查看更多>>摘要：This paper addresses the effect of the post-process heat treatments on the microstructure and fatigue crack growth behaviour of the functionally graded (FG) laser powder bed fusion (L-PBF) Inconel 718 (IN718) superalloy. Sets of samples were additively manufactured (AM) altering the process parameters, namely the laser power, the laser scanning speed, layer thickness, hatch distance, and beam distribution function, resulting in distinctly different microstructures. Two categories of samples underwent heat treatment (HT) and hot isostatic pressing followed by HT (HIP+HT), while one category was kept in the as-processed (AP) condition to reveal the effects of the post-treatments. Additionally, to study the effect of microstructural anisotropy, samples were printed in horizontal (H) and vertical (V) building directions. To better understand the behaviour of the FG materials, non-graded (NG) L-PBF samples and wrought material were investigated as references. Significant variations in terms of porosity, grain size and elongation, crystallographic texture, and content of the strengthening precipitates or detrimental phases were found in different AM groups. The fatigue behaviour of the NG and FG materials was also studied by conducting three-point bending tests. Findings in terms of the role of different microstructures on the fatigue-crack initiation and fatigue crack growth rate are presented and discussed for all samples. The study demonstrated that heat treatments can enhance the damage tolerance of L-PBF IN718 to the level of wrought material. Interestingly, the effect of the roughness induced crack closure was found to be a function of build orientation, especially in the low stress ratio regime.
Ferreira, Andre A.Emadinia, OmidAmaral, Rui L.Cruz, Joao M....
13页
查看更多>>摘要：The direct laser deposition process successfully produced a bulk material by mixing 50% Inconel 625 powders (M625) with 50% AISI 431 steel powders (M42C). The properties of this new material, such as tensile strength and wear resistance, were evaluated. The microstructure was also analysed using scanning electron microscopy. Moreover, the formation of defects and second phases in the bulk material were investigated by applying a tomography analysis. M625-M42C bulk material shows tensile strength and abrasive wear behaviour similar to Inconel 625 alloy, suggesting a potential replacement material for the more expensive Inconel 625. This study is focused on an innovative material, which had not yet been produced as a bulk, allowing the evaluation of the mechanical and metallurgical characteristics promoted by this mixture of powders. In addition, this deposition methodology seems very interesting for cladding or repair objectives since the failure did not happen at the transition interface between deposited bulk and substrate.
McGregor, Davis J.V. Bimrose, MilesTawfick, SamehKing, William P....
10页
查看更多>>摘要：Additive manufacturing (AM) can produce complex geometries, resulting in features that can be hidden or obscured, and the measurement of these features is important for many applications. X-ray computed tomography (CT) is the only non-destructive inspection technique capable of measuring internal features that are inaccessible to optical or tactile measurements; however, batch processing of CT data can be challenging and time consuming. There is a need to develop efficient CT measurement strategies to better understand how the accuracy of internal geometries varies across different parts, processes, and materials. This study presents an automated method for batch CT metrology using open-source software, and investigates 48 nozzle parts made using 11 polymer materials and 3 AM processes. The nozzles have features critical to performance, including internal channels whose measurement would otherwise require destructive evaluation. The parts are measured using CT and the data is automatically processed, resulting in over 1000 measurements per part. The deformations that occur during manufacturing result in highly nonuniform variability within the parts, and features have significantly different accuracies depending on whether the features are located on the interior or exterior of the part. Part-to-part variability is low within a batch of parts made from a single material, generally within 35 mu m. However, part variability changes significantly between materials, even when the parts are made using the same process. The research demonstrates measurement results and insights enabled by large batch CT metrology of AM parts with internal features, as well as the need to monitor part-to-part variability.
查看更多>>摘要：The combination of light metals (aluminum, magnesium and titanium) and innovative casting processes provides cost-effective technologies to produce lightweight components and systems for many industrial applications. This article provides a comprehensive and yet critical review of light alloy development for cast components used in lightweight and high-performance structural and propulsion applications. It also summarized some latest process innovations in gravity casting, high pressure die casting, and low pressure casting, to overcome some fundamental issues related to defect formation in casting processes. Emerging casting processes developed in the last twenty years, such as semisolid processing, squeeze casting, ablation casting, bimetallic overcasting, and diffusion solidification processing, are discussed for further development. Recent advances in casting simulation and the concept of Integrated Computational Materials Engineering (ICME) are summarized for casting applications. Finally, future perspectives in light alloy development (including green alloys, high entropy alloys and metal matric composites), process innovations (such as high integrity casting, multi-material manufacturing and additive manufacturing), and ICME development are presented to stimulate further research and sustainable development in this important field of metals processing technology.
查看更多>>摘要：This study reported a strategy of three-stage heat treatment to simultaneously improve yield strength (YS), ultimate tensile strength (UTS) and elongation (EL) of laser melting deposited (LMDed) Ti-6Al-4V titanium alloy. After the three-stage heat treatment, the basketweave microstructure consisting of acicular alpha laths in the as-built sample was transformed to a multiscale-alpha microstructure consisting of the coarse-plate alpha, fine-plate alpha and ultrafine alpha in the heat-treated sample. The effect of microstructure on the tensile properties was revealed via in-situ tensile test combined with the analysis of the deformation and fracture mechanism. Although the coarse-plate alpha in heat-treated sample is larger than the acicular alpha in as-built sample, the combination of multiscale alpha grains with a certain relative content aroused an increment of the YS from 879 +/- 28 MPa in as-built sample to 973 +/- 9 MPa in heat-treated sample. The good deformation compatibility among the multiscale alpha grains impeded the crack propagation effectively, which resulted in the improvement of the EL from 14 +/- 2% to 16 +/- 1%. Furthermore, the improvement of the EL enhanced the dislocation multiplication and strain hardening in the multiscale alpha microstructure to induce the increment of the UTS from 945 +/- 40 MPa to 1092 +/- 20 MPa. The results could provide a guidance for tailoring microstructure and improving the strength and ductility of additive manufacturing titanium alloy.
查看更多>>摘要：Existing ploughing-based process damping models oriented for the cutting processes did not consider two important factors, i.e. the dead metal zone (DMZ) in front of the rounded cutting edge and the material elastic recovery rate under the clearance face, and thus, they cannot exactly detect the underlying mechanism of process damping in the cutting processes with small cutters. This article systematically investigates the generation mechanism of cutting process damping for small cutters, and proves that the DMZ and the elastic recovery rate have combined contribution to the process damping of small cutters' cutting. It is theoretically found that in contrast to the full elastic recovery assumed in the macro cutting processes, the material under the cutter's clearance face is partially recovered in the cutting processes with small cutters, due to the relatively high proportion of plastic deformation. The actual recovery height is numerically calibrated based on the ideal plastic assumption of the stress-strain relationship. Expressions of the statically and dynamically indented areas, which are required for deriving process damping model, are analytically formulated as the functions of the DMZ and the actual recovery height since they greatly change the indentation boundaries between the rounded cutting edge and the clearance face. Above derivations are then utilized to derive the expressions of dynamic cutting forces, and subsequently, the process damping effect is considered to analyze the milling stability. Finally, a series of milling tests with small cutter prove the reasonability of the proposed process damping model.
查看更多>>摘要：In this work, laser metal deposition (LMD) technique was applied to fabricate SiCp/AlSi10Mg composites. Innovatively, the effect of SiCp of different scale (micron, submicron and nano scale) on the microstructure and mechanical properties was studied. With the decrease of SiCp size, the reaction between SiC and aluminum matrix was more intense, and the volume fraction of Si precipitates and grain boundary Al-Si eutectic phase increased. Few micro-SiCp and agglomerated nano-SiCp were all unevenly distributed in the aluminum matrix, which caused the bimodal distribution of grain size in varying degrees. The mechanisms of defect formation, phases evolution and mechanical property enhancement were also discussed. Due to the agglomeration of nano-SiCp and its decomposition under laser irradiation, the seriously uneven microstructure of nano-SiCp/AlSi10Mg limited the mechanical properties. Moreover, the addition of SiCp increased the Marangoni flow instability of molten pool, leading to the high porosity and reducing the tensile strength of composites, which was more prominent in the samples containing micron and nano SiCp. Submicron-SiCp/AlSi10Mg presented uniform equiaxed crystals and the best comprehensive mechanical properties (microhardness 118.37HV, wear rate 1.60 x10(-3) mm3N- 1m- 1 and UTS 269.08 MPa). Based on the experimental results, adding multi-scale reinforcements will be more conducive to the performance optimization of composites. This study provides theoretical guidance for the engineering application of SiCp/Al composites.
查看更多>>摘要：Incremental Sheet Forming (ISF) is a rapid prototyping based die-less forming process. In this process, curved end based forming tool deforms the sheet by a user-defined Numerical Control (NC) toolpath. This paper focuses on the formability response of the sheet stretching during the ISF process. The stretching in the axial direction primarily depends on the wall angle of the profile and the incremental depth. During the die-less deformation of the constant wall angle based geometries (truncated cone or pyramid); with each increment uniform stretching of the sheet occurs. However, in case of the variable wall angle-based geometries (curvilinear wall profiles), higher sheet stretching occurs at steep wall angles. Adaptive increment based strategy has been developed for the die-less forming of the curvilinear geometries so that uniform sheet stretching in the axial direction can be sustained. The response of the developed strategy towards sheet formability, equivalent stress and strain distribution has been investigated in this study. For implementation, the toolpath for the Finite Element Analysis (FEA) simu-lations (ABAQUS (R)) and experimentation has been defined using an in-house developed Computer-Aided Manufacturing (CAM) module. Experimental and simulation results exhibit the improvement in the sheet thickness and stress distribution.
Roula, Ahmed MehdiMocellin, KatiaTraphoner, HeinrichTekkaya, A. Erman...
12页
查看更多>>摘要：Flow forming is an incremental sheet forming (ISF) process during which a sheet metal is compressed and stretched multiple times by means of one or multiple rotating roller tools. The local tool-workpiece contact zone evolves during the entire process. The necking phenomenon, which corresponds to an uncontrolled thinning of the part wall, is introduced. This phenomenon represents a major issue for ISF processes. A review of the state-ofthe-art about ISF processes shows that most studies do not consider the loading path complexity when choosing the mechanical characterization test and its associated constitutive model. Besides, the prediction of necking occurring during sheet flow forming is poorly studied in the literature. In this paper, a finite element analysis (FEA) using the FORGE (R) software enables a detailed understanding of the loading path (strain and stress states) prevailing during the flow forming operation. Based on the peculiarities of this loading path, different mechanical tests associated with adequate constitutive models are chosen to characterize the material behavior. The ability of each constitutive model used within the FE approach to predict necking is then assessed. Results show that the best prediction of a geometry exhibiting necking issues is obtained with the cyclic in-plane torsion test (ITT) associated with its calibrated isotropic - kinematic hardening model. These results suggest that the behavior characterization under cyclic shear loadings is relevant. Using a simple tensile test with associated power-law provides a faster and conservative necking prediction.
NSTL
Elsevier