with optimized deposition parameters. The coated specimen exhibits a good oxidation resistance with a little mass loss of 1.25% after oxidation at 1500 °C for 80 h.  相似文献   

6.
Laser surface alloying technique was applied to fabricate a metallic porous coating on a solid NiTi shape memory alloy. By laser surface alloying a 40%TiH2-60%NiTi powder mixture on the surface of NiTi alloy using optimized laser process parameters, a porous but crack-free NiTi layer can be fabricated on the NiTi substrate. The porous coating is metallurgically bonded to the substrate NiTi alloy. The pores are uniformly distributed and are interconnected with each other in the coating. An average pore size of less than 10μm is achieved. The Ni content of the porous layer is much less than that of the original NiTi surface. The existence of the porous coating on the NiTi alloy causes a 37% reduction of the tensile strength and 55% reduction of the strain as compared with the NiTi alloy. Possible biomedical or other applications for this porous surface with good mechanical strength provided by the substrate are prospective.  相似文献   

7.
Laser aided direct metal/material deposition (DMD) process builds metallic parts layer-by-layer directly from the CAD representation. In general, the process uses powdered metal/materials fed into a melt-pool, creating fully dense parts. Success of this technology in the die and tool industry depends on the parts quality to be achieved. To obtain designed geometric dimensions and material properties, delicate control of the parameters such as laser power, spot diameter, traverse speed and powder mass flow rate is critical. In this paper, the dimensional and material characteristics of directed deposited H13 tool steel by CO2 laser are investigated for the DMD process with a feedback height control system. The relationships between DMD process variables and the product characteristics are analyzed using statistical techniques. The performance of the DMD process is examined with the material characteristics of hardness, porosity, microstructure, and composition.  相似文献   

8.
The internal void of cross wedge rolling (CWR) part can be treated as porous material due to their similar physical property and deformation characteristics. Aiming at the CWR process of aluminum alloy 7075 workpiece, the numerical simulation model for internal void was established by means of the rigid-plastic FEM method for the porous material. The relative density was used to research the influence of three primary parameters on the internal void in CWR process, including the forming angle α1, the stretching angle β and the area reduction ΔA. The experimental results show that the expansion of internal void occurs in the stretching zone, and the knifing zone just has a little influence on it. The stretching angle has a great influence on the internal void, while the area reduction has a small influence on it. The size of internal voids decreases with the increase of area reduction, stretching angle and forming angle. When designing the CWR tool geometry and operating conditions, to prevent the internal void, the area reduction is suggested to be 55%–65%, the stretching angle to be 8°–10°, and the forming angle to be 29°–32°.  相似文献   

9.
《CIRP Annals》2020,69(1):173-176
Using powder-based directed energy deposition (DED), composite materials can easily be produced by mixing powders. In this study, a foam stainless block is fabricated through DED by combining SUS316L and titanium-hydride (TiH2) powders together. Although TiH2 successfully foams the melt pool and leaves many pores inside the deposit, it is difficult to enhance the porosity rate because the porous structure is destroyed when the upper layer is deposited. This study demonstrates a laser power control and deposition trajectory that can be used to create a low-density porous structure and measures the compression strength of the fabricated block.  相似文献   

10.
In this work, electrostatic deposition was used to prepare porous lanthanum strontium manganite (LSM) films on a silicon substrate for cathode application in solid oxide fuel cells (SOFCs). The precursor solution was prepared by dissolving lanthanum nitrate hydrate, manganese nitrate hexahydrate and strontium chloride hexahydrate into a mixture of methanol and water. The morphology of the LSM film depended on process parameters such as substrate temperature, precursor flow rate, nozzle-substrate distance, and deposition time. The effect of heating temperature on the film’s crystal structure was investigated with X-ray diffraction in the heating temperature range of 700 °C to 900 °C. Porous LSM film was successfully prepared in the solution flow rate range of 2 l/min to 4.5 l/min, substrate temperatures of 127 °C to 330 °C, the nozzle-substrate distance range of 3 cm to 8 cm, and deposition times of 1 min to 16 min.  相似文献   

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