Influence of processing parameters of selective laser melting on high‐cycle and very‐high‐cycle fatigue behaviour of Ti‐6Al‐4V

Orthogonal experiment design together with the analysis of variance was used to examine the processing parameters (laser power, scan speed, layer thickness and hatch spacing) of selective laser melting (SLM) for superior properties of SLM parts, in which nine groups of specimens of Ti‐6Al‐4V were fabricated. The results clarify that the influence sequence of individual parameter on the porosity is laser power > hatch spacing > layer thickness > scan speed. Ultrasonic fatigue tests (20 kHz) were conducted for the SLMed specimens in high‐cycle fatigue (HCF) and very‐high‐cycle fatigue (VHCF) regimes. The S‐N data show that the fatigue strength is greatly affected by the porosity: the group with the smallest porosity percentage having the highest fatigue strength in HCF and VHCF regimes. Then, the tests on the validation group were performed to verify the optimal combination of SLM processing parameters. Moreover, the observations by scanning electron microscopy revealed that fatigue cracks initiate at lack‐of‐fusion defects in the cases of surface and internal crack initiation.     

Selective laser melting of AlSi10Mg alloy: Process optimisation and mechanical properties development

The influence of selective laser melting (SLM) process parameters (laser power, scan speed, scan spacing, and island size using a Concept Laser M2 system) on the porosity development in AlSi10Mg alloy builds has been investigated, using statistical design of experimental approach, correlated with the energy density model. A two-factor interaction model showed that the laser power, scan speed, and the interaction between the scan speed and scan spacing have the major influence on the porosity development in the builds. By driving the statistical method to minimise the porosity fraction, optimum process parameters were obtained. The optimum build parameters were validated, and subsequently used to build rod-shaped samples to assess the room temperature and high temperature (creep) mechanical properties. The samples produced using SLM showed better strength and elongation properties, compared to die cast Al-alloys of similar composition. Creep results showed better rupture life than cast alloy, with a good agreement with the Larson–Miller literature data for this alloy composition.     

Investigation on processing of ASTM A131 Eh36 high tensile strength steel using selective laser melting

ABSTRACT

In this paper, selective laser melting (SLM) technique was used to investigate the processing of EH36 high tensile strength steel commonly used in the shipbuilding applications. EH36 powder was produced according to ASTM A131 standards using gas atomisation process. SLM process parameters, including scanning speed and hatch spacing, were investigated to produce test specimens with high density. Parts were successfully built using SLM without cracks. Density tests were performed according to ASTM B962 standards. Light optical microscopy and scanning electron microscopy showed slight porosities and martensitic microstructure respectively. The study concluded that EH36 parts could be produced using SLM and this provided foundation work for the technical feasibility of fabricating high tensile strength steel components for the shipbuilding industry.     

Experimental Investigation on Selective Laser Melting of Bulk Net-Shape Pure Magnesium

In this study, bulk net-shape pure magnesium was fabricated by selective laser melting (SLM). Effects of Mg particle size and processing parameters on the properties of SLM specimens were investigated. The scan speed and laser power were optimized based on macro-observation of the forming process and resulted specimens. Through the comparison analysis of topology, density, and micro-hardness, it was found that the bulk magnesium specimen made of ?250 mesh powder showed better results than that made of ?400 mesh powder. The relative densities of both SLM specimens were over 95%, and their micro-hardness values were higher than that of as-cast magnesium. It was also revealed that the scanning time interval (STI), as a relatively new processing parameter, had an obvious effect on the properties of SLM bulk magnesium in terms of surface morphology, roughness, and micro-hardness.     

激光选区熔化316L不锈钢凝固特征与微观组织结构

对不同工艺参数下激光选区熔化(Selective Laser Melting, SLM)成形316L不锈钢微观组织结构进行表征,研究不同工艺参数下SLM成形316L不锈钢微观组织结构演化规律、单熔化道凝固特性。结果表明,SLM成形316L不锈钢具有跨尺度、非均质凝固组织特征,包括微米尺度柱状晶粒、小角晶界、熔池界面和纳米尺度亚结构。单熔化道的稳定成形是三维块体成形的基础,熔化道稳定性由激光工艺参数与金属粉体物理特性共同决定。不同的激光工艺参数显著影响SLM成形316L不锈钢微观组织结构,通过改变激光参数可实现微观组织结构的调控,在不同的激光逐层旋转角度下,SLM成形316L不锈钢晶粒尺寸随着扫描间距的增大而增大。强制定向热流使得外延生长机制主导凝固晶粒的生长,在不同的激光工艺参数下,沿增材方向的柱状晶粒形貌普遍存在。     

TiB2/AlSi10Mg激光选区熔化成形工艺研究

目的 针对TiB2/AlSi10Mg开展激光选区熔化成形研究,获得工艺参数影响规律并优化工艺参数.方法 采用正交试验法设计三因素四水平正交试验,进行TiB2/AlSi10Mg激光选区熔化成形,分别研究激光功率、扫描速度、扫描间距等3种工艺参数对TiB2/AlSi10Mg致密度和硬度的影响规律,分析激光能量密度对铝合金内...     

激光选区熔化成形工艺对304L不锈钢冲击韧性的影响

目的 了解激光选区熔化(SLM)成形工艺参数对304L不锈钢冲击韧性的影响,从而得到304L不锈钢的最佳成形工艺参数。方法 对激光功率300~340 W,激光扫描速度800~1 500 mm.s^?1条件下的激光选区熔化成形304L不锈钢开展冲击试验,通过表面硬度、微观组织及断口形貌观察对冲击韧性的影响规律进行分析。结果 SLM成形304L不锈钢微观组织为跨越熔池生长形成的不规则柱状晶粒,成形工艺参数对试样表面硬度影响不显著;随着激光功率的增大和激光扫描速度的降低,304L不锈钢断面致密程度提高,孔洞类缺陷尺寸减少且数量减少,冲击韧性增大,冲击功最大值为141.9 J。结论 基于冲击试验结果,在激光体能量密度为100~140 J/mm³的条件下,304L冲击韧性稳定在138 J左右,为SLM成形304L材料的最佳成形参数区间。     

Influences of processing parameters and heat treatment on microstructure and mechanical behavior of Ti-6Al-4V fabricated using selective laser melting

Selective laser melting (SLM) has provided an alternative to the conventional fabrication techniques for Ti-6Al-4V alloy parts because of its flexibility and ease in creating complex features. Therefore, this study investigated the effects of the process parameters and heat treatment on the microstructure and mechanical properties of Ti-6Al-4V fabricated using SLM. The influences of various process parameters on the relative density, tensile properties, impact toughness, and hardness of Ti-6Al-4V alloy parts were studied. By employing parameter optimization, a high-density high-strength Ti-6Al-4V alloy was fabricated by SLM. A relative density of 99.45%, a tensile strength of 1 188 MPa, and an elongation to failure of 9.5% were achieved for the SLM-fabricated Ti-6Al-4V alloy with optimized parameters. The effects of annealing and solution aging heat treatment on the mechanical properties, phase composition, and microstructure of the SLM-fabricated Ti-6Al-4V alloy were also studied. The ductility of the heat-treated Ti-6Al-4V alloy was improved. By applying a heat treatment at 850 ℃ for 2 h, followed by furnace cooling, the elongation to failure and impact toughness were found to be increased from 9.5% to 12.5%, and from 24.13 J/cm² to 47.51 J/cm², respectively.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-022-00389-y     

激光选区熔化成形18Ni300工艺参数优化及组织性能分析

目的 研究工艺参数对18Ni300马氏体时效钢激光选区熔化成形质量的影响。方法 采用正交试验方法研究激光功率和扫描速度对18Ni300相对致密度、硬度的影响,得到铺层层厚0.03 mm、扫描间距0.1 mm时为18Ni300最佳工艺参数,并对最佳工艺参数成形的试样进行组织及力学性能表征。结果 激光功率为230 W、扫描速度为1100 mm/s时,试样硬度为44.7HRC,相对致密度为99.98%,相对最优;材料鱼鳞状组织均匀致密,气孔较少,部分柱状晶沿熔池边界呈外延生长,熔池边界细小晶粒取向基本随机,熔池内部分粗大柱状晶有一定的择优性。结论 最优参数情况下SLM成形的18Ni300主要由体积分数为99.8%的马氏体和0.2%的残余奥氏体组成;试样的力学性能有明显的各向异性,拉伸断口有明显的颈缩,断裂形式为韧性断裂,纤维区可以看到明显的等轴大韧窝、孔洞,并伴有明显的撕裂特征。     

The effects of laser machining parameters on roughness and contact angle for boron carbide ceramic surface

Hydrophobicity or Hydrophilicity properties of boron carbide ceramic surface can be controlled by manipulating the roughness of the surface and thus the contact angle. In this study, the wettability of the boron carbide surface was manipulated by laser with different parameters. The contact angle was measured at 9^th seconds after the droplet was dropped onto the laser-treated surface. Also, the change in contact angle in the first 9 seconds after the droplet was dropped was examined. For a more hydrophobic surface, it was aimed to have the largest contact angle at 9^th seconds after the droplet was dropped and the smallest change with time in contact angle. The effects of laser scan speed, power, frequency and overlap rate on the contact angle of the treated surface were investigated using the Taguchi method. It was calculated to what extent each examined parameter affected the result. The effectiveness rates of the two most effective parameters which were scan speed and overlap rate were obtained. Since the results of the verification tests performed to confirm the results obtained are quite compatible with the results predicted by the Taguchi method, the Taguchi method can be regarded as a reliable method in optimizing laser parameters.     

An intelligent parameter selection system for the direct metal laser sintering process

As one of the promising Rapid Prototyping (RP) processes, the Direct Metal Laser Sintering (DMLS) technique is capable of building prototype parts by depositing and melting metal powders layer by layer. Metal powder can be melted directly to build functional prototype tools. During fabrication, four important resulting properties of interest to the users are: the processing time, mechanical properties, geometric accuracy and surface roughness. By adjusting an identified set of process parameters, these properties can be properly controlled. The process parameters involve: the laser scan speed, laser power, hatch density, layer thickness and scan path. But the relationships between these parameters and their resulting properties are quite complicated. In many cases, the effects of different parameters on the resulting properties contradict one another. In this paper, an intelligent system to assist the RP user to choose the optimal parameter settings based on different user requirements is presented. For the accurate prediction of the resulting properties of the laser-sintered metal parts, a method based on the feed-forward neural network (NN) with backpropagation (BP) learning algorithm is described. Through experiments, some input–output data pairs have been identified. After continuous training by using the data pairs, this NN constructs a good mapping relationship between the process parameters and their resulting properties. The system developed can determine the most suitable parameter settings containing the process parameters and predict resulting properties from the database built based on different process requirements automatically. It is very useful to RP users for saving material cost and reducing processing time.     

Densification and microstructural evaluation during laser sintering of M2 high speed steel powder

Abstract

In the present work, the densification and microstructure of M2 high speed steel powder processed by direct laser sintering method was studied. Test specimens were produced using a 200 W continuous wave CO₂ laser beam at different scan rates ranging from 50 to 175 mm s^?1. The building process was performed under argon and nitrogen atmospheres in order to evaluate the role of sintering atmosphere. It was found that the sintered density strongly depends on the laser scan rate and thus on the duration time of the laser beam on the surface of the powder particles. Generally, with a decrease in the scan rate higher densification was obtained. However, formation of large cracks and delamination of the sintered layers is feasible at low scan rates. The results also demonstrated that sintering under argon atmosphere yields better densification compared to a nitrogen atmosphere, in particular at higher scan rates. The microstructure of laser sintered parts consisted of large and elongated pores parallel to the building direction. The metal matrix structure was found to be heterogeneous, i.e. carbon rich austenite was formed due to carbon segregation. This structure consisted of fine cellulars or dendrites of martensite and retained austenite. This article describes the influence of manufacturing parameters on the densification of laser sintered M2 high speed steel powder. The microstructural features of the processed parts are also addressed.     

Finite element simulation of the temperature and stress fields in single layers built without-support in selective laser melting

Overhanging and floating layers which are introduced during the build in selective laser melting (SLM) process are usually associated with high temperature gradients and thermal stresses. As there is no underlying solid material, less heat is dissipated to the powder bed and the melted layer is free to deform resulting undesired effects such as shrinkage and crack. This study uses three-dimensional finite element simulation to investigate the temperature and stress fields in single 316L stainless steel layers built on the powder bed without support in SLM. A non-linear transient model based on sequentially coupled thermo-mechanical field analysis code was developed in ANSYS parametric design language (APDL). It is found that the predicted length of the melt pool increases at higher scan speed while both width and depth of the melt pool decreases. The cyclic melting and cooling rates in the scanned tracks result high VonMises stresses in the consolidated tracks of the layer.     

On direct laser deposited Hastelloy X: dimension,surface finish,microstructure and mechanical properties

Abstract

For the first time, the influence of laser power, scan speed, scan spacing and nominal laser power density on the tensile properties, dimensional accuracy, surface roughness, number of cracks and top surface concavity of samples of Hastelloy X manufactured using a laser powder bed facility, has been assessed systematically on three-dimensional samples. It has been found that the nominal laser power density is the dominant factor, but the influence of scan spacing and scan speed can sometimes be significant. Density of >99·5% can be obtained using most conditions. Cracks are observed at corners of the samples. An optimised process window can be derived from the above systematic analysis under which the component can be built smoothly, with good surface finish and dimensional accuracy, consistent mechanical properties and the properties are comparable with those of forged products.     

铝合金交叉筋壁板激光热诱导锥面成形边缘效应的研究

目的 减小铝合金交叉筋壁板激光热诱导锥面成形过程中的边缘效应。方法 利用有限元分析方法,通过对扫描线温度、应力应变分布的分析,得到边缘效应产生的原因;研究激光功率、扫描速度、扫描次数对边缘效应的影响,选择合适参数,采用激光热诱导成形系统,对5A06铝合金交叉筋壁板进行锥面成形试验,并用扫描仪检测成形精度。结果 边缘效应随着扫描速度的减小、激光的功率变大而减小,与单次扫描相比,两次扫描能有效减小边缘效应。试验证明,扫描速度对边缘效应的影响最大,将扫描速度保持在30 mm/s以下,调整激光功率和扫描速度控制能量密度,在保证弯曲角度的同时,也能较好抑制边缘效应。     

Effects of processing parameters on direct laser sintering of multicomponent Cu based metal powder

Abstract

Direct laser sintering of a multicomponent Cu based metal powder was successfully processed through the mechanism of liquid phase sintering with partial melting of the powder. The effects of processing parameters such as laser power, scan speed, scan line spacing and layer thickness on the densification and microstructural evolution of the laser sintered powder were investigated. It was found that with increasing laser power or decreasing scan speed, the density of the sintered parts increased and the microstructures became denser. However, the combination of higher laser powers (>400 W) and higher scan speeds (≥0·06 ms^?1) gave rise to 'balling' effect. A successive transition from discontinuous scan tracks to coherently joined ones occurs with decreasing scan line spacing. Lowering the thickness of the powder layer promises an improvement in bonding coherence between sintered layers. A single factor termed 'energy density by volume' is defined to evaluate the combined effect of various processing parameters on the density of laser sintered powder. With increasing the energy density by volume up to ～0·16 kJ mm^?3, the densification rate is relatively high. However, with intensifying the energy density over ～0·23 kJ mm^?3, the mechanism of particle bonding may change into full melting/solidification, leading to a decrease in the sintered density.     

Simulation and experiment of curve irradiated laser bending process of titanium alloy sheet

Abstract

Laser bending along a curve scanning path is a complex 3D forming process. To analyse the deformation behaviour of the process and the effect of process parameters on the bending angle of sheets, numerical simulation becomes indispensable. In this paper, non-linear transient heat transfer and dynamic structural computational models including thermal mechanical coupling analysis, in which the temperature dependence of the thermal and mechanical properties of the material are taken into account, have been developed. The temperature, stress, and strain fields as well as the effect of process parameters on the bending angle were calculated on the basis of models using the finite element method. Meanwhile, an experimental parameter investigation was also carried out. The results showed that, compared with the linear laser bending, curve irradiated laser bending has a significant reduction of the bending angle and the bending angle decreases with increasing path curvature. The bending angle increases with increasing laser power and decreasing spot diameter, and decreases roughly with decreasing scanning velocity. Good correlation was found between the numerically simulated results and the experimental data.     

Effects of processing parameters on tensile properties of selective laser melted 304 stainless steel

Selective laser melting (SLM) technology based on powder bed has been used to manufacture 304 stainless steel samples. The effects of slice thickness, overlap rate, building direction and hatch angle on tensile properties of SLMed 304 stainless steel samples are investigated. It is found that tensile properties of SLMed 304 stainless steel are independent of slice thickness and overlap rate, but increase slowly with increasing interval number of deposited layers. The hatch angle of 105° with the maximum interval number of deposited layers and vertical building direction are preferred to get excellent tensile properties. Importantly, all the SLMed samples feature much higher σ_0.2/UTS values of nearly 0.8. The tensile strengths and ductility of SLMed samples at proper parameters are higher than those of the wrought 304 stainless steel.     

扫描间隙对激光粉床熔融GH4169合金微观组织及硬度的影响

目的 研究相同激光功率、扫描速度及粉层厚度条件下,激光粉床熔融GH4169合金微观组织、硬度及密度在不同扫描间隙条件下的演变规律.方法 采用激光粉床熔融设备制备了GH4169合金试样,通过扫描电子显微镜对微观组织进行了观察,采用硬度仪测量了试样硬度,基于阿基米德原理测量了试样密度.结果 随着扫描间隙的增加,激光粉床熔融...     

On selective laser melting of ultra high carbon steel: Effect of scan speed and post heat treatment

Selective laser melting is a laser‐based additive manufacturing process applying layer manufacturing technology and is used to produce dense parts from metallic powders. The application of selective laser melting on carbon steels is still limited due to difficulties arising from carbon content. This experimental investigation aims at gaining an understanding of the application of the process on ultra high carbon steel, which is a special alloy with remarkable structural properties suitable for different industrial applications. The feedstock ultra high carbon steel (2.1% C) powder, 20 μm to 106 μm was prepared by water atomizing technique. This powder was used for the selective laser melting to build specimens 10×10×40 mm in dimensions. To decrease the thermal stresses during layer by layer building, laser scanning was done through 5×5 mm random island patterns while layer thickness was 30 μm. Laser beam diameter, maximum power output, layer thickness and scan speed range were 0.2 mm, 100 W, 30 μm and 50–200 mm/s respectively. The process was done inside high purity nitrogen environment, with less than 0.5% oxygen content. The results illustrate the influence of scan speed from 50 to 200 mm/s on product geometry and dimensions, surface roughness, internal porosity and cracks, microstructure and surface hardness. The effect of post heat treatment by heating and holding for one hour (annealing) at different temperatures of 700°C, 750°C, 950°C is studied. The results indicate that selective laser melting is able to produce near to 95% density of ultra high carbon steel parts with acceptable geometry and surface quality. Porosity cracks, and microstructure formed during the process could be controlled through proper selection of process parameters and post heat treatment. Industrial ultra high carbon steel products can be rapidly fabricated by selective laser melting.