Search

Ti-6Al-4V is an α+β phase Ti alloy which is widely used because of its microstructural features. Complex three-dimensional (3-D) parts can be created directly from computer models by selectively melting (SLM) the metal powder using additive manufacturing (AM) technology. In this present work hot corrosion experiments were performed on the selective laser melted sample and as received sample in laboratory air and NaCl environment at 600°C for 50 cycles. The parabolic rate constants were calculated for different environments from the thermogravimetric data obtained for the samples and they show that corrosion rate is minimum in laboratory air and maximum for SLM sample in NaCl environment due to the presence of gaseous chlorides. The microstructure morphologies and the oxide scales formed upon hot corrosion was characterized by optical and scanning electron microscope (SEM) while the constituents were determined with energy-dispersive X-ray (EDX) analysis to understand the corrosion mechanisms. The high corrosion rate of SLM compared to the as-received sample was studied by analysing the area percentage of porosity. Since helicopters and planes are used in sea areas this work is practically important in the aeronautical field. [ABSTRACT FROM AUTHOR]

To improve the performance of selective laser melted 316L stainless steel components the effects of laser power and heat treatment methods on the surface morphology and mechanical properties of the formed parts are studied. The research results show that with the increase of the laser power, the surface morphology quality and mechanical properties of the formed parts initially increase and then decrease. When the laser power is 170 W a formed part with better surface morphology and mechanical properties can be obtained. The grain size and elongation can be increased by heat treating the formed part. Among them, the air cooling method can obtain better mechanical properties than the water cooling method. The combination of laser power and heat treatment is a promising method to improve the performance of selected laser melted 316L stainless steel parts. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) is an innovative additive manufacturing (AM) technique that starts with a three-dimensional (3-D) computer-aided design (CAD) model and uses high energy laser beams to selectively melt and fuse thin layers of metal powder to simplify the design and manufacture of complex components. The current research compares the wear performance of SLM processed AlSi10Mg alloy to that of conventionally cast AlSi10Mg alloy at both ambient and elevated temperatures. A pin on disk tribometer with EN31 alloy steel as the counter body was used in the dry sliding wear experiment. The SLM AlSi10Mg alloy sample showed higher wear resistance at both testing conditions as compared to cast sample owing to the significant enhancement in hardness via microstructural refinement of SLM technology. [ABSTRACT FROM AUTHOR]

A periodic open-cell AlSi10Mg alloy with a porosity of 54% was prepared using selective laser melting (SLM), and the microstructure, mechanical properties and deformation behaviour during compression were studied. The eutectic Si precipitated in the network. The average surface roughness along the building direction was 8.96 µm and along the vertical building direction was 4.22 µm. This finding could be attributed to the fact that there were more unmelted particles attached to the building direction than to the vertical building direction. The open cell AlSi10Mg alloy designed in this study has typical elastoplastic deformation, collapse and densification stages during the compression deformation process; however, its joints have not fractured during the compression deformation process due to the high compressive strength. All of the pillars connected at the joint fractured after compression, ductile fracture occurred. [ABSTRACT FROM AUTHOR]

AlSi10Mg aluminium alloy is mostly produced using selective laser melting (SLM) technique which is widely adopted in automotive and aerospace heat exchangers. Along with mechanical performance, vibrational behavior of selective laser melted parts becomes a paramount to enhance the part quality and repeatability of the process. This paper investigates the effect of SLM process parameters on the vibrational behavior of AlSi10Mg to enhance the damping capacity. The range for laser power, scanning speed, hatch spacing were selected as 290 to 370 W, 1.0 to 2.2 m/s and 50 to 150 µm, respectively. The vibrational characteristics such as natural frequency and modal damping were measured using fast Fourier transform (FFT) analyser and were compared with numerical analyses. Regression models were developed using response surface methodology (RSM). The natural frequency and damping were affected mostly by the scan speed. Based on the results obtained, a maximum modal damping of 1.0348% was achieved at 290 W laser power, 2.2 m/s scan speed and 150 µm hatch spacing. [ABSTRACT FROM AUTHOR]

Graphene/Ti6Al4V matrix composite powder was prepared by vacuum ball milling. Thereafter a graphene/Ti6Al4V matrix composite was prepared by selective laser melting (SLM) using a Yb fibre laser. With the increase of milling time, the distribution of graphene was gradually homogeneous. Increasing the ball to powder ratio improved the dispersion of graphene, but the Ti6Al4V powders were deformed when the ball to powder ratio exceeded 8:1. The graphene was gradually dispersed evenly with the increase of the ball milling rotational speed. The optimum parameters of ball milling time, ball to powder ratio, ball milling rotational speed were 3 hours, 8:1, 240 rpm. After optimizing SLM processes, when the laser power was 250 W, the point distance was 65 µm, and the exposure time was 60 µs, the graphene/Ti6Al4V matrix composite was prepared. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) is an advanced metal additive manufacturing (AM) process used in the automobile, aerospace, and electronics industry to manufacture complex components. During the printing process, the meltpool is created, which controls the build parts' microstructure and quality. So, it is crucial to determine the meltpool size and establish the effect of process parameters on the meltpool dimensions. An analytical approach is utilized to determine the meltpool size. These predicted data from the analytical approach were validated with experimental data. Inconel 718 powder was used to fabricate the cubed shaped samples with a combination of different SLM process parameters; namely, laser power; scanning speed; and hatching space. Meltpool dimensions were measured from the microstructure images of the samples. After the validation of analytical data with experimental data, the effect of SLM process parameters on meltpool dimensions was established. The result shows that the SLM process parameters significantly affects meltpool geometry, which is very useful for selecting suitable process parameters. [ABSTRACT FROM AUTHOR]

A graphene/AlSi10Mg alloy composite powder was prepared by vacuum ball milling, and used to fabricate components by selective laser melting (SLM). When the ball to powder ratio was in the range of 4 to 10, with the increasing of the ball to powder ratio, the dispersion of graphene was, improved; however, when the ball to powder ratio was higher than 8 it was not favourable to the dispersion of the graphene. When the ball milling rotational speed was in the range of 80 to 250 rpm, with the increasing of ball milling rotational speed, the distribution of graphene became homogeneous, but when the ball milling rotational speed was higher than 230 rpm, the Al powders were deformed. When the ball milling time was in the range of 0.5 to 3.0 hours, graphene was dispersed more homogeneously with the increase of ball milling time, when the ball milling time was more than 2.0 hours, the deformation of Al alloy powder occurred. When the ball to powder ratio was 8:1, the ball milling rotational speed was 230 rpm, and the ball milling time was 2.0 hours, the graphene/AlSi10Mg composite powder with the homogeneous distribution of graphene was prepared. And then the graphene/AlSi10Mg composites were used to fabricate components by SLM, the graphene/AlSi10Mg composites exhibited excellent microstructure and grain refinement. [ABSTRACT FROM AUTHOR]

AlSi10Mg porous alloy was prepared by selective laser melting (SLM) with a Nd:YAG laser beam, and the compression properties were studied using both experiments and the finite element method (FEM). The results illustrate that the porous alloy undergoes elastic deformation, plastic deformation and densification stage. The joints of the porous alloy are preferentially fractured, and the Si content at the bottom position of the dimple is higher than the dimple edge. During the compression process of the porous AlSi10Mg alloy, the stress and strain distribution at the joint are concentrated, resulting in joint fracture. The inherent elasticity, shear stress and forced contact of supporting plates or chips are the causes of these compression stages. The distribution of Si element in the fracture is caused by the dimples that are easily formed at the a-Al/Si interface, eventually resulting in the Si content at the bottom of the dimple being higher than the dimple edge. [ABSTRACT FROM AUTHOR]

Recent experimental works on the influence of laser emission modulation on the selective laser melting (SLM) process demonstrated the interest of using a pulsed energetic input to prevent typical defects observed in SLM-built thin structures; however, the underlying physical phenomena are not yet fully understood. Two in-house platforms, one experimental and one numerical, allowing for the study of pulsed wave (PW) versus continuous wave (CW) laser emissions were developed. Both experiments and finite element (FE) simulations were performed comparing the two strategies for the building of thin structures (1 × 10 mm2) in AISI 316L stainless steel. Comparison of in situ process monitored and simulated melt pool widths and lengths showed the ability of the model to describe the thermal field behavior during the SLM process. Numerical results were used to identify and analyse the phenomena creating the empirically observed defects. Excessive heating was denoted in CW regime, which can be circumvented using PW laser emission. Simulations confirmed PW as a promising alternative to reduce defects such as part protrusion. The model proved to be a relevant tool to speed up process parameter optimization procedures and prevent defects at a design stage. [ABSTRACT FROM AUTHOR]

Titanium and titanium alloys have unique properties such as high strength to modulus ratio corrosion resistance and exhibit similar characteristics for biomedical devices. It is, therefore, considered to be a potential material and have a wide range of application in the field of biomedics. Due to the difficulties in obtaining the optimized parameters required for the laser processing, the titanium is still used little. This study lays the foundations for better understanding and control of the selective laser melting (SLM) process parameters mainly laser power, scanning speed and beam diameter. Since, in SLM of titanium, controlling the degrees of porosity and increase the build rate is quite a challenge and, in this study, the commercially pure titanium (CP-Ti) formation is investigated by means of single layer track formation to understand the processing mechanism and the effect of SLM processing parameters on the resulting porosity of the final track. The optimized parameters based on optimum surface porosity which is mainly around 25 to 30% achieved are presented. The resulting surface morphology of the CP-Ti processed track was examined and explained. Balling phenomenon was observed at low laser energy density and the combined effect of lower scanning speed and higher laser power results in formation spatters. The chemical composition of the laser track surface is studied and it was found that formation of protective oxide coating occurred. The influence of SLM processing parameters on porosity is statistically modelled and analysed using regression analysis and analysis of variance (ANOVA). This study mainly focuses its attention on the increase in build rate and porosity of optimized selective laser process parameters. From this study, it is shown that scanning speed and laser beam diameter are the dominant factors which affects the porosity of selective laser melted track. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) was used to form 316L stainless steel. Furthermore, as-built samples were subjected to two solution treatments at 1050°C for 2 hours followed by air cooling, and 1150°C for 2 hours followed by water cooling. Microstructural characteristics and grain boundary character distribution (GBCD) are determined and tested by optical metallography, electron backscatter diffraction (EBSD), etc. The results showed that the as-built specimens consist of columnar crystal with the molten pool boundaries. After heat treatment, the molten pool boundaries and the dendrites disappears, the austenite grains grow, and the grain is mainly composed of columnar crystals that grow parallel to the direction of heat flow after HT at 1050°C, and there is an obvious texture in the <101> direction. After solution treatment at 1150°C, the grain is mainly composed of equiaxed grains, and the texture is no longer obvious. The small angle grain boundaries at 0 to 10° after 1050oC solution treatment account for about 80% of the total grain boundaries, S3 CSL is the most in low-SCSL. Compared with the solution treatment at 1050°C, the grain growth was obvious at 1150°C, the content of low-SCSL increased obviously, the grain boundary energy of low-SCSL was lower than that of the random boundary, the corrosion resistance was enhanced. The small angle grain boundary of the sample cross-section decreases, the large angle grain boundary increases and the twin crystals appear, in which the increase of the large angle grain boundary is the most obvious with the difference of the misorientation angle of 60°, which is mainly <111>/60° twin boundaries, which belongs to the S3 CSL boundaries. [ABSTRACT FROM AUTHOR]

The microstructure and mechanical properties of overlapping and nonoverlapping areas of AlSi10Mg samples fabricated by selective laser melting (SLM) were investigated. The results showed that the columnar grains with a mean size of 0.8 µm, which grew epitaxially perpendicular to the boundary of the meltpool, dominated the microstructure in the meltpool. The inside of the overlapping area was mainly cellular dendrites, with an average diameter of 1.5 µm and different orientations. The finer fibrous eutectic Si phase was well distributed in the meltpool, the microhardness was 5.2% higher than that in the overlapping area, and the track-track overlapping area was the main area that gave rise to the formation of initial cracks when the sample was compressed. The reason for this phenomenon is that in the meltpool, the fibrous eutectic Si phase is finely dispersed, and the grain size is small, resulting in greater hardness than in the overlapping area. In the overlapping area, the distribution of the Si phase was heterogeneous, and the grain orientation was different in the adjacent region. When compression was applied, the force could not be uniformly dispersed, and this resulted in cracks. The loading direction of the force was perpendicular to the growth direction, and the slip surface direction of the overlapping area was parallel to the direction of the applied force; therefore, the crack initiation occurred mainly in the tracktrack overlapping area. [ABSTRACT FROM AUTHOR]

This study focuses on the microstructure and mechanical properties of the Inconel 718 alloy fabricated by selective laser melting (SLM). The crosssection of the selected laser melted alloy shows an elliptical crystal structure, while the longitudinal section exhibits fine equiaxed crystal structure. Meanwhile, the overlapping area is equivalent to laser remelting treatment, and the strengthening γ " phase (Ni3Nb) is dispersed and precipitated in the substrate, leading to microhardness of the overlapping area is 5.8% higher than that of the non-lapping area. The fast cooling rate promoted the precipitation of γ phase (Ni-Cr-Fe), and significantly improved the properties. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) could be a prospective candidate to replace certain conventional production processes. Microstructure, hardness, precipitates and phase transformation on the X-Y surface of Inconel 718 Ni-based alloy fabricated by SLM are studied herein before and after a suitable heat treatment. The test results show that the obvious weld beads structure can be observed on the unheated X-Y surface of the alloy and the microstructure shows serious inhomogeneity with distributing columnar crystals and fine dendrites. With the increase of solid solution temperature, the microstructure on the surface of the alloy shows an obvious refining characterization. The hardness value on the surface is also reduced gradually. The typical columnar crystals, dendrites, intermetallic compounds and precipitated hardening phases (FeNi and Ni8Nb) are also reduced or could not be found. Under the solid solution process of 950°C, the fine homogeneous d phase and ?'phase in the grain or near the grain boundary have an important effect on the X-Y surface hardness value (476 to 500 HV) of the alloy. [ABSTRACT FROM AUTHOR]

Porous 316L stainless steel powder was processed by selective laser melting (SLM) and the compressive behavior of the porous 316L stainless steel fabrications were studied. The lattices were parallel to building direction, when the porous 316L stainless steel was compressed along the building direction, the compressive stress initially increased and then decreased with increasing deformation. When the 316L stainless steel fabrications were compressed perpendicularly to the building direction, the compressive stress increased and then decreased periodically. The lattices collapsed in a layer-by-layer sequence from outside to inside. At the early stage of compressive deformation, the stress concentration occurred at the joints of the struts, forming a slip band, which promoted microcrack formation. The grain boundary was the preferred site for the microcrack pile-up through pinning the movement of the microcrack. Many microcracks accumulated near the grain boundaries, causing the eventual formation of a crack, which extended along the region of misorientation. [ABSTRACT FROM AUTHOR]

The temperature field of a Ni-based GH4169 alloy powder during selective laser melting (SLM) with a Nd:YAG laser onto a Q235 steel plate substrate was studied. When the scanning speed was constant, the meltpool width and depth increased with the increment of laser power. Because the heat resource density of the laser beams increased with the increasing laser power. When the laser power was constant the highest temperature in the meltpool, the meltpool width and depth increased with the decrease of scanning speed. The reason was that the interaction time between laser beam and powder increased, and the heat flux increased, which resulted in the increase of the meltpool size and the scan line width. The temperature in middle of single track was lower than that of both ends, there were larger temperature gradient and high thermal stress in the position of scanning direction alteration, which gave rise to the occurrence of warping deformation. When the layer thickness was 0.15 mm, laser power was 150 W, scanning speed was 150 mm/min, the GH4169 alloy powder was successfully prepared by the SLM process. [ABSTRACT FROM AUTHOR]

The clearance feature is the key issue in the direct manufacturing of nonassembly mechanism by selective laser melting (SLM). Although support structures can prevent warpage and collapse of overhanging surfaces within the clearance feature during the laser beam irradiation, the motion performance of mechanism is however reduced. Taking the avoidance of an overhanging surface within the clearance as the goal in this study, the critical building angle of overhanging structure was determined as 40°, and influences of process parameters on clearance size were studied. Furthermore, optimized structures of kinematic pairs were proposed to reduce the overhanging surfaces. Finally, the optimized kinematic pairs were applied to a typical mechanism. The result shows that mechanism can be manufactured perfectly by using the optimized kinematic pairs and process parameters without considering the overhanging surfaces within clearance feature. [ABSTRACT FROM AUTHOR]

A three-dimensional (3-D) finite element method (FEM) model was developed to simulate the thermal behaviour during selective laser melting of Ti-Ni two-component powder in the ration 60:40. The moving heat source with a Gaussian distribution was considered in the simulation. The development of temperature distributions, molten pool configurations and cooling rates were comprehensively investigated. The numerical results showed the maximum temperature of the molten pool was increased from 1858 to 2429°C and the resultant molten pool dimensions were enlarged (width: from 44 to 215 μm; depth: from 34 to 98 μm ) as the laser power increased from 150 to 300 W at a constant scan velocity of 100 mm/s. In contrast, the maximum temperature of the molten pool was decreased from 2345 to 1702°C and the corresponding molten pool sizes were lowered (width: from 152 to 39 μm; depth: from 88 to 11 μm) when the scan velocity increased from 50 to 200 mm/s at a fixed laser power of 200 W. The average temperature of the powder bed increased as the selective laser melting (SLM) process proceeded. The cooling rates were negative before the laser beam reached the centre of the top surface of powder bed, whereas the cooling rates were positive as the laser beam moved away. The maximum cooling rate was found to occur near the centre of the top surface of the powder bed. [ABSTRACT FROM AUTHOR]

Metal to ceramic bond strength is a critical issue in porcelain fused to metal restoration. This study investigated the effect of firing temperature on the metal to ceramic bond strength of porcelain fused to metal restoration of a Co-Cr alloy fabricated by selective laser melting (SLM). The specimens were fused to porcelain according to ISO 9693:1999 standard at the firing temperature that is increased from 915 to 935°C by a step size of 5°C. Three-point bending tests were carried out to measure the bond strengths. The results show that the maximum bond strength is 49.2 MPa at the firing temperature of 930°C for the SLM porcelain fused to metal restoration. Scanning electron microscope (SEM) analysis indicates that protruding structure formed in SLM process enhances bond strength by forming mechanical locking structure. Energy dispersive X-ray spectroscopy indicates that the firing temperature influences bond strength by changing the interfacial bond thickness. At the optimum firing temperature of 930°C, the largest thickness is about 2.0 µm. This findings shows that the SLM metal to ceramic system exhibited a bond strength that can meet the requirement of ISO 9693:1999(E). [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) is a nonlinear process which involves melting of powder metal using laser to manufacture intricate metallic parts. During laser melting, the meltpool dynamics are influenced by initial laser processing parameters such as laser power and scan speed. Understanding of the meltpool flow physics and associated heat transfer is important for producing stable meltpool and hence high quality layers and parts. This research work focuses on the steady state numerical simulation of heat flux driven flows in the meltpool of pure metal (24 carat gold powder). Experimental observations indicated a relationship between the sizes of balling and the laser energy density, while no such relationship could be deduced for the change in the spatial gap between the droplets or balling. The splitting of meltpool away from the path of scan and first line bailing was also observed. Simulation results predict the formation of different types of balling at different scan speeds and heat flux to be linked with heat transfer from the meltpool. Results indicate that the size of meltpool is largely dependent on the applied heat flux and its rate of transport to the surroundings i.e. boundary conditions. The steady state velocity patterns in the meltpool, driven by heat flux from the neighbouring surfaces, match well with experimental results. [ABSTRACT FROM AUTHOR]

The influences of thermal history and isostatic pressing on the microstructure evolution of a selective laser melting (SLM) component were studied in this paper. It showed that with the increase of line energy density from 1.1 to 1.9 J/mm, the as received grain size tended to coarsen from 0.7 to 1.2 µm, due to the longer thermal duration. The layer thickness also had an appreciable effect on the microstructure evolution. With the increase of layer thickness from 0.05 to 0.5 mm, the grain size coarsened from not more than 1 µm and 3 to 5 µm, because of the lower heat conductivity of powder and resultant longer solidification duration at a thicker layer thickness. The cantilever structure of SLM part also had a great influence on the microstructure evolution. In the inner of SLM part with a cantilever structure, the grain size of the cantilever zone was larger than that in the non-cantilever zone. In the lower limb of SLM part with a cantilever structure, with the gradual increase on the sloped angle, the microstructure evolved from cellular, to dendrite, then isometric in sequence. hot isostatic pressing (HIP) technology, as a post-treatment route of SLM, could enable the crystal growth from about 1 µm to 20 to 100 µm, accompanied with many substructures with triangle shapes. [ABSTRACT FROM AUTHOR]

In this work Ti6Al4V powder was manufactured by the rotating electrode comminuting (REC) method to produce particles showing a spheroidal shape with an average size of 6.9 μm. The influence of laser scan speed on density and mechanical properties was investigated. It was found that selective laser melting (SLM) technologies are capable of directly producing near to full density titanium alloy parts with fine α+α microstructure. This fine and stable microstructure demonstrated high hardness and tensile strength with low elongation at break. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) is an additive manufacturing process that directly consolidates metal powders to form near net shape or net shape components. A few commercial SLM systems have started to process a select choice of aluminium alloys. These alloys are generally based on conventional casting alloys that do not represent the highest performance aluminium alloys for aerospace application. This paper studies the consolidation behaviour and resulting microstructure of pure aluminium, 6061 alloy powder and a mixture of 6061 alloy powder with copper powder under different SLM processing parameters. It has found that the addition of copper powder to 6061 Al powder considerably changes the consolidation behaviour and microstructural characteristics, resulting in a denser and much finer microstructure. This work therefore demonstrates the premise to develop specific aluminium alloy powders for the SLM process and enabling the fabrication of high performance aluminium based products. [ABSTRACT FROM AUTHOR]